car stals out

[chevy art]

my buddy has a 408cu in ford engine. hyd roller single plane intake new holley 750 center section and AFR 195cc heads. runes ver strong.when he comes to a traffic light it stalls right out and sputters when stalling. he can prevent this stall only by giving it gas and keep it up a little over 2,000 RPMs. he made no changes to any parts or timing curve or carb reworks. he thinks it is the carb and i think it is electrical. has MSD vac. dist and a regular MSD high output coil, and suggestions are appreciated. it is a 5 speed car. thanks Art in ny

[cgarb]

I would tend to think it's a carburator issue also.

[HQM383]

I notice this too on AFR gauge, I don’t stall but idle is a little off. Driving around AFR will be good and steady between about 13.7 to 14.7 depending on speed coming to a stop like traffic lights AFR goes way up, sometimes 16’s but it eventually creeps back down to where it was set at about 13.0 AFR. This happens over 5 different carbs I have to different degrees. They all have lowered IFR and bottom (position #5) e-bleeds. What I am hypothesizing is that the bottom e-bleed is being exposed during driving and coming to a stop fuel is backfilling the air well through all e-bleeds from the main well and this is somehow affecting total fuel delivery to IFR until air we’ll is full again. I came to this hypothesis due to playing with various e-bleed combinations in the past. Changing nothing on a carb but either introducing an e-bleed at pos 5 that was blocked or making pos 5 larger changed the idle quality. The larger the e-bleed hole, the better idle quality. 383 sbc single plane manifold 245 @ .050” cam.

Caveat is different problems can show as similar symptoms.

[Tom68]

Fuel pressure too high commonly results in this scenario, spits out the vents.

[mag2555]

If when the motor stalls out he can pretty much start it back up again without opening up the throttle then you rule out the Carb flooding out at least.

With that being said thought if with the car out of gear and sitting still you can buzz it up to 5000 rpm and let it drop right back to idle and it does not stall out then you have to factor movement into the equation and that then leads right back the Carb and fuel level control if you want my two cents worth.

[rp930]

Float levels too high?

[skinny z]

Is the vacuum advance connected to manifold or ported vacuum?

[chevy art]

Skinny i guess you mean is it connected to the small port on bottom of carb on base plate. i asked my buddy that very question and i didnt get a straight answer. i will go check that out myself tomorrow. thanks Art

[skinny z]

Skinny i guess you mean is it connected to the small port on bottom of carb on base plate. i asked my buddy that very question and i didnt get a straight answer. i will go check that out myself tomorrow. thanks Art

The reason I ask Art is often, when connected to full manifold vacuum, the idle timing can get a little weird.
It can be a particular problem with stick cars on initial off idle acceleration. I believe the effect is known as torque sag.
That said, it may be an issue when bringing the engine down from higher cruise vacuum to what you would at idle.

[chevy art]

thanks skinny for good explanation. thanks to our other members who have put some good input in to my friends engine problems Art in NY

[chevy art]

i checked back with by buddy and he now tells me it stalls out immediately when he just starts it up sitting in his driveway and not moving. in other words he just starts it up, it runs for a few seconds and cuts out. same thing happens when he drives it and comes to a light. in other words, it just wont idle. it was fine till he took motor apart and put it back together. i dont think it is carb. i could be wrong. any ideas. thanks Art

[skinny z]

Seeing as the engine has been apart, it could be any number of things.
On a fundamental level, has anyone put on timing light on this?
A vacuum gauge would also be useful for diagnosis.

[chevy art]

went to friends house with one of my good carbs. car does the same thing with my carb as his does with his carbs within about 200 RPSs. starts up, rev it up a bit, and let it idle down and at around 1300 to 1500 RPMs it cuts out and also diesels back through the carb. he says the timing at around this rpm is aprox 18 to 20 degrees.. car just wont run when the idle goes down. and it is hard to restart.. i suspect distributor internal problem, or other ignition parts problem. it is an older MSD vacuum advance dist.(vacuum is disconnected for all these tests. also wonder about the stock type fuel pump. is there a way to test Ga. per Hr pump capacity of these types of fuel pumps?. this one baffles me. thanks Art in NY

[HQM383]

Weak spark?

[cgarb]

Vaccum leak somewhere?