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1982 yamaha IT 250 running rich

10 Oct 2020 11:00
Isaac
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1982 yamaha IT 250 running rich #1
My IT 250 is running rich and I haven't been able to sort out what's going on with it.

I bought this from a retired machinist who hadn't ridden it in 8 years. It was stored in his garage, but had a gummed up carb.

It fouls plugs and won't rev at all, just bogs down and smokes in all rpms. It also won't idle without keeping throttle input.


Here's what I've done so far:

- Cleaned the carb and checked to see what jets were in there. It was all at factory stock jets and settings. I set the idea air screw to 2 turns out. I installed a new spark plug. I tried it again and nothing changed.

- I cleaned the carb again, being sure to check for wear on the needle and the emulsion tube. All looks good. I set the float level to factory setting (I think this is 24.5mm or something, I cant remember now but have it written down in my log book). Nothing changed.

- I decided to swap carbs with a good running 1980 IT 250. No change in the way it ran. Still boggy, smokey and founding plugs. I re installed the old carb.

- I changed the crank seals. It started and ran like a champ, revved clean and sounded great. That was last night at around 9 and to be a good neighbor I didn't try it until this am. I went to ride it this am and it started acting exactly like it had before. The plug is wet and oily. Swapped plugs and the same thing happened.

I am running 32/1 maxima oil and NGK BR8ES plugs.


I read a few other threads about similar issues with an IT250. What I found was some folks were saying the timing could need adjusted or that the pipe could be clogged with soot.

I have not found any thread saying that cleaning a pipe makes it run better, sounds like most do it because of placebo for power.

Should I focus on timing?

Anything else I am missing? Sorry for any typos.

Thanks!

Isaac

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10 Oct 2020 11:23
isetta
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1982 yamaha IT 250 running rich #2
i did once have a kawasaki KH250 (two stroke triple) that was having trouble with one of the cylinders. That was due to the exhaust on that cylinder being clogged up with like crystalised carbon. so I don't think you could rule that out. I have no idea if you can removed the baffle pipe, or if it even has one.

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10 Oct 2020 11:25 10 Oct 2020 11:25 by isetta.
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1982 yamaha IT 250 running rich #3
also you have not mentioned what the situation is with the air filter - like if it has one and if it is clogged

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10 Oct 2020 11:32
Isaac
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1982 yamaha IT 250 running rich #4
Ah yeah the air filter is clean and oiled. It has been since before I tried to start it the fist time.

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10 Oct 2020 14:18
RT325
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1982 yamaha IT 250 running rich #5
Forget the timing. Nothing will alter there unless crank key has broken, which isn't unheard of but nothing to do with rich running. I'm still thinking a grossly blocked exhaust, so try it minus the tail muffle, pull the complete thing off & run it & try to poke something of similar size to the pipe right into the main chamber from the rear just to be sure. Luckily i live out of town so can make a bit of noise when i have to. Only other things are restriction in the air cleaner department. Choke not closing. Wrong slide with guide pin slot on wrong side so has to be fitted back to front which puts the cutaway forward & goes all rich, very rich. That's unlikely--but. Main jet fell out. Blocked air feed in where it gets air to the needle jet. Still thinking exhaust though. Spark arrester deep in the tail bit gets blocked. I just read again & see it came right for a bit with a carb change so might have to eat my words. Although i did have an AG100 that got plugged in the tail muffler but when i shut the throttle the ball of carbon would drop off as was sitting against the inner end of a straight through baffle. Eventually it got well & truly stuck & when i pulled the baffle it was still there so instant diagnosis.

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10 Oct 2020 16:47 10 Oct 2020 16:49 by bluntz465.
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1982 yamaha IT 250 running rich #6
When you did the crank seals did you use any sealant? Do a pressure test

1957 Cushman Eagle 1969 Honda 90 ATC 1969 Honda CB250
1973 Yamaha AT3 1974 Kawasaki KH440 1974 Honda XR75
1975 Suzuki TS75 1975 Kawasaki GreenStreak 90 1975 Suzuki GT550
1975 Suzuki TS250 1976 Suzuki GT550 1976 Indian Chief
1976 Yamaha YZ80 1978 Yamaha IT175 1980 Suzuki GS550
1982 Yamaha IT465J

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10 Oct 2020 18:07
MarkT
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1982 yamaha IT 250 running rich #7
I have a Suzuki that has exhibited "irrational" extremely rich running that comes and goes. Swapped carbs and CDI boxes with no change.

One time I just started leaning out the jetting and got it running great. Then on a long test ride whatever it was went back to normal and it went really lean and soft seized.

I had a temp gauge and from the sound of engine and seeing gauge suddenly start to climb rapidly I pulled the clutch and engine stopped. After cooling a few minutes I was able to limp home.

Swapped to a spare top end and put jetting back to stock. Ran perfect. It's been pressure and vacuum tested several times, no leaks... including right before I tore it down and right after new top end installed.

Took it to an Endurofest and after a couple hours of running great, went super rich again. That's when I swapped CDI boxes with no change. It's been parked since then. I haven't tried to troubleshoot since then but I do strongly suspect it's an ignition issue of some kind. I have a stator and flywheel I got from ebay that I'll swap on sometime to see if that helps. I suspect it has to be the stator.

1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250

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10 Oct 2020 18:23
MarkT
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1982 yamaha IT 250 running rich #8
Here's an MX175 I worked on with a confirmed bad CDI stator. Sounds a lot like what you are describing. Would not rev and sounds really rich. Coil and CDI box were both tested with another stator and they worked fine. In video, suspect stator is installed on a previously good running bike that then would not rev. Definitely the stator on this one.




My Suzuki isn't as bad... it will rev and can be ridden... it's just blubbery rich.

1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250
The following user(s) Liked this Post RT360Fan, mdscott

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10 Oct 2020 18:48
RT325
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1982 yamaha IT 250 running rich #9
MarkT #7, i'm obsessed with exhaust blockages as you probably gather from other post haha. Does sound like you had pieces of stray carbon randomly blocking things the dropping away. Maybe not.

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10 Oct 2020 22:19
MarkT
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1982 yamaha IT 250 running rich #10

RT325 wrote: MarkT #7, i'm obsessed with exhaust blockages as you probably gather from other post haha. Does sound like you had pieces of stray carbon randomly blocking things the dropping away. Maybe not.


I know what you're saying Morley... pipe is definitely clean. What I've considered is that maybe there is some of that internal screening/baffling that has broken loose and randomly blocks the pipe? But I've compared the "puff" out of the pipe outlet when it's running good and when it's not and it's very strong even at idle. You can feel the pulse a good foot away from the outlet with your hand at idle. I've removed the baffle and spark arrestor (which are NOS because they were missing, removed by a previous owner no doubt) and no change in running except it gets louder. It acts rich from idle to full throttle.

I did manage to find a brand new aftermarket pipe for it so maybe I'll try throwing that on first when I get around to working on it again.

I've also taken the pipe off and shaken and thumped on it with a mallet and it doesn't feel like anything is loose... no rattles.

1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250

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