honda cm400 1980

Since: Jun 12

Hampton, NH

#1 Jun 24, 2012
would like your thoughts on the following
I have 9000 miles on my 1980 cm400
I can only seem to ride with choke partial out. It backfires often when I let up of the gas. It is also slow for the power to catch up
Until it reaches say 3500 rpm...I have used high test gas & Carb cleaners all to no avail.... kept in a garage for years it is in real good condition for its age..

Ottawa, Canada

#2 Jul 13, 2012
Sounds like the low speed jets in your carbs are partially blocked. It is basically starving for fuel at low rpm. Having the choke on allows it to draw enough fuel to run at low rpm and once you get up to higher rpm it is now running on the mid to high speed jets which are larger and less prone to obstruction. When storing your bike at the end of the season it is a good idea to drain the float bowls using the drain screw on the bottom.

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