It's an edelbrock carb. The plugs only fouled after the car ran like crap. It also doesn't make any difference if the car is hot or cold.

I'm not going to start throwing parts at the car just because a company has an iffy reputation. I've heard both sides on the ignitor. Some folks have had nothing but problems with it and some have never had issues. And it seems like everyone who's had a problem with it ends up with a no start condition. Most of those are because the ignitor's not wired up correctly and getting the full 12v it requires.

Everyone seems to think this is an ignition problem, and it may well be part of the problem, but how many of you guys have had ignition problems that showed an erratic vacuum at idle as one of the symptoms?

Now for the new info that may help to crack this puzzle.......

Pulling plug wires while it's idling show it to be an even bank problem. When I pull an even cylinder's wire, the idle doesn't change and it's like it is when it's plugged in. Pulling an odd wire made the idle stumble badly.

Also, I'm running an edelbrock carb. There are two vac ports next to the idle mixture screws. They're sealed off from one another and pull vacuum from their corresponding primary barrel.

The driver one shows normal vacuum and is responsive to its idle mixture screw. The pass side one shows only 1" of vacuum and doesn't respond to the screw.

Is it possible this is a carb problem? If one side was screwed up, it'd show up as an erratic vacuum problem since everytime an even cylinder fired, the vac would drop off. And a car could cause a misfire, either from being way too lean or way too rich on that side.

I'm running a dual plane intake and a carb spacer that adapts the square bore edelbrock carb to the intake. So the even and odd banks are sealed off completely from each other from the barrels of the carb all the way through the exhaust(no h- or x-pipe).

 

Of the two vacuum ports, one is ported and the other is full vacuum. What you guage is showing you is correct. As for pulling wires, sounds like it all keeps coming back to ignition related.

 

OK, NOW you say something.....IF it's a Edel Qjet repro....you maybe having a problem with the carb/manifold gasket not sealing one side or other....I fergit which....too many years...there were TWO common carb gaskets...and using the rong one would open up vacuum leaks....

surprised you would not hear the hissing....but I didn't either...so....
since it's coming from the carb area, it souldn more or less normal....

IF you are using a AFB Edel repro....it MAY be subject to same sort of problem, but not by MY experiences....

 

It's an AFB style edelbrock. The gaskets I'm using(one for the adapter to manifold, the other for the carb to adapter) are the ones that came with the adapter, which is an edelbrock unit, specifically meant to adapt the square bore edelbrock to spreadbore intakes. The gaskets only fit one way, otherwise they don't like up with the 4 holes for the primaries and secondaries. If that was the case, though, I would have noticed something for the last week I drove the car around with no issues.

Are you sure one is ported? Both have the same small holes in the barrel and both hold vacuum with a vac pump when I put my finger over those holes. If one was ported, wouldn't the other end's openings be somewhere other than the same place as the opposite one?

Again, nobody can tell me why or how an ignition problem would cause an erratic vacuum.

Everyone's fixated on the miss and assuming it's ignition related. Misses can also be fuel related, too much or too little.

Chris

 

Chris,

I'm not an expert, but here is some info that might be helpful.

http://www.tracyvette.com/enginevacuum.html

Paul

 

mechanical issues are seldom erratic....they come and stay and get worse they don't suddenly get better.....

how much vac gauge bouncing around do you have?


you asked how could the igniton effect timing....if the timing is late it can be 2-3" lower then normal and timing that is too early can be 2-3" above normal....so thats a 6" variation based on timing....lets say that the mechanical advance is hanging up on something.... and not moving freely...that could alter your timing and give you wierd vacuum readings.....i still think its your ignition or carburetion

according to the peterson test book...." continous movement of the meter 1" above or below normal indicates need to check for further checking of the ignition system...."

 

The vacuum is NOT a steady low(like you'd see if timing was off), but it bounces from 0" to 10"(normal vacuum for my motor and altitude...you loose about 1" of vacuum every 1000ft and I'm at almost 7k feet). Unless my timing is changing fast enough to go from too retarded to too advanced every split second. And the timing light on the balancer shows the timing to be spot on with no variations. Also, there should be no mechanical advance at idle. Checking the timing, it seems to operate completely normal, advancing with rpm and settling right back down at idle.

The vacuum is erratic at idle, bouncing fast enough that the needle is a blur.

And please, nobody quote chiltons, haynes, and every website on the internet that it's worn valve guides. I highly doubt I wore out a set of valve guides on one rebuilt set of heads in 40 miles and did the same to the other heads in the same time. Even stranger is that one minute, the valve guides would have been fine, the next, they're worn out.

There is nothing erratic about the problem except that it came about 40 miles after the first head swap, went away after I put the old heads back on, and came back again after another 40 miles or so. It WAS suddenly better, then just as suddenly bad again. One minute I started the car to pull it out of the garage. When a friend showed up, I started it up and it all of a sudden ran like crap. There was no degradation of performance or tip offs that the problem was coming. One start up it was fine, the next, 10 min later, it was not.

Ignition issues can cause vac problems, but not the kind I have. Which is why I don't think it's ignition related.

Another reason I don't think this is ignition related is because the miss shows up AFTER the vacuum and bad idle problems. Several difficult, flooded engine starts. That's why the plugs are fouled.

Would it appease everyone if I swapped the even plugs with the odds along with their wires and moved each wire over one position on the distro? Cyl one would be moved to 8, 8 to 4, etc. That would completely rule out ignition as the cause if only the even bank still had problems.

Carburetion I can buy since it's only the even bank. The only items that are specific to the two sides of the motor are the carb, that side of the intake(it's a completely divided dual plane), the heads and the exhaust.

I wish I had a spare carb to toss on to see if that's the issue. The carb that's on there was put on by the previous owner shortly before I aquired the car. It still even looks brand new. That doesn't mean a piece of crud or something didn't lodge itself into some crucial spot.

 

any thing you can do to rule something out is a good idea....i would rather see you put a known functioning distributor in it.....then you know you can rule it out.....can you get the coil tested while you are at it?

 

Much like the carb, I don't have a spare distro.

The coil's brand new, less than 75 miles old.

Because it's an even bank problem, anything shared, like the coil, distributor,etc, can't be the issue.

 

isn't the plenum on the intake divided into two?........i wonder if the carb feeding that side of the plenum is screwed up some how.....maybe a clogged jet or something inthe primary side?

 

It is divided and that's what I was thinking. I don't think its a jet, since they're easy enough to check and I didn't see anything. I pulled the air horn off and didn't see anything.

It would explain why swapping the heads worked for a little while. Maybe some piece of debris clogged some passage way and having the carb off the car dislodged it only to come back......like a rocky movie.

Chris

 

Hate to say it but I posted on your original problem before. http://forums.corvetteforum.com/show....php?t=1541135 Pulling the 041 heads and rebuilding them with the parts off the smog heads with new guides is STILL a good option. Pretty cheap and you wouldn't be taking them off again. Sounds like a carb rebuild is in your future also. It might look new but these cars sit for extended periods sometimes and that is harder on carbs than more mileage on a regularly driven car. Good luck with whatever you decide.Noticed your in Colorado, How far are you from Lars? Might be worth a short trip, carb in hand.

 

I have no idea where Lars is, so I'm not sure.

The carb does not need a rebuild. It was put on by the last owner about 250 miles ago, brand new, and the car hasn't sat at all between then and now except a few weeks here and there when I'm travelling. The carb is less than 5 months old. I can't see a carb needing a rebuild that quick.

Again, and this was stressed so much in the earlier post, money is not unlimitted. I don't want to yank the heads for the 3rd time in a month to spend several hundred dollars swapping pieces from the smog heads only to bolt everything up again, have it run great for 30 or 40 miles and have the same problem reappear.

There has got to be a viable solution to the problem. I doubt the heads are it since these heads worked fine before I started digging into it.

Anyhow, I just got back in from the garage. I took the carb off, took a good portion of it apart, squirted carb cleaner through the various passages and nothing seemed block. Certainly nothing came out cept the cleaner.

I bolted it back up and it ran exactly as before, same symptoms.

I also swapped over the plugs/wires from each bank to the opposite and it ran exactly the same. Still the even bank with issues.

And I moved each wire over one slot on the distro cap, readjusted the distro to get the timing right again and it ran exactly as before.

I've pretty much exhausted the things I can think of. Unless anyone has any other ideas to try, I'm pretty much ready to give up on this one. Maybe bubba can figure it out.

Chris

 

hi, i had my top plate in the distributor, the one the rotor screws on to, get loose and wobble and cause the problem you are discribing. i replaced and overhauled everything else in the car before i found the problem. I had irradicate vacuum and misfiring cylinders too.The misfiring was interesting because it wasn't the same cylinder. all this caused by the wobbling rotor.

good luck fixing your problem, i hope someone helps you find the answer.

 

Lars is in Lafayette CO. He is the carb and distributor guru here. PM him, if anyone can help with this it is him. He is 90 miles down RT 25 from you

 

i still don't think its your heads......or a mechanical internal engine problem....my money is on ignition first and carb second......have you taken your distributor apart to ensure everything is working properly?

 

Give me a call or bring the car up. We can fix it. No problem.
Lars
Lafayette CO
"A Pleasant Drive From Anywhere"
V8FastCars@msn.com

 

he made me an offer i couldn't refuse........

 

Maybe bad head and or intake gaskets ? But I betcha Lars will be able to straighten it out for ya no matter what it is,,,,Peace,,, Moosie

 

I agree. It's very, very doubtful the same problem would show up with 2 different sets of heads, one set rebuilt and the other a known good set.

My money would be on the carb first, then the distro. I just have a hard time blaming the distributor since it's only the even bank giving me fits.

Lars,
I sent you a pm and an email.

Thanks
Chris