QuestionGreetings,
This is a little story about a 250 Nighthawk. I purchased it about 6 months ago, it
had been kept in a shed for a while.
It would jerk a bit, and ran a little odd so I took it to a honda shop in Daytona.
The guys there tuned it up, cleaned out the carb, cleaned out the tank, fixed the
timing, modified the air ratio, and said it was all cleaned up and ready to go.
Yet, it's still jerking, and it's even stronger than before.
Now, what it does is this:
It seems to take the motorcycle a little while to warm up before it start bucking a
great deal. When it's cold, it may skip a little bit, but not very much and much
more infrequently than when it's cold.
It'll start jerking at pretty much any speed, any gear, and sometimes will backfire.
It'll backfire so bad at times that the engine will stop, even at high speeds.
Sometimes, it won't do ANYTHING for 20 - 30 miles, purring along nicely, and then
it'll start bucking like a bronco, and then it will stop again.
The guys at the shop keep telling me it's bad gas. So I siphoned out the gas, and
put in high-test ... same deal.
My intuition is that it's an electrical problem, a lose wire perhaps, or one of the
hoses is messed up, but have no idea."
AnswerKeith, a little more info would be more helpful... Mileage, year and overall condition.
After all the money you spent, I would have thought that the shop would take it back for diagnosis. If they cleaned the carb and tank, how could the gas be bad?
Backfiring can come from either electrical or air leaks/lean conditions in the carburetion.
Did you try to apply the choke when it starts bucking? If the choke helps smooth it out, then probably it is a lean condition. That could come from a problem with the canister purge valve (emisson control) a plugged up venting system for the fuel tank, fuel screen that is part of the petcock, stuck up inside the fuel tank, or bad O-rings for the carb manifold/carburetor mounting.
I would check the spark plug caps for matching resistance values. Had a friend in the past year who had problems like that and the plug cap had cracks up inside the body, which was flashing arcs over the outside to the head. If the bike has a lot of miles or is 5-10 years old, change out the spark plug caps. If they start breaking down, they will cause a misfire and the unburned fuel will go BANG when the sparks come back online again. Other odd places to check might be the handlebar switch where the KILL switch is located and the wiring going to it.
The ignition is factory sealed CDI, so no adjustment can be made. You can check it with a timing light to verify that it is advancing properly.
If the bike is older, I would be inclined to remove the seat and fuel tank and go over all the wiring connections to see if corrosion is present or there are any that are loose fitting.
Bill Silver
