yesterday i rejetted my carb and made some small adjustments on it with some test and tune drives. I also played with the vacum modulator for the th 350. as i pulled the vacum line of from the modulator nipple i noticed there was a lot of fuel coming out the vacum line? i am running a edelbrock performer intake manifold on the 403 cui. I hooked up vacum from the port attached. Any ideas why there is fuel in the vacum line that goes to my modulator from the tranny?

greets from germany
Jonas

 

Vacuum should be causing the flow to be FROM the transmission TO the intake manifold, not the other way around. Are you sure that the fluid coming out of the line is gasoline and not transmission fluid? I know the two are quite different, but I have to ask. It is not uncommon for the diaphragm in the vacuum modulator to fail, allowing engine vacuum to pull transmission fluid into the intake where it will get burned up. This is usually indicated by white smoke coming out of the exhaust. Have you noticed this at all?

 

Every time an intake valve opens, there is a positive pulse in the intake tract. This is called reversion and it causes atomized fuel to move out of the intake manifold. If you took a high speed video of the top of the carb with the engine running, you'd see the fuel droplets above the air horn. This also means that atomized fuel is being pushed out every vacuum port in the intake, including the modulator line to the trans. Once the atomized vapor hits the metal modulator line, it condenses back into liquid and rolls downhill toward the trans.

 

Does this mean that gasoline in that vacuum line is normal and that we should all expect to find it in the vacuum modulator line on our engines? Or does the OP have a problem?

 

I've always found some fuel residue in vacuum lines coming off the engine. Obviously it shouldn't be gallons, but you'll smell it.

 

The OP says he has "a lot" of fuel coming out of that line. That doesn't sound normal. From what you say, I could understand a whiff of gasoline vapor when the line is first disconnected, but the OP sounds like he's getting gasoline by the tablespoonful (but I'm just guessing as "a lot" can mean anything).

 

yes it was a small amount but not that much and no gallon.... car runs normaly and without white smoke out of the exhaust

 

How much did you change the jetting? A stock 403 and a stock Qjet?

 

We can only go by what you say. You first said that "a lot" of fuel was coming out. To most people, "a lot," when there should be nothing coming out at all, is cause for concern.

Now you reply again and say, basically, never mind. It's a "small amount."

First it was "a lot," but then it became "a small amount." To most people, those are two significantly different things. You can see why we might throw up our hands in frustration.

 

sorry for confusing. as i pulled the vacum line there was quit a bit coming out of the line and flows all over my arm and then suddenly stopped. Sorry my english is not the best..... i am running a quickfuel slayer series 750 cfm and changed the primary Main jets from 72 to 70. i also changed the pump nozzle from 33 to a 35 nozzle. the car was running to rich as i read it from my spark plugs. now the car runs smoother in idle speed but still have a hesitation when accelerate. readings from my spark plugs is ok now but still have hesitation as i said when i accelerate. Engine is a stock 403