* * * H E L P * * * Major Misfire / running like crapola !!!

So let me fill you in, it's been a long journey, had all 3 carbs redone on my 427/400 4spd. Car ran a little rough before, stalling when making a hard right turn, & minor misfire. The carbs needed to be redone anyway and recolored etc..........so after they were done & installed, I developed a M A J O R - M I S F I R E - runs like crapola, sounds & feels like running on 5 cyl not 8. Checked compression, cyl 1= 155 all the rest are 170 -175 except one at 165 - changed all plugs, ( none were fouled ) new cap, rotor, points, wires, & new coil. Still runs like crap, rough idle, stalls like it's cold,backfires through exhaust when I let off the gas, & i smell gas with NO leaks anywhere in the garage after turning it off at night & returning a few hours later at times. Runs decent at high RPMS on the highway, but not at low speeds or idle. Also thinking if it had an internal bad air leak it would smoke.....there is NO smoke anywhere EVER !

If you put your hand over the center carb it smooths out at idle. WOW was thinking vaccume leak. My carb guy that redid them came over & changed the power valve, ( didnt do it ) & took the center carb off to have it flow / bench tested, thinking only other internal carb related thing could be the metering block, After looking down the carb at ilde not much gas is coming through the venturis / when you place your hand over it it flows better...... thinking possibly NOT the carb now, but an internal vaccume leak possibly, we tested it at the manifold, and pulled 15, but it moved up to 25 when coving the center carb...........we sprayed carb cleaner around the base & manifold the old fashion way searching for air but there was nothing obvious. At the time the carbs were replaced, the rear one was not sittting poerfect on the manifold, showing a liitle warping possibly in the aluminum intake, but not really bad, nothing 2 gaskets didnt / couldnt cure & not leaking air there after spraying either.

What do you think ? ideas ? suggestions ? where would you go next ?

1. Timing ?
2. Distributor ?
3. Warped / cracked intake manifold ?
4. Still carb related internal ? or the 2 outboards ?
5. L A R S ??? where are you ............?

 

The very first thing to do is go look in both secondaries, with the primary throttle normally closed and BE SURE neither of the secondary butterflies are open. This would be a result of not having the secondary mechanical closing linkage adjusted properly.

Dan

 

What is your ignition system?
What is you initial timing?
Are you running the vacuum advance, if so is it per OEM or another source?

 

I have not yet checked timing, everything is factory STOCK / OEM set up 100%

 

Did you get the proper base gasket on the center carb ?

 

Ok. When you can, IF it will idle, start it up/air cleaner off and look in both front and rear secondaries. Both sets of throttle plates should be COMPLETELY closed, no gaps around the wall of the venturi.

If there is a gap, then fuel is being drawn into the engine above and beyond it's need. Take the mechanical linkage off and go through the entire process of reseting it slowly step by step per the book. If that doesn't fix the problem let me know.

Check your PM box


Dan

EDIT:

Timing must be checked to insure it is not an issue. If you have fresh 93 octane in the tank, then set initial timing to 14* to begin with. If you don't do this first, other issues will become very difficult to discover. As Roger has said you must also be running the correct center carb gasket as well as the end carb gaskets. I am assuming you have all of the correct parts and all the correct parts installed correctly. The gaskets have a specific orientation that must be right.

So, if you are certain all the right parts are there and they are all installed properly, it's a simple step by step process to solve your issue. Check your secondaries to be sure they are closed and check your timing, then we can go from there.

 

Check post #42,this is what I'm referring to.
http://forums.corvetteforum.com/c3-t...uestion-2.html

 

Just throwing this out...........possibly broken valve spring???

I had similar symptoms.......Broken valve spring!!

 

yeah / but funny you should ask, I bought them on e-bay from Chicago Corvette.......... my installer said one of them in the bag of 3 was incorrect......wondering what made you ask that .

Well now i'm also wondering if it's correct or not ???

 

wouldnt that make a lot of noise or smoke or cause compression issues ? ?

 

From your original post it sounds as if you needed the carbs overhauled,giving the overhauler credit that he did a good job to me the next likely thing would be the installation. Its not uncommon with these old cars for the gaskets to be mismatched. The older intakes required special attention in many cases.

 

You can do a compression check.......

I found my broken spring visually and by touch.....

One spring looked a little shorter and I could turn it by hand until

I saw where the spring had broken.( I was lucky)

 

I`m curious, have you ever googled "Chicago Corvette"? or did a search at the NCRS site or here at CF? did you look at their feedback on both their ebay names before you made your purchase?

 

no why ?

 

I did a compression check see the numbers in the first post.

 

Wouldnt spraying the base with carb cleaner at the base of the carb at the manifold show the leak if the gasket was leaking at that spot ?

I was also confused what the 2 outer carbs have to possibly do with this, since it only idles on the single center carb & when i cover it, it smooths out. Some said to make certain the 2 outers are closed at idle....?

 

I'd look to #1 for a broken exhaust or intake spring.....

Good luck

 

I don't think that it being off a bit from the others is enough for concern 155 is still within range NO ?

 

Yes spraying should give a response if there is a leak.
Covering the carb is like closing the choke it richens the mixture and will compensate for a vacuum leak.

 

The bottom gasket is supposed to be the correct one ?? it came with 2 of these & 1 ( not correct ) of the others & the top one is almost 2x's as thick as the lower one that should be CORRECT.... ??

CORRECT ??