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Discussion Starter #1
First post here, looking for some help with this damned 300... I will cut right to the chase.

It will start up and run but not well, and as soon as you try to rev it up, it boggs/dies. Almost like it is losing fire as it revs up.

I have:

Cleaned carbureator about 20 times. Checked for missing pieces/correct jet sizes/etc. Everything seems perfect. Ruling this out. Has fresh gas as well.

Replaced CDI box/Stator. Bench tested coil on machine. Everything seems fine here too.

Replaced piston/rings/gaskets. Motor now has great compression (was low before) No problem here now.

Any ideas? My last thought is possibly the flywheel losing magnetism, I have been in this business for many many years and have only seen this maybe 2-3 times, once was on a motorcycle. When I check for spark, it has plenty when the motor turns over slowly, but as soon as I put a boost on the battery and use electric start, it seems to lose fire...

I am really stumped and have thrown myself at the mercy of the internet. Any help you can give me will be greatly appreciated, I will have a cold beer ready for each of you!

Thanks!
 

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HOw does the intake hoses to the carb look? also when you set the pilot jet how manyturns did you go out I think stock is 2 1/2 to 3 depending upon altitude. I know these seem like dumb questions but in order for me to fully understand you in my perspective I ask these. Also how does your timing look? I'm sure you are fine if you have done this before. does this have a back-up kickstart? if so you might want to check your detent adjustment, my quad is a 91 but a 250X full kicker no electric :( . I do know if the detant is out you will not gat a good running experience. What does the spark plug look like after you run it?? That's all I can think of until you get back to me.
 

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Discussion Starter #3 (Edited)
Carb hoses/lines/boots are all in great shape, no cracks or dry rot. Mixture screw has been set at every adjustment you can think of, and it does not seem to make much difference. Currently at 2 1/2 turns out. Spark plug looks black (rich) after it runs, which is normal for the situation. (see below) Timing is good, was checked twice with a light. Have not checked the detent, will do that, however:

the major problem is that when the machine turns over fast(holding electric start), it seems to lose spark/fire. when it turns over slowly (pull slowly, or tap the start button so it spins slower) it seems to have nice bright blue spark. this has lead me to believe it could be a flywheel problem, as i have replaced everything else or at least had it tested. Seems to lose fire over 1000 rpm... pulling my hair out!

thanks a bunch for the suggestions, and i will try the detent, but i do not think that is the issue. any other ideas???
 

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Running rich.....Hmmm Where are you located (for altitude purposes)? I know you have the carb issue in hand but i think you have an air restriction somewhere check the air inlets in the frame for those pesky mud Dobbers. I'm tossing ideas until I can do a little more research. do you have a manual? if not I may be able to get you some Ohm readings on all the accesories
 
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could be a short in something like the light switch witch has a high draw on the battery causing the spark to drop off at higher revs.
 

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Discussion Starter #6
Carb hoses/lines/boots are all in great shape, no cracks or dry rot. Mixture screw has been set at every adjustment you can think of, and it does not seem to make much difference. Currently at 2 1/2 turns out. Spark plug looks black (rich) after it runs, which is normal for the situation. (see below) Timing is good, was checked twice with a light. Have not checked the detent, will do that, however:

the major problem is that when the machine turns over fast(holding electric start), it seems to lose spark/fire. when it turns over slowly (pull slowly, or tap the start button so it spins slower) it seems to have nice bright blue spark. this has lead me to believe it could be a flywheel problem, as i have replaced everything else or at least had it tested. Seems to lose fire over 1000 rpm... pulling my hair out!

thanks a bunch for the suggestions, and i will try the detent, but i do not think that is the issue. any other ideas???
i am located close enough to sea level that it should not make a difference in jetting. have tried another carb on the machine, but once again, the issue is spark...

i have just (for shits and giggles) replaced the flywheel. no difference. still has nice spark when turning over slow, and loses fire when the RPM picks up. (electric start)

so stumped... about to just get some dynamite and put this thing out of its misery...
 

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ok you replaced the stator and CDI box Check your ground also check your alternator and pulse generator also you might want to ohm out your plug wire.
Ac regulator measures 0.1-1.0 Ohms
At the CDI 4 pin plug BL/Yellow and ground 0.1-.02 ohm for ignition coil primary coil
pulse generator blue/yellow and ground 290-360k ohm
reverse switch gray and ground , no continuity with lever up or engaged , continuity not engaged
ground line green/white and ground Check for continuity.

At the 2 pin plug
Alternator exciter coil black/red and ground 100-300 ohm
ignition switch line black/white and ground no continuity with switch on , continuity with switch off
coil inspection disconnect and measure resistance 0.1-.02 ohms
remove spark plug wire measure the secondary coil resistance between the plug cap and green terminal 8.8-14k ohm
if the resistance is out of range remove the plug boot and measure the secondary coil resistance 5.8 - 7.2 k ohms
Give this a shot maybe this will help this is from my manual but my quad is a 1991 250 but it should be the same??
 

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Discussion Starter #8
Thanks for posting those test specs, can anyone verify if they are in fact the same for the 300 vs the 250? I will be testing this shortly.

If anyone has a manual on the 300, or can direct me to an online version, it would be HUGE if I could get some specs (if these are not the same)

Thanks for all your help, I will keep you updated.
 

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The 250 and 300 were basically identical engines the diffrence comes in the bore/stroke,and of course you have the electric start option.
 

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Discussion Starter #10 (Edited)
ok, I am doing the tests now, I will post my results in a bit. thanks!

EDIT: my wiring is completely different than what you told me. My CDI box has 2 (two) plugs going into it, one is a 4 prong (with only 3 wires) and the other is a 2 prong. The 4(3) prong has a black wire, brown/red wire, and green wire. the 2 prong has a pink wire and a blue/red wire.

any thoughts? there is another box near the CDI that honda seems to call an "alarm" box... not sure what this is for?

EDIT AGAIN: disregard the above, i had the wrong box unplugged... as there are two side by side. The CDI appears to have the same wiring as you described, testing it.
 

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yeah i would suggest getting a service manual it will come in handy for more than just the electrical.
 

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Discussion Starter #12
New Developments:

I can unplug the "alarm box" (box next to the CDI, smaller one) and I get full spark while turning the motor over with the electric start now. However, when I run it, it will not rev up much... Any ideas? When I plug in the "alarm box" my plug fire drops off and becomes very erratic/non-existent at high rpm.
 

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What # are you looking at?
 

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Ok.. My buddy had an old three hundred and both boxes cdi and alarm box both went bad.My guess is if you unplug the alarm box and the problem improves that MAY be the problem.But then again thats just a guess.
 

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Agreed^^^^^^ Process of elimination


Ok.. My buddy had an old three hundred and both boxes cdi and alarm box both went bad.My guess is if you unplug the alarm box and the problem improves that MAY be the problem.But then again thats just a guess.
 
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