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Is it overheating?

1698 Views 12 Replies 4 Participants Last post by  drainyoo
Maybe I'm just imagining things but it seems like that the colder my bike is, the better it runs. More power, smoother ride, gears change without any problems. But after riding it for about an hour straight, the bike seems like it loses power, gears stick and sometimes I cant get it out of gear, the right cylinder back fires and the bike begins to idle poorly and shuts off at times.

Could it be that the engine is overheating? Maybe it's the oil? Or maybe Im just going nuts?
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hondy gearboxes get a little notchy when then come up to operating temp. As for the cylinder backfiring or cutting out that is not normal. An overheating honda tends to detonate...a lot. It will sound like pebbles in a coffee can when you first let out the clutch. It could be that your ignition timing is off and causing overheating and backfiring. It could also be fuel delivery. As for the idle quality, you are supposed to set the idle when the bike is warm, which means that if you set it when it was cold then as the bike warms up the idle will drop, if it was low to begin with it will stall.

Makes sense.

I dont here any pebbles and I just had the bike's ignition set and points replaced.

What causes backfiring? Even now and then Ill get a load bang backfire but most of the time its just a soft pffffff and it always happens when I left off the throttle when Im coming to a stop.
Backfiring is primarily caused by two things, timing and fuel delivery. backfires out the carb are usually timing, backfires out the pipe are usually fuel delivery although they can also be a misfiring plug (like a bad plug wire - look for cracks in the coil too). From what you describe, it sounds like the pipe is loading up with fuel, I would check for intermittent spark on that cylinder and then go from there.

So you are saying that the fuel in the cylinder isnt completely burning and come of it is reaching the pipes and then igniting? So basically there is something up with the spark? Either the plug is shot or there isn't enough of a spark from the plug/coil?

Here's a question. If this were the case, wouldnt it always backfire, even when cold? The bike only backfires after I've ridden it for at least 30 min.
A backfire out the exhaust is uburned fuel igniting either in the combustion chamber when the exhaust valve is open or in the pipe itself. Conversly a backfire out the carbs is caused by the fuel igniting when the intake valve is open. IT could be the spark timing is off, there is a weak spark, there is a problem with fuel delivery, etc. A backfire out the carb is almost always timing since there are very few ways to cause fuel to ignite before TDC is reached. A lean condition can cause a backfire out the pipes almost as easily a a rich condition if it were caused by something like an air leak in the manifolds, a bent or stuck valve that is not seating properly, or a stuck carb float and clogged carb drain. A hot exhaust pipe can also cause the fuel to ignite which may explain why it only happens when your bike is warm. It might be that the bike is a little lean and when you go from accelerating to decelerating it changes to slightly rich and the overheated pipe ignites the excess fuel.

Are the pipes stock? some aftermarket pipes or stock pipes with the baffles removed will cause a natural backfire since when the engine is decelerating it tends to run a little rich and load up. All carbed engines backfire a little on deceleration but you rarely hear it because the muffler quiets the sound and supressed the backfire. A loose baffle may also cause this since it is not really doing its job. I guess I would have to see the bike and exprience this backfire to go any further.
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Ok, as far as the shifting into neutral goes, that is the usual thing with Hondas of this vintage. It is generally caused by the clutch heating up and dragging a little bit. You may be able to cure it for a little while by replacing the clutch plates, both fiber and steel, and very meticulouslly adjusting the clutch within an inch of its life. This might cure it for 20 minutes or so. The easiest cure is to learn to click the tranny into neutral as you roll into a stop while the bike is still moving. It becomes second nature after a while. As far as the trans dropping out of second can be caused by a slightly bent shift fork or a less than positive shift into second and a weak shift drum detent arm spring. Try being very authoritative in you first to second shifts and see if that helps. If it does then the shift drum stopper arm detent spring is suspect.
As far as your backfire issues go, put a new set of plugs in it and ride it around until it shows the symptoms and then pull the plugs and tell us what they look like( see my previous post).


PS what oil are you running?

Vintage racing - old guys on old bikes
Not sure what oil was put it when I had it tuned up.

I'm going to try the other stuff and see what happens. Thanks.
about the shifting, popping out of second usually means that the bike was abused (powershifted, etc). However I have noticed a trend amoung younger honda riders (myself being one) of putting pressure on the lever when they are not shifting, either by resting the top of thier foot against the lever (like they are prepairing for an upshift) or resting the sole of their foot on the top between shifts. Any pressure on the shift lever will cause the bike to jump out of gear when you back off the throttle - I found I am guilty of this between 4th and 5th gear since 4th is such a long gear (as compared to 1st and 2nd which are pretty short on a cb750 and require fast shifts) and I have caused my bike to jump out of 4th a bunch of times without thinking about it.

I will probably be around sunday if you want to ride over and have me take a look.
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