C! Will not idle unless choked

[Wayne Hagopian]

My 1960 283 with WCFB will not idle unless it is just about fully choked and then while at idle pulls about 18 on the vacuum gage. When I open the choke more than about 3/16" it dies. I've checked the intake with propane at every gasket and jetted propane under the manifold through the vent pipe opening next to the distributor and no leak is evident. I thought perhaps it was a carb problem so using an adapter I put on a good 2 barrel with the same result: When the engine is fully warmed up it stalls unless choked.
Background: I just replaced the timing chain and installed the correct intake manifold. I'm using a WCFB that I've rebuilt and double checked before testing with the 2 barrel mentioned above. I installed the distributor with #1 facing forward. The engine timing is correct and the compression is 125 on every cylinder. Does anyone have any suggestions.

[Stephen W.]

Re: C! Will not idle unless choked

Try taking a can of air like the ones they use on computer keyboards. remove the idle mixture screws and give then a shot.Its clear your not getting fuel at idle.Replace the mixture screws , gently tighten till they bottom. Back off 1.5 turns and fire it up. If your certain you do not have any vac leaks then you need to determine why your not getting enough fuel. Clogged passage in carb idle circuit?

[Wayne Hagopian]

Re: C! Will not idle unless choked

Well I'm sure the actual passages are wide open. I went through the carb and of course when I put the 2 barrel with the adapter plate on the 4 barrel manifold the symptom were exactly the same. Any other ideas?

[Stephen W.]

Re: C! Will not idle unless choked

sorry I misunderstood the comment about the 2bbl having the same problem. .

[Mike M.]

Re: C! Will not idle unless choked

How many inches of manifold vacuum is the engine pulling at idle and warmed up?
Mike

[Wayne Hagopian]

Re: C! Will not idle unless choked

It pulls about 18 while choked but as the choke is opened the vacuum drops quickly to Zero and it dies. It requires almost full choke to stay running but it runs very smooth while choked and the 18 is constant.

[Mike M.]

Re: C! Will not idle unless choked

If the choke plate is partially closed then the carb is not delivering enough fuel through the idle circuits. And it does this with both carbs. The following is thinking out loud, so if I repeat what you all ready know, it is just to make sure I am covering all bases.
My assumptions:
1) the carb worked ok as installed with the previous intake manifold
2) this is a 230 HP car.
3) the carb does not feed enough fuel to the engine at idle with the choke plate fully opened (obvious)
4) there are no problems with the fuel delivery to the carb, i.e, fuel flow not restricted in any way or the fuel pump not delivering enough fuel.
The carb requires a certain level of vacuum to pull the fuel out of the bowl at idle. It has idle tubes that draw the fuel from wells in the fuel bowl. They use manifold vacuum to pull the fuel out of the bowl. The fuel then sprays into the manifold through the mixture screws (and in some cases small fixed ports). By closing the choke plate you are creating a "false" vacuum in order to pull the fuel over. So it seems to me there is a vacuum issue somewhere in the intake system. You have leaked checked and not found anything, but I think you probably need to pull the manifold and examine it and the gaskets carefully. I also think 18 inches of vacuum to be on the low side of what the engine should pull at idle. The only thing I can think of that would create this situation is a leak between the heat riser passage and the fuel delivery side of the manifold. That leak may not show up via your testing procedure.
Good Luck,
Mike

[Wayne Hagopian]

Re: C! Will not idle unless choked

I appreciate your thoughtful response. Both carbs respond the same way and the 2 barrel worked ok with the old 2 barrel manifold and since the only other thing I've changed has been the timing chain I'm thinking it has something to do with the 4 barrel manifold. I just hate to remove it without an idea where the leak may be or if there is a leak. Can we assume the valve timing is correct? I lined up the marks and the ignition timing is correct and I can't imagine I would have 125 compression if the valve timing was far enough off to cause the vacuum to be so weak. Do you have any idea what the vacuum should be if I block the intake completely and crank the engine? If I take off the manifold and the gaskets look good what else should I look for with regard to the manifold. - I suppose I could bolt on the 2 barrel manifold and carb and remove all doubt about other possibilities.

[Mike M.]

Re: C! Will not idle unless choked

Wayne,
I really don't think the problem has to do with the timing. If the timing marks line up as you describe and the engine starts and you do not experience backfiring then I assume the timing is correct. However, have you tried advancing the timing at all to see if it makes any appreciable difference? That in itself would increase the vacuum at idle (to a certain point). I don't know what the cranking vacuum might be, I've never done that test before.
While I have never personally seen a SBC manifold crack between the heat riser passage and the fuel passage, I am guessing it is a possibiliy. That is the only place I could imagine a leak other than the manifold or carb gasket. I am not so sure about the effectiveness of putting propane under the intake. This area is vented to the outside and you cannot be sure that the quanity of propane required to indicate a leak would be sufficent, especially with all of the oil being splashed around under the manifold (just might absorb some of the propane). Did you plug the crankcase vent when you did this test?
I empathize with you about pulling the manifold, but I think it has to be done to rule out possible problem areas.
If you do not find a gasket problem, the manifold could be tested for a crack between the heat riser and the fuel passage by turning the manifold upside down and filling the heat riser with a low viscosity fluid. Let it sit overnight and check the next day for fluid in the intake passages.
Mike

[Roy B.]

Re: C! Will not idle unless choked

Have you checked fuel pump presser or a clogged line before the fuel pump.Choking forces the engine to pull fuel through the pump.

[Wayne Hagopian]

Re: C! Will not idle unless choked

Yes, The pressure is such that when you remove the fuel line a few minutes after the engine has been shut off, fuel sprays out nicely. Also, I have removed the carb top and found the fuel levels in the carb to be normal. I've cleaned and recleaned the carb passages and checked the gaskets for possible misalignment with no result. I'm using a thin carb base gasket without a spacer. I was able to get the engine to idle properly with my old 2 barrel and an adapter after I corrected a vacuum leak in the base gasket so I've narrowed it down to the WCFB or an internal leak in it's base gasket. I wish I had another 4 barrel to put on for testing purposes but all I have here is some old thermo-quads that will not bolt on.

[Mike M.]

Re: C! Will not idle unless choked

Wayne,
Congrats on getting the two barrel to run correctly. Question on the WCFB, is your WCFB the type with an idle by-pass circuit or a "normal" idle system? Some WCFB's, AFB's and Rochester 4GC's set the idle with an air by-pass system in lieu of the normal idle stop screw. A real PITA to set up. Just finished rebuilding and installing one of these on a '58 Cad Eldo. They can be distinguished by the big idle by-pass screw in the BACK of the carb and the lack (at least with the rochester's) of an idle stop screw. Some 283's used this type of carb, but not all. On these carbs, the primary plates are supposed to be completely closed at idle. Air for idle is supplied by the by-pass system. If you have this type of carb, let me know and I can help with the set-up. If not, then for whatever reason your WCFB is not pulling enough fuel to mix with the air supplied by the idle system. The idle mixture screws really do not change the air/fuel ratio of the idle system, that is set by the internal idle jets and air bleeds. The screws just control how much of the air/fuel combo gets into the engine.
Mike

[Wayne Hagopian]

Re: C! Will not idle unless choked

Mike, This WCFB has an idle speed adjustment screw on the high idle choke cam but nothing like you describe in the back of the carb. I believe it is the correct carb for this car but I may be wrong. I have had this thing apart at least 5 times now so I'm begining to get familiar with it. I've blown out every little hole I can find and when I put it together it idles fine as long as I stuff a shop towel in it. At a slow idle it pulls 18 on the vacuum gage and as I remove the towel it stalls. When I first start the engine without the towel it runs great for about 3 seconds before stalling. It can then be restarted without the accelerator pump and run for another 3 seconds.

[Roy B.]

Re: C! Will not idle unless choked

Check to see that the metering rods assy are working properly. pull the cover off and watch to see if they are held down when running at idle.

[Wayne Hagopian]

Re: C! Will not idle unless choked

Roy, The rods are working correctly. I'm wondering if the jets and rods are the correct ones for the carb. How can I tell if they are correct? When I accelerate and the accelerator pump fuel is gone the engine falters and runs poorly. This is an engine and chassis only so I'm not able to drive it.