fuel in vacuum advance canister

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Hipo65

Hipo65

Yeah I'm "That Guy"
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Just as the title says im getting fuel in my vacuum advance canister. Its ruining the diaphragm in it then leaking. Im dam Lucky it didn't blow up the distributor or cap! Its hooked to manifold vacuum sorce on the 750 race demon carburetor. The motor is a very healthy 340 with a 242 247 @ 050 camshaft so the reason I have on manifold sorce is for the added timing at idle & cruise. I sstitched to directly to the intake runner to see if it helps or not. Ill run it a bit and see. Anyone else ever run into this before? There solution? Thanks guys.
 
Hipo65 said:
Just as the title says im getting fuel in my vacuum advance canister. Its ruining the diaphragm in it then leaking. Im dam Lucky it didn't blow up the distributor or cap! Its hooked to manifold vacuum sorce on the 750 race demon carburetor. The motor is a very healthy 340 with a 242 247 @ 050 camshaft so the reason I have on manifold sorce is for the added timing at idle & cruise. I sstitched to directly to the intake runner to see if it helps or not. Ill run it a bit and see. Anyone else ever run into this before? There solution? Thanks guys.
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That's strange. The only way I can think that fuel would travel from the carb fitting too the vac diaphragm is that fuel is being pushed out the fitting instead of applying a vacuum. I can't even see a surging problem causing that but I guess that could be possible? Try running the engine with the vac hose detached and see if it's pushing fuel out.
 
[QUOT="dart_68, post: 1971788089, member: 50493"]That's strange. The only way I can think that fuel would travel from the carb fitting too the vac diaphragm is that fuel is being pushed out the fitting instead of applying a vacuum. I can't even see a surging problem causing that but I guess that could be possible? Try running the engine with the vac hose detached and see if it's pushing fuel out.[/QUOTE]
With it disconnected from the full manifold sorce at the base pf the carburetor when running it does as it should. Pulls vacuum unless throttle is snapped then vacuum drops. Im guessing that the issue is when the engine is shut down the canister retracing (remember on manifold vacuum sorce) pulls in a very slight ammout of vapor in then condense's after so many times. Im trying to figure out a way to correct this issue! Car runs great set up this way. 17º initial 35º total all in at about 2800-3000. The vacuum can adds another 16º at idle & light throttle/higher vacuum. So at idle its 32-34º snappy as hell and even runs a bit cooler. But this fuel in the can will kill another can in short order if I don't "fix" it! I put the vacuum sorce directly into the intake manifold runner now well see if the helps it.
 
Try locking the distributor in at 35 degrees, maybe less depending on your compression and disconnecting the vacuum. Never worry about it again.
 
Its a street car & runs noticeably better cruising & runs cooler with a combined 47-50º timing at light throttle. Added benefit is its better on fuel for what its worth. Also ttying to start it hot @ a locked 35º would be a joke.
 
If you have distributor vacuum at idle, then using wrong port, or curb idle too high.

Never had a carb put gas into vacuum hose.... Seems like gas would be dropping down barrels for that to happen. Float setting???
 
Its on the manifold vacuum port not the timed port. The timed port was developed for emissions purpose only. Carb settings are rite on. So farvno problom now since switching to intake runner for vacuum sorce.
 
You probably have quite a lot of reversion going on inside the intake at loe rpms. Next time the intake is off look at the intake runners and see how far up the runners are stained. What is the LSA of the cam you are running? A tall spacer may help reduce reversion.
 
Its on a 110 lsa. About middle of the road for lsa. Im hoping moving to the intake runner & vertical will help.
 
Hipo65 said:
Its a street car & runs noticeably better cruising & runs cooler with a combined 47-50º timing at light throttle. Added benefit is its better on fuel for what its worth. Also ttying to start it hot @ a locked 35º would be a joke.
Click to expand...

He means 35° full mechanical advance, and leave the vacuum disconnected.

I'm not saying that will be right for your motor, just an attempt to clarify.
 
Anyone who runs there car on the street & can pull enough vacuum to properly work a vacuum advance canister is missing out on easyer starting (lower base/initial timing) soon as engine fires vacuum adds timing at idle & low power conditions. And it picks up mileage believe it or not. Its also alot more responsive at lite throttle due to have in the 40-50º timing range at high vacuum low load situation's
 
The idle feed and transition slot for the right front venturi are really close to the manifold vacuum port on my 650 Mighty Demon. I run a 1" 4 hole spacer, Eddy airgap and have no issues. You could try putting a T on the large rear port normally used for PCV or add a small port on the rear of a spacer if you use one.
 
I have zero hood clearance for a spacer. Im hoping relocating vacuum sorce to the intake runner will cure it. Mine isb a 750 mighty demon so that could make sense then.
 
Well Ive figured it out! Mderoy340 I think nailed it. The manifold vacuum sorce is basically below the transition slot on the mighty demon carbs! Took the ol girl out for a drive. Run loke a scalded cat. Came home pulled vacuum line off distributor & dry. Then pulled vacuum cap off carburetor where I was using for manifold sorce and sure enough fuel in my vac cap! It has started to soften the rubber vacuum cap! SO there is somthing goofy with the manifold vac sorce plumbing/design on the demon/barry grant carburetor base plate I see. Just an fyi to all those who have one. There AWESOME carbs but go the the intake manifold itself for a manifold sorce!
 
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