View Full Version : Weber carb hesitation under load...

04-16-2013, 12:37 PM
Just wondering if anybody can help me with this problem. A few months ago, I was driving up a hill on the highway, and out of nowhere my car started leaning out and backfiring through the carb. Once I got to the top of the hill, and levelled out, the car started running just fine. But from then on, it would start to bog at about 65mph when you were heavy on the gas, like passing somebody on the freeway. Light throttle, and the car ran just fine.

The problem seems to be getting worse now. Even giving it like 50% throttle up hills, it bogs really bad. I used to be able to make it through gears 1-4 without problem, and then 5th would start bogging. But now, it seems to happen in every gear. If I'm super light on the throttle, everything is fine.

I've replaced the fuel filters, replaced the fuel pump. I thought maybe the fuel pump wasn't keeping up with the carb. So then I tore down the carburetor, I soaked it in that big ass can of NAPA carb cleaner for 20 minutes, then blasted out every passage I could with compressed air, and I replaced EVERY part on the carb with new parts. I checked the float level, and it looks perfect as far as I can tell.

Any other ideas or suggestions? I feel like there is a clogged passage still on the secondary barrel, but I was so goddamn diligent rebuilding the carb. Oh yeah, and I thought maybe it was a clogged cat in the exhaust since it always pinged really loud when I'd shut the car off, so I took it out, and replaced it with some pipe, and had the same problem...

Could it be a spark related issue? Maybe a weak coil pack? I replaced the plugs and wires, but maybe the spark just isn't good enough for a heavy load? Is that even possible? Any ideas would be awesome... I'm all out of them, and I'm super frustrated.

04-16-2013, 02:30 PM
Have you tried re-jetting the secondaries to be richer? That would be my first guess if you're leaning out when heavy on the throttle. I'm not sure how the Weber's are, but Edelbrocks come with a chart. If you want to richen up the secondaries, then get jet #x and metering rod #y from this handy kit we sell for extra money. How good are you at tuning aftermarket carbs is the question, I guess.

04-16-2013, 02:44 PM
Well, this just started happening out of nowhere. I could increase the jet sizes, I have tons of them hanging around, but it's ran fine for the last 4 years with the current jetting... :/

04-16-2013, 04:26 PM
Probably some debris in there, you should be able to take it apart without needing any parts. My idle jets get junk in them every few months, looks like scale maybe or filter material.
I would clean out the whole thing though.

04-16-2013, 07:15 PM
Mine will feel like it's running out of gas at around 3000 RPM in 5th gear. From what I've read on other forums, mainly Jeep and Datsun, is that the secondary jet is too small resulting in the lean condition. Some people get it through all gears, others just the high gears. Leaks at the adapter and manifold can also cause issues. I'm going to get the performance jet kit and see what happens. Everything up until around 2800 in 5th is liquid smooth.

You might notice your issue in more gears now that the carb has been cleaned and properly rebuilt. The carb is running more consistently which could make it seem worse. That would be my best guess.

04-17-2013, 08:04 AM
On my 1g (1976 model year), I had a similar situation. The car just started losing power out of the blue. I didn't get any pinging or backfiring, but I might not have pushed it hard enough to cause that. Anyway, it turned out that there was a design flaw in the exhaust manifold. There was a baffle that broke off and fell down over the exhaust outlet creating a giant restriction. When that happened, the car had no power like what you are experiencing. I couldn't even pass big rigs on the highway. IIRC, that flaw got worked out by 1981, but it's something to consider. If you feel so inclined, you can drop the exhaust pipe and point a flashlight into the exhaust manifold. You should have no problem seeing the baffle restriction if there is one. Take pics and post them here if you aren't sure.

Here are some more possibilties: Causes of an Engine Carburetor Backfire | eHow.com (http://www.ehow.com/list_6402725_causes-engine-carburetor-backfire.html)

Hope it helps.

04-17-2013, 09:02 AM
Well, I tried upping the secondary main jet sizes just to see. I had a 152 in there, and I upped it to a 155 then a 160, and then upsized the secondary idle jet from a 55 to a 60, and it made zero difference. I am really starting to think this is an ignition related issue at this point.

The one big change that I do have, is that I no longer have the backfiring through the carb since I rebuilt, that may have been an additional problem that the carb rebuild actually fixed. That backfiring went away before I changed jets out. I wish I could get a spark tester that I could see while I drive the car, and see if the spark is getting weak under load.

I also have a little bit of a miss at idle that I can't seem to make go away either, and I'm wondering if it's not related. And my headlights seem to be flickering lately too a bit, which makes me think maybe something is going on with my electrical system... Too many fucking symptoms!

Also, snooz, I took the whole exhaust off the car, and checked everything out for blockages, and it all looks good. But that was definitely a good suggestion.

04-17-2013, 10:36 AM
Sorry, I didn't read #1 very well did I...and yeah the plate intermitantly leaking can drive ya nuts.
Primary voltage problem could throw off the whole megaj set up couldn't it?

04-17-2013, 12:08 PM
Primary voltage problem could throw off the whole megaj set up couldn't it?

That's what I'm wondering. I can't figure out for the life of me why it's doing that though. I've put in a new voltage regulator and alternator with no luck. Maybe the battery is bad? It holds a charge just fine. Gonna have to take it and have it load tested and see what they say I guess...

04-17-2013, 03:59 PM
Did you check for vacuume leaks?
If not an easy way to do this is get a can of carb spray and start spraying from the carb down. Keep the engine running while you do this and when the RPMs go up you found the leak. RPMs will settle after the carb spray is sucked into the manifold and air starts to rush back in the hole. Keep doing it till you pinpoint the leak if there is one.

04-17-2013, 04:19 PM
Yep, I tried that too... :( Everything seems good there. Sprayed it around the carb base and the intake manifold gasket. No change in idle at all...

04-17-2013, 06:13 PM
This is coming out of left field but I'm looking at what you replaced and have you checked the pressure coming off the fuel pump yet? I'd see if you can get a fuel pressure and volts gauge then hook them up and drive around and monitor.

04-17-2013, 09:11 PM
Well the voltages look fine according to my multimeter. It's like 13.5 at idle and 14.9 over 1000RPM. I can't imagine it changing while driving, but I suppose it couldn't hurt to find out. Fuel pressure, you think even the new fuel pump could be bad still? It seems to work just like the stock one.

News when I got home tonight from work though. After it's first long drive (an hour on the freeway), I got home and could smell gas. And there was evidence on the intake manifold of fresh gas that had leaked onto it. Now I'm chasing another problem. URGH!!! It didn't leak at all in all the testing that I did over the weekend and the last few days...

04-17-2013, 09:15 PM
I'd look at fuel pump pressure. These operate off RPM so it might be flooding the carb when it really gets going. How much gas is blowing out of the top of the carb into the air filter?

04-18-2013, 09:40 AM
There's no gas blowing into the air filter that I can see. Inside the air filter is clean as a whistle.

The pump doesn't necessarily operate based on RPM. It simply uses the coil signal to turn the pump on and off. I've actually had that relay bypassed for about 4-5 years, since my coil pack doesn't quite send out the right kind of signal to trigger the fuel pump relay. I should probably take care of that when this whole debacle is finished.

Also, on the drive to work today, I did get one backfire through the carb, so that problem has not gone away either. I don't feel like the rebuild really did anything whatsoever. Not to mention, I don't understand for the life of me where the carb would be leaking from. I feel like maybe something might be fucked internally on the carb, like one of those stupid lead plugs popped out or something. Every seal, diaphragm, and valve is new in it...

I am going to try replacing the EDIS ignition control module today. If that doesn't do anything, I'm going to drive to the local carb shop and pick up a new Weber. I just really need to get this thing going before the meet this weekend. I can get a brand new one for $219.

Before I go the carb replacement route though, I think I should go get some gauges like you suggested. I hope I can get a fuel pressure gauge with a remote sending unit. I need to be able to put that gauge inside the car and watch it as I drive.

04-18-2013, 02:22 PM
With the bypass on the relay and new fuel pump you really need to check the pressure on it. The Weber wants no more than 3 PSI otherwise it will flood. With your fuel pump always pumping I wouldn't be surprised if it's flooding it when you put your foot down. It probably got worse with the new pump since the new pump is going to be stronger than the old part.

I got bit in the ass and had to pay for a $120 tow because I replaced my ICM when I didn't need to. Always check the parts you've replaced before you throw more parts at it. This really sounds like fuel pressure based on what I've read on other forums.

04-18-2013, 02:27 PM
Check this out:

Cheapo fuel pressure regulator - $23
Buy Spectre Fuel Pressure Regulator Chrome 2517 at Advance Auto Parts (http://shop.advanceautoparts.com/webapp/wcs/stores/servlet/product_fuel-pressure-regulator-chrome-spectre_22905569-p)

Cheapo fuel pressure gauge - $18
Buy Spectre Fuel Pressure Gauge with Inline Fitting 59013 at Advance Auto Parts (http://shop.advanceautoparts.com/webapp/wcs/stores/servlet/product_fuel-pressure-gauge-with-inline-fitting-spectre_22906125-p)

$41 is far less than $200+. I'd try that first

04-19-2013, 09:40 AM
So I'm wondering if maybe it's just running too rich over all? You said it's bogging down during acceleration, maybe it's almost flooding itself out? have you tried running smaller jets? You have the 38/38 right? The idle mixture screws only adjust the idle mixture on that one don't they? The 32/36 uses the same fuel circuit for idle as it does for light/half throttle...just wondering if you have any control over the "on throttle" mixture or if it all just comes down to the jet sizes.

04-19-2013, 09:46 AM
OK my bad, you've already covered what I was asking about. Please feel free to ignore my last comment.

04-19-2013, 01:24 PM
So I took my ICM into O'Reilly auto. Turns out they have a machine that specifically tests them. I had no idea they could test such a specific part! It failed almost instantly. New one is coming in tonight! Here's hoping that it fixes it!!!

04-19-2013, 02:18 PM
Awesome! I'm going to get mine tested and see if it's causing the surging in 5th. Might as well before throwing jets at it.

04-19-2013, 03:23 PM
Well, remember too, I'm using Ford distributorless ignition system on my car. They have a whole suite of adapters for testing all sorts of DIS systems. Can't hurt to find out if they can test yours or not though! Would solve a lot of headache if they can.

Also, before you buy your jet ket, verify what jets are in your carb, and what jets the kit comes with. I wound up buying mine, and it turns out it had the jets that were already in my carb, and only 1 size up and 1 size down. So it was kinda useless at the time.

04-19-2013, 04:43 PM
Will do. I can get the car to reliably start feeling lean now so I'm really thinking jets. It's only in 5th and it starts around 2800. All other gears don't do it but those gears don't allow for a light foot at that high of RPM.

Good luck, I hope this fixes it!

04-19-2013, 10:42 PM
New ICU didn't fix anything. Same problem.

So I put a fuel pressure gauge in. I bought a nice one, since I have purchased that one you showed me, and it didn't work half the time. Sits at 2psi, then pumps up to 2-1/2psi. Seems perfect to me. However, I can't see it while I'm driving around. I guess I'll just have to see how it acts on the dyno tomorrow. Since I paid for the time, I might as well utilize it as a diagnostic tool. They have an AFR meter on it, and now I can watch the fuel pressure to see exactly what the problem might be.

I had my dad take a look, who has a knack for this since, since he's built many old British cars and is a magician with multi-carb setups on motorcycles. He took one look and found a loose throttle shaft. Not sure how I didn't notice it, but I wasn't really looking for it either. So I figured that alone probably warranted a new carb, so I picked one up. Swapped out my jets into the new carb, and it's actually much better, but the problem still persists. But like I said, I can't see the fuel pressure while I'm driving. So I'll see tomorrow if fuel delivery is an issue.

04-20-2013, 03:44 AM
Way out there but I wonder if the cruise mixture (in cc) would be affected by gummed up cvcc port? It is not fully utilized at all rpm so that invites unused half baked fuel to hang around=varnish.

Pretty sure that and ability of the fuel to maintain pressure, are the only fuel side problems left.

Threads like this are great but I forget or misread what has been attempted as a fix as it progresses lol

There is a troubleshooting flow chart for MJ?

04-20-2013, 06:09 PM
If you remove the hood, would you be able to see FP gauge while driving?

04-21-2013, 03:52 PM
I got it on the dyno this weekend. I'll have to post the chart. You can see the power completely disappear at 3000rpm. The air/fuel ratio starts getting a little bit more rich as the RPMs climb, even while it's hesitating, but it's not out of whack enough to cause the huge power loss. We were able to watch the fuel pressure on the dyno, and it looked good too.

What you can see on the chart over 3000RPM is power spikes, where its completely unsteady and climbs and dips. The tuner at the shop said it's definitely an ignition problem when I showed him the dyno chart, long before I ever mentioned it was carbureted. So I need to somehow test the pickup sensor on the trigger wheel, or replace it, and take the wiring apart and redo it. I think there's gotta be a bad ground or loose connection or something somewhere in the harness I built for the Megajolt. Maybe this is why you should use butt connectors instead of solder?

Sorry the thread has been so hard to follow, it's just this long, retarded chain of events that I can't even keep straight in my head. I let some of these problems go too long after they started popping up.

04-21-2013, 04:44 PM
As I understand it, your A/F ratio should get slightly richer as you approach WOT, so that's working fine. Very interesting problem. I can't wait to see what you find.

04-22-2013, 01:06 AM
Solder > everything else, as long as its done properly it should last forever. I have yet to see any of my connected/spliced wires/connectors fail even after 3+ years of use.

I've seen many failed poorly crimped terminals and of course, twisted and taped wires before soo

04-22-2013, 02:09 AM
:confused:I could see at least part of the spikes being carb transistions, generic powr valve parameters, sec idle jet selection, air correcter and emulsion tubes that may not be ideal for altitude or other enviornmental properties.:rockon::barf:
That is awesome you were able to see it on the dyno, I bet that is exciting to know your car has power & performance yet to be unleashed!

04-22-2013, 09:55 PM
Well, the power doesn't just drop off a little bit, it's completely gone. Torque goes from ~95lb-ft to about 30lb-ft. Can't be a jetting issue. Couldn't even get the car to pull up past 4000RPM until I got it down to 2nd gear.


And check out the air-fuel ratio on the blue line. That was the run where I was able to pull it higher up in the RPM range. It's pretty damn spot on, and just starts getting richer with the misfiring. But it's not rich enough to cause that kind of power loss. I mean at 4000RPM, it's still well above 13:1AFR.

Rendon LX-i
04-22-2013, 11:13 PM
Just as a witness is my prospective. its a ignition issue for sure. has to be with the hall effect or wiring. one of the two you did mention that the air gap is dead on from what you told me was 1mm correct? but most certainly a ignition issue. Lmk what happens john.

04-23-2013, 01:30 AM
Dat torque o.o

I would love to see how much you're making with a properly running engine now ahh!

04-23-2013, 01:17 PM
The shop said they'd let me have an hour of free time with their tuners there to help out. So once it's running right, and with the help of the MegaJolt and my jet kits, should have it tuned in to perfection.

04-25-2013, 01:21 AM
good good (Y)

04-29-2013, 06:30 PM
So I'm still having this strange problem. I'll try to re-summarize what I've got going on at this very moment:

Hesitation under heavy "load." I say heavy load, because it requires a lot of throttle at low speeds, but on the freeway, even a little bit of extra throttle, like going up and incline causes this hesitation.

My other symptom is flickering lights. Like the cabin lights, dash lights, and headlights. I feel that this electrical problem is likely what's causing the hesitation, and a bad spark that can't ignite the denser air-fuel mixture... or possibly no spark.

I replaced the alternator, main grounds, and tried 3 different voltage regulators, and this light flickering still seems to happen. Only thing left to check is wiring? I'm not really an expert at that part...

Rendon LX-i
04-29-2013, 07:42 PM
Do this How To Perform a Parasitic Draw Test - EricTheCarGuy - YouTube (http://www.youtube.com/watch?v=KF1gijj03_0) an this basic voltage drop testing for automotive electrical testing - YouTube (http://www.youtube.com/watch?v=9aioZN33xsA). shouldnt see 0.50 in the system.

04-29-2013, 08:51 PM
^ good links.

When you say flickering lights, are they only when the engine is running or doing the same even with the engine off? Whats the voltage reading like?

04-29-2013, 09:39 PM
Thanks Josh! That Voltage Drop testing looks like the fucking ticket. I had no idea about the multimeter actually measuring the voltage difference between the leads. Damn, that is super fucking helpful. And now that gives me a lot more ability to go through and test my wires! I've been tearing apart harnesses and looking at wires, but having no actual idea if the circuit is any good deep down in the harness. I can't wait to start testing stuff tomorrow night. I figured even a shitty connection I'd see 12v, but not know if it was actually a good connection or not. This is awesome.

Hazwan, the headlights only flicker when the car is running. I actually even started the car with the plug on the alternator disconnected (the 3 pin connector) and there was no light flickering then. The weird thing is that the voltage actually looks steady with my meter, but it is the cheapo $3.00 meter so maybe it's not fast enough. Around 14.5 volts or so when charging and like 12-13 when the engine isn't running. Maybe I should borrow the Fluke from work. :)

What alternator did you wind up using on your car that has the built in regulator? I'm guessing there are a million that will fit, but when I eventually do the wire tuck (yes asking for more wiring hell) it will be nice to not have the voltage regulator over by the battery, and it would be nice to eliminate all the unnecessary wires.

04-30-2013, 02:50 AM
That sounds a lot like alternator issue to me or the regulator issue I don't know >< Knowing these cars I wouldn't be surprised if the 3 wires from the alternator to the voltage regulator is old. You did bypass the stock main charging cable with the jumper cable before too right? One more thing left to do would be testing each of the 3 wires from the alternator to the regulator for resistance, if its too much then it might be possible that the alternator didn't know the exact battery voltage and would kept trying to charge like 15v and then realized oh nvm its too high, going back to 14ish and it would go on forever causing your flickering lights issue. I'd check the main charging wire for resistance too.

I used a Sentra B11 alternator or at least thats what the parts guy said. Everything lines up perfectly, minus the 3 pin plug, its 2 pin for the Nissan alternator I think? idr lol but yeah you just gotta bypass the external regulator obviously and boom (Y)

04-30-2013, 02:52 AM
One more thing since you said you multimeter shows a rather steady voltage.. I would check the underdash fuses/main battery cable (fat white single connector) going to the dash harness. Thats the main power cable for the rest of the cars electrical system, lights, fans, engine etc.

It could be old and been causing every single of your problems too. Check for the resistance for that fat cable and the positive cable or at the main 55A fuse too. Or check the voltage at the fuse box/fat white cable and see if you get anything weird.

04-30-2013, 06:51 AM
All awesome ideas. I'll probably have to wait until tomorrow night. Also, I need longer leads for my meter!

04-30-2013, 06:59 AM
Some random wire connected to the end of the lead will do the trick :D

05-01-2013, 05:19 PM
The weird thing is that the voltage actually looks steady with my meter, but it is the cheapo $3.00 meter so maybe it's not fast enough.

An analog meter would be better for capturing fluctuating voltages.

05-01-2013, 10:13 PM
I should probably have an analog meter...

So I went through and did the voltage drop tests. All my ground points seem solid, there's no voltage difference at any of them that I can find.

I tested the 4 connectors on the alternator. Worst drop I saw was 0.3v on one of the wires, and something like 0.1v on the rest of them.

I tested the power connections in my harness I made to the coil pack and to the EDIS ignition control module. Got strong voltage there. Ground to that seems to be excellent too.

I tested every circuit in the fuse panel. 0.3v drop was what I saw on everything, except the headlights, I saw a 1v drop. Doesn't seem to be anything of a concern.

I did do a voltage test on the VR sensor. Supposedly, you're supposed to have 2.5v AC when cranking the engine. I only got 1.3v. So I'm not sure if that means it's bad or what. I did re-solder the connections to it, since I did a shitty job on one of the wires, and the car is a LITTLE better now, but not much.

My other question is, can the spark plug wires be a concern if they are close to a ground or anything? They do run a little bit close to the alternator, but they don't touch it... It wasn't a problem before though, but I do want to eliminate everything. They are brand new though and they don't shock me when I touch them, so I don't feel like it could be the problem.

05-04-2013, 01:41 PM
Seems to me like either the coil can't keep up (and is putting out too weak of a spark) OR your total timing isn't "broad" enough. I've had the dead spot issue before, I.E. She just WOULDN'T go over 4000, no matter what, the problem was basically I had the timing advanced (or retarded?....can't remember) and essentially the timing wasn't advancing enough for the engine to actually work any faster than 4 grand, it was acting like a governer.

I would either try to tweak your timing curve or check for lack of movement in your advance mechanism, BUT you don't have a Distributor anymore do you? I guess I'm not much help but I really do think it's either a spark strength or spark timing issue.
Have you changed the octane rating of gas you use?
It seems trifling, but assuming you tuned your timing by using a particular octane rating, buying a higher octane fuel would move/change the ideal ignition moment. As for the spark plug question, yes, spark will always take the easiest path to ground, so even a tiny little crack in the wires can cause big problems.

05-04-2013, 05:37 PM
I know a lot has been done since #1 so can you say exactly what the symptoms are now and which one is unchanged without varience? I know on my Ford the set up stays the same but sometimes it won't get out of it's own way, the variables are fuel quality and air temp. Sometimes it runs great , had a certain tone in the engine that sounds right.
My B20 carbed does the same thing but the air temp is a huge deal with it, i should have never drilled those divots in the plenum floor. These carbs really need spacers o even swirl spacers like they make for toyotas. The fuel/air charge needs to build or disperse a little more before leaving the plenum. Of course heating it accomplishes a lot of that, makng more gas than liquid... This is where the fuel blend differences come into play I suspect. A real cool humid day the car runs like crap.
It also makes a lot of sense that an ignition problem could affect the carb mixture transistions, especially timing curves. It would be chasing gremlins to keep making changes on both ign and carb without documenting each action and timeline.

10-05-2013, 11:03 AM
So, what 5 months later... I finally got off my ass to try to figure out what's up again. I've been using the car pretty much exclusively for short trips around town, but I can't commute to work, since 50mph is about my top speed.

So I threw a distributor in the car, to try to isolate the problem, and see if I was right to suspect the MegaJolt. And it turns out that the EXACT SAME PROBLEM is still happening. While I'm super glad that I did a proper job, and that my MegaJolt wiring was not the problem, I am bummed as I can't figure this issue out for the life of me.

I mounted a fuel pressure gauge out on the cowl of the car that comes up through the hood. Fuel pressure does seem to dip down to about 1psi after a sustained load on the engine. So maybe I should get a different type of fuel pump, or maybe my wiring to the fuel pump is weak and the pump isn't getting enough juice. I'm going to run some fresh wires on a dedicated circuit to the fuel pump and see if that does anything. The stock pump never had problems keeping up with the engine for the last 4 years...

Also as a side note I do still have the headlight pulsing when the alternator is kicking in to the high output mode (IE, RPMs over 1000). So I'm still suspecting some kind of major electrical issue with the car. Maybe today is the day to rip the harness apart and see if there are some broken wires or something...

10-06-2013, 06:10 AM
Told you to put a fuel pressure gauge before lols but good luck!

10-06-2013, 03:43 PM
Maybe today is the day to rip the harness apart and see if there are some broken wires or something...

Oh... goody! :barf:

10-06-2013, 04:34 PM
I've had a pressure gauge on it for a while. I just couldn't see it while driving. I saw the same 1psi on the dyno while the car was under load. However, the air fuel ratio never leaned out like I would suspect if the carb was running out of fuel. I'm still not sure that dropping to 1PSI is enough drop to cause what's happening. Especially since there should be a steady flow of fuel through the carb...

Also sometimes the pressure comes back up to 3psi after I let off the gas, and I still get hesitation. I really have to ease off the throttle for a while for it to come back and be able to slowly work the car back up to speed.

The big thing that is concerning me is the 28Volts AC I'm seeing at the battery when the car is running. DC voltage seems normal. I'm still suspecting that it's causing problems with the coil or something...

10-06-2013, 04:52 PM
What would cause you to measure for ac at the battery? That could be just slight "ripple" fromvthe charging circuit, bled thru diodes in the sys.
A fail col could producecthese symptoms. Im curious of tbe wiring changes right there at the coil circuit with mj, guess ill have to find the thread me thinks you showed the schematic diagram there?

10-06-2013, 05:56 PM
I measured for AC because at the same time that this hesitation started, my headlights began pulsing over 1000RPM. I read online that a good test is to check for AC current at your battery. From what I can tell, you shouldn't have much more than a half a volt of AC being picked up. But I didnt really have a reliable source for that...

I got rid of the MegaJolt and went back to a distributor. I thought maybe that was part of my problem, but the stock ignition system changed nothing in the way the car is running.

The problem is so hard to be specific with. I gave it a run up the freeway tonight. I was able to get up to 70mph no problem. Then I turned around and came back, and it started running like shit again, and I could barely keep it at 55mph. Even light throttle was causing stumble. Down hills was better. Had hesitation even at 2.5PSI, while earlier I had it floored and was having hardly any symptoms... it's killing me.

10-06-2013, 08:34 PM
Just want to say that I appreciate you guys chiming in here in this thread. I know that its super confusing all the stuff that's going on and all the things that I have tried. I'm happy to start from scratch and explain again exactly what is going on to clarify if it helps... I'm just at a total loss right now...

10-07-2013, 07:05 PM
Sorry if this is a repeat suggestion, but 1 PSI seems low to me. I'm not an expert of course, but it's not unheard of for a carb to want 6-8 PSI and 2.5 PSI is about the bottom of the acceptable range in most cases. Have you tested flow? As in how many liters in one minute?

I thought the dyno guys had taken care of this for you?

10-07-2013, 08:01 PM
The manual for the car says 2-3 psi is the nominal range for the fuel pump when there's only a gauge hooked up. I thought it might be kinda low too for the Weber. However, if that's what my old pump was putting out, and it worked fine for me for like 4 years, I'm not totally sure that's a problem (though I can't verify the old pump's output, I'm guessing it was probably in the factory spec).

I guess I can check flow rate, accurately, but it seems to just dump fuel out and an amazing rate.

The other thing is too, I've had it hesitate at full pressure (near 3psi) when on the freeway. So fuel pressure doesn't 100% coincide with when it hesitates. But that doesn't mean it's not part of the problem I guess. My only real option to get more fuel is to get an aftermarket pump.

Rendon LX-i
10-07-2013, 10:21 PM
i would swap the pump an go from there john. wish i had that car for a day i would test a bunch of crap. i love diagnosis i get alot of shops that push there cars to us cause we figure out the mess. most of the time people tend to over look and dont go to the basics.

you have spark nows its a fuel pressure deal. adding a relay to your fuel pump prolly help if anything.

10-08-2013, 09:48 AM
Allright. I'll grab my Holley red and regulator off of my other Honda and see what happens. Can't get to it for a few days though... I hate waiting.

07-19-2014, 08:55 AM
What was the outcome?!? I'm going crazy with this same exact thing!!! Have to maintain exactly 4k rpm. If it drops, power is gone. If I tap the gas just a smidge, power is gone. Wtf, Car?!?

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07-20-2014, 01:57 PM
What was the outcome?!? I'm going crazy with this same exact thing!!! Have to maintain exactly 4k rpm. If it drops, power is gone. If I tap the gas just a smidge, power is gone. Wtf, Car?!?

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Weber carb?

07-20-2014, 01:58 PM
No. :/

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07-20-2014, 01:59 PM
Ok. But here's something different about mine. It does the power loss only after I increase my elevation 3000ft.

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01-31-2015, 09:17 AM
I just got my car working and it was jets/blowby. When I first built the engine nothing was set and the car required big jets to get any kind of power out of it. My first oil change also smelled like gas. Over time the gas smell went away in the oil and I noticed the car really started to hate the big jets so I started dialing it down. My guess is the rings needed time to seat and as they became more seated there was less blowby resulting in less gas needed to get a boom.

I took it through DEQ recently and it blew 300 (!!!) on CO which failed me. I replaced my air cleaner and brought everything back down to stock jet sizes and the car runs like a dream. It also also now passes DEQ with a score of 120 on CO which is 70 points lower than what the car did on stock jets right after the engine was rebuilt.

Everyone told me it was too much gas but I didn't believe them. It did end up being too much gas and by lowering jets everything now works fine. You might want to try to stagger your jets so the secondary is 5 lower than primary. The Webber is 140/140 by default so try 140/135 or maybe even 135/130. Your dyno shows that this is only happening when both primary and secondary barrels are receiving gas since it's over 3000. You could try lowering the secondary idle as well but that seems to affect the 2000-2700 range more than anything.

I also still think that OEM Honda fuel pump can't keep up. I don't get the surging uphill or at 65+ anymore but the float still needs to be way higher than I feel it should be to keep everything running right. Redline makes a low psi, high flow fuel pump that I'm going to try now that my car is working. It still requires a regulator but it allows you to fully remove the return line.

Have you done a compression check? I'm thinking your rings could be bad.

11-12-2015, 09:51 PM

Did a compression test. Got 180psi, which I'm pretty impressed with. Did a leakdown test and the worst cylinder (#2) was 15% (this being a cylinder that I keep fouling a plug on).

So I got a borescope, and thought maybe if the plug is fouling over and over, that the pre-chambers are clogged with crap too. Sure enough:


Gonna check and see what the other cylinders look like. Not sure why this one is misfiring so bad and getting clogged. Gonna dive into the manual and see about pulling that chamber and cleaning it out. Maybe a crack in the intake manifold is letting in coolant? More investigation to come.

Rendon LX-i
01-04-2016, 09:52 PM
Well that would do it eh. glad progress was made john. Update us on whats going on.

01-05-2016, 01:04 PM
Well the update is that IT IS NOW RUNNING LIKE A CHAMPION!

The carbon buildup in the pre-chambers was the problem. You can see in the attached pics, the one looking down inside has a black ring, that's ALL carbon. There was only enough room in the chamber for the valve to move!

Also in the other two pics, you can see how when I shine a light through the clean pre-chamber, vs when you shine a light through the dirty one. The spark has to ignite the fuel that's inside the chamber, then the flame comes through those holes into the combustion chamber to ignite the main mixutre...

It required pulling the head off, and modifying some tools to pull the pre-chambers apart. But I wound up getting them all apart, replacing the gaskets, and cleaned out all the carbon buildup. Slapped the engine back together and it ran so well!

Rendon LX-i
01-14-2016, 12:07 AM
holly cow. well that explains it. Looking good. Now ripper vids please lol

09-22-2016, 11:05 AM
Test Bump.

04-19-2017, 07:09 PM
Bump confirmed.

Thanks for posting final solution for posterity. Seriously. Too many threads like this just end with no conclusion. Glad your 1G is back in action.