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Discussion Starter · #1 ·
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?
 

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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?

EDIT:
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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Discussion Starter · #6 ·
Both carbs are OEM.
I have cleaned, buffed every electrical component and added dielectric grease.
Brand new ngk spark plug. Gapped... .035 or something like that
It's 2000.
Only part that's not OEM is the gear reduction and the clutches.
 

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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. :)
 

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Gotta be either fuel or fire. Gravity feed gas tank so check your tank feed for any restrictions. As I recall these didn't have an inline filter but a screen at the petcock.
The tank is metal and subject to rust and these petcocks like to get clogged.
If fuel system is clean I would suspect an ignition component
 

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Discussion Starter · #10 ·
@goober

Well I tried to call my buddy who's got my bike and ask him to switch gas tanks and well,
He done pulled the top end apart.
It was off time.
Got a new chain for it already so I'll keep everyone and let y'all know if this was the problem or not.
This is a very annoying problem. That I hope no one else has to deal with
 

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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. :)

EDIT:
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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