Weber carb hesitation under load...

[2ndGenGuy]

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.

[Dr_Snooz]

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.

[2ndGenGuy]

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... :/

[2oodoor]

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.

[PDXAccord79]

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.

[Dr_Snooz]

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

Hope it helps.

[2ndGenGuy]

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.

[2oodoor]

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?

[2ndGenGuy]

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...

[Skellington]

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.

[2ndGenGuy]

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...

[PDXAccord79]

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.

[2ndGenGuy]

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...

[PDXAccord79]

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?

[2ndGenGuy]

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.

[PDXAccord79]

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.

[PDXAccord79]

Check this out:

Cheapo fuel pressure regulator - $23
Buy Spectre Fuel Pressure Regulator Chrome 2517 at Advance Auto Parts

Cheapo fuel pressure gauge - $18
Buy Spectre Fuel Pressure Gauge with Inline Fitting 59013 at Advance Auto Parts

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

[lostscotiaguy]

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.

[lostscotiaguy]

OK my bad, you've already covered what I was asking about. Please feel free to ignore my last comment.

[2ndGenGuy]

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!!!

[PDXAccord79]

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.

[2ndGenGuy]

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.

[PDXAccord79]

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!

[2ndGenGuy]

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.

[2oodoor]

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?