Originally Posted by
Jaketab
Getting ready to maiden a new Delro Models Turner W4X with a 250 and older top hat ignition and fuel pump.
Stihl Ultra at 45/1 with 90 octane no ethanol gas. Voltage regulated to 5.5v. Motor is not new.
Some issues with the motor I would like a little help with.
1. Running on the ground with the cowl in place, I get a lean condition - possibly as result of heat build up in the cowl.
2. The motor runs like a gyro except at the mid range 2500 - 3000 rpm range where the motor shakes like a wet dog.
When running without the cowl the motor does not sag at max rpm. After about 5 - 7 minutes running with cowl in place, that is when I am getting the sag at high end.
The cowl has baffles in front of the motor and I have 4 vent louvers around the cowl. I will be installing 3 more louvers.
As for the 1st issue, should I expect better cooling when the plane is in the air as opposed to running on the ground ???
As for the 2nd issue, no amount of needle chasing will completely cure the shaking at mid rpm. Current setting for the needles is H - 1 1/2 and L - 3/4.
Since this motor has the older ignition, could that be the cause mid range issues? Is the voltage input a possible cause?
Thanks for any suggestions.
Regards - J Tab
Hi!
I am almost certain that the old ignition has nothing to do with your Problem. I am running new and old ignitions and there is no difference. I would get rid of the pump, it is absolutely unnecessary as long as your fuel tank inside the plane is mounted a little bit above the carburator. The pump can cause more trouble than it actually helps.
Although I believe that the cooling will be better once the plane is airborne, there is most likely not enough space for the exit air. By the way, you can easily Close the additional vent holes you have in your baffle. The air that can enter the cowl around the cylinders is enough. I am not sure, but I think you Need at least 2 if not 4 times the space for the exiting air compared to the air entering the cowl.
Most likely your engine is getting too hot. Did you check if all cylinders are running?
/T