Motor will not turn past 6000 rpms

[00 racin]

Had my first race of the season last week (been out due to back surgery).Money was a little tight due to doctor bills. Got a rebuilt motor from a friend for a great deal, he does a good job for the price. Ran a 6.20 gear last week and turned 6k. Felt like i was hitting a rev limiter coming out of turns and down straights. Switched to 6.50 gear for this week, exact same thing, 6k is it! From past racing it should be around 6800 with that gear. On starts and restarts it will stay on the bumper of the top 5 cars thru first turn and then fall flat. Brand new street fire MSD, not locked, brand new Holley red fuel pump, new ar 135 plugs. tried timing from 32 to 38, no difference. Could it be carb, fuel pressure, cam, plug wires, Im at a loss. Im Gonna put a flame thrower 50k coil and matching module in this week, new plug wires. 355 motor, 425 lift cam, 600 holley carb, engine builder adjusted valves last night at track and no change, heads are fresh 882's.

[DaveBauerSS6]

floating the valves?

[moose52]

Maybe look towards the red pump. My guess would be fuel pressure/flow.

[00 racin]

Whats the best way to check fuel flow? I thought going from 6.20 to 6.50 gear would make a change but not even 1 rpm. Runs the same every lap. I have the pump about 12 inches from cell and its above the cell also, directions said mount below fuel cell but that would be pretty dangerous,lol. The guy who built the motor builds several for local racers and no problems, he said he didnt think it would be floating the valves... Thanks for the suggestions guys

[00 racin]

I moved the motor back and didnt cut the cross member out enough so i put a electric one on, also installed a low oil pressure cut off switch,below 5 lbs of oil pressure and cuts off the pump.

[Driver88]

I had that happen to me. It was my air filter, it wouldn't let it breath enough. And it was a brand new K&N. 14x4. It would actually run better half throttle. I had to put one of them filter tops on it.

[RACR_73s]

Do you have a throttle stop on the carb? That was the problem with my buddy's car, wouldn't let the butterflies open all the way.

[moose52]

I ran a red pump on a 351c. 5-6 psi at idle but dropped to zero at around 5500 rpm. If you can manage a fuel gage outside the cowl or with an isolator to see what's going on that's your best bet.

[Leftterns]

I would agree that the ability to monitor fuel pressure under power would be a good place to begin.

You can buy a good filter designed for a dirt car but whatever you do, don't put one of those tops with the filter media on the car. A disaster for carburetor signal.

[JustAddDirt]

I would bet weak valve springs

[dirtracer2a]

I had the same problem last year, mine was weak valve springs, and floating the valves.

[jedclampit]

That's where I would be looking. Vsprings

[bmodracer]

Valve springs

[floppyfoot]

We have had a few problems with the engine not turning the RPM's that it was. Turned out there were several problems. The valves were jsut a little too loose, this is with anti pump-up lifters, the ignition timing just a few degrees to low and have had a lot of trouble with bad spark plugs right out of the box. Went to NGK spark plugsand have not hada problem with them.

[DaveBauerSS6]

Weak valve springs are identifiable at the track. Down the straight, when it starts to miss, back off the throttle until it runs clean. Do it again on the next straight. A bad valve spring will repeat exactly at the same rpm. Fuel and ignition will vary on load. New springs and expensive springs can be bad out of the box.

I would cut the frame and ditch the electric fuel pump.