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Another jetting question


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Hey guys just finished putting together an 06 rm250 I bought and the jetting was stock. I want to know if im somewhat in the ball park here- I put a 45 pilot in, droped the needle one notch, and went to a 165 main. I am going to be running R50 at 40:1.

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This question has so many answers because there are so many variables:

Altitude, pipe, reeds, and riding area.

If you buy an aftermarket pipe, the manufacturers will generally give you ballpark jetting to start.

ProCircuit has this chart -

http://www.procircuit.com/jettingspecs.htm

FMF has this page

http://www.fmfracing.com/TechSupport/JettingCenter

Then if you add aftermarket reeds, well then you get to start over.

My RM was doing great, but I changed the reeds and now it seems like it is pre-detonating. So I'll be chasing that down.

I am also setting it up for the sand next week - which means generally going up 2 in the main jet, and also up one clip position, to run rich. In the sand you also generally go up a tooth in the front sprocket as you run WFO the whole time and things get mighty crispy. I've blown up my YZ250 twice and my KX500 once in the sand - so crossing my fingers this time - I will also run race gas as an additional precaution.

Sucks being towed back to camp.

anyway the best way to test your jetting is to put in a new plug, run WFO then kill it and then look - if all is well your plug should be a nice chalky brown - like a camel hair coat (or the way I like my coffee).

good luck!

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I actually got to ride the bike today... it seemed to have no bottom end like it was too rich... but it also seems like it took a little longer to idle down after I let off the throttle like it was lean.... but the plug looks perfect... Do you think a crappy basket/ hub/ clutch could make the bike rev erratically when i let off the gas by not dissengauging when i pull in the clutch?

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I actually got to ride the bike today... it seemed to have no bottom end like it was too rich... but it also seems like it took a little longer to idle down after I let off the throttle like it was lean.... but the plug looks perfect... Do you think a crappy basket/ hub/ clutch could make the bike rev erratically when i let off the gas by not disengaging when i pull in the clutch?

clutch side crank seal installed properly? metal ring goes to the inside of the crank and on the magneto side the metal ring faces the flywheel.

air leaks around the intake? Carb boots tight?

Unrelated to the clutch.

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He needs to scrap it all and START OVER! Look at how many things he changed right off the bat. Problem with the hanging idle could be because he dropped the needle which shuts off the main faster. Hanging idle could also be changed by lowering the idle set screw and then adjusting the air screw. He's changed so many things you can't tell what's going on, but I wouldn't start tearing the rest of the bike apart or looking for problems where there weren't any before.

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He needs to scrap it all and START OVER! Look at how many things he changed right off the bat. Problem with the hanging idle could be because he dropped the needle which shuts off the main faster. Hanging idle could also be changed by lowering the idle set screw and then adjusting the air screw. He's changed so many things you can't tell what's going on, but I wouldn't start tearing the rest of the bike apart or looking for problems where there weren't any before.

He's in the ball bark with his jetting and these bikes are notorious for having their crank seals in backwards. The diagram they give in the manual isn't the greatest and very difficult to translate. In my experience the 2 main causes of hanging idle are an extremely lean pilot or an air leak.

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I didnt replace the crank seals... This is a low hour bike so I left everything alone. I actually put the needle in the stock position before I rode after reading what you guys posted. I did not adjust the air screw it is 1.5 turns out which is stock. I did leave the main at a 165 and the pilot at a 45. I think what im going to try next is just putting the 48 pilot back in seeing hows everyones jetting recommendations tells you to leave the 48 in there. If that doesnt help ill probably just check for air leaks..

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Someone else had this same problem on their bike about 2 months ago. I told him to pull his jug and put some yamabond on the area where the 2 cases and the jug meet. It solved his hanging idle problem. I'll look for the thread but I'm sure it was immediately after a topend rebuild that this happened.

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I went into the garage and put the 48 back in but I probably wont be able to ride it until tomorrow just because today is easter and i dont want to piss the neighboors off lol. Are you running a 48 mihylo?

I'm running a 45 currently but using a JD jet kit with a 170 main and a 32:1 ratio. Its a little warm now so I should drop to a 168 and to a 165 later during summer. Did I send you a copy of the jetting predictions chart for this bike? How fresh is the topend on this bike? It will be hard to jet if the topend isn't relatively fresh.

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Yeah you did. The top end is a brand new wiseco, and I just replacked the silencer. I actually ended up going to a friends track today and rode it with the 48 back in and I had the same problem... the wierd thing is it only hangs when im going into a corner and i pull in the clutch. when im in neutral and rev it it goes right back down just fine.

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doesnt matter.... any corner...which is why i thought it was a clutch problem... i guess my next step would be to run the bike and spray brake cleaner on all the intake boots and the flywheel side crank seal and see if i can get it to idle up? But like ai said its odd because it doesnt hang when im in nuetral

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There is some play in it... the cables not pulling because I can be going into the corner before i even start turning the bars. I could just have the clutch in rolling down a hill going straight and it will hang

Sure sounds like a leak to me.

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