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Motorcycle Repair/2009 300cc Johnny pag


So I did a compression test all seems good both are at 180psi open throttle my left cylinder at idle has a popping sound and doesn't seem to get hot the compression test at idle read 70 psi and 125 psi
Not sure why the left cylinder is not running / sounding like the right
Cleaned out the carbs / jets float
Added sea foam  added engine restore product
Newer spark plugs brand new battery
Any help ...

Paul, it sounds like the bike needs a good valve adjustment first. I would set them to a minimum of .002" cold for both valves on the compression stroke and see if that doesn't fix the problem.

As the engine warms up the valves tend to grow in length so the valve clearance is reduced. If you are starting at near-zero or .001" perhaps, that would explain how the engine drops the left side when it warms up. A drop in compression like that, so quickly, indicates valve sealing issues, probably due to lack of sufficient clearances.

Make sure that your intake manifolds are in good shape and the carbs are fully engaged with the manifolds.

Bill Silver

Motorcycle Repair

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Bill Silver


Need help with vintage Hondas from the 1960s? I am an expert with 250-305cc bikes in particular and most all of the other pre-91 models, in general. I do NOT claim to have a great deal of experience on Gold Wings, Cruisers, ATC/ATVs and dirt bikes.


I have owned/ridden/maintained Honda motorcycles for 35 years. I have written five books on Honda repairs and collecting. I was a service manager for two Honda shops back in the 1980s.

VJMC (Vintage Japanese Motorcycle Club) of North America

VJMC newsletter, as editor for two years and as contributing editor currently.

3 years auto shop in high school, teacher's aide in Automotive Technology in Jr. College, Diesel mechanic course in college, self-taught mechanic and automotive writer.

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