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.

[mohadib]

that oil looking stuff is un-burned fuel. Usually means you are way rich.

[threewheelin-feelin]

i havent got to do any of that stuff yet..i only had about an hour to mess with it today...i just tryed it with the 142and the 145 main jet and it ran just like it did with the 135...it would just want to die if i didnt stay on the gas...and would miss bad and not rev out...then i noticed the oil coming out of where the expansion chamber and silencer connect...go ovrit im sorry i cant remember your name lol...but im sure we will be back out there soon....i just got to get this thing going before busco next month...

[RoscoW]

I'll mention this only because I did it once, I cleaned the air filter and somehow left a paper towel in the intake tract. would start but wouldn't rev up at all and acted like it was super rich. Went searching for electrical issues and such and just ran across the paper towel all waded up in the carb, thought I was a real dummy and the next summer I witnessed the exact same thing happen to a buddy we were riding with. Had the air filter off and put a rag in the carb to keep out the dirt. Made me feel a little less embarrassed.

Ross

[threewheelin-feelin]

Ran horrible as in still rich? flooding?

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

i pulled the reeds out today...but quickly relized i had no clue what to look for...this is my first time really messing with a 2stroke..
i also made sure the air boots were all clear...im starting to think mayber its not a carb issue at all

[RIDE-RED 250r]

Ok, with reeds you want to pull out the reedcage and check them for chipping/fraying at the edges where they rest against the reedblock. Look for obvious "that don't look right" stuff. If they appear to be in good order the next step is to hold them in front of a light source and look into the cage from the carb side and look for signs that one or more reed petals are not coming to rest completely on the reedblock. You should see very little if not zero light coming through between the reed petals and reedblock. If you can see a reed petal/petals that leave a gap between the petal and reedblock at rest then you need new reed petals. That's about all there is to checking reeds. It's not a terrible idea to replace them periodically just as preventive maintenance because they work hard! There are different schools of thought on that. Personally I inspect them periodically and replace as necessary and have not had problems.

Now, I have not experienced it myself, but I have read many a thread about guys having what they thought was an erratic jetting problem that was impossible to zero in on only to find they had a faulty CDI. Only way I know to check for that is to replace your CDI with a known working and reliable unit and run it and see if the problem persists or not. Thanks to some guidance from Mosh, I now know that '85 and '86 250r CDI units do NOT interchange.

I know this seems like we are bouncing around alot, but the problem you are experiencing could be a symptom of several problems.

[threewheelin-feelin]

Ok, with reeds you want to pull out the reedcage and check them for chipping/fraying at the edges where they rest against the reedblock. Look for obvious "that don't look right" stuff. If they appear to be in good order the next step is to hold them in front of a light source and look into the cage from the carb side and look for signs that one or more reed petals are not coming to rest completely on the reedblock. You should see very little if not zero light coming through between the reed petals and reedblock. If you can see a reed petal/petals that leave a gap between the petal and reedblock at rest then you need new reed petals. That's about all there is to checking reeds. It's not a terrible idea to replace them periodically just as preventive maintenance because they work hard! There are different schools of thought on that. Personally I inspect them periodically and replace as necessary and have not had problems.

when i looked at the reeds the pplastic piece that is held in by the 3 screws is it sopposed to close all the way?

Now, I have not experienced it myself, but I have read many a thread about guys having what they thought was an erratic jetting problem that was impossible to zero in on only to find they had a faulty CDI. Only way I know to check for that is to replace your CDI with a known working and reliable unit and run it and see if the problem persists or not. Thanks to some guidance from Mosh, I now know that '85 and '86 250r CDI units do NOT interchange.

I know this seems like we are bouncing around alot, but the problem you are experiencing could be a symptom of several problems.

when i looked at the reeds the pplastic piece that is held in by the 3 screws is it sopposed to close all the way? i was thinking maybe cdi myself...but dont have one to test it with

[RIDE-RED 250r]

Yes, the reed petals are what it sounds like you are describing. Old school reed petals were made of stainless steel. Nowadays they are carbon fiber. Yes, at rest they should seat evenly and completely against the reedblock on all sides.

[MTS]

So, you have your float problem fixed with the new carb...no overflowing...ect. Unless the reeds are really spread out or broken it would only run like trailprotrailprotrailprotrailpro at an idle and just off the throttle...you have put a new spark plug in after fixing the flooding issue right? could be just a crank case full of oil and gas that needs burned up...IE run the snot out of it.

[threewheelin-feelin]

ok guys i finally got some time to mess with it tonight. i did a compression check. i set the chock fully open and had the trottle wide open. when i first kicked it, it came to 100 psi the second time around 140, then the third time it went to 175. the 4th and 5th kick it went up to 176 and would not go any higher. does this sound right? i repeated this about 5 times and got the almost identical results everytime. the book said to kick it several times. ok ride red the reeds do have small gaps in them. i also see that they are either after market or someone removed the stoppers. mts yes i finally got the flooding problem under control. should i drain the lower end fluid?

[El Camexican]

ok guys i finally got some time to mess with it tonight. i did a compression check. i set the chock fully open and had the trottle wide open. when i first kicked it, it came to 100 psi the second time around 140, then the third time it went to 175. the 4th and 5th kick it went up to 176 and would not go any higher. does this sound right? i repeated this about 5 times and got the almost identical results everytime. the book said to kick it several times. ok ride red the reeds do have small gaps in them. i also see that they are either after market or someone removed the stoppers. mts yes i finally got the flooding problem under control. should i drain the lower end fluid?

You shouldn't have much if any fluid in the "lower end" What MTS meant (if I can assume here) is that you may have a bunch of un-burnt (and by now un-burnable) old fuel in your crankcase. This is not the same as the crankcase on a 4 stroke. There is no drain plug, just an empty "pot" that the fuel air mix is sucked into through the reed cage and then when the piston comes down it pushes it up though the transfer ports and into the cylinder where it is compressed and ignited. If you leaked a bunch of fuel into this area it may be difficult for your engine to run properly as besides being too small (due to the old fuel taking up space meant for air) whatever does get forced up into the combustion area does not burn and gets pushed into the pipe where it gurgles around in the head pipe and soaks the muffler packing. Once you get it running and warmed up take it for a good rip and you'll likely leave behind a trail of white smoke behind you. Just don't get too aggressive with the reves if you aren’t sure that main jet is in the range of safe. It may take a while but you should feel improvments very soon. I hope this works for you.

[MTS]

starting to sound more like an ignition problem...or a few things toghter,one clogged air filter, it ever backfire or pop hard on any perticular start cold or hot?? comperssion seems fine...but that only comfirms your rings/ring is decent.

[1984 honda 200s]

Ever try running it with the fuel turned off? start it up and switch off the fuel, you might see a difference...

[jb2wheels]

When I bought my 85 250R last year, it would start and idle fine but with lots of smoke. However, it would never "clean out" and always seemed to run rich and smoky and crappy.

After rebuilding and cleaning the carb multiple times, cleaning the exhaust system, and changing the crank seals, I put an ohm meter on the stator, The spec is 50-250 ohm. Mine was on the low side around 130 if I recall. After some digging, the consensus is the 3rd gen Rs don't like a stator with a low reading. I bought a used stator that read 220 ohm or so. Problem solved.

[threewheelin-feelin]

starting to sound more like an ignition problem...or a few things toghter,one clogged air filter, it ever backfire or pop hard on any perticular start cold or hot?? comperssion seems fine...but that only comfirms your rings/ring is decent.

it did back fire on me a couple times yesturday when i was trying to start it. it is puffing alot of smoke for the short periods i can get it to run. but it doesnt want to idal, wont rev past about half trottle and breaks up bad then just suddenly dies wether im on the trottle or not

[atc300r]

Try a new coil.I had the same problem in 09 with my 85 250r.I changed crank seals,carbs,carb kit.It ended up being the coil.It would start and idle fine.Anything over 1/4 throttle and it acted like the choke was on.

[MTS]

might want to pop your mag cover off and take a look at the mag and stator, get a multimeter andstart checking, heck it could be a bad kill switch.

[threewheelin-feelin]

might want to pop your mag cover off and take a look at the mag and stator, get a multimeter andstart checking, heck it could be a bad kill switch.

the kill switch hasnt worked since i got the bike lol...and as far as it being the coil it may be but it doesnt even run good at idal

[threewheelin-feelin]

ok i went out to find my multi meter doesnt work anymore...so for the hell of it i pulled the plug out and kicked it over with it dark out side and i was getting a bright blue spark..but i guess it could still be a ignition problem?

[threewheelin-feelin]

ok got my multimeter working tonight...i checked the ignition coil resistence and it was right in the middle of specs. i then checked the stator and pickup coil both tested right in the middle of specs...next up was the cdi...i checked every connector in the plug and got no reading at all. so i was excited thinking that was the problem but then i read back and saw you have to have a special multimeter...so what do you guys think? take a shot in the dark and just buy a cdi?

[threewheelin-feelin]

hey guys still chasing this problem...out of the discription i have tried to give is there anything else i should be checking...i was told crank seals can cause it to run like this...i am trying to take this to busco beach in 2 weeks so i am in a time crunch...i have new reeds on the way and im hoping they will be in tomorrow...stator and coil tested good but is it possable they could still be bad? i got nothing out of my cdi when i tried to test it but apparently you have to have a certain tester...so does anyone have anymore ideas? i am going to try my hardest to get a video up of what its doing this weekend

[threewheelin-feelin]

reeds fixed the problem

[mohadib]

Nice, glad to hear you got it fixed and thanks for letting us know!

[WJG1000W]

glad to here you got it running

[threewheelin-feelin]

i still think it was a combination or a fuel filled crack case fouled plug and bad reeds but it is running pretty good now

[threewheelin-feelin]

ok i jumped the gun on saying i had it fixed...ok after you take in all the info on this tread i have giving. this is wear i am now...i put new reeds in and a new plug...and the bike ran so well like a bat out of hell for about an hour then it started running bad and fouled the plug..but as soon as it put a new plug in...it ran pefect again for about an hour of riding.,...then i changed from a 145 main jet to a 135 and no change...it seems to want to smoke alot when its cold.. then when it warms up it clears up while riding but smoke alot at idal all the time any ideas

[threewheelin-feelin]

ok i worked up the nerve to try again at it...i put an extra coil i had on with no change both coils tested about the same...i tested to exicter coil it was at 150...i then tested the stator it tested at 147...so how confident are you guys that the stators have to test about 200 to be good before i spend $150 on one? i also slightly opened the gap on the plug and it ran worse...i closed it back and it ran the same...i have been thrue about 7 plugs in the last 3 days of trying to diagnois this bike...it just makes no sence..it runs like a bat out of hell for about an hours worth or riding every time i put in a new plug...then fouls it out...it is smoking alot at idal and seems to foul the plugs faster the more i let it idal...i am about to drag this damn bike down the road behind my truck

[TtownJoeShow]

I think it's an air leak.... I'd check your reeds, make sure they're seating properly still! Your problem sounds like mine, bad bore hone job???

[threewheelin-feelin]

havent had a bore or hone job done...and an air leak i think would cause a lean condition not rich

[SteveCZ28]

its worth a shot to make a leak down tester and check to make sure you dont have a seal out...you and i are chasing similar problems, only mine wont run for the hour or so like yours does. i made a leak down tester for about 15 bucks.

[xman2rman]

I agree with Steve, you need to do a leak down test and a compression test if you haven't already. I just built a leak down tested and I'm still chasing leaks! The first on was the spark plug of all things, I had to loosen and tighten several times and actually had to tighten up more then I liked to get it to seal. My cases were also leaking... you'll get bubbles from the crank case vent on it. I got lucky and was able to tighten the two case bolts behind the flywheel/stator and it stopped. I still have a slow leak and have a fly wheel puller and new seals on order. Also, without going back and reading 3 pages, is your air/fuel screw doing anything when you adjust it? Try this if you haven't already: put a new plug in, set the air/fuel screw at 1.5 turns out, warm it up, get the idle set, slowly turn the air/fuel clockwise... the rpms should drop and the engine may die. Back it out and crank it back up, now start slowly turning the air/fuel counter clockwise until you get the highest RPM's then turn it back 1/4 to 1/2 turn clockwise. This should be real close for the air/fuel circuit and shouldn't be fouling plugs. IF... the carb WILL NOT adjust like I described, you have an air leak! I really don't think you have an ignition problem... Good luck! :)

[atc300r]

How old are your crank seals.! way to tell if they are worn or bad is your flywheel cover will smell like raw gas.On the clutch side if your seal is bad it will suck tranny fluid in and your exhaust will smell bad. Like burnt rotten fish.

[threewheelin-feelin]

I agree with Steve, you need to do a leak down test and a compression test if you haven't already. I just built a leak down tested and I'm still chasing leaks! The first on was the spark plug of all things, I had to loosen and tighten several times and actually had to tighten up more then I liked to get it to seal. My cases were also leaking... you'll get bubbles from the crank case vent on it. I got lucky and was able to tighten the two case bolts behind the flywheel/stator and it stopped. I still have a slow leak and have a fly wheel puller and new seals on order. Also, without going back and reading 3 pages, is your air/fuel screw doing anything when you adjust it? Try this if you haven't already: put a new plug in, set the air/fuel screw at 1.5 turns out, warm it up, get the idle set, slowly turn the air/fuel clockwise... the rpms should drop and the engine may die. Back it out and crank it back up, now start slowly turning the air/fuel counter clockwise until you get the highest RPM's then turn it back 1/4 to 1/2 turn clockwise. This should be real close for the air/fuel circuit and shouldn't be fouling plugs. IF... the carb WILL NOT adjust like I described, you have an air leak! I really don't think you have an ignition problem... Good luck! :)

its makeing 175psi on compression specs in the book is 170 to 199 so thats good...now for the air screw mixture i have messed with that but i turned it all the way in and it wanted to die...i put it back to specs in the book because i didnt know that method you described...if when i turned it in and it wanted to die does that sound like an air leak? i believe the crank bearings and seal around 4 to 5 years old...i also have no strange smells comeing from the exhaust just blue smoke...the blue smoke almost completly clears up when im running it...but always tends to get alot smokier at idal...does any of this info help?

[threewheelin-feelin]

everytime i start this bike now i get a thick cloud of blue smoke for about 30 second to a minute...would this be caused by oil leaking thrue the clutch side crank seal while it isnt running and building up..and then when i crank it burning up a puddle of oil? if this sounds right to you guys what is a good brand of seals...or should i only use honda seals

[xman2rman]

It will die when you turn the screw all the way in because you just cut off all air which makes it run rich. If there was an air leak in the manifold area, the air screw may not have an effect so it doesn't sound like an air leak there. If it's running rich (black and fould plug) then either lean the air fuel screw (counter clockwise), drop the main jet size or lower the neddle clip. It can also foul a plug from a bad crank seal, sucking trans oil. The key to setting the air/fuel mixture correctly is simply trial and error. I explained how I do it earlier. As far as smoke, both my R's smoke more when you first start them and at idel and one of them probably has less than 50 original hours on it. I believe that is normal, the rings and piston expand as the engine warms creating a better seal. As far as the seal kit, I just got a set of TUSK for less than $20 shipped to the door, they look like good seals to me but you sure couldn't do better than Honda so it's up to you. I haven't seen the results of your leak down test? I'm guessing you did one since your buying seals...

[threewheelin-feelin]

It will die when you turn the screw all the way in because you just cut off all air which makes it run rich. If there was an air leak in the manifold area, the air screw may not have an effect so it doesn't sound like an air leak there. If it's running rich (black and fould plug) then either lean the air fuel screw (counter clockwise), drop the main jet size or lower the neddle clip. It can also foul a plug from a bad crank seal, sucking trans oil. The key to setting the air/fuel mixture correctly is simply trial and error. I explained how I do it earlier. As far as smoke, both my R's smoke more when you first start them and at idel and one of them probably has less than 50 original hours on it. I believe that is normal, the rings and piston expand as the engine warms creating a better seal. As far as the seal kit, I just got a set of TUSK for less than $20 shipped to the door, they look like good seals to me but you sure couldn't do better than Honda so it's up to you. I haven't seen the results of your leak down test? I'm guessing you did one since your buying seals...

i havent done a leak test i dont even know what the leak tester looks like lol...i was just assuming i had a good theory on what was going on...and i see what you mean about them smokeing more at start up...but i mean it fills my entire back yard up ...just seems like way to much for it to be normal and i never got smoke like this till all this started happening...also if it helps ive got a 135 main jet in it...needle clip at stock position...and the air fuel screw i believe i left it at 2 and 3/4 turns out...im starting to get scared to go any leaner...

[xman2rman]

I would also assume your theory is theoretically correct BUT you really need to diagnose the problem. Here you go:

http://www.3wheelerworld.com/showthread.php/71487-Building-and-operating-a-leak-down-tester.-My-technical-process-and-suggestions?highlight=leak+down

and

http://www.3wheelerworld.com/showthread.php/96856-Make-a-leak-down-tester-for-about-20?highlight=leak+down

[riverrat]

Mine did a similar thing and it was seals. Really look close at the oil around the exhaust. Tranny oil is more black, but 2 stroke oil is more blue. Plus you will see the tranny oil on the plug when it is getting fouled,it can easily be mistaken for carbon, but it is actually oil.