Is this normal?
Thread Starter
Pro
Joined: Sep 2004
Posts: 690
Likes: 0
From: Madison WI
Is this normal?
Hey guys, just had a quick question about something my Vette has done a couple times in emergency situations...it's not a big deal at all, more of a curiousity thing...
Anyway, under very hard braking (as much pressure on the pedal as I can apply from 55-60mph) and in neutral, my Vette will die before I come to a stop. My guess is this is because as the nose dives hard, the fuel from the idle jet can't be sucked out enough as it is being "pushed" to the front. Now as you guys can probably tell, I'm a carb newbie...I have a lot more experience/knowedge with EFI and this is the first carb'd car I've ever had any experience with...is my explanation correct or is it something else entirely?
Thanks guys
Anyway, under very hard braking (as much pressure on the pedal as I can apply from 55-60mph) and in neutral, my Vette will die before I come to a stop. My guess is this is because as the nose dives hard, the fuel from the idle jet can't be sucked out enough as it is being "pushed" to the front. Now as you guys can probably tell, I'm a carb newbie...I have a lot more experience/knowedge with EFI and this is the first carb'd car I've ever had any experience with...is my explanation correct or is it something else entirely?
Thanks guys
Drifting
Joined: Sep 2004
Posts: 1,532
Likes: 4
From: Fairview Heights Illinois, near Saint Louis MO, STL C3 Shark
I've heard of this, and experienced it in my brother's 79 subird where we put a 283 small block in it. I think it was that the g-force of the decelleration caused the gasoline in the fuel bowl of the carb to rush forward and let the engine to go without fuel and die. Or If the float drops when this happens, more fuel is pumped into the bowl, when you finally stop, the engine gets flooded and dies. I know this was the case on my bro's car as it was always hard to start afterwards as if it was flooded. But I definitely think it is carberator related.
my $0.02
my $0.02
Burning Brakes
Joined: Jul 2000
Posts: 1,162
Likes: 2
From: Beaverton, OR
Is it a Q-Jet, Holley, ??? I know on a Holley (I have this problem now with mine) you can get fuel slosh from the rear bowl up the vent tube and down into the carb which will flood the engine. There are several "solutions" to this problem, including lowering the float level, installing a tube between the vent tubes with a hole in the apex to let air in, and installing fuel bowl vent baffles. So far with my problem nothing has worked 
On a Q-Jet the problem is different, I think it is normally fuel starvation, but I don't recall for sure. I'm not very familiar with Q-Jets, so someone else will chime in I'm sure.
-dath
On a Q-Jet the problem is different, I think it is normally fuel starvation, but I don't recall for sure. I'm not very familiar with Q-Jets, so someone else will chime in I'm sure.
-dath
Drifting
Joined: Oct 2004
Posts: 1,259
Likes: 7
From: Ontario
I have this problem with my Holley. Must be design. A forum member suggested that I drop the fuel level in the secondary. I did that and it made it much better but not completly eliminated. I do not want to drop the level down lower...but it is now acceptable to me since it now only happens except on very aggressive stops.
Thread Starter
Pro
Joined: Sep 2004
Posts: 690
Likes: 0
From: Madison WI
It's a Holley Street Avenger 670...
Thanks for the replies guys. I'm probably not gonna do anything about it as it has only happened twice on extremely aggressive stopse (like I said, 60mph+ and full pedal pressure), I just wanted to know what was causing it
Thanks for the replies guys. I'm probably not gonna do anything about it as it has only happened twice on extremely aggressive stopse (like I said, 60mph+ and full pedal pressure), I just wanted to know what was causing it
Melting Slicks
Joined: Dec 2000
Posts: 3,407
Likes: 2
From: Carmichael CA
I believe all single reservoir carbs have the reservoir in front of the venturae. Thus, the metering jets are at the bottom of the fuel bowl closest to the venturae which puts them at the back of the bowl and will cause the engine to go lean under braking. There are indeed carbs such as the Holley double pumper which has a reservoir at the back of the carb as well as the front.
It's still not a final solution though, because, of course this problem is totally corrected with fuel injection where pressure and not fuel level determines the amount of fuel to meter.
This problem also occurs taking sharp fast turns. I find my fuel metering going bad when I'm taking freeway onramps at 50+...I'm not totally sure if I'm getting starvation or flooding...in other words I'm not sure if the fuel is sloshing over into the venturae, or exposing one of the metering systems to a lean condition, all I know is that I lose power until I straighten her out.
It's still not a final solution though, because, of course this problem is totally corrected with fuel injection where pressure and not fuel level determines the amount of fuel to meter.
This problem also occurs taking sharp fast turns. I find my fuel metering going bad when I'm taking freeway onramps at 50+...I'm not totally sure if I'm getting starvation or flooding...in other words I'm not sure if the fuel is sloshing over into the venturae, or exposing one of the metering systems to a lean condition, all I know is that I lose power until I straighten her out.
Burning Brakes
Joined: Jul 2000
Posts: 1,162
Likes: 2
From: Beaverton, OR
All of this being said, with my old motor and the Q-Jet it had, I didn't have any of these issues. I could hit my brakes as hard as I wanted and I had no cutout. I could take corners to just before the point of sliding and no cutout. I'm having more issues with the Holley which I got because I thought it would be an easier carb to learn with. I think it has been that, it is very easy to work on, but it has been more problematic as well . . . Well, really just this one issue (I think I have the cornering problem as well, but it is harder to tell because I've been braking very hard on corners where I had issues in my work parking lot) . . .
I also have a fuel injection setup sitting in a cupboard that I am thinking of using, but I need a computer for it as it is setup for marine use . . . I'll save that story for a new thread though
-dath
I also have a fuel injection setup sitting in a cupboard that I am thinking of using, but I need a computer for it as it is setup for marine use . . . I'll save that story for a new thread though
-dath
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Instructor
Joined: Jul 2005
Posts: 220
Likes: 0
From: Oakdale Ca
I had a similar situation many years ago, turns out I had two issues...my carb floats were too high (780 Holley, forget the list # but a vacuum secondary carb)...corrected this and 75% of the problem went away...took it to a friend who found my vacuum booster diaphram for the power brakes has a small rupture...we replaced it and no more issues.
Burning Brakes
Joined: Feb 2005
Posts: 1,235
Likes: 0
From: Mesa AZ
Originally Posted by 72Tornado
...
Anyway, under very hard braking (as much pressure on the pedal as I can apply from 55-60mph) and in neutral, my Vette will die before I come to a stop.
Thanks guys
Anyway, under very hard braking (as much pressure on the pedal as I can apply from 55-60mph) and in neutral, my Vette will die before I come to a stop.
Thanks guys
Burning Brakes
Joined: Jul 2000
Posts: 1,162
Likes: 2
From: Beaverton, OR
Well, if he is pushing as hard as possible and he can't lock up the tires, then he probably needs to look at the brakes as well . . . Being able to lock up the tires is a feature, not a bug Not that you want to lock up the tires, but the brakes should easily be able to apply that much force. . .
-dath
Not that you want to lock up the tires, but the brakes should easily be able to apply that much force. . .-dath
