my new 250r =]

[Showcase]

hello, i just picked up a 87 250r. it has many mods from what i can see. fox shocks i think. i was told it has a 295 big bored, borred out to 301, i havent really been able to get it up to speed yet. but my question is, i got it, and the guy told me i have to mix 110 octane and 92. and i think ive read something about different domes making it different octanes. i got an extra 19 dome with it? im new to 250r's thank you. my compression is at 180 also.

pics.sorry for big pics.
http://img126.imageshack.us/img126/8331/img00262ps2.jpg (http://imageshack.us)
http://img380.imageshack.us/img380/3264/img00263ac9.jpg (http://imageshack.us)
http://img72.imageshack.us/img72/4880/img00265dl0.jpg (http://imageshack.us)

[GT300]

Nice Find. Has just about everything you could want. Good job!

[zedicus00]

180lbs. is fine on pump gas, 93 octaine or 91 if 93 isnt avaible. dont go less then 91 though.

the 19cc dome is for real race gas. it should bump compression to about 210. then u would just want to run race gas.

[Showcase]

so you dont think the guy knew what he was talking about having to mix the 110 and 92? i can just go with some 93 and be fine? thats good to hear =]

[GPracer2500]

Originally posted by Showcase
....i can just go with some 93 and be fine?...

Maybe. The porting (specifically exhaust port duration) matters too as far as minimum required octane (I'm assuming the cylinder has been ported). Cranking compression alone doesn't tell the whole story; although it is a major factor and is easy to check.

IMO, the best way to determine minimum required octane requirement is to test a fuel under conditions that favor engine knock and rate the fuel pass/fail. But you have to be comfortable detecting detonation. If you're not comfortable with that, it's much safer to error on the side of a higher octane rating than may be necessary.

[Showcase]

so what happens if i was to run lower octane fuel? just not run as hot and it wont work and blow up or what? sorry im not getting it.

[GPracer2500]

If you run a lower octane fuel than the engine requires it could experience what's known as detonation. This is an abnormal combustion phenomenon. It's also known as knock, engine knock, spark knock, or pinging. The knock and pinging names come from the fact that deto kind of sounds like an irregular "knock" or "ping" while it's happening. Very mild knock may go unnoticed. Moderate or heavy knock will create an audible signature. The sound is hard to describe precisely with words. It's most likely to happen under high air density, high temperature, high load conditions.

It's bad because it can melt your piston and/or hammer your piston, rod, crank, crank bearings, head, etc.

[Showcase]

im gonna give it a try with the 92, and listen really carefully and if it knocks at all just pull it out and use the 110 race gas if i can find that. that sound good?

[mxduner]

it will sound like someone took a hammer to your cylinder but in a quiet kinda way:ermm: do a compression check or check squish band check on it and let us know what you come up with,if possible:p

[mxduner]

hey showcase,unbelievable,someone with an r that lives close to me!i'm a half hour north of ya! isanti cambridge ish :eek: dont hear of much r action round here:confused:

[Showcase]

idk how to check my squish, but compression was at 180. and yea i was riding on 65 today =] fun stuff. now im about outa the gas that came with it and dont know what to put cuz idk where to get race gas around here...im in ramsey.

[mxduner]

ok, if your at 180psi compression AND IF YOUR TOP END IS IN GOOD SHAPE,you probably have at least a 21 cc dome in your motor which is gonna work fine with 93 octane.BE CAREFUL but u should be plentty good with piss pump gas.Nice machine btw. where did ya git it?

[mxduner]

what stretch of 65 did ya run?:devil:habeeb, next to the tech. school used to sell 110 @ the pump but seems they are not around anymore nothing i know close sells it. they sell 110 out of the pump in isanti, or go to anoka sherburne or cambridge airports and get 100 low lead gas

[Showcase]

the top end has like 10 hours on it...im gonna try a lil 92 today, and see how it goes....umm, we rode from 221st, going towards the isanti ice arena. it was my first time out there so we were just taking it slow having a good time...i got it at haydays, its a snowmobile grass drags and they have a swap meet. =] thanks.

[mxduner]

i got it at haydays, its a snowmobile grass drags and they have a swap meet. =] thanks.

yea almost went there to.

[Showcase]

it was sweet! shoulda gone. lots of fun, got there at 715 saturday morning. and there was a hour line of trucks to get in!! lol

[mxduner]

Originally posted by Showcase
it was sweet! shoulda gone. lots of fun, got there at 715 saturday morning. and there was a hour line of trucks to get in!! lol :D :D

[Showcase]

it was sweet, but i tryed some 92 octane mixed 32:1 with oil. it would go fine, i couldnt tell any wierd knocking. but when i was driving, it would bog down in second gear and such. idk what to do. i pulled the carb off and gave it a good cleaning with some carb cleaner. it didnt seem to change anything. think i should try changing the jets or something? idk i dont really wanna mess with the jets. thanks to anyone.

[Showcase]

any help would be great =] i cant wait to get riding!

[Showcase]

sorry for all the questions....but there is a 340 main jet in there, i have a bunch of other jets. do you think i should change that? im gonna be running 92octane gas.

[mxduner]

Originally posted by Showcase
sorry for all the questions....but there is a 340 main jet in there, i have a bunch of other jets. do you think i should change that? im gonna be running 92octane gas. i don't know about what you should have in your machine,but, with a 301cc and a 340 main that might be a little high,but i could be wrong :confused: there is some threads on here for jetting.do a search, btw whats the plug look like?

[Showcase]

the plug was darker.

[wilkin250r]

What kind of carburetor do you have?

[Showcase]

kehien i think its spelt....

[wilkin250r]

You may have read it wrong. I'm pretty sure Keihin doesn't make a 340 main. The biggest I've ever seen is 225, and the biggest I've ever heard of somebody actually using is 200.

A 340 is so large, it's absurd. Literally. It simply can't possibly be.

[Showcase]

well i know its a 340, maybe its a different kind of carb? i tryed them all pretty much and they all pretty much came out the same?

[GPracer2500]

230 is the largest Keihin series 357 (i.e. "hex head") main jet Keihin makes. And I don't believe any other type of Keihin main jet goes any higher.

Mikuni main jets on the other hand DO go into the 500's for sizing. I'm thinking you either have a Mikuni carb or if you've got a Keihin you've either got 1) an aftermarket main that uses a weird sizing scale or 2) the wrong type of main jet.

[Showcase]

sorry, it is a mikuni......and i checked again, its a 340...mikuni.

[wilkin250r]

That's what I was thinking. Because even the Dynojets for the Keihin carbs don't go up to 340, all their numbers are SMALLER. And Lectron doesn't use "jets", they adjust with a needle.

[Showcase]

lol yea, that was my bad....i didnt type the right name.....anyone got any advice for me now knowing what kinda carb it is?

[Showcase]

anything? thanks.