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04 RM250 - pulsing &/ knocking

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replaced main bearings, crank, top end. cylinder bored to 67.5mm. I wasnt thinking I'd need to rejet. The plug looks great. Problem I'm having is that it seems to be getting hot, it'll dribble out some coolant from the overflow hose. it seems like every now and then itll pluse and few times going into a corner with the clutch in, a couple ding dingss before idle drops; not all the time though. Possibly an air leak? just put new crank seals in! maybe from somewhere else? what do you guys think? I ran it hard at southwick for 4 motos and it held up (1st ride after rebuild & heat cycles) maybe just being paranoid after the rebuild?

afraid its detonating but plug doesnt look lean. im running 93 pump gas and trying to stay away from mixing race gas 50/50, @ $9.75/gal F that. my best bet is to probably pop the head off and take a look huh?

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id look for an air leak, have you re sealed your airbox yet? if not, do it. then, check your dry side crank seal. if you have access to 100LL AVGAS around you, run that 50/50 with pump, its only like $5/gallon and leaded. its always worked great for me, ran it since i was on 80s without issue.

hope this helps

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ya i sealed it with rtv earlier this season, i guess it wouldnt hurt to do it again. then ill check the dry side seal. thanks

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yes, itll probably need to be fatter on the pilot and leaner on the main.

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check the power vavle, call Ron Bushey aka Ragin ron tell him john adamy told you to call him he helped me out tremendously with my rm, hes like a wizard with those things, if you're from ct hes local hes out of southern mass, and he's one of the best mechanics around he was kyle chisolms factory mechanic, and also john dowds factory mechanic. He knows mx bikes for suree!! If you want his number pm me and ill give it to you.

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yes, itll probably need to be fatter on the pilot and leaner on the main.

Wheres your logic there? I get being bored and running fatter because its sucking more air, but then why leaner on the top?

I took the rubber boot off my airbox last night, there were in fact area that I could see air getting sucked in. i gobbed a crap load of rtv around there and sealed up good. I also dropped my clip 2 places. i was planning on testing it out today but it looks like its gonna be a wash..again. im going up to crow hill tomorrow, ill bring a couple pilot and main jets with me. Thanks again dtha

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Wheres your logic there? I get being bored and running fatter because its sucking more air, but then why leaner on the top?

Generally, it's leaner since the stronger vacuum is pulling more fuel into the motor.

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*UPDATE*

Just an FYI for anyone in the future:

Gave Wiseco a call, they said usually this will not require re-jetting, even up to a 1.5mm overbore they usually don't have to re-jet. He did say that leaner would be the direction to go if in fact it needs some tuning; do to the stronger vacuum sucking more fuel. kan was correct. Thanks again guys, appreciate the help.

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so I was impatient this morning and sent an email out to Wiseco prior to calling them. I got a response after I had spoke with whoever it was i spoke to over the phone. Heres his response:

"You should not have to do any jetting changes. I would just do a plug

check after you get it broke in to make sure it's not lean. The oversize

piston will draw a little more air in which could lean it out a little

bit.

Regards,

Alan Pizzino

Technical Sales

Wiseco Performance Products"

So basically I need to either lean out my jetting or richen it up, haha thanks for the help, I think I'll toss a coin. A little irritating to get conflicting responses from Wiseco

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does overboring (~+0.020) typically require re-jetting?

My 05 RM250 is bored to 265 and it did NOT require any rejetting at all. I called PC and they said that there is usually no need to jet differently for an overbore of that size. Now i don't know what end CC your bore is but if i remember what Eric Gorr told me, my big bore is has the same piston size so i'm assuming yours is a 265 as well (feel free to correct me if i'm wrong) But in the end, i didn't need to jet any different than standard.

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its just an overbore,on a cast iron sleeve, not a BB kit, i think it comes out to like 253cc

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its just an overbore,on a cast iron sleeve, not a BB kit, i think it comes out to like 253cc

AH, i see. well either way that wouldn't be any bigger than my motor and like i said i haven't had any jetting issues yet. i have been thinking about going to a 48 power jet (talked about in another thread here) but that is still what PC recommends for the stock 250 bore....

Very long story short, i don't think that you should need to jet differently...

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so i rode it hard yesterday on my corner track. getting a better seal between the airbox and rubber boot was the ticket. no more pulsing/hanging idle. i did notice when i was warming it up a few drops of antifreeze came out of the overflow...i know that never used to happen...

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If you guys still think its and air leak then check the right side of the base gasket. If you used a thin base gasket, it could leak between the studs on the right side. I don't know why the Suzuki's weap on the right, but that is the first place the base gasket will fail. The thin aftermarket bases push out or you will notice a oil film between the cylinder and the cases. Not to say it may not be a carb boot to reed box leak, but the first place to check is the base gasket.

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