Fuel Bowl Drains Overnight - Team Camaro Tech
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post #1 of 38 (permalink) Old Jan 11th, 07, 06:55 PM Thread Starter
Mike
 
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Fuel Bowl Drains Overnight

Hi All - Here's my problem:

Speed Demon 750 Vacuum Secondary

I bought this carb about 2 years ago and it had never given me problems until a few months ago. One day when I went to start the car as usual, it wouldnt start and the engine was completely flooded. I waited a few hours and tried again, the car barely ran, flooded and fouled the plugs. After doing the usual checks, I came to realize that both fuel bowls are draining into the intake and letting raw fuel into the motor when it sits overnight(sometimes it takes a day or so). I have rebuilt the carb 4 times, using new gaskets,PV,needle/seat, etc....and still have the problem. Right now the carb is sitting on a stand in my garage, and over a weeks time the fuel level goes from the top of the site window to the bottom. (normally the floats are set with fuel at the bottom line on the window, i just filled em up to the top for testing purposes) If i put the carb on now, it fires up and runs fine....but let it sit and the same issue.

I know it is not a fuel pressure/pump problem, b/c i have an old holley on the car now, and all works fine - car starts up everytime w/o issue. I have used Holley rebuild kits with the blue gaskets and the barry grant kit with red gaskets. I cant figure out what is wrong....I am thinking that fuel is just trickling out of the transfer slots somehow as it sits...Both bowls will drain, but the primaries seem to go quicker.

Anyone had a problem like this before, or any ideas why its leaking? Any ideas are appreciated except "buy a holley/Qjet" THANKS
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post #2 of 38 (permalink) Old Jan 12th, 07, 04:20 AM
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Re: Fuel Bowl Drains Overnight

With it leaking, I would figure you would see tell-tale signs of fuel.

During your 'bench test' for leaks, you might add some food coloring for a better leak detect to see the problem. Lay the carb on a sheet of paper and check the location of wet spots. If sheet shows spotting, wonder if colored lamp oil could be sibbed for leak detector?

If it takes a week to drain the diameter of the sight glass, the fuel could be evaporating. Surface temp of carb bowl with a temp gun?

Might be too porous of material used. Gravity is a powerful tool.

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post #3 of 38 (permalink) Old Jan 12th, 07, 06:22 AM
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Re: Fuel Bowl Drains Overnight

Not familiar with the Speed Demon, but if it has power valves, have you changed them ?? If the diaphragm is ruptured, they may be able to seep fuel.

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post #4 of 38 (permalink) Old Jan 12th, 07, 06:29 AM
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Re: Fuel Bowl Drains Overnight

I can't answer your question, but if this has been happening alot, you might ought to sniff for fuel in your oil...just to be careful you're not gonna have another problem due to this one.
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post #5 of 38 (permalink) Old Jan 12th, 07, 06:31 AM
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Re: Fuel Bowl Drains Overnight

(706) 864-8544

That's the product support number for Barry Grant carbs. I'd call them................

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post #6 of 38 (permalink) Old Jan 12th, 07, 06:34 AM
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Re: Fuel Bowl Drains Overnight

We forgot ......... Welcome to the Club!

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post #7 of 38 (permalink) Old Jan 12th, 07, 06:47 AM
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Re: Fuel Bowl Drains Overnight

Quote:
Originally Posted by Everett#2390 View Post
We forgot ......... Welcome to the Club!
YUP... ...didn't notice it is your first post !!

...38 Chev coupe, street rod
...54 Chev 210 coupe
...62 Impala SS, driver/project
...67 Camaro, ss/rs LA built driver/project
...66 Chevelle SS, Atlanta built 138 driver/project
...69 C10, cab and clip may end up on the '89 rollback
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post #8 of 38 (permalink) Old Jan 12th, 07, 07:10 AM
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Re: Fuel Bowl Drains Overnight

I think the Demon's larger, shiny fuel bowls have a greater tendency to evaporate fuel into the engine after shutoff than other carburetors. Did you recently change gas stations or did they do anything to their mix? I simply cannot run cheap gas in mine. Fuel today isn't designed for a carburetor... in my opinion.

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post #9 of 38 (permalink) Old Jan 12th, 07, 10:06 AM Thread Starter
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Re: Fuel Bowl Drains Overnight

Thanks for all the replies and welcomes.

-I actually bought the food coloring early in the week to do the same test you spoke of everett...b/c gas isnt showing by itself on the sheet of paper it sits on now.

-I have changed the power valve about 4 times.

-Yes, fuel did get in the oil, and I have drained and changed already.

- I called the BG tech line and got no help...the guys response was "thats odd, dont know how thats happening" As we discussed, the only thing he said was to send it to BG for a full rebuild & flow testing($225 + shipping) and the carb will run like new. Considering the carb will work now, i am worried that they could bench test it and see no issues..only to send it back to me with the same problem. I then asked him if there would be a full warranty on the rebuild (like i want a new carb if the same issue occurs) and he said if it happens again it must be the car. I hung up.

- I have used the same Shell gas station for years...and only run 93 octane. I wouldnt know if they changed anything.

-Also some more info, when the carb is on the car and its running.....it tends to backfire back through the carb when snapping the throttle open quickly. With the 650 holley on the car - i dont get any backfires. Not sure if this will help anyone think of a solution, but im throwing it out there.

Sorry for the miracle sized post, but wanted to answer all questions. Heres a bit about the car...'69 Camaro - 383, 9.5:1, AFR 195cc heads, edelbrock performer air gap intake, .512 lift cam 232 duration, accel HEI, 700r4 and 3.73 rear.

Thanks again for the help.
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post #10 of 38 (permalink) Old Jan 12th, 07, 10:34 AM
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Re: Fuel Bowl Drains Overnight

pull it apart, and check all the flat surfaces with a straightedge.
i don't know what this will accomplish, but it sounds good to me..
oh, yeah......

get a q-jet..
hehe

you don't plan sincerity.
you have to make it up on the spot.

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post #11 of 38 (permalink) Old Jan 12th, 07, 02:26 PM
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Re: Fuel Bowl Drains Overnight

I can't think of any way for fuel to get into the engine when off other than the orfices in the metering plates. Should be same as holley . I have heard stories that their metering plates have more porosity? How about wrong gaskets on the block to body side? Wonder if you could, put the holley meter plate on the BG on the bench and test? Seems fuel has to go thru the meter plate to get into the ventri or transfer slot and into engine. How about the base plate screws, are they tight? Is the bowl vent unplugged?

Don
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post #12 of 38 (permalink) Old Jan 12th, 07, 02:35 PM
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Re: Fuel Bowl Drains Overnight

I don't have the answer, but I had the same exact problem with that same carb.

It would drain the primary bowl when sitting over night, and gas would run down and puddle on the intake.

I tried everything too. The blue gaskets, power valves, and checked all the surfaces with a straight edge. Everything looked fine.

This was on a brand new Demon and still under Summit warranty.

Porosity was my guess, but I couldn't find it.

I sent it back and went with the usual Holley carb.

I should also mention that I have installed 2 other Demons on different cars with no problems at all, other than finding chips/filings from the machining inside the float bowls.

Don ~ TC Member #15 ~
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post #13 of 38 (permalink) Old Jan 12th, 07, 03:56 PM
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Re: Fuel Bowl Drains Overnight

I'm sure your probably doing this right but, are you sure the gaskets on the pwr valves arn't getting caught on the edge of the valve and preventing getting a good seal.

Dennis
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post #14 of 38 (permalink) Old Jan 14th, 07, 02:16 PM Thread Starter
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Re: Fuel Bowl Drains Overnight

Thanks for more thoughts....especially ZZ430DropTop67RS - it makes me feel a bit better that im not the only one.

I have done the power valve so many times, i doubt i screwed it up everytime.

zdld17, why did you ask if the vents are unplugged? I never really did anything with the vents...

I just set up my food coloring test to see if I can nail down exactly where the fuel is coming through. After that I will begin to test using different parts with some holleys I have. Im going to try using the metering blocks and base plates interchangably next to help nail down the problem.
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post #15 of 38 (permalink) Old Jan 14th, 07, 02:43 PM
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Re: Fuel Bowl Drains Overnight

Quote:
Originally Posted by rossi1369 View Post
Thanks for more thoughts....especially ZZ430DropTop67RS - it makes me feel a bit better that im not the only one.

I have done the power valve so many times, i doubt i screwed it up everytime.

zdld17, why did you ask if the vents are unplugged? I never really did anything with the vents...

I just set up my food coloring test to see if I can nail down exactly where the fuel is coming through. After that I will begin to test using different parts with some holleys I have. Im going to try using the metering blocks and base plates interchangably next to help nail down the problem.
Only think I can think of was after motor was hot, and fuel bowl was plugged at top vent, it would build pressure and force out thru main jets and on to ventri?? Looking at bowls. there is no way for fuel to escape fuel bowl, UNLESS , you have a accellorator pump diaphram with a hole in it and the little red check valve flapper is dried up. But you will see it on the manifold in drops unless it dries up and never see anything unless you put some thing like a paper napkin to pick it up. Thats my best guess.

Don
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