Zane Bridgers
New Member
Hello - I wanted to compile a list of the potential causes of low max RPM for those trying to diagnose the same problem. My research has yielded the following:
Fuel Delivery Issues See Troubleshoot-Fuel-Delivery-Problems-
.... Carb rebuild
Water Control Valve/Regulator Limits revs to ~5000 - detach from exhaust and check for lower water flow at higher RPM (don't run for long, exhaust will melt things)
Rave Valve Limits revs to ~6000 - try removing springs to test or rebuild.
Rectifier Causes lots of issues - in MPEM, 3 yellow wires, 1 red - try unplugging red wire (no charging so don't run it long).
Bad ground connection Causes erratic ignition - Run jumper cable from negative battery terminal to somewhere on engine.
Impeller Issues - mismatched, worn ring, altitude.
Low Compression - 110 psi is the low limit for older engines, though this is certainly debatable
Crankshaft bearings - lots of bad noises coming from engine bay.
Please add others in the reply and I will update this post
___________________________________________________________________________________________________________
My problem: 1997 Challenger w/ single 787. Cannot sustain above 6000 RPMs or 5500 w/ 4 people. Compression is 127psi at 3,500ft elevation. Have troubleshooted all of the above except crankshaft bearings (some knocking at low rpm but not too nasty) and the impeller.
Boat struggles to accelerate and plane, so even though my RPMs still seem low, I'm leaning towards impeller issues.
Fuel Delivery Issues See Troubleshoot-Fuel-Delivery-Problems-
.... Carb rebuild
Water Control Valve/Regulator Limits revs to ~5000 - detach from exhaust and check for lower water flow at higher RPM (don't run for long, exhaust will melt things)
Rave Valve Limits revs to ~6000 - try removing springs to test or rebuild.
Rectifier Causes lots of issues - in MPEM, 3 yellow wires, 1 red - try unplugging red wire (no charging so don't run it long).
Bad ground connection Causes erratic ignition - Run jumper cable from negative battery terminal to somewhere on engine.
Impeller Issues - mismatched, worn ring, altitude.
Low Compression - 110 psi is the low limit for older engines, though this is certainly debatable
Crankshaft bearings - lots of bad noises coming from engine bay.
Please add others in the reply and I will update this post
___________________________________________________________________________________________________________
My problem: 1997 Challenger w/ single 787. Cannot sustain above 6000 RPMs or 5500 w/ 4 people. Compression is 127psi at 3,500ft elevation. Have troubleshooted all of the above except crankshaft bearings (some knocking at low rpm but not too nasty) and the impeller.
Boat struggles to accelerate and plane, so even though my RPMs still seem low, I'm leaning towards impeller issues.
