My car is always nearly stalling when I slam on brakes. I've been trying to figure out what the deal with it is for a while. Its a Holley 650 DP. It has the whistles in the float bowls so i doubt fuel is flying down into the venturis from the vents or whatever.

I then thought maybe it's the fuel pressure regulator getting weird at high g's like that...but I dont know that that would instantly overflow teh fuel bowls to make the car nearly stall.

And the only other thing I can think of is that I hae the brake booster running off the big port in the back of the carb. Would it be better to run my brakes off a vacuum port in the intake instead of the carb baseplate?

I built this car for autocross, and I've been taking care of all the other nagging issues for a while (I just got it together about this time last year), but this one isnt going away and I cant really do the autocross thing if I have to be taht touchy with the brakes. It's really starting to get on my nerves.

 

I got the same carb and the same problem with a few other problems. Subscribed.

 

It's usually caused by too low of vacuum. What is happening is that when you take all the vacuum away from the engine it stalls. (Remember vacuum is what pulls fuel from the carburetor) A common problem is that the initial timing is too low and can cause this issue. A higher timing setting can create more vacuum for the engine. This may sound high but reset your initial timing at 16-18 degrees then use a vacuum gauge to set the idle mixture screws to the highest reading on the gauge at idle. Sorry if you already have done this but this has fixed my problem in the past with this issue.

 

The problem is that the fuel inside the bowls is flying forward inside and staying there...uncovering the main fuel circuit and causing the stumble....not an issue for the secondaries but is for the primaries. I think if you get some jet extensions from Holley, that will fix your problem. This should keep your main jets submerged in fuel even under hard braking and cornering. Verify your float level though....hope this helps.

 

Please DO NOT put jet extensions into the primary side!!

This will cause the jets to be uncovered when you excelerate. In fact, it isn't really recommended for street driving at all. Kind of a drag only device. Although I've seen street cars with them plenty of times.

I have seen this issue before at the dragstrip when someone is doing a burnout and slams on there brakes so that they don't go past the staging beams. (RULES) Most of the time it takes a few cranks to get the car restarted because of the time it takes to pump more fuel into the bowl.

Another thing to check is make sure that your float level is set properly and not too low. BTW, I still think that your issue is timing if your engine isn't completely dying.

 

i think it would be more of a problem of flooding. i would make sure the fuel level in the bowls are slightly below the site plug and not at the bottom. maybe run a hotter spark plug and maybe a little less pump shot. make sure the timing is not too retarded.try raising the idle speed to around 1000rpm.

 

1. Initial timing is at 17 degrees. It used to be set at 19. Made no difference.

2. Floats are set to barely trickle out of the sight plug when my fuel pump is on.

3. It pulls about 15-16 inches of vacuum. I dont think that's low enough I should be having vacuum problems... but maybe it is?

4. Im running R45LTS plugs, they're the same heat range as R45TS. That's a fairly hot plug right?

5. The car used to idle around 1000 all the time due to some weird issue I was having with the carb, it would do the same thing then. It didnt make much of a difference.

But yesterday I was just cruising along at 5 mph with the car in neutral, and I decided to just stomp the brakes at low speed just to see what it would do, and just going from 5 mph to 0 that briefly made the car stutter and flutter. It then recovered a couple of seconds later.

Is it maybe a better idea to use a vacuum port on the manifold?

The brake booster still has vacuum after I turn the car off. And if I hold the brake in at idle it doesn't do anything funny at all. So I dont think it's a brake booster vacuum leak.

Maybe I should tape a vac gauge to the windshield and see what the vacuum does?

And yeah, it's a PITA trying to scrub the tires at the strip, because I have to go slam the brakes and it always dies as I get the car stopped. So its the same issue. I've found people complaining about the same problem online, but I havent found ANYTHING conclusive on how to fix it yet None of them have ever said how they resolved it. Im thinking I wont ever fix it at this point. Lots of talk about whistles and jet extensions but I've heard far more things that suggest to me those jet extensions are a bad idea, and it already has the "whistles" in it anyway.

 

all sounds ok except float level. it needs to be about 1/8" below the site plug with the engine at idle.

 

Give Patrick a call at this number. He is a tuning expert. (727) 490-5717

I think he can set you in the right direction and is always willing to help. Post up results of this conversation.

http://www.prosystemsracing.com/index1.html

 

Any update on this?

 

I never was able to fix it.

 

I had a problem similar to this once, the brake booster was plugged into the carburetor, so i switched it over to the intake, and it worked fine after that.

 

Mine stalls under hard braking when I'm low on fuel.

(305 TBI)

 

That's because your fuel pump gets starved. Us carb guys have our own little fuel tanks attached to the intake (the fuel bowls), so even if the pump is momentarily starved, there's still fuel ready to go into the engine for short time (I'd guess 20-60 seconds worth of it depending on situations).

 

Does anyone out there have a carb setup that doesnt want to stall when you slam on brakes? Im starting to wonder if this is just normal.

 

Is there a conventional check valve on the 1/2" hose that connects to the Booster? If so I think I might (as a test) pull that out cover it with a piece of heavy plastic or duct tape and plug it back in. Then being aware that you don't have power brakes, take up a strait road with no traffic and hit the brakes... See what happens.

Also that check valve could be bad, seen it a couple of times..