Dead spot in the throttle!

The motor hesitates the moment I hit the throttle for the burn out. After that no problems. It also shows on the data recorder that the fuel pump pressure goes to 0 when the motor comes up on the two step. My guess it would show the same thing for the burn out but it is not captured by the recorder. Very new car, very fat, still working on getting the fuel/egts/everything else into a happy place.
Any ideas?
Thanks ITA!

 

Are you monitoring fuel pressure?

 

Yes. The recording does not go back far enough to show the hit for the burnout but it does show the when it go onto the two step.

 

Try richening the idle.

 

You did use a wire reinforced hose to connect the hard line to the bottom of the fuel pump? It will suck a plain hose shut.

 

fuel psi going to ZERO its not a BV problem, check the line from pump to tank for seal. And like Jody said, be sure it has the wire in it. I am gonna bet its sucking air, or sucking shut, or its the tank itself creating a vortex at the pick up

 

I would think the engine would have to quit to read zero, mine holds pressure on the sensor momentarily after shut off on the log. Pump turns at 50% of the crank rpm so even at 500 rpm its spinning 250 rpm , where as an Air pocket or sucked shut intake hose would briefly spike down, until the engine lost rpm and the pump recovered. Reading Zero on the log. If it were holding some psi, I would for sure agree with the BV diagnostic. But he said the only time it hesitates is on the burnout and after that its fine, but that it does go to ZERO on the data log briefly when on the two step, but he didnt say it tried to lay over.

 

We set the barrel valve leak down with gages as a starting point, then we start the engine and crack the throttle, if it hesitates we richen the BV 1 "flat" at a time until the hesitation goes away.

 

The fuel line is the thick style that is methanol approved and has the wire reinforcement. I will check the clamps to make sure that it is not leaking air. As the tank goes this is an older McKinney funny car and I can not see the bottom of the tank too many baffles.

If I were able to collect the fuel pressure at the start of the burnout I wonder if it drops there too. I would guess that there is a hesitation/dead spot when it goes on the two step, but the car is not moving and the pedal is all the way down/open so its not as noticeable.

Thanks

 

It's an RPM. It can be triggered manually but currently it is armed by the crew after the burnout and is triggered by drive shaft movement.

 

Check the idle return check valve is not jammed partially open.

 

old gremlin

Just asking..............on the barrel valve side of the injector, is the linkage in front of the throttle blade cross shaft or behind it ?





Bob Meyer
Meyer Race Cars / San Diego
2015 Our 50th Anniversary

 

My bet is the spool is 180* out. The ramp closes then opens to the back side of the spool hole.