A20 Engine Rebuild

[Xaisk]

Alright. Its been awhile since I posted haha.

My last big project was installing the Weber which worked well.

My engine is still having a massive idle fluctuation like with the old carburetor so I am thinking about doing a engine rebuild.

If I do decide to do the rebuild, im going to replace the pistons, valves, springs, rehone the block, replace the gaskets, and paint the thing red (maybe)

What else would be wise to look into while I have it apart like this?

Also.. What else could be causing this bad idle fluctuation?

Itll idle steady until it warms up. Soon as it warms up the idles go from 700 - 1200 and back down over and over and over when it idles. It gets worse and worse till it shuts off and to get home I have to pop it into neutral and keep it revved.

I wouldnt assume its the carb since its a brand new one and the install went perfect.

I think it has to be something in the internal engine causing this. Way back when before I got the car (my dad owned it new off the lot) The timing belt apparently broke and possibly caused some damage on the internal engine componets.

That is my basis for why it would need the engine rebuild, That and it has a good 230k on it.

Any insight would be amazing guys. Thanks.

[2ndGenGuy]

Before you rebuild the motor, you should find out what's causing the fluctuation. Chances are that you will rebuild the motor, and reinstall all your stuff, and still have the same idle problems.

Have you checked for vacuum leaks? You can spray a little carb cleaner around the base of the carb and see if it idles differently, it's a pretty typical place for the carb to leak... Also make sure you have everything capped properly, a lot of times when you are tuning the carb, you will get some lean backfire and it will blow off a cap.

[Edison Carasio]

I agree, that sounds like a vacuum issue. I'd imagine that rebuilding the engine would be a lot of work and not solve the problem (but it's still a good idea on engines THIS old).

[Xaisk]

Before you rebuild the motor, you should find out what's causing the fluctuation. Chances are that you will rebuild the motor, and reinstall all your stuff, and still have the same idle problems.

Have you checked for vacuum leaks? You can spray a little carb cleaner around the base of the carb and see if it idles differently, it's a pretty typical place for the carb to leak... Also make sure you have everything capped properly, a lot of times when you are tuning the carb, you will get some lean backfire and it will blow off a cap.

I can 100% assure you it isnt a vacuum issue because the old keihin carb did it too. Alot worse than this one. The new weber carb has maybe 1-2 vacuum hoses going into it.The hoses are all new and fit perfectly. The old keihin one worked for about a month then one day at the bank it started doing the fluctuation thing. Its really abnormal. The engine sounds like it is revving and not just slowly fluctuating. I dont see what else it could be.

Keep tossing me input though plz guys. I appreciate it.

[Edison Carasio]

Compression test it? I dunno what else to recommend cuz I'm a newb. lol

[cygnus x-1]

How long does it take to go from high RPM to low RPM? Is the timing of the fluctuation consistent or more random? If you let it sit there for 15 minutes will the fluctuation get worse?

This sounds a lot like something you get with an improperly tuned fuel injection, called idle hunting. It happens when there is a lean spot in the fuel map at idle. When the engine hits that lean spot it either speeds up or slows down, but then it's no longer at the lean spot so it goes back to where it was before (the lean spot). So it sets up an oscillation. This can also be caused, and/or exacerbated by, a problem with the ignition timing as well.

If there is indeed a lean spot it could be caused by a few different things. Here's something to try: Disconnect the vacuum advance diaphragm and plug the line to the manifold. Start the engine and let it warm up. When it's warmed up, open the throttle just enough so that it idles at the same speed that it normally would with the vacuum advance connected. Hold it for awhile and see if the idle still fluctuates. If it doesn't, then there is something possibly wrong with the distributor. If you have a vacuum pump, check the vacuum advance diaphragm on the distributor to see if it's leaking. Or just put a hose on it and suck on it to see if it holds vacuum.

Another thing to try: With the engine warmed up and idling, everything connected normally, wait until it starts fluctuating. Get a propane torch and open the gas valve a little bit but don't light it. Put the nozzle near the air cleaner and see if the idle smooths out. (don't worry, it won't blow up or anything) If it does smooth out, your idle mixture is set too lean. Actually I would probably try this test first.

It's also possible there is something wrong with the EGR valve; like maybe it's leaking exhaust gas into the intake. This would cause a lean condition much like a vacuum lean, but with exhaust gas instead of air.


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[ecogabriel]

Sounds like a vacuum leak somewhere; and there are a bit of places to look at besides the carbureter itself

My car (EFI) would go from 900ish to 1600ish once warmed up. The power brake booster was broken; one could hear the air being sucked in when sitting in the cabin. I plugged that line and the idle hunting stopped.

I assume you no longer have the black box. A/C still in the car? There is a idle speed boster that works when A/C is on; ditto for the auto trans when in gear (auto or manual
in your case). I have seen several carbed 3G in the junkyard and there are vacuum hoses all over the place. Get hose plugs from NAPA and start unplugging hoses to see what happens

[Xaisk]

Idle Hunting huh? new term to me haha. My car is carbureted.

My car has no A/C. For now. I intend on getting one in the future when money is more set. I have to get this car fixed soon so I can focus on moving out on my own. I have a deadline haha.

The fluctuation is pretty consistant. It starts fluctuating when it starts to warm up and as it becomes fully warm, the car wont idle and I have to rev it at each stop.

Im wondering if my MAP sensor could be bad. Im dreading that because it is an expensive part. My dizzy could also be the problem. The dizzy cap has to have RTV sealant seal it back onto the thing as a gasket. Air might be leaking through there but I dont wanna put any carb cleaner on it to test it because it might eat the sealant away.

I should probally look at the brake booster just to be on the safe side. Im pretty sure its fine but anything is possible with cars.

My EGR valve.. I dont want to disable it because ive heard it helps with engine knocking, But I also dont want to spend 130 dollars on a new one.
The EGR valve is mechanically fine as in it will hold vacuum like it should. The haynes manual said it could be tested by pushing up on the EGR unit and checking for binding or cracking. Also if I cover the vacuum port with my finger and let go of the valve, the valve wont drop back until I remove my finger, so it definatly holds vacuum.


I will try to get a youtube video of what it is doing. I think that would be really useful because yall will be able to hear and see the tachometer and engine. Dunno when ill have the time to do it but hopefully really soon.

(edit) To 2ndgenguy;

I overlooked your post and just reread it and ran out to look. I indeed found a missing cap on the back of the intake manifold.

VERY interesting.................................

But also a new stupid thing happened to me. I took out my spark plugs to inspect them and I broke the threads on the 3rd cylinder plug on the engine block..
Ive heard you have to by some kind of sleeve and stick it in there to be able to put the spark plug in.

Im not to worried because my dad said this has happened to the car before when he was my age and owned it. Told me its a really easy thing to fix so hopefully I will get that fixed soon.
Either way. Yeah.. Found an uncapped end on the intake. It must have blew off when there was some lean backfire or when I was testing out the weber in the backroads.

[2ndGenGuy]

Don't worry about the MAP sensor being a problem. Carb'd cars don't really have one. After the black box / vacuum removal, there's definitely nothing like that left. :)

I see you already have a heli-coil thread started. That's how you'll have to fix that, I dunno of any other way, short of welding and retapping the hole.

[ecogabriel]

Idle Hunting huh? new term to me haha. My car is carbureted.

But also a new stupid thing happened to me. I took out my spark plugs to inspect them and I broke the threads on the 3rd cylinder plug on the engine block..
Ive heard you have to by some kind of sleeve and stick it in there to be able to put the spark plug in.

Im not to worried because my dad said this has happened to the car before when he was my age and owned it. Told me its a really easy thing to fix so hopefully I will get that fixed soon.
Either way. Yeah.. Found an uncapped end on the intake. It must have blew off when there was some lean backfire or when I was testing out the weber in the backroads.

I heard that one should remove spark plugs with the engine cold; I am a little wary with aluminum heads as the material is far softer than the steel in the spark plug body. I started using anti-seize paste when installing the spark plugs; it makes removal a little easier.

I was about to ask whether it is running OK now -you found a vacuum leak- but maybe you could not test it at all because of the spark plug problem. Tough luck!


Don't worry about the MAP sensor being a problem. Carb'd cars don't really have one. After the black box / vacuum removal, there's definitely nothing like that left. :)

I see you already have a heli-coil thread started. That's how you'll have to fix that, I dunno of any other way, short of welding and retapping the hole.

Do you have to tap the stripped hole and then insert the trheaded sleeve that comes with the set?
I saw one of those repair kits and it came with a tap and a couple of inserts but I have never used one of those

[cygnus x-1]

That cap was likely the problem. When the engine is cold the choke is closed so it will get plenty of fuel, making a small vacuum leak insignificant. But as it warms up the choke opens and the mixture leans out. So that small vacuum leak becomes a much bigger deal.

Bummer on the stripped plug, but it's common with aluminum heads. Definitely put anti-seize on the threads whenever you have the plugs out. In fact I put anti-seize on just about every threaded part on my car before I put it back together. Seized threads are a way of life in places where they salt the roads in the winter.


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[Xaisk]

Yeah. I dont think I will be able to get the Heli-coil until next friday though =(

I really want to get it and recap the end and test it. Why must I always wait?
Oh well haha thanks guys.

Btw I did remove the spark plugs with the engine cold.. im just really bad with bolts and screws.. I crossthreaded it.. Xaisk <--- retard

[Civic Accord Honda]

i know efi cars get that idle problem when there is air in the cooling system... not sure on carb cars.
my 4th gen has the same idle problem and ive bleed the system over and over again and then determined it was a bad iacv and just turned the idle down really low and until it stopped bouncing, this had some side effects tho, like no more AC when idling which sucks ><

[cygnus x-1]

Btw I did remove the spark plugs with the engine cold.. im just really bad with bolts and screws.. I crossthreaded it.. Xaisk <--- retard


It happens with aluminum threads. They have a tendency to gall and just get generally hosed up. So don't feel to bad.


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