Board index Flathead Power-Technical Questions, Answers, and Suggestions K-Models M53 High Speed Operation

M53 High Speed Operation

Post Mon Oct 19, 2009 11:24 pm

Posts: 121
Yeah I know it's not an M88 question but I've had no luck in the K section...

We have a 54KH that is running an M53; now historically this engine has been a bad smoker. We've mooted the oil restrictor idea that got kicked around in the K forum a while back but we aint buying that they left the factory like this... We've just installed a third set of rings, perfect bore and hone, we tried different grades of honing... (by an expert level machine shop that builds a ton of engines) to .004" – no good still smoking... NOW we noticed that the high sped adjustment on carb is doing nothing. ie. we screw it all the way down at speed and the engine runs on fine, SO our new theory is that the carb is far too rich and is thinning the oil allowing it to pass the rings?

Any belivers out there?

If so what is the most likely scenario for wear on the high speed side; the part we suspect is listed as a #9 type, I'm no expert but have had the bike running well for 20 years but must confess the high speed adjustment never seemed to alter the power much at all? Now that I own a 45 also and have been repairing the KH for all eternity I have to say the 45 is far more trouble free bike...

Thanks fellas, Nick.

Post Tue Oct 20, 2009 6:22 am

Posts: 3159
Location: Central Illinois, USA

The first thing I would suggest is get a .070" drill for a plug gauge and see if your fixed jet has been hogged out.


Post Tue Oct 20, 2009 8:31 am

M53: bombsight or plain tube?
Are you sure you have the right nozzle?

Post Tue Oct 20, 2009 10:42 am

Posts: 767
Location: CA USA
Are you sure you have the correct needle. I have seen the wrong needle installed in the M53. Looks right but doesn't do anything. Check it out.

Post Wed Oct 21, 2009 12:33 am

Posts: 121
What should be the overall length of the high-speed needle I wonder? Maybe someone has ground it down or used the wrong one...


Post Wed Oct 21, 2009 7:25 pm

Posts: 693
Location: somerset, oh usa
Also check that you have the air bleed jet in the carb, located just under the low speed needle.

Post Mon Oct 26, 2009 7:41 am

Posts: 121
Hi guys,
we have checked the high-speed needle, seems to be seating correctly; still hoping someone can measure the correct length?

Also Cotton, the metering plug hole (jet #9) measures .060 so less than you refer to, what other sizes are available? Is it worth us trying one with a much smaller hole?

Thanks again, Nick.

Post Mon Oct 26, 2009 10:46 am

Posts: 767
Location: CA USA
How did you check the seating of the needle?

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