hlep - engine missing bad at part throttle

MistressMotorsports · #1 (**permalink**) 10-16-2001, 09:46 PM

While at Willow Springs, I noticed that after about two laps, my car would stumble badly while downshifting in braking zones and then while cornering. Once I got back on the throttle hard, the car caught and ran well. It was suggested I raise the floats, which I tried with no luck (Barry Grant carb.) Fuel pressure appears good, although the gauge is under the hood, so I can only check in neutral. The fuel filter is clean. Maybe running out of fuel? But, if so, why doesn't it miss at the end of the straights under load? Any ideas?

Mike

Leroy · #2 (**permalink**) 10-17-2001, 12:32 AM

It could be while cornering and braking the fuel in your float bowls are closing the float valve-also could be a fuel pickup in the fuel tank. you might try calling barry grant and explain the problem. I know that after changing to center hung floats that are taper at each end to solve the cornering problem, I had the same problem.I believe Barry Grant has the road race floats.
Good luck,
Lee

dalola · #3 (**permalink**) 10-17-2001, 06:09 AM

Mike,
How far did you raise the floats? I experienced the same problem with my BG, and kept raising the floats. Eventually, I had the fuel level at the very TOP of the sight plug, and that eliminated the problem. If you are still around half or 3/4, you may want to crank the floats up more. Amazing what that little extra will do. The BG's seem to be very sensitive to this, and respond well.
Just a thought.
Dave

CobraEd · #4 (**permalink**) 10-17-2001, 06:13 AM

If you have the vacume advance hooked up, you can get a breakup at part throttle or when you are off the gas during these high vacume conditions. If you have your overall timing set pretty high, that extra advance that the vacume advance produces can cause the engine to break up and miss. Once you step on the gas, the vacume drops, and the extra advance from the vacume advance goes away. To test this out, just pull the vacume hose off at the distributer and plug it. Then drive the car and see if the problem goes away.

Ed

Dominik · #5 (**permalink**) 10-17-2001, 08:20 AM

Mike,
can you mount the fuel pressure gauge inside the car?
It's almost worthless under the hood.

Check for bent fuel tubes that may tend to close when the engine moves.

Dominik

chopper · #6 (**permalink**) 10-18-2001, 09:18 AM

A couple of questions for you: (1) Does the problem manifest itself when going into turns of one direction, eg left turns as opposed to right turns? (2) Does the carb have side-hung or center-hung floats? The purpose of these questions is to determine if you have a problem caused by improper float type. Holleys (upon which Barry Grant carbs are based) can be equipped with either center-hung or side-hung floats. The center-hung floats were developed for the roundy-round cars, while the side-hung (older) floats are more suited for the straight-line crowd. The center-hung floats tend to be a little more forgiving and fuel-level self-correcting during the lateral forces present in the corners. Check to see if your carb has the proper floats for the track.

Dominik · #7 (**permalink**) 10-18-2001, 11:45 PM

There is also a version of the center hung float with a cut edge giving a little more fuel at that side in the carb.

I bought it once but never installed them.

Dominik

JAM1775 · #8 (**permalink**) 10-19-2001, 06:46 AM

Does your BG carb have jets extensions in the rear ? I once had a stall problem on hard braking and BG advised to remove the equipped jet extensions. They are reall only for hard launching drags race cars. If the fuel rolls to the front of the bowl (hard brake)the extensions actually inhibit flow rather than enhance it.

MistressMotorsports · #9 (**permalink**) 10-20-2001, 10:41 AM

Well, I was concerned that the fuel pump I had was borderline for volume, so I put a larger one on. No change, but I feel better. We raised the float level pretty high and noticed an improvement. The problem moved to a stumble only under low rpm coasting, like first gear tooling around the pits. So we cleaned and messed with the air bleeds, which helped. That lowered the idle rpm to around 500, which is easy to change. Ran out of daylight, so I'll adjust the idle and check again. Big improvement, though. I really don't know what floats are in the carb, since the motor came with the car, but I'll check and put in the road race type if not already there. So, it works now, but I'm not really sure why it changed, maybe the weather. Thanks for all the help.

Mike