Help with my Rm250

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Jul 18, 2007
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#1
:bang: I’m am having a problem with my 1993 RM 250, when I start the bike and try to take off after putting in gear it bogs down and loses power, I have checked everything and at first thought a may have been a spark problem and cannot find a simple solution. I have an FMF Fatty pipe with Boyesen power reeds, Keihin 38mm carb with 52 pilot and 185 main jet the carb has been cleaned and , new cdi unit, spark plugs, compression 155 lbs when hot, did leak down test and held pressure for one minute. If I pull clutch in rev and let out I can slowly give it gas and get it moving but with uneven acceleration and will not go into power band, starts cracking up. I bought this bike with what the previous owner who thought this was a carb problem. I found a vacuum leak that I fixed that enabled it to start easier. When the bike stalls after bogging it can be started on the first kick. I am unsure if the bogging is from too lean or too rich.What is a good stating point for jetting sizes with this configuration .Any suggestions would be appreciated.
 
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#3
I guess my question is the bog from startup, is it caused by lack of fuel or too much fuel? so i can adjust my jetting.
 

_JOE_

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#4
Try turning the air screw in or out and see if it makes a difference.
 
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#5
What does your plug say? Soon as it dies yank the plug! Almost anywhere in the country that bike should run on stock jetting,if it is stock! So you have some bolt on goodies,anything done inside? If jetting changes do not effect how it runs,then it must be something else. With the bolt ons, and stock jets,your engine should be lean. On another note,how are you with an ohm meter? Outside chance of ignition issues!
 
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#6
Thanks for your responses,I have played with the airscrew and it does not effect the idle speed that much except when i get close to closing it off it stumbles an dies, I set it at 1 1/2 turns .The jets are richer than stock, pilot stock;45, mine is 52. Main stock;180, mine is 185. Needle is r1471ns-3rd clip notch which is stock for my bike.As far as anything done inside ,i do not know i bought this bike used. As far as ignition issues I have tested out the stator and pick up coil and ign coil with an ohm meter both were within range as well as watched the blue spark jump across the electrode on a test plug.Could reed vavles be a reason for all my problems ?,even though they looked like new when i checked them.
 
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#7
Pulled the plug, looking down the walls of the insulator they appear to be dark brown on one side, tan on the other, but this was during a more idling than riding for about five to ten minutes.
 
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#8
On the reeds,if there is any gap between the block and reed,then there is an issue. Over tightening will do this,and fatigue. If it is running real bad off bottom I would expect the plug to be wet! In jetting I prefer to start at the bottom,drop the pilot,as warm as it is here,I would expect to be leaner than stock! The needle would be next,again go leaner. The main is where the bolt ons come in,you may be okay,short of a plug viewer,you are not going to be able to read the main,unless you cut the plug! Dark deposits on the porcelain could mean you could run a hotter plug. Have you read the plug reading 101 thread? You are getting second hand imfo from me,the search vault here is priceless! If you cannot adjust the choke to get an idle it will tell you which way to go on the pilot,and replace the float valve for sanities sake,should be replaced once a year,without question!
 
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#9
Check that your exhaust is not plugged up. My kids quad will do the same thing when the spark arrestor screen in the muffler gets plugged up. Make sure your silencer fiberglass isn't wadded up inside the silencer.
 
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#11
Did remember one of the reed petals was not seating perfectly and appeared to be slightly raised off the end of the reed cage less than .5mm. Could this cause all my problems above?I think I will try a new set of reeds and see what happens.
 
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#13
If a reed petal was not seating properly wouldn"t that cause a back draft of gasses that would effect the preformance,cause it to bogg ,as well as starting hard? When I pressure tested the crankcase again, I loosened the oil fill cap and then heard the hiss of air with about 6psi of pressure, but will close of the leak when you tighten the cap. I assume this is a side seal leak. Could this be the reason for the hard starts and bogging or could it be something else?