BF90 not reaching 5500 rpm, runs great not a prop issue
This is my 1st post here. Have been reading and can see there are knowledgable people here.
Here is a brief history of my motor. The motor sat up for 2 yrs before I bought it. Previous owner said it got 5000 rpm at WOT. Currently I am only getting 4000 rpm at WOT.
I have accomplished the following up to this point:
Clean & flush gas tank and fuel lines, replace water separator, replace inline fuel filter, clean and inspect fuel pumps, Disassemble and clean carbs twice (1st time soak for 24 hr, 2nd time ultrasonic clean each for 1 hour), verify valve lash gaps, verify thermostat operation, adjust throttle cable for correct WOT operation, adjust carb linkage for correct operation, replace CDI unit with new one, syncronize all 4 carbs, check for air leaks around intake manifold and carbs, replace tach with new unit, replace spark plugs.
The motor runs very well. Starts easily, idles well. Accelerates without a miss, quickly decelerates without missing. No carb sputtering at all. The issue is that it tops out at 4000 rpm in the water under load. . Checked the plugs while out on the water to ensure not running lean. Tan color indicates correct fuel mixture.
In nuetral the motor will rev up to 4300 rpm then start missing. That is why I replaced the CDI unit as the timing is electronically controlled. This test rules out a propellor problem. I verified the pulser coil and ignition coil resistance (in spec)
Using a seperate fuel tank with new gas and a fuel transfer pump, I bypassed the fuel pumps and fed directly to the carbs. 4000 rpm was all the motor would turn.
Spark will jump a 3/8" gap. Not sure what else to try. Perhaps someone has seen something similar to this problem and can give me some insight.
|
Linear Mode
