OS-75 fuel problem
 

<p class="MsoNormal"><span style="font-size:12.0pt;line-height:115%;font-family:"Times New Roman","serif"">This engine ran great before a tree ate the airplane (the tree ate the airplane but left the engine and prop intact).<span style="mso-spacerun:yes"> </span><span style="mso-spacerun:yes"></span>Idle is fine but now I cannot get it to run at high RPM.<span style="mso-spacerun:yes"> </span>When RPM is increased the engine cuts out, as if the plug got wet.<span style="mso-spacerun:yes"> </span>Indeed, after a run I have fuel all over the place.<span style="mso-spacerun:yes"> </span>It is pumped out by what I think is unusually high pressure in the fuel tank.<span style="mso-spacerun:yes"> </span>I have been modeling for over 50 years and cannot recall this ever happening before.<span style="mso-spacerun:yes"> </span>I have dismantled the carburetor and cleaned it well using high pressure air.</span></p><p class="MsoNormal"><span style="font-size:12.0pt;line-height:115%;font-family:"Times New Roman","serif"">Is there some kind of pressure vent in the engine that could have gotten plugged?<span style="mso-spacerun:yes"> </span>Accepting any suggestions.</span></p><p class="MsoNormal"><span style="font-size:12.0pt;line-height:115%;font-family:"Times New Roman","serif"">Thanks,</span></p><span style="font-size: 12pt; line-height: 115%; font-family: "Times New Roman","serif";">Lee</span>

RE: OS-75 fuel problem
 

First, replace glow plug regardless if you think it is ok.
Then, make sure the crank shaft is not slightly bent.
Also, pull the hi needle screw and make sure it is not bent or damaged.
Also, check to make sure there are no air bubbles passing through your fuel line going to the carb as you get to the point to where the engine begins to cut out. This will definitely cause what you are describing.
Is this the OS 75 AX engine?
Sounds as though this is a simple glow plug issue.
Worse case senario would be bent crank shaft or bent piston rod from the sudden stop of the engine.
Keep us updated.

Jim

RE: OS-75 fuel problem
 

Jim

Thanks for your response. Glow plug was replaced needle screw is fine no air bubbles OS75 AX engine. Crankshaft "looks/feels" fine but I also concluded that its a bent crankshaft. I don't have a dial indicator so its hard to tell. Ordered a new one this morning.

Although I have not looked at the piston rod I don't think a bend there would result in an after run fuel "dump". I think the bent shaft resulted in an air gap that allows fuel to be pressured past and out the venturi (its a side mounted engine).

Will update,
Lee

RE: OS-75 fuel problem
 

Jim,

Once again, thanks for your response. Problem solved! I replaced the crankshaft and the engine runs fine! It sure did not feel bent!

Lee