facel6

Thank you Frankie

i have seen this document some months ago, but didn't pay attention to it at that moment

On my carbs, these bushing/tubes are clearly missing, but they are not stock. WCFB manual doesn't mention them





Do you really think that adding these tubes could fix my problem ? If yes, from where can i get them ? Are they part of a rebuilt kit ? Can they be ordered separately ?

It's hard to figured out that raw gas can run down thru this vacuum passage straight into the manifold.

Frankie the Fink

Here is the Service Bulletin on the topic - so, no, its not in the manual. If your air/horn and carb main body are milled flat (as they should be) and a good gasket is used this fix shouldn't be necessary....but I put them in just as 'belt and suspenders' approach.

You can take tubing stock of the size shown....bevel the end to go in the passage with a jeweler's file so it'll start in easily and carefully tap a short piece of tubing down into the passage - its a tight fit and its supposed to be.

Again, this fix is for the 'left-turn-stall' issue due to fuel slosh, IMO I don't see it addressing your problem. I don't see it as relevant on a car sitting still at idle

facel6

i've made a longer road test this morning. What i've found out, is that with all mixture scews fully closed, the car doesn't idle at all on the street. Curiously, it idles well in my garage, but at the first stop, the engine stalled
I had to turn out the screws between 3/4 and 1 turn to obtain a smooth idle on the road.
Apart of this, the car drives well, but it still smells gas

Frankie the Fink

So, idling during a drive requires the mixture screws to be backed out - e.g. enriching the mixture with the mixture screws at near-normal settings. In the garage the mixture has to be completely leaned out to idle the best. So the car is running abnormally rich only in the garage ??

None of your symptoms are typical of carb problems I usually see. The difference between idling during a road trip and idling in your garage is mainly that you are manipulating the linkage by hand when troubleshooting in your garage and, if you idle long enough while tuning, your carb may well 'load up' and run rich.

I'd examine the range the linkage moves through, how well it comes to rest without sticking and ensure it moves freely through the ignition shielding and is not even close to touching anything. With the linkage resting on the idle stop screw the primary AND SECONDARY throttle plates must be completely CLOSED.

The ONLY other thing I can think of relating to a car moving through traffic and occasional idling vs garage tuning is if a float is sticking against a bowl sidewall at various times causing inconsistent symptoms. I can't overemphasize the importance that these be EXACTLY centered on these old WCFBs. If, as you say, you have the Carter float level/positioning gauges that's hard to screw up...

As an incredibly long shot I would remove and clean the WCFB sintered bronze internal filter and make damn sure your gas tank is vented properly.

Frankly, I don't know what you have going on at this point. You should put your general location in your profile; some nearby member might be willing to put 'eyeballs' on the situation and offer some suggestions.

If you were near me I'd have my spare carb swapped on your car in 10 minutes and that would tell the tale.

facel6

the linkage is moving freely and seems not to make a problem.

Frankie, as you wrote it, my problem is not typical from carburetor problems, and so, my current conclusion is that my carburetors are correctly set up and working as they are supposed to do. I think i have another problem somewhere on the engine.

What could be the origin of the low vacuum of my engine ?

Compressions are homogeneous, but probably a little bit low for a new engine (about 120 dry).
I would like to do make a leak down test, but i don't have the tool to do it.

to be honest, i'm not very confident in the specialist who had rebuilt the engine

PS i'm leaving in France and don't know a good Corvette expert in my neighborhood

Frankie the Fink

Short of typical vacuum leaks you could recheck the valve lash and make sure its precisely correct.

You can take an UNLIT propane hobbyist torch and pass the unignited gas around typical engine vacuum leak points as the engine idles - the carb base, all around the intake manifold, etc.. If you find the engine speeds up at any point you've found your leak. Be damn careful doing this though...

Its more important that compression checks show consistency across the 8 cylinders than they be at some specific number (but they shouldn't be inordinately low). Many do a compression check incorrectly so ensure you are following the proper procedure.

facel6

And what's the proper procedure for you ?

I sprayed brake cleaner all around the carbs and the intake manifold. There is no evidence of a vacuum leak. i couldn't notice any engine speed variation

Frankie the Fink

I prefer the torch method as the light gas is drawn towards a vacuum leak rather than having to hit the right spot with the heavier spray - but so be it. Here is a good article on compression testing and some other diagnostic procedures.

facel6

removing all spark plugs on a hot engine is not very easy !!??

Frankie the Fink

Well -- get the shielding out of the way on a COLD engine, then warm it up and shut it down. Let the engine cool a little bit.

Use a socket/ratchet to break the plugs loose then an old rubber, straight spark plug boot to unscrew the plugs without burning the crap out of your hands and arms...

I can do it without issue...

40ZR1

This is a little of topic but, Frankie, I enjoy reading your responses to threads because not only for your helping knowledge but your illustrations and pictures to explain what you are trying to convey. Really helps helps me understand and learn.

CJ