Poor engine performance

I have an old plane that originally had a K&B sportster .20 on it. That
engine worked great but I wanted more power. I had set the plane up with
the crazy K&B engine mount that bolts on the back of the motor, so the
sportster .28 seemed like a perfect and very easy solution. I've only run a
few tanks on this motor, but the performance is pretty bad. Considerably
less than the .20 version. I think it may have some carburetion issue.
It's ornery to get the needle set right, and it seems like the last 1/3 or
more of the throttle doesn't give my any more RPM. Any suggestions? This
motor is pretty much unused. I've only run it a couple of flights and
probably a half hour on the test stand.
Thanks,
Clayton
Reply to
Clayton
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The consensus on the K & Bs seem to be that they need much break in time.
My suggestion would be to run it for a couple of hours more on the test stand (rich, of course) and then evaluate it again.
Reply to
mike tully
I was actually considering doing that anyway, because I was at a complete loss. I did notice when I first bought this engine it would actually kind of grab at TDC, so perhaps it is a bit extra tight.
Thanks...
If anybody has any other bits of wisdom please post 'em.
Reply to
Clayton
I'm a compllete noob at this stuff.. but is there a point at which adding more rpm's to a prop becomes ineffective? Perhaps a different pop is needed? Again, this is only a question, not a suggestion..
Reply to
ralph
Yeah, I considered that. I've tried a few different prop sizes and none of them are getting the kind of RPM that they should.
Reply to
Clayton
What plug are you using, and what others have you tried? Try a fox miracle plug.
Reply to
John Alt
This tightness at top dead centre is not bad at all, and the running engine does not notice it since the liner will expand, and oil wedge pressure also expands the liner. Just run in some more, use sufficient oil, and give the engine a break. It should improve in time.\ If it does not, sell it on E-bay :-)
Reply to
Pé Reivers
This may be dumb, but is the cylinder the right way around? The transfer ports must open later than the exhaust port. It never hurts to check.
Reply to
Pé Reivers
It sounds like you may have it over propped.
Considerably
Reply to
jeboba
Well, I don't remember if I ever took the thing apart. I don't think I have. I could check though.
Reply to
Clayton
I've tried everything from 9-4, 9-5 and 9-6. 9-6 used to work fine on my sportster .20, although that's probably somewhat overpropped.
Reply to
Clayton
Wow! way too much prop, IMHO. I use a 9 x 6 on a .40, to get it wound up on a small plane! Try a 8 x 4, or 8 x 5.
Reply to
Morgans
These do accept larger props than most comparable motors. I ran an 8*6 MA on my 20, and a 9*6 MA on the 28. It didn't have any problem with it. I'd asked earlier about the glow plug. What have you done in that area?
Lastly, the carbs are the same on the 20 and 28 if you want to swap and see if it makes a difference. If you have the remote needle on the 28 it doesn't matter, they can still be changed. The early 28's, like mine, had the needle up front.
Reply to
John Alt
Hey, I'm just going by the manual.
Reply to
Clayton
I haven't had much of a chance to work on it lately. I haven't messed with the plug but I intend to. Also, pulling the carb off my older .20 sounds like a good thing to try. I'll have to do that.
Reply to
Clayton
Hint: If the 20 is running good, swap the plug. Always start with the plug.
Reply to
John Alt

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