Secondary carbs on tripower - Pontiac GTO Forum
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post #1 of 18 (permalink) Old 07-10-2016, 04:40 PM Thread Starter
 
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Secondary carbs on tripower

I am having a problem with the rear carb with excess fuel running into the bores. I originally thought it was a problem with the float, but that looks really good with no leaks. I submerged it for several minutes in water, about 20, when I released it, it came right back up to the surface, and no water was inside when I shook it.

Next I checked for pump discharge leakage. There was a small gasket between the venturi cluster and difuser, (synchromesh), but no gasket between that and the screw head. So I placed a gasket there.

That only leaves the needle and seat.

This had been a problem up until 3 years ago when I pulled the entire intake set-up off and ran the Carter AFB. 2 years ago I rebuilt the carbs and checked everything out with a fine tooth comb. So it has been sitting on the bench for the last couple years until a month ago when I decided it was time to reinstall it. When I put fuel to the carb it looked like a faucet running.

Even though the needle and seat and gaskets were new. Is this just from sitting and need a new needle and seat, or is there a bigger underlying problem that I am not picking up on? Thank you for any help.
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post #2 of 18 (permalink) Old 07-10-2016, 10:16 PM
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I have been running tripowers since the '70's, and have had good results using the old all brass needles without the rubber tip. I think the new alcohol-tainted fuels can hurt the rubber tip and the accelerator pump cup. My buddy has replaced two cups in his tripower car in the past 6 months.....I haven't worked on my '65 tripower's carbs in about 30 years, but they have brass needles and leather cup seals. I think you have a needle/seat problem, or the float is physically bent and hanging open against the side of the bowl, etc, keeping the needle/seat open. These are simple carbs, and, once set with original quality parts, are really bulletproof. Don't overthink it. Check the float, and needle/seat. Good luck.
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post #3 of 18 (permalink) Old 07-11-2016, 08:43 AM Thread Starter
 
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Thanks Geeteeohguy, I placed the airhorn back on the body, and turned the carb back and forth. I can here the float moving freely opening and closing the needle. I have been researching the needle and seats, and see a new style from Daytona Carburetor. Have you heard anything about these and how they might work?
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post #4 of 18 (permalink) Old 07-11-2016, 02:59 PM
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Nope.
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post #5 of 18 (permalink) Old 07-12-2016, 01:06 PM
 
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What are you running for a fuel pump? The original A/C Delco fuel pump was calibrated to supply only 4-5 psi. Aftermarket pumps routinely supply in excess of 7 psi, which is enough to unseat the needle from the seat in some carbs. It could affect one carb and not another in your tri-power set up.

When the only tool in your toolbox is a hammer, you tend to see every problem as a nail.
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post #6 of 18 (permalink) Old 07-13-2016, 08:53 AM Thread Starter
 
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I've got an older AC-Delco fuel pump, believe I purchased it from Ames many years ago.
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Quote:
Originally Posted by gtoguy389 View Post
I've got an older AC-Delco fuel pump, believe I purchased it from Ames many years ago.
You should be fine for fuel pressure. I'd look at the neoprene tip on the needle and see if it's damaged. Or just replace it.

When the only tool in your toolbox is a hammer, you tend to see every problem as a nail.
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post #8 of 18 (permalink) Old 07-13-2016, 01:01 PM Thread Starter
 
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After looking closely at the rubber needle tip, there is one little spot that just doesn't look right. It does not look like enough to be a problem with the naked eye, but I just ordered a new needle and seat assembly from Daytona Parts. Hopefully this will fix the problem.
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post #9 of 18 (permalink) Old 07-14-2016, 10:48 PM
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Garage
Make sure the throttle plates on both end carbs are closing completely - 100% - if even a little air is leaking past them at idle, you'll have problems. GM had a special epoxy sealer they sometimes applied to the plates to make sure they sealed shut at idle.

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post #10 of 18 (permalink) Old 07-15-2016, 10:00 AM Thread Starter
 
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Thanks Bear. When I had the Carbs up on the bench I did a lot of work to ensure they were closed completely. The Daytona valves came today, hopefully by Sunday I will have time to work on them again.
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