Hitman's Pontiac Trans Am Forum

Trans Am Information => Trans Am Tech => DriveTrain => Topic started by: kapn71karl on July 10, 2017, 06:55:21 AM

Title: Stalling when hard braking 78 T/A
Post by: kapn71karl on July 10, 2017, 06:55:21 AM

Stalling when braking. Push clutch pedal in, put in nuetral, brake hard from 15mph or higher and stalls out but starts back up with no problem re starting.
1978 Trans Am Pontiac 400, 4 speed, Just put on a new Holley 750 double pumper mechanical secondaries and manual choke, has an edelbrock performer intake with 1967 GTO heads (ram air). Stock fuel pump. Did not have this problem before when I had the Edelbrock 750 carb on it. Replaced brake booster thinking this was causing a problem. No other vacuum leaks found, did a thorough test! Floats are all adjusted properly. Idle is 800 RPM, timing is set properly.  Vacuum is 15-16 psi.  Car still stalls when braking hard, but starts right back up with no problem. CAR RUNS AND SCREWS down the road beautifully. Tried a vacuum reserve tank, and still have the same problem. Fuel pressure seems to be fine but did not check exact pressure yet or for fluxuations. However, the car would run like s#^* if it was a fuel related problem, wouldn't it?
Anyone please help.... Im at my wits end...

Title: Re: Stalling when hard braking 78 T/A
Post by: NOT A TA on July 10, 2017, 10:54:01 AM

Possible vent issue. When the brakes are slammed fuel slosh in the secondary bowl pushes gas out the vent tube and floods the engine for just a split second and at idle speed shuts the engine off. Vent whistles are available and you can test old school style by using a piece of fuel line arched up between the two vent tubes with an air hole cut in the top of it. If you google "Holley vent tube modification" you should find lots of detailed explanations.

Title: Re: Stalling when hard braking 78 T/A
Post by: kapn71karl on July 10, 2017, 07:16:57 PM

NOT a TA,
  Thanks! I did what ya said and it fixed it!   ;D

Title: Re: Stalling when hard braking 78 T/A
Post by: NOT A TA on July 10, 2017, 09:58:42 PM

Excellent! Glad I could help.

Title: Re: Stalling when hard braking 78 T/A
Post by: kapn71karl on July 06, 2018, 06:54:03 AM

Float adjustment in front bowl and needed a Vacuum reservoir because of the big cam. FIXED!