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Help please. Power issue, throttle issue

2286 Views 11 Replies 3 Participants Last post by  retro
I'm lost.
Have a Honda 300trxfw 4x4
Carburetor is good.
I know this because I swapped it with a bike that is running good. My carb had no problems on my friends bike and ran great. And his carb in my bike, the same problems occured.

Coil is good.

Idles perfect.
At 1/4, 1/2 and 3/4 throttle when it reaches steady rpm it continuesly drops and raises rpm like if I were to be tapping the throttle
At wot it runs fine.

It did this before I snorkeled it. It did this before the gear reduction.

Im at a lost. My friend says timing chain?
Anything else u think it could be?
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While the motor is running at a steady cruising speed in any gear, it cuts out and then regains power rapidly? Is it cyclical as if you were hitting the kill switch momentarily every second or so?
By the way, welcome to the forums!
You're welcome! First thing to mention is that the timing chain is the least likely cause of your issue... even then only as a contributor, not the cause.

I am assuming that the two carbs you have had on the motor are both OEM. Let us know if that isn't fact?

First things to suspect would be a failing or mis-gapped (very tight gap) spark plug (new Champion plugs are the worse offenders, buy NGK to fix), sucking air through a cracked or warped intake manifold, spark plug cable deteriorating or pulling apart from the boot, etc. It can even be a bad CDI but don't jump to any conclusions with that... odds of a bad CDI are a long shot bet, and may waste your money chasing that ghost.

It can be a combination of things adding up to cause the problem too. First thing to do is make sure the intake is not leaking between the carb and the head. If there are any issues in the motor (bad or worn out valves for instance) those oddball issues can be contributors to other problems and make diagnosis a bit more difficult.

What year is your 300? Is it all stock? Any non-OEM replacement parts on it?

Check all your wiring harness connections too. They must be clean and tight, no moisture in them. Check the ignition switch and kill switch too, if the spark plug and intake are proven good.
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Thanks, does it have the stock airbox on it? Is your snorkel ducted into that airbox or direct to the carb? What about the condition of the other things I mentioned above? I gotta leave for the day... sorry. Hopefully someone else will help nail it down for you. :)
Its probably an ignition or electrical problem if the intake & exhaust checks out. I'd be wondering about the ignition switch and the kill switch and would probably bypass those temporarily to test. Then I think I would troubleshoot the ignition components one at a time with a multimeter after rechecking the grounds on the frame and motor. The service manual has the specs for everything but the CDI. Maybe your friend will let you swap the CDI...? But don't try that unless those two part numbers match exactly.

It is a headscratcher for sure, cause its symptoms are backwards from things I normally expect. :)

This reminds me of the old points & condenser ignitions from the 60s and earlier. Those motors could act just like yours is now, whenever the condenser went seriously bad. Remembering those experiences makes me wonder whether your CDI is failing...? After all, they function by loading and unloading a capacitor into the ignition coil primary windings...
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