Engine stall on hard braking (demon carb)- HELP

[DAVID GAGNARD]

Originally Posted by Grubby

My Cobra has a 351W with Edelbrock heads, Performer cam and intake with Demon carb. It runs really good and was dyno tuned by the previous owner. I think it is a speed demon with vac secondaries.

During hard braking the rpm drops and stalls. I suspected fuel sloshing from the rear bowl and flooding the engine, so I connected both bowl vents with a piece of fuel line. No change.

I have set the float level from bottom of the sight glass to 3/4 with no apparent change.

The car runs fantastic in all rpm ranges. The only issue is stalling.

Any suggestions?

John

No suggestions to your problem, but my road race car with a 650 Demon has done the exact same thing from day one, I've tried re-setting the floats and a few other things and nothing really helps..... the only thing I do is downshift and brake while the clutch is out so the engine keeps running.....

BTW: my street car,65 fastback with a 600 DP Holley DOES NOT do this!!!!!!!!!!!!!!!!!!!!!!

I have no clue or answer...........

David

[Grubby]

It is interesting that several others have the same problem.

David,
I have been doing what you do. I shift into lower gears and keep the rpms up to keep from stalling it. That really gets to me. I will get the problem fixed. If I have to buy a Holley, I will.

Note; I am not pulling the engine down by not pushing the clutch in. I was doing a lot of testing today with various float settings. During much of the testing I was getting the car to 45 mph and then putting in neutral before the hard stop.

I plan to call Demon Tech help line on Monday. If they give me anything worth mentioning, I will post here.

John

[DAVID GAGNARD]

John;

I like the Demon carb, I think it is a better carb in some ways than the Holley and easier to work on and tune, that's why I have one on the race car and a Holley on the street car.....

The Demon carb was/is supposed to have some of the things like the extended vents,better floats/better needle/seats and such to prevent the same thing we are expirencings, I made those changes myself to the Holley some time back....

I've tried re-setting the float levels and this seems to make no difference, I've tried a few other little things and have gotten the same results....If you find the problem or figure it out, you'll be both rich and famous!!!!!!!!!!!!!!!!!!!!!!!!

Keep me posted...........

David

[PurpleVenom]

I have two vacuum taps - one for the vacuum advance and one for the newly installed PCV (problem was happening prior to the PCV being added). Under hard braking, the fuel can slosh or move only in the tank and the fuel bowls. That being said, could the fuel pump pickup not be getting fuel? However, the carb should burn the fuel in the bowls. If the fuel in the bowls "sloshes" away from the metering blocks, could that starve fuel creating a lean condition? My thought is the fuel would move away from the primary metering block, and in to the secondary metering block. So maybe a higher float level in the primary bowl would be better? I'm sure you have it, but here is the link to the manual http://www.barrygrant.com/fromBarryG...n%20Manual.pdf

[ray humbel]

had same problem with my 428 with 750 deamon, stall at hard breaking also at slow stop down steep hill. it didn't die, but tried. i had to push the clutch in and hit gas peadle a couple of times. deamon tech said to raise float level. i raised it to top of glass and it helped. ask deamon if longer pickup tubes will help. i think it's starving.

[CHANMADD]

How about the fuel,in the carb fuel bowl, rushing to the front of the car and leaving the jets uncovered by gas.....Lean!!..instantly!
The jet extensions are designed to overcome that. They extend the jet intake towards the front of the fuel bowl keeping them covered. I always blip the throttle and downshift when slowwing down...well 90% of the time.Makes everything smooth.
I think, One has to always remember that when driving a Cobra most things happen a little quicker than in most other cars.
John