txfirefighter628
Registered User
Brownwood, TX
Okay guys need some help/ideas to try to figure this one out. I'm a new A&P and have tried everything I can think off except getting the carb overhauled which is about $800 and I'm not 100% sure its the problem so that's the last resort If nobody else has any other suggestions.
I went to fly my PA-12 with a O-235-C with about 200hrs SMOH in 2011(that I've owned about 1 1/2yrs and put about 100 hrs on it with no issues) the other day and it started and ran fine. While I was taxing from the hanger to take off it died. I thought it may just be a little cold so I primed it again and it started fine. Taxied to the runway and did a run up a mag check, every thing checked out good. Pulled on to the runway and throttled up, ran up to 1500 RPM and tried to die. Pulled back the throttle and it smoothed out. Did this 3 times and Pulled off the runway and tried it again a couple of times, same thing. It acts like its not getting enough fuel at the higher RPMs. If I slowly advance the throttle it will get up to 1700 RPM before it starts to stumble.
I pulled all the plugs and they were a little sooty but not fouled. Cleaned them, and checked the gaps, ohm tested and all were good. These are fairly low time plugs, autolites (which are now owned and built by tempest).
Checked the mag timing and tested the ignition leads, all good. The right Mag is a fresh overhauled that I put on in January. So I'm 99% certain that my ignition system is good. It runs the same way on both mags and runs fine at low RPM. So I'm now thinking fuel system.
I pulled the strainer bowl on the firewall and it was clean. Turned the fuel on and it flowed out fine from both tanks. Pulled the inlet screen out of the carb and checked it, was clean. Turned the fuel on and let it run through the hose from the strainer to the carb, flowed good. Did a compression test and all cylinders were 78 or higher. Pulled all the rocker box covers and checked for a sticking valve and they are all moving fine. Went and ran the plane again and still wont run above 1500 RPM.
So now I think I have it narrowed to the carb so I pulled it off and split it apart. The carb is a MA-3A and is a really simple carb. There is no accelerater pump and the only thing that really moves in the carb is the float and needle. The float seems to be floating with no leaks and the needle looks good too. I blew out all the holes and passages I could and never saw any trash come out. The bowl was clean. The bowl gasket looked good and the engine mounting gasket looked good so I put it back together. I would not return it to service without new gaskets, just put it back together to see if maybe there was some trash that may have cleaned out. Test ran and same thing, wont get above 1500 RPM. I called Marvel-Schebler tech support and talked to Mark and he said it didn't sound like a carb problem to him after telling him about all the trouble shooting I did.
Not sure if its related but I ran some 87 octane ethanol free auto gas in it the flight before this happened and it ran fine then. The plane is STC'ed for it. The first time I ran auto gas in it was about a month ago and I got 5 gallons of it from Steve Pierce in Graham and burned it all coming home and it ran fine. A new gas station in town is carrying the ethanol free fuel so I thought I'd try it. The first flight with it was last week and I flew for about 45 minutes and did several take offs and landing and the plane ran great. The next time I went to fly which was this Wednesday is when the issue started. I have the autogas in one tank and 100LL in the other and have tried running back on just 100LL with the same problem. I have a Dakota Cub fuel selector that I installed last year.
So any ideas/suggestions to try would be greatly appreacated, Thanks, Ron.
I went to fly my PA-12 with a O-235-C with about 200hrs SMOH in 2011(that I've owned about 1 1/2yrs and put about 100 hrs on it with no issues) the other day and it started and ran fine. While I was taxing from the hanger to take off it died. I thought it may just be a little cold so I primed it again and it started fine. Taxied to the runway and did a run up a mag check, every thing checked out good. Pulled on to the runway and throttled up, ran up to 1500 RPM and tried to die. Pulled back the throttle and it smoothed out. Did this 3 times and Pulled off the runway and tried it again a couple of times, same thing. It acts like its not getting enough fuel at the higher RPMs. If I slowly advance the throttle it will get up to 1700 RPM before it starts to stumble.
I pulled all the plugs and they were a little sooty but not fouled. Cleaned them, and checked the gaps, ohm tested and all were good. These are fairly low time plugs, autolites (which are now owned and built by tempest).
Checked the mag timing and tested the ignition leads, all good. The right Mag is a fresh overhauled that I put on in January. So I'm 99% certain that my ignition system is good. It runs the same way on both mags and runs fine at low RPM. So I'm now thinking fuel system.
I pulled the strainer bowl on the firewall and it was clean. Turned the fuel on and it flowed out fine from both tanks. Pulled the inlet screen out of the carb and checked it, was clean. Turned the fuel on and let it run through the hose from the strainer to the carb, flowed good. Did a compression test and all cylinders were 78 or higher. Pulled all the rocker box covers and checked for a sticking valve and they are all moving fine. Went and ran the plane again and still wont run above 1500 RPM.
So now I think I have it narrowed to the carb so I pulled it off and split it apart. The carb is a MA-3A and is a really simple carb. There is no accelerater pump and the only thing that really moves in the carb is the float and needle. The float seems to be floating with no leaks and the needle looks good too. I blew out all the holes and passages I could and never saw any trash come out. The bowl was clean. The bowl gasket looked good and the engine mounting gasket looked good so I put it back together. I would not return it to service without new gaskets, just put it back together to see if maybe there was some trash that may have cleaned out. Test ran and same thing, wont get above 1500 RPM. I called Marvel-Schebler tech support and talked to Mark and he said it didn't sound like a carb problem to him after telling him about all the trouble shooting I did.
Not sure if its related but I ran some 87 octane ethanol free auto gas in it the flight before this happened and it ran fine then. The plane is STC'ed for it. The first time I ran auto gas in it was about a month ago and I got 5 gallons of it from Steve Pierce in Graham and burned it all coming home and it ran fine. A new gas station in town is carrying the ethanol free fuel so I thought I'd try it. The first flight with it was last week and I flew for about 45 minutes and did several take offs and landing and the plane ran great. The next time I went to fly which was this Wednesday is when the issue started. I have the autogas in one tank and 100LL in the other and have tried running back on just 100LL with the same problem. I have a Dakota Cub fuel selector that I installed last year.
So any ideas/suggestions to try would be greatly appreacated, Thanks, Ron.
(we had a cracked crankshaft that tore up everything in the 3 test flights as we tried to figure out why 185 would go flat pitch...)
