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  #1  
Old 06-06-2012, 05:43 PM
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Default I need help My bike will not rev up and very boggy

hey everyone kinda new to this. but i have 1998 yahama yz 125.
I cleaned the carb out many times just to make sure i got everything.
new jets 350 main and 45 p jet.
new spark plug has good spark
new air cleaner
fresh gas
i mix amsoil 50:1
has great compression

the bike always starts on the first kick. i always let it warm up and i try to give it some gas it will rev up and be really boggy. will not hit the power band. the boggy is more in the low to mid range. I checked the reeds they are not cracked or anything. some one please help been messing with this for awhile and cant figure it out.
thanks

Last edited by mn_rider; 06-06-2012 at 06:14 PM.
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Old 06-06-2012, 06:32 PM
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Default OK

Ok, if all is good as you have indicated, then I would check the exhaust valve set up to see if they are working. If they are stuck down that will not allow it to rev. If they are stuck open, then the engine will run poorly at slow speeds, but then run well at only high rpms.

Paw Paw
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Old 06-06-2012, 08:30 PM
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start with telling me what the sparkplug looks like. you mention that it is only boggie on the low end or midrange, after you have said it doesn't hit the power band. Please be more descriptive in what it does, ie does it not get past the midrange? does it miss? things like that would be helpful. try not to use the words power band to describe any part of what it is doing. PLEASE.
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Old 06-07-2012, 04:31 PM
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the spark plug is blackish. bike runs smooth does not back fire or nothing like that just really boggie. idles fine... with the black spark plug that means it to rich or lean correct. and to fix that i can either mess with the air screw. how do you check and see if the valves are sticking?
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Old 06-08-2012, 05:30 AM
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The black plug indicates rather rich than lean, a leaking cran seal also gives you a darker color on the plug. To see if you running at a good jetting the plug is not enough IMO.

Float valve is the first part of a carb which needs to be correct in order to adjust jetting.
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Old 06-08-2012, 09:55 AM
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Unless you have some different carb or are way up in the sky, that Main Jet seems awful high to me. Are you sure it is a 350? I think that model's range is around 260-290. The pilot seems right, though.

Your symptoms say "boggy" but the evidence shows rich. When you crack the throttle, does it go "BOOO-WAH!" or does it sputter and not clean out?

Arnego beat me to it about the leaking crank seal. It is a very common problem that mimics poor jetting and I think that I write at least one to two posts a day on here about it.
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Old 06-08-2012, 09:59 AM
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my 36 mm mikuni equipped 125's are happy with jets in the low 300 range, but mine don't run pump gas and they are big bores. try setting the float as was suggested.
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Old 06-08-2012, 01:27 PM
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Quote:
Originally Posted by Randog Leader View Post
Arnego beat me to it about the leaking crank seal.
Yuppi, finally I won
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Old 06-08-2012, 03:08 PM
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Ha! The irony of it is that is what crapped out on my daughter's bike, so I had to take my own advice.
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Old 06-08-2012, 07:15 PM
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this happened on my pitbike and i changed the spark plug and everything and cleaned the carb out and it was still borking out with know power turned out the throttle cable was streched replaced that and all was cured

ATB
Rich
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Old 06-12-2012, 12:09 AM
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sorry everyone i was out of town for work a couple of days.. is there a way you can check to see if the crank case seal is broke, and for the jetting i called the Yamaha dealer here in Minnesota and asked them whats the stock jetting for Minnesota level and he told me 350 for main and 45 for pilot jet.. floats are set are stock height. low idle is fine its just when i try to kick it down it bogs out it does not sputter or anything just bogs?
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Old 06-12-2012, 12:24 AM
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350 was too rich for mine stock, but it varies by where you are
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Old 06-12-2012, 05:34 AM
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Quote:
Originally Posted by mn_rider View Post
is there a way you can check to see if the crank case seal is broke?
put in the exact amount of oil needed, ride a few hours and pull the oil again. You have more than 50ml loss you should replace the crank seal. Few hours should be 2 to 4max. Before you replace the seal take a large screw driver and try to wiggle the crank. If it moves up and down, even just a little you should replace the roller bearing too.

To do that you have to pull the engine.
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Old 06-12-2012, 09:50 AM
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Have you checked your reeds?
Does the powervalve work properly?
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Old 06-12-2012, 06:51 PM
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I checked the reeds they where fine.. how do you check the powervalve to make sure its working correctly
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