85 250r carb driving me insane

[threewheelin-feelin]

ok i am really about to lose it with this carb...let me give you a little background on this machine. i bought it back in may of 2008 when i bought it the previous owner said it had been bored .40 over but was stock other then that...it had original oem exhaust on it and he said he rejetted it after boreing it...so i get it home and the bike runs perfect. it ran better then any four stroke i had every had. even in the dead of winter it would wrong perfect..and it did that for almost 4 years...so i bought an fmf fatty and turbine core silencer...i installed them and rode it around a few times in the back yard...it seemed fine but never really got to open her up...i rode it maybe 3 times with the fmf on it and then the carb starts pouring gas out of it and everything went to hell...so i put in a new float valve and replaced every thing except the jets...i measured the float level about 10 times now...and the bike is running horriable ..so i replaced the pilot and main jet wich im guessing is a 142 and that didnt help...i read the jet that came out and it was a 135...so ive already desided to buy another carb off ebay today after i post this...my question is should i go with another 135 main jet or something different...and where can i get them from?

sorry to have such a long post but im so frustrated with this carb i just want to get it right

[86ATC 250r]

i had almost the same problem gas was jus leaking out of my over flow so i tore the carb out and cleaned it up nice put it back together and still did the same thing. so what i ended up doing was bending the little tab on the float slightly till i got it jus right and finally it stopped running out the over flow..

[RIDE-RED 250r]

The jetting wouldn't cause it to overflow/flood like that.

I woulds start the jetting with the main jet at stock +2 sizes richer for the FMF exhaust. Are you getting the roundslide carb from ebay?

If so, stock jetting specs are as follows: #142 main jet, #52 pilot jet, jet needle 2nd groove from top, airscrew 2 turns out.

Again, these are stock baseline jetting specs for the '85 model with the roundslide carb as stated in the Honda service manual. I would go with a 145 or 148 main jet to start with and go with the stock size pilot jet (#52). Just running an upgraded exhaust rarely requires a pilot jet change.

You may also find that you will need to raise the jet needle a tick or 2 as well. Might even be a good idea to raise it one notch to start with anyway. Better to start rich and work your way leaner to dial it in. Sparkplugs are cheap, topends are not.

And as to where to get your jets. Any dealer/motorcycle parts shop worth it's salt will have them on hand or at the very least be able to get them for you easily. There are places online too. Might be a good idea to order a complete jet kit and have an assortment to work with. Just be sure and order jets for the right carb. Between the '85 roundslide carb and '86 flatslide carb the main jets are the same, but the pilot jets do not interchange. If you have the roundslide it is a type "PE". So you would then want a jet kit that has jets that work with the Keihin "PE" carb. The '86 flatslide is a type "PJ". And of course if that is what you have you will want jets that work in a "PJ" carb.

Oh, and a .040" overbore should require minimal (if any at all) jetting changes.... So a little on the rich side of stock jetting should work fine. But as I said, start rich (148 main, raise the needle 1 position) and work your way leaner.

[threewheelin-feelin]

The jetting wouldn't cause it to overflow/flood like that.

I woulds start the jetting with the main jet at stock +2 sizes richer for the FMF exhaust. Are you getting the roundslide carb from ebay?

If so, stock jetting specs are as follows: #142 main jet, #52 pilot jet, jet needle 2nd groove from top, airscrew 2 turns out.

Again, these are stock baseline jetting specs for the '85 model with the roundslide carb as stated in the Honda service manual. I would go with a 145 or 148 main jet to start with and go with the stock size pilot jet (#52). Just running an upgraded exhaust rarely requires a pilot jet change.

You may also find that you will need to raise the jet needle a tick or 2 as well. Might even be a good idea to raise it one notch to start with anyway. Better to start rich and work your way leaner to dial it in. Sparkplugs are cheap, topends are not.

And as to where to get your jets. Any dealer/motorcycle parts shop worth it's salt will have them on hand or at the very least be able to get them for you easily. There are places online too. Might be a good idea to order a complete jet kit and have an assortment to work with. Just be sure and order jets for the right carb. Between the '85 roundslide carb and '86 flatslide carb the main jets are the same, but the pilot jets do not interchange. If you have the roundslide it is a type "PE". So you would then want a jet kit that has jets that work with the Keihin "PE" carb. The '86 flatslide is a type "PJ". And of course if that is what you have you will want jets that work in a "PJ" carb.

Oh, and a .040" overbore should require minimal (if any at all) jetting changes.... So a little on the rich side of stock jetting should work fine. But as I said, start rich (148 main, raise the needle 1 position) and work your way leaner.

i have tried bending the tab...it has done nothing...i am getting a round slide stock carb...you say i should be going up to a 148 main...do you have any idea why it would have had a 135 in it? i think i will try it with the stock un touch carb first to see how it does

[threewheelin-feelin]

if it helps i always run 32:1 ratio and i am at sea level

[AngusJustice]

when it comes to carbs before messing with them see if you can find another one off a machine that runs and try it on yours this can save a mountain of head aches.

[RIDE-RED 250r]

i have tried bending the tab...it has done nothing...i am getting a round slide stock carb...you say i should be going up to a 148 main...do you have any idea why it would have had a 135 in it? i think i will try it with the stock un touch carb first to see how it does

I have no idea why there would have been a 135 main in it. It's possible someone somewhere along the line did some shadetree "jetting" for more power? Or maybe they were riding it at high elevation? That's a fair bit leaner than factory. Not drastic, but definitely noticeable and could very well have your engine running on the edge.

Since you have the FMF exhaust, I stand by my recommendation to start 2 sizes richer on the main and the jet needle raised 1 notch. Upgraded exhaust usually requires some jetting adjustments, usually a tad richer than stock. Better to be safe than sorry for the cost of a few jets. Start rich and work your way leaner.

The jetting specs I listed are for sea level-5,000 feet with temp range of 22-104 Fahrenheit per the Honda service manual for '85-'86 250r.

[threewheelin-feelin]

I have no idea why there would have been a 135 main in it. It's possible someone somewhere along the line did some shadetree "jetting" for more power? Or maybe they were riding it at high elevation? That's a fair bit leaner than factory. Not drastic, but definitely noticeable and could very well have your engine running on the edge.

Since you have the FMF exhaust, I stand by my recommendation to start 2 sizes richer on the main and the jet needle raised 1 notch. Upgraded exhaust usually requires some jetting adjustments, usually a tad richer than stock. Better to be safe than sorry for the cost of a few jets. Start rich and work your way leaner.

The jetting specs I listed are for sea level-5,000 feet with temp range of 22-104 Fahrenheit per the Honda service manual for '85-'86 250r.

running on the edge? like blow up...or getting everything it has out of it? i just dont know what the hell is going on...it ran perfect, best running bike i ever had...till the gas started pouring out...oh well i have a new carb on the way and i ordered a 148 145 and 135 main jets for experiments

thanks for helping me with this man...ive asked these questions before and no answers and im lost with jetting 2strokes...ive always worked on 4 strokes

[RIDE-RED 250r]

No problem, happy to help any way I can. I just don't want to see you start a thread about a blown topend. You did right by ordering the 145 and 148 mains. I'll bet it will settle on one of the 2 nicely.

When I say "on the edge", I'm referring to on the edge of too lean and possibly engine damage if you ride it on a cold day.

I have an assortment of main jets from 162 to 205 for my modded R. It's really nice having an assortment to work with. If I were you I would look into a jet kit/assortment from about 140 to 150 for your engine the way it is set up. A bit of searching around on google should net you some results for jet assortments.

[threewheelin-feelin]

got my carb today...they sent me a flat slide for a 86...so im trying to get in contact with them for an exchange...so we will have to wait longer ugh

[jb2wheels]

The flat side from an 86 is supposed to be a better carb - will it bolt on?

[threewheelin-feelin]

you have to change out the intake boot, air boot, and the trottle slide to 86

[threewheelin-feelin]

ok got the carb tonight...only had time to try the 145 main jet...still ran horriable and i noticed it looked like oil comming out of where the expansion chamber connects with the silencer...im lost...

[RIDE-RED 250r]

Ran horrible as in still rich? flooding?

By any chance through all this have you pulled the reedcage and checked the reeds?

[GO OVRIT]

You should probably do a leak down test. If you come back out to Gloucester soon I'll let you borrow the tester I've got. If you have an air leak you'll never get it jetted right. What did your plug look like? Is your air filter good and clean? Are the reeds good? As far as a place to get jets...try jetsrus.com Also, you shouldn't have any leaks in the exhaust, esecially right at the head.