gonna sound dumb, but my rear cylinder sounds like its running at a slower idle than the front. i haven't put a tach on, but regardless of cold/hot engine, the front cylinder runs at a steady clip (appx 1000), while the left is sort of syncopated, letting a big thud every so often.
the plugs are good, and no air leaks.
any suggestions where to look next?

 

The two pistons in the two cylinders are attached to a common crankpin, so they must run at the same speed otherwise I'll buy it from you for any amount you name.

What you may be hearing may be the result of a few things, an intake leak, bad or intermittent plug, loose terminal on the top of the plug, bad wire or an arking/cracked coil.

You didn't say if you are carb or FI. It could also be a lean mixture causing what you are hearing (more than likely)

You could try switching the plugs to the opposite cylinders and see if the problem moves to the front cylinder.

Let us know.

 

what kind of ignitionsystem are you running? on my crane hi4 tc the rear cylinder timing is adjustable

 

A friend of mine had a similiar problem (non- harley). Turned out to be a sticky valve. Try putting your hands near both exhaust outlets while its running. See if the flow feels equal. Just a suggestion, good luck with your problem.

 

i know they are running at the same speed, just don't sound like it. already tested the plug and terminal, didn't think of switching them. i'll give that a shot tomorrow. also look at the intake and wire/coil.
i'm running the flatslide carb, so wouldn't a lean mixture effect both cylinders?

 

Not always, If the leak is at the intake seal for one cylinder, it will only affect that cylinder mostly.

Do the spray test around the rear cylinder intake seal and see what you get.
https://www.hdforums.com/m_85102/mpa..._/tm.htm#85102

By the way, don't confuse the rattle of the slide in that carb for engine noises.

 

yeah, figured out that carb noise awhile back.

thanks for your advice tc, i'll post back when i figure out whats what.

 

turns out, a leak at the intake as you suspected. also, a small leak at the muffler end of the exhaust. haven't done the fix on the intake yet, but i'm pretty sure its the culprit.

 

Glad you tracked it down. They can be a bear to isolate at times

 

much grass.
someone was telling me oversized valves would be the next step in performance. any thoughts there?