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Ok if I cant figure this out soon Im not going on the 91 cruise:mad: This problem is the last thing holding me back from registering my car. If I dont fix it quick I dont think I can justify testing fate to go on the cruise with fuel dumping on my manifolds.

BACKGROUND:
Swapped single Rochester (BV) for an identical model from another member. The old carb leaked as well as a nasty off idle hesitation. The new carb ran better, but still leaked. I put a rebuild kit in, and....(wait for it)....STILL LEAKS!

I only replaced the gasket, accelerator pump, needle valve and a few other parts. Not the whole kit with all the check balls. The float was in adjustment and I left the thing alone.

It still leaks from the main case gasket. I can only think this is a warped case (damaged seal surface), not torqued down properly, or the float is sticking/not closing the needle valve off soon enough.

It seems to seep out and coat the body of the carb with a fine film of fuel.
I can only think to pull the case apart and blow into the fuel inlet with the carb inverted to test the needle valve (read from another thread) or test to see if the float binds or travels freely. I dont feel very good about either of these solving my problem!

Anyone know if this is a common Rochester problem? I was sure that a rebuild with a new gasket would do the trick. Boy was I wrong!
 

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I know this is going to sound dumb but what fuel pressure are you showing. The old Rochesters are very sensitive to pressure and new fuel pumps are all over the place when it comes to pressure. I say this because of 2 carbs, same problem. Also, I fixed a leak similar to this once by using two gaskets. You should always tighten the carb down using the X method of tightening one turn at a time after seating. Just a few thoughts....Jack
 

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John I was thinking of trying to file it down, but figured this might be polishing the railing on a sinking ship..If you suggest it I guess its worth a try though. Would I be able to spot any imperfections with a straight edge on the case?

I have also heard that debris could be getting into the needle valve and locking it open..but my thoughts are, even if the float level is high, the gasket shouldnt leak anyway! It is a gasket after all!

Jackel I have the original fuel pump (the one I bought the car with) and havent tested the pressure yet. Would I be able to tee off a fuel line somewhere to a fuel pressure gauge? What range am I looking for? A quick internet search turned up nothing but numbers in the 40-60psi range. Fuel injection id assume. I would guess my pressure should be in the 4-8psi range with my mechanical fuel pump?

For what its worth, I have been needing an inline fuel filter for a while now. The one on the car looks like a holocaust survivor. Needs to go!
 

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John I was thinking of trying to file it down, but figured this might be polishing the railing on a sinking ship..If you suggest it I guess its worth a try though. Would I be able to spot any imperfections with a straight edge on the case?

I have also heard that debris could be getting into the needle valve and locking it open..but my thoughts are, even if the float level is high, the gasket shouldnt leak anyway! It is a gasket after all!

Jackel I have the original fuel pump (the one I bought the car with) and havent tested the pressure yet. Would I be able to tee off a fuel line somewhere to a fuel pressure gauge? What range am I looking for? A quick internet search turned up nothing but numbers in the 40-60psi range. Fuel injection id assume. I would guess my pressure should be in the 4-8psi range with my mechanical fuel pump?

For what its worth, I have been needing an inline fuel filter for a while now. The one on the car looks like a holocaust survivor. Needs to go!
I don't know much about Rochester carbs but if the needle valve is sticking and the chamber floods it will leak from the overfill/air tube. I doubt it's the needle valve if you said you replaced it. Did you replace the floats? Did you reset them to the proper height? Are they sealed? Sometimes, if there's a leak in the float it'll fill up with gas and won't close the needle valve.

It's probably what John mentioned. The mating surfaces on the carb are not square. Have you thought of maybe getting a new carb and putting her on to see if you have the same problems?

John
 

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all it would take is one or two LIGHT passes which will leave witness marks. that should be an indicator as to whether the top/base is warped. also, you're not looking to file anything as it'd be almost impossible to keep flat and have all sides be parallel, hence the glass... which is flat. no filing, use wet-or-dry paper and do the poorman's "mill" job. very very lightly though. first you want the witness marks to determine if that's even the problem.

the accelerator pump bore on those carbs can wear and affect the pump seal from completely sealing. that's where the bog/hesitation will come from. you don't really want to fool around with that too much either. i'd suggest some "000" steel wool and LIGHTLY burnish the accelerator pump bore to remove any possible build up that dipping/cleaning the carb didn't remove.

if the kit comes with a rubber style pump, lightly coat it with some petroleum jelly, if it's leather i'd soak it in fuel for a while prior to installation...

those 1bbls are about as simple as a carb can get but they can also be very finicky due to age. i've seen so many cars that are driven into the yard and left for years. the fuel varnishes and a chemical reaction takes place over the years that can damage the carb bodies. they get etched which makes it almost impossible for the pump seal to seal... very very lightly burnish the accelerator pump bore being careful not to score it...

having the extra carb on hand might prove helpful if parts are needed...
 

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Discussion Starter #7
I don't know much about Rochester carbs but if the needle valve is sticking and the chamber floods it will leak from the overfill/air tube. I doubt it's the needle valve if you said you replaced it. Did you replace the floats? Did you reset them to the proper height? Are they sealed? Sometimes, if there's a leak in the float it'll fill up with gas and won't close the needle valve.

It's probably what John mentioned. The mating surfaces on the carb are not square. Have you thought of maybe getting a new carb and putting her on to see if you have the same problems?

John
John I have the old carb that came off originally, but that one has the same problem. Just good for parts now, if anything. I did replace the needle valve, the floats were within a 1/16" or so of spec...almost right on...so I left them alone. Did not test to see if they floated, but a visual inspection pleased me. It didnt look like anything was wrong, but then again, I could have missed something. They are the sealed brass double pontoon deal.

all it would take is one or two LIGHT passes which will leave witness marks. that should be an indicator as to whether the top/base is warped. also, you're not looking to file anything as it'd be almost impossible to keep flat and have all sides be parallel, hence the glass... which is flat. no filing, use wet-or-dry paper and do the poorman's "mill" job. very very lightly though. first you want the witness marks to determine if that's even the problem.

the accelerator pump bore on those carbs can wear and affect the pump seal from completely sealing. that's where the bog/hesitation will come from. you don't really want to fool around with that too much either. i'd suggest some "000" steel wool and LIGHTLY burnish the accelerator pump bore to remove any possible build up that dipping/cleaning the carb didn't remove.

if the kit comes with a rubber style pump, lightly coat it with some petroleum jelly, if it's leather i'd soak it in fuel for a while prior to installation...

those 1bbls are about as simple as a carb can get but they can also be very finicky due to age. i've seen so many cars that are driven into the yard and left for years. the fuel varnishes and a chemical reaction takes place over the years that can damage the carb bodies. they get etched which makes it almost impossible for the pump seal to seal... very very lightly burnish the accelerator pump bore being careful not to score it...

having the extra carb on hand might prove helpful if parts are needed...
John yea I guess this is worth a shot. Ill take it apart today and see if I can get any good results. Under no circumstance should I need a silicone sealant right? Ive had a few opinions like this, but I want to fix it right, not apply a band aid.

Does anyone know how long the 91 cruise registration takes to get back to you? Supposed to send to City of Industry (from Anaheim), I would assume 1 day there 1 day back and a day or so to process..Cutting this pretty damn close!
 

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IMO, it's a float problem or a needle & seat has junk in it, or it could possibly be excessive fuel pressure. I do not agree that a good gasket seal would necessarily keep it contained. I've seen even brand new carbs leak through the gaskets if the float doesn't work properly. The extra fuel has to go somewhere!
 

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Let's see!

Almost 50 year old carbs!

Gasoline with ethanol!

Heat!

Hummmmmmmm~! :rolleyes::rolleyes::rolleyes::rolleyes:
 

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Discussion Starter #10
Hmm..I guess you guys do have a point! Looks like Ill try to check pressure today too!
 

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Jackel I have the original fuel pump (the one I bought the car with) and havent tested the pressure yet. Would I be able to tee off a fuel line somewhere to a fuel pressure gauge? What range am I looking for? A quick internet search turned up nothing but numbers in the 40-60psi range. Fuel injection id assume. I would guess my pressure should be in the 4-8psi range with my mechanical fuel pump?!
Rochester carburetors love fuel volume, but hate pressure. If you have proper volume, the optimal fuel pressure should be as close to 4PSI as you can get it.
 

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IDK if this is bad practice but my gasket sealer I can't remember the brand.. lists carburetors as one of its uses. Obviously you wouldn't want pieces of it getting stuck in your needle and seat but maybe you can install the air horn and smear some around the seam with your finger to seal it.. I have a rochester I'd basically give you but I think mine leaked a little too. They warp very easily.

Alternatively you could take a sheet of glass cut a hole in the middle for the center part that sticks out, glue some fine grit sand paper to it and just rotate on the sand paper it till its flat.

I have used a hammer on a flat piece of steel like the top of a vice grip to straighten it some but I never got mine perfect.

-Tom
 

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Discussion Starter #13
Jackel, Supposing I have excess pressure, the correct course of action would be to swap out fuel pumps or install a regulator inline? I wouldnt think the old fuel pump would be pumping out MORE than spec, especially if it is old...but then again, this is the third attempt at fixing this problem..Im starting to suspect pressure now...

Tom I think Ill try a variation of what you and John are saying. A very light sand on the case just might do it. I noticed when I had it apart that there was a slight lip around the seal surface, but I was thinking that was there to SEAL it tight, and left it alone for the most part. Would I want the seat surface along the edges of the case to be perfectly flat?!?

So far, when I get home:

1. Replace filter
2. Test pressure
3. Break case apart and check seal surface/repair if necessary
4. Verify float operation and measure travel
5. Clean out case again with carb cleaner

This should rule out or expose: pressure problems, max level out of spec, float binding, bad seal surface, dirty needle valve...Cant think of anything else it would be...I am very hesitant to start wasting money throwing new parts at it...Especially since a 250 is next on the to do list after my paint.
 

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I just reread and saw that you have not replaced the float. I'd try that, along with adjusting the new float properly.
 

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...Cant think of anything else it would be...I am very hesitant to start wasting money throwing new parts at it...Especially since a 250 is next on the to do list after my paint.
HEAT!!!!!!!!
Ethanol mixed gasoline of today, fuel has a very very low boiling point. 6cyc Chevy engine have exhaust cross over under the carb. It's a two fold problem. The heat under carb is bad, and it's worse with today's gasoline, the exhaust temp is higher.

Also your exhaust flapper valve in the bottom of the manifold could be stuck closed or partial open. Causing even more heat at the carb.

The fuel you seeing on top of the carb IMHO, is from heat boiling the fuel. See it to many times. The engine temp can be normal and the carb still over heat.

Low timing can cause excessive exhaust heat, (and needs to be advanced more because of today's fuel)

Put a 160 t-state in the engine also, reduce the heat!~

Cover the stock fuel line that goes in front of the valve cover also, it gets heat from rad!

===============================================


You said kit? What about the float?
 

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Discussion Starter #16
I just reread and saw that you have not replaced the float. I'd try that, along with adjusting the new float properly.
Im going to price these out right now! I think this would be a wise idea!

HEAT!!!!!!!!
Ethanol mixed gasoline of today, fuel has a very very low boiling point. 6cyc Chevy engine have exhaust cross over under the carb. It's a two fold problem. The heat under carb is bad, and it's worse with today's gasoline, the exhaust temp is higher.

Also your exhaust flapper valve in the bottom of the manifold could be stuck closed or partial open. Causing even more heat at the carb.

The fuel you seeing on top of the carb IMHO, is from heat boiling the fuel. See it to many times. The engine temp can be normal and the carb still over heat.

Low timing can cause excessive exhaust heat, (and needs to be advanced more because of today's fuel)

Put a 160 t-state in the engine also, reduce the heat!~

Cover the stock fuel line that goes in front of the valve cover also, it gets heat from rad!

===============================================


You said kit? What about the float?
Yes I have a bunch of issues that pile up into a trainwreck. The motor runs hot it seems like, the manifold design, the fuel line routing, all a bunch of things. My heat riser plate under the manifold is stuck Im almost sure, whether open or closed is anyones guess. It makes me a bit uncomfortable that my fuel could be boiling wtf is that about!??! I put a huge fire extinguisher in the car yesterday in preparation for the worst!
 

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HEAT!!!!!!!!
Ethanol mixed gasoline of today, fuel has a very very low boiling point. 6cyc Chevy engine have exhaust cross over under the carb. It's a two fold problem. The heat under carb is bad, and it's worse with today's gasoline, the exhaust temp is higher.

Also your exhaust flapper valve in the bottom of the manifold could be stuck closed or partial open. Causing even more heat at the carb.

The fuel you seeing on top of the carb IMHO, is from heat boiling the fuel. See it to many times. The engine temp can be normal and the carb still over heat.

Low timing can cause excessive exhaust heat, (and needs to be advanced more because of today's fuel)

Put a 160 t-state in the engine also, reduce the heat!~

Cover the stock fuel line that goes in front of the valve cover also, it gets heat from rad!

===============================================


You said kit? What about the float?
As Al stated, it could also be your boiling the gas in the carb with excessive engine heat and the vapor pressure is pushing around the gaskets. Used to have this problem on my 390FE Furd motor. Had to install a phenolic spacer under the carb to cut down the heat.

Those old brass floats are notorious for leaking. They're usually brazed together and, after a while, will develop pinhole leaks.

John
 

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Discussion Starter #18
As Al stated, it could also be your boiling the gas in the carb with excessive engine heat and the vapor pressure is pushing around the gaskets. Used to have this problem on my 390FE Furd motor. Had to install a phenolic spacer under the carb to cut down the heat.

Those old brass floats are notorious for leaking. They're usually brazed together and, after a while, will develop pinhole leaks.

John
I found a float for $13 but its not local. Still searching. If I can replace the float, adjust and tend to the gasket area, I may be home free. Is their a sure way to test for leaks? Besides shaking it next to my ear or dropping it in a tub of water? I have two of them to play with between my two carbs.

Thats really not a bad idea at all! I might have to swap thermostats anyway. Ive never liked how hot that thing got!
 

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I sold my working riser but.. If its stuck better stuck closed shielding it from heat than stuck open. Try wedging a screw driver in there and lever it closed.

I know the lip in the carb you are talking about but I think its more important to get the surfaces flat than worrying about sanding off the lip. I've worked on carbs that don't even have that lip.

-Tom
 
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