34scarab

Looking for suggestions to my problem: I have a pair of fresh 525 sc's that I finally got an opportunity to run. When I get up on plane and hold the throttle steady, say at 3000 rpm, everything is fine. However, when I push the throttles forward, the stb. motor "pops", as if it was hitting a rev limiter or slight backfire. I think it is popping out the exhaust. If I gently ease the throttles on, I and get them up over 4000 rpm. Could this be a vacuum problem or ignition, or both?
It will cruise all day long at a steady speed, it just occurs when you want to get up and go!
I swapped ignition modules but that had no affect.
Watcha all think?

BajaRunner

timing, cracked spark plug, loose or bad wire??

mopower

Sounds like a lean condition when you try to accelerate and it pops , but that's usually the intake side.

Gary Anderson

Check the plugs, see if it's running lean on all cylinders. If only one cylinder seems to be a problem, check the plug/wire. Also check the cam lift for a flat lobe.
Gary

MESABALANCING

IF THE MOTORS ARE INDEED FRESH AND CONSIDERING THERE ARE NO INTERNAL PROBLEMS.CHECK THE FUEL PUMP PRESS. AT THAT RPM IF THE PRESS FALLS OFF UNDER 3 LBS MAKE SURE YOUR CHECK VALVES IN THE TANK ARE NOT PLUGGED UP OR HAVE SOME KIND OF OBSTRUCTION. ALSO ANOTHER THING I'VE SEEN ON THESE ENGINES SOMETIMES THE BALANCER AND THE TIMING COVER DO NOT COINCIDE WITH TOP DEAD CENTER AND THE TIMING WILL BE OFF. YOU CAN CHECK THIS BY REMOVING #1 PLUG AND FINDING TOP DEAD CENTER BEING CAREFUL AND TURNING THE ENGINE OVER WITH A WRENCH SO YOU DON'T DAMAGE SOMETHING. BOTH THE TIMING AND THE FUEL PRESS CAN CAUSE THE POPPING YOUR DISCRIBING AND THAT POPPING WILL DAMAGE AN ENGINE IF YOUR NOT CAREFUL AND GET IT FIXED RIGHT AWAY.HOPE THIS INFO WILL HELP YOU AND OTHERS THIS IS A COMMON PROBLEM IN THESE ENGINES I HAVE THREE IN THE SHOP RIGHT NOW AND THEY HAD THE CHECK VALVES PLUGGED IN THE TANK. LAZ MESA WWW.MESABALANCING.COM

34scarab

Thanks.
I'll check these out.
Dare I ask how to go about checking the check valve?
Is that thru the access panel to the fuel tank?
It only happens to one motor and I am not sure if there are two pickups in the tank. I think fuel is supplied from a manifold which splits it to each motor.
I will mess around with it this weekend and let you know.

Thanks.

GO4BROKE

Sounds lean. I bought fuel pressure gauges. Cheap insurance.

Hot Boat

one fuel line and one pump feeding two motors........... Not good.......... Get a fuel presure gauge and see what happens at 4000 rpm. you should have a steady 7-8 psi all the way up to WOT.

Huffer

34Scarab,
Are the #5 and #7 plug wires laying parrallel and against each other.A light lean condition sometimes shows up at this site because #5 & #7 fire in order.The induction between these two wires can cause #7 to try to fire early and make it pop back through the intake system.Especially if your a little bit lean with a big overlap cam.It's rare but it happens!
Huffer