85 ATC250R jetting...

[phatcat600]

I have an 85 ATC250R and it has recently been rebuilt. I rode it for a while and it fouled out almost instantly, I dropped the jetting down 2 sizes to a 135 and it fouled out after about a half gallon of gas (32:1 mix). Should I try a smaller jet (I dont have a set, i have to buy them individually) or could that lean it out to much? Where are the needles and float supposed to be set?

I havent had the jetting right in this piece since I got it. I enjoy the 10 minutes of riding I get at a time, the thing absolutely flys; Im just wanting a bit more than 10 minutes at a time without swapping 3 dollar a pop plugs.

[x.system]

Stock settings for the 85 are

Air screw-2 turns out
needle- 2nd groove from top
plug-BR9ES, cold weather BR8ES
float-16mm (0.63in)
Main jet-142

If your bike is stock I would start here then fine tune it. The manual recomends you drop the clip to the 3rd position from the top and change to a 145 main for tempatures of 0 F to 22 F @ 0 to 5,000ft

When it gets colder I go up in jet size not down. What mods do you have? Do you do plug chops? It should be starving for fuel with a 135 main, you may want to check your air screw and float level settings.

I'm about 2 hours north of you, were ice racing sunday if you want to bring that bike up, I can help you dial it in.

[a-camp]

Stock settings for the 85 are

Air screw-2 turns out
needle- 2nd groove from top
plug-BR9ES, cold weather BR8ES
float-16mm (0.63in)
Main jet-142



I'm about 2 hours north of you, were ice racing sunday if you want to bring that bike up, I can help you dial it in.
This is good advise . I agree . May want to stay 1 or 2 sizes from stock and play with your air screw and needle clip. Nice offer as well I want to check out some ice racing .

[phatcat600]

so would returning all the setting back to stock with a 135 jet and switching to 50:1 be safe?

[350x'inNY]

50:1?? I wouldn't do that unless you want to starve the cylinder for oil. My 82R says to mix 20:1... I go 32:1. If it's stock, I'd do what x.system said. Usually if it's modified, you'd have to go UP on the jet. I'd put in the stock jet, stock adjustments and go from there.

[KASEY]

135 is way to lean for a 250,,,,,, you got something else going on,,, after reading your first post i think your so fat on the bottom ,,and your trying to clean it up with a smaller main,,,,, THAT WON'T WORK,,,, you also say its never been right since you have had it,,,, so i say what are all the numbers? main jet size,pilot jet size,slide cutout# jet needle # needlejet# ,,,, float level set to high? ,,, if its jetted right it should be crisp off the bottom and not all blubbery,,,, cause if its all rich on the bottom and you continue to try to fix it with a main jet,,,, all you will end up with is a seized piston from being lean ,,,,

[phatcat600]

Ok, I have everything back to stock settings except for the 135 main, I cant find my 140 and 142 now grrr. This is frustrating because I dont have enough money to drive 40 miles to buy the stock jet (im only 17, and broke).

[Lots_Of_Nothing]

135 is way to lean for a 250,,,,,, you got something else going on,,, after reading your first post i think your so fat on the bottom ,,and your trying to clean it up with a smaller main,,,,, THAT WON'T WORK,,,, you also say its never been right since you have had it,,,, so i say what are all the numbers? main jet size,pilot jet size,slide cutout# jet needle # needlejet# ,,,, float level set to high? ,,, if its jetted right it should be crisp off the bottom and not all blubbery,,,, cause if its all rich on the bottom and you continue to try to fix it with a main jet,,,, all you will end up with is a seized piston from being lean ,,,,

Kasey is the man to listen to for R jetting... Sounds familiar, when I got my 85 the dude had a 130 main! and it was bored with a wiseco, ported, k&n and fmf exhaust.. .. And he WONDERED why the piston melted! :rolleyes:


50:1?? I wouldn't do that unless you want to starve the cylinder for oil. My 82R says to mix 20:1... I go 32:1. If it's stock, I'd do what x.system said. Usually if it's modified, you'd have to go UP on the jet. I'd put in the stock jet, stock adjustments and go from there.

Bruce, as long as you jet to the mixture your running it will be fine, I ran 50:1 amsoil for a year of hard beating and then when I sold the machine I checked, topend was perfect.. I dont remember who it is on here, but hes running 100:1 .. phatcat600- I am NOT saying do this.. So dont take me the wrong way. But if you can jet correctly, you can run any mixture you want. I ran 75:1 In my 84.

[Lots_Of_Nothing]

Ok, I have everything back to stock settings except for the 135 main, I cant find my 140 and 142 now grrr. This is frustrating because I dont have enough money to drive 40 miles to buy the stock jet (im only 17, and broke).

Ask a couple of the R guys on here, I'm sure someone can hook you up for a couple bucks.

[phatcat600]

yeah gettin them isnt a problem eventually, its just that i thought i was seconds away from riding and now i cant cuz my parents threw the jets away. grr.

[x.system]

Kasey is the man to listen to for R jetting... Sounds familiar, when I got my 85 the dude had a 130 main! and it was bored with a wiseco, ported, k&n and fmf exhaust.. .. And he WONDERED why the piston melted! :rolleyes:



Bruce, as long as you jet to the mixture your running it will be fine, I ran 50:1 amsoil for a year of hard beating and then when I sold the machine I checked, topend was perfect.. I dont remember who it is on here, but hes running 100:1 .. phatcat600- I am NOT saying do this.. So dont take me the wrong way. But if you can jet correctly, you can run any mixture you want. I ran 75:1 In my 84.

I am one of the guys that runs amsoil at 100:1. Heres a couple pics of a years worth of riding at 100:1 and the only reason I took this cylinder off was to bolt on a paul turner top end. I was surprized how good this looked when I took it off, I was expecting a few scratches but it looks great. I will end up checking the specs and then honing this cylinder and re using it in a trike project with new piston and rings if I don't have to bore it.

[HRC1]

I live in southern mich and own a 85" R, I run a 135 with clip in middle position and it runs fine. I have a k&n and a fmf pipe and a rad valve. Other than that it's on it's first overbore witch i did. It would foul plugs every 20 min when i got it from the sec owner. Thats why he sold it to me, he couldnt keep it from fouling out. If that is too lean, then what jets are u guys running? Also, i run 32:1 super techniplate with 87 oct. From what i understand u go down jetting when switching pipes on a 2 stroke as the pipe pulls stronger vacume, therefore sucking more fuel from the main. Any imput?

[Lots_Of_Nothing]

Ahh, I thought it was you Xsystem, just didnt wanna say a name I wasnt too sure about. The cylinder looks good, You probly had your jetting spot on eh? what were you running for a main? I cant even remember what I was running in my R before I sold it, a 160 or 170 something I think , that was with a polished out 38mm.

[Lots_Of_Nothing]

From what i understand u go down jetting when switching pipes on a 2 stroke as the pipe pulls stronger vacume, therefore sucking more fuel from the main. Any imput?


...............................................

An aftermarket pipe increases flow out of the engine, therfor you burn more fuel quicker, and if you lean it out, its begging for more fuel, but all its getting is more air which will equal a lean condition, which is what you DONT want.

[HRC1]

So what are your jetting specs? i have a stock pilot as far as i know, 135 main, witch all my friends have in theirs also, and clip in middle.
I will play with it if everyone else in the worls is running a fatter main, but untill i get a idea of what everyone else is running, i cant see messing with it. Oh, when i put a new piston in after 2 summers of riding it, dunes and all, the Stock piston was fine, i coulda got another summer out of it easy, but didnt want to push it as i didnt know the history of the bike.

[Lots_Of_Nothing]

Well, running klotz at 32:1 you could probably run a 120 and get away with it, that is rich for synthetic oil.

And as I allready said, I cant even remember what exactly I was running, My R has been sold.

[TimSr]

I saw several different gas/oil ratio recommendations, but I dont see any mention of what kind of oil he is running. That does matter. I run 50:1 with Blue Marble. If I did it with Yamalube Id probably have a problem. I also did not see what pipe he is running. That makes a difference too. Aftermarket pipe can make it run leaner, richer, or the same as stock, depending on what kind of pipe it is, and what its made for. I dont know where the rumor got started that aftermarket pipes automatrically require a bigger jet, but its just not true. Factory jetting is rich. Top end pipes may need more fuel. Low end pipes may need less fuel. Fiber reeds make it run richer. My 250R had a 165 in it when I got it. It ran like a turd and fouled plugs all the time. I jetted all the way down to 135, and melted the piston in an MX race. After a fresh bore, I discovered it suddenly ran a lot leaner, as the bore was shot the whole time, and I tried to jet around it. I ended back up at 145, until I switched to Blue Marble, and then dropped to 140 with the needle in its leanest setting. The whole point here is that 135 is not really out of the ball park, especially if its mostly stock, but there are a whole range of factors where it could be. First, figure out what gas oil mix your going to run, and carburate around it. You cant be tweaking the carb and experimenting with your mix at the same time.

My first suspicion for fouling plugs and dogging at low end is low compression. You said it had just been rebuilt, but didnt go into specifics. What exactly was done to it, and when, and who did the work?

[x.system]

Ahh, I thought it was you Xsystem, just didnt wanna say a name I wasnt too sure about. The cylinder looks good, You probly had your jetting spot on eh? what were you running for a main? I cant even remember what I was running in my R before I sold it, a 160 or 170 something I think , that was with a polished out 38mm.

I jet my bike before every ride but that cylinder was using anywhere from a 160 to 175 with a 36mm during the summer. When I jetted it for winter I put a 39mm with a 190 main for 0 temp. I jetted my new cylinder today for tomorrows race and am using a 180 at about 30 degrees. I still have to dial it in tomorrow but its close enuff to break in the new piston and rings tonight. Tomorrow at the track I will do a couple plug chops and lean it out as far as I dare for the race.

[QUOTE=phatcat600] Ok, I have everything back to stock settings except for the 135 main, I cant find my 140 and 142 now grrr. This is frustrating because I dont have enough money to drive 40 miles to buy the stock jet (im only 17, and broke).

Have you done a plug chop with it set up this way yet? With the temps the way they were today you should be close but lean compared to stock. Tomorrows temps are suposed to be like todays but a little warmer. I would do a plug chop at half throttle then again at full. You want to run it in 3rd or 4th at half throttle after warm up for a good distance then hit the kill and check the plug. Carry a plug wrench with you. Then do one at full throttle, get it up to speed in 5th or 6th, hold it WOT for about 5 seconds and hit the kill switch. I normally do the half throttle chop just to make sure I'm not running to lean before I do a WOT plug chop. Let us know what your plug looks like after each chop. If your plug is white or chalky colored I wouldn't do the WOT chop just to be safe.

[KASEY]

This is frustrating because I dont have enough money to drive 40 miles to buy the stock jet (im only 17, and broke).

maybe you should park it till you get it soarted out.... if you can't afford to run to town to get the right jets ,,, then i am really sure you can't afford a TOPEND,,,,,,,,,,,,,,,

[phatcat600]

I have been running it with all stock settings except for a 135 main. It seemed to be running fine but now all of a sudden it decided to foul out.

Could this be the pilot jet causing this? What should the pilot be?

[phatcat600]

We did the rebuild, 185 psi compression...is this ok...

I put in a new plug with the 135 main and after about 10-15 minutes of riding it isnt idling and soon it will foul out and not even start. Im running my moms polaris snowmobile oil 32:1, I dont relaly wanna use the synthetic arctic cat oil we have cuz its 28 dollars a gallon. People keep tellin me switch to 50:1, what do you guys recommend I do next?

[hrc85250r]

thats about wat i had, with the stock carb....i had 190, but that was after i seated the rings.......i had a 142 main in it, with a dg pipe.....ran awesome and was jetted perfect.....everything else was stock on it....since then i bought a 38mm a/s carb from deathman,new 261cc top end after i seized it, ported it, rechambered and lapped the head, added a cr head gasket and carbon reeds in the stock cage, and it is a whole new beast now!lol....i suggest a new carb though....that stock carb really holds back its potential....

[phatcat600]

Its a beast already! Eventually I wanna do aftermarket stuff but right now all I want is for it to run! Im gonna try to clean it up a bit this summer but I dont think Im gonna get anything new really besides a chain and hopefully some decent used shrouds.

[Fox250R]

My 85 has a 142 main running 50-1 with a PtHr pipe and it runs awesome! Fouls about every 20 rides so i guess thats ok :)

[phatcat600]

mines stock, should i stick with the 135 and try 40:1 and eventually 50:1?

[Fox250R]

135 seems a little lean to me for 50-1 but it might be ok...

[TimSr]

mines stock, should i stick with the 135 and try 40:1 and eventually 50:1?

Go to 50:1 if you are going to use the good synthetic oil. If you are going to run that $2 per quart stuff I wouldnt go a drop past 32:1. $28 a gallon is hardly what Id call expensive. At 50:1 it treats 50 gallons of gas. When you are comparing prices, figure that against the 32 gallons you treat with a the cheap stuff. Then if you want to throw in the cost of a few spark plugs, I just dont understand why somebody would spend all the extra money to run an inferior product. Im all for selling Blue Marble, but at least go to the dealer and get a $5.00 bottle of belRay MC1, HR1, or some Spectro or something!