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View Full Version : Strange 300ex jetting issue, need advise...



flyboy1294
11-01-2009, 05:59 PM
Hey guys,
I'm a 400ex guy, and a fairly noobish one at that. But my family owns a 300ex that isn't mine, but I'm still responsible for the maintenance of it and I only have time to fool with it around 2-4 times a month, so if you all could help me figure this out, when I get back I'll just try to get it put back together and save some time.

Here is the deal,
stock 300ex (Moose Air-filter, but it's not different than stock.) and the jetting was 'ok' this summer. Maybe a bit in the lean or rich direction, but still well tuned enough to where I thought it was good to ride.

About 2 months ago, it started acts a bit odd. It would bog when you'd punch the gas (used to be flawless), but it wasn't enough to make me concerned.

Then 2 weeks ago, it was bogging significantly, being extremely cold natured, and not performing as it used to. I changed the sparkplug because it seemed to me that might be the issue, also I cleaned the airfilter real good...

This week, however, it has gotten to the point where its not ridable. The bogging is not only when you rev the bike in neutral, but when you try to change gears it will bog and cut off and throw you over the handle bars if you're not careful. I took out the plug, and checked it, its like burnt black, and it's less than a week old. I'm guessing the problem is the jetting. What do you guys think, lean or rich? And what size jets do you recommend?

Thanks for helping out a fellow noob.
:macho

no1 300ex
11-01-2009, 07:40 PM
If the spark plug is black its to rich. If the plug white its to lean.

flyboy1294
11-01-2009, 08:24 PM
Well it was blacker than night. So it's definitely too rich.

Does anyone have any recommendations of how many jet sizes to go down?

no1 300ex
11-03-2009, 08:04 AM
What does it have for a exhaust? I would start by pulling the carb and give it a good cleaning, then get it adjusted properly. It might just be full of crap if it is not used much.

flyboy1294
11-03-2009, 03:10 PM
Exhaust, along with the rest of the bike, is totally stock. But yeah I will try to clean it really good over the weekend or something

flyboy1294
11-08-2009, 06:43 PM
I won't be able to tear the bike down until this weekend coming. But I made a video to show you what its doing, sort of.

Please don't be hatin'. I was tired and it was late, I know the video sucks.

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no1 300ex
11-09-2009, 05:02 PM
I watched the vid. Mine does the same thing when I first start it and the machine has not been used for a few weeks. If ya hit the gas it dies, however mine will clear up after a few min. of warm up. When I first got the 300 ex it had been sitting unused for a long time. It would start & run but if you hit the gas at all it would die (warm or cold). I pulled the carb and cleaned the chit out of it . I also use sea foam in the gas. So far no problem.

flyboy1294
11-09-2009, 05:07 PM
Originally posted by no1 300ex
I watched the vid. Mine does the same thing when I first start it and the machine has not been used for a few weeks. If ya hit the gas it dies, however mine will clear up after a few min. of warm up. When I first got the 300 ex it had been sitting unused for a long time. It would start & run but if you hit the gas at all it would die (warm or cold). I pulled the carb and cleaned the chit out of it . I also use sea foam in the gas. So far no problem.

Sounds like it needs to be torn down and cleaned. Then ran on higher quality gas. I will check back after I do those suggestions.

flyboy1294
11-17-2009, 02:20 PM
I don't even know what to say at this point. WTF?
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Tommy Warren
11-24-2009, 01:42 AM
your running stock jets right? also check your valve clearance I think this is your problem.....clearances should be .004 for intake and exhaust.

flyboy1294
11-24-2009, 02:42 PM
Yessir, stock jets.

Well that might be part of it, but that is NOT what is causing all the smoke. I never touched the valves, only rebuilt the carb.

Tommy Warren
11-24-2009, 03:13 PM
the valves with work themselves out of adjustment over time thats why it takes it so long to start...

flyboy1294
11-29-2009, 04:41 PM
It started fine, it was once it warmed up that problems occurred. But anyway this morning I broke down and took it to a shop. They'll get it fixed. I'll let you know what was wrong with it.