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Ok....problem I cannot figure out. 1961 Corvette, 283 2x4bbl. Excessive sooty black dry fouling on #1 cylinder only. Had carbs rebuilt, new floats, etc. Replaced plugs, points, condenser, rotor, distributor cap, and spark plug wire. Removed valve cover and checked for stuck valve...not stuck yet I still get a LOT of black sooty dry fouling on #1 only. Any thoughts? Pictures... plugs after about 300 miles and this black crap spits out of the exhaust on both sides....
Last edited by ByByeAmericanPie; 07-20-2016 at 07:06 AM.
First off -- all of those plugs seem a little dark to me; burning modern gas should have more of a tan look (see pic of my plugs from my stock 283ci 270hp dual quad car). And, if soot is blowing out both exhausts then you have more issues than just the #1 cylinder (BTW - blowing out some soot on a cold start up is pretty normal).
You could start with a compression/leak down test but I suspect your carbs are running rich for one thing. Until you get that straight I don't know if you have an individual cylinder problem or not.
I switched to NGK-XR4 plugs several years ago and they seem to burn better tan the AC-Delco stock plugs for what it's worth
Last edited by Frankie the Fink; 07-20-2016 at 07:26 AM.
I believe that the left primary barrel of the front carburetor feeds the #1 & #4 cylinder.
It looks as if the #4 plug is also very dark, which could be the reason for the black out of both tail pipes.
I would look down that barrel with then engine running at idle and cruise speed and compare it with the right primary barrel.
Look for excess fuel at cruise and dripping at idle.
I had an issue when I put my two fours on and I also was fouling the front plugs. What I found was that someone put the wrong primary throttle plates in the carburetor they were .030" larger that stock which uncovered the transfer slot at idle. That took me a while to fiqure out!
I would remove that primary carburetor and check the throttle plates, maybe on is bent, and check the float levels.
Joe
This is my throttle body with the large primary throttle plates:
This is what it should look like, notice the rectangular transfer slots are not uncovered:
Problem solved...or at least mitigated for the time being. Turns out that the front carb, although just rebuilt, was dumping fuel even at idle. So until the winter when I can take the whole mess out for rebuilding and restoration, I simply disconnected the front carb and will run off the rear. The improvement was immediate and dramatic. No more miss. No more black spew from the exhaust.
Removing the carb is a half hour job, I would fix it now and enjoy the summer. There are good carb rebuild people in most towns. Ask around at a local car show, someone will have a source for you. Nice looking car by the way.
Removing the carb is a half hour job, I would fix it now and enjoy the summer. There are good carb rebuild people in most towns. Ask around at a local car show, someone will have a source for you. Nice looking car by the way.
I can have a WCFB off the car, disassembled and a diagnosis made in a half hour. I wouldn't run long with just the rear carb. Its not optimal for fuel distribution as you can well imagine...
If that front carb is drowning your engine I'd be on the phone to the guy that "just" rebuilt it...
I can have a WCFB off the car, disassembled and a diagnosis made in a half hour. I wouldn't run long with just the rear carb. Its not optimal for fuel distribution as you can well imagine...
If that front carb is drowning your engine I'd be on the phone to the guy that "just" rebuilt it...
Actually the car is designed to run off the rear only unless you are really getting down on it...right?
No. Where did u hear that? If that was true u would have some kind of progressive throttle linkage and vacuum operation like the tri-power motors.
Like Frank said those front cyls will get leaned feed from the rear carb only. And maybe dangerous lean at WOT.
If your running a dual quad carbs you really need to learn carbs or they will always haunt you. Sounds like u may have a inlet valve needle that wont seat.
No. Where did u hear that? If that was true u would have some kind of progressive throttle linkage and vacuum operation like the tri-power motors.
Like Frank said those front cyls will get leaned feed from the rear carb only. And maybe dangerous lean at WOT.
If your running a dual quad carbs you really need to learn carbs or they will always haunt you. Sounds like u may have a inlet valve needle that wont seat.
Hit the books my friend.
The way the carbs are set up the motor runs off the rear carb. The linkage connecting the front carb doesn't engage the throttle on the front until you get down on the pedal quite a bit
Technically, yes, at a light cruise you are running off the front primary barrels on the rear carb. That's at a VERY light cruise. If you drive like that much then you might not even need a Corvette. As I've said, I've done it for short periods...as shown.
Not real proud of it though...you run around with 'performance anxiety' and I have enough of that at my age
Running around with just the rear carb won't hurt a thing. Car does indeed have progressive linkage, just like a Pontiac tripower. And is designed to cruise on just the primaries of the rear carb for economy. No worries either way. Me, I'd yank and fix the front carb, though....these are really basic carbs, and easy to r&r........
Well, to throw my two cents worth in on this - I went through extensive/expensive hell with a similar problem. But, for sure, everyone's suggestion could be the issue, as we are not seeing the car. But, some things you said parallels problems I had. First, the carb could be getting dirt inside that then clogs the flow and causes the carb to "dump fuel at idle." Easy to spot by letting the car run and look down the tops of both carbs and at idle it will drip gas. If this is the case, just remove the carb, unscrew the top and clean everything thoroughly. Use lots of carb cleaner to blast out all openings, etc. THEN search for where the dirt is coming from. Mine was grit in the tank so I flushed the tank out a number of times until it ran clear. Twelve months later no problems and it runs like a Corvette. Of course, this was the solution, but I went through many other avenues until I found that this was the problem. Good luck, but fix it - it's such a pleasure to hear the 2 carbs open up!
Actually the car is designed to run off the rear only unless you are really getting down on it...right?
If that was true why do you have idle mixture screws and transfer slots in the front carburetor?
Why do you have to adjust all FOUR idle mixture screws when setting up the carburetors?
Yes you can run off just the rear, I had to block off the front carburetor with and aluminum plate to diagnose my problem I stated above.
Joe
Well, it turns out that when I got the front carb apart, there was a miniscule bit of dirt in the needle valve seat...something so tiny causes so much problem. Cleaned out the valve seats, tips, reset the floats and voila...runs like a champ.
07-20-2016, 06:56 AM
Fouling Issue
