I have an older Mikuni TMX - wr250 2005 . Its not revving clean from around 1/2 to full throttle Running rich Ive tried leaning out needle and main settings but doesn't seem to affect it . I am pretty sure float height is standard . Starts easily and idles nicely What else internally can affect the carb - blocked vent ? I don't think its the crankshaft seal as it seems to be fine with a newer design Mikuni fitted ( which doesn't fit well)
Needle float seat o-ring? If it has one of those, they can get old and cracked. Then it won't matter how carefully you set your float level.
The o-ring looks ok but the needle seat ? was not that tight so o-ring could be an issue , Ive swapped this and oring for another one I had in a spare newer carb . Thanks for the suggestion. Ive also lowered the float I tried the other RB designs carb again and it works well - was actually lean with richer jetting settings . Its shorter - front to rear than the older carb so need a longer intake boot I think ? The base is also square not rounded and it hits on casing
did this problem develop suddenly? would be a good idea to check compression. as it gets lower you can get rich symptoms mid-top
I bought the bike as is . Compression is strong . Its definitely just related to the original carb - another newer carb works fine - actually was running lean. I am thinking about getting a spacer for the intake so I can run newer ( shorter) Mikuni or a get a newer intake. I like the old intake though the rubber seems better. I like how its shorter too which I think might help with response. ( I base this on the shortness of the yz125 intake and how those things run ) So the other option is to somehow extend the airbox boot or move sub frame forward
I need to look at alignment of that brass sleeve around float needle again - I t may be out of alignment so it would be leaning out
Guys this can be a very long list of issues...it's an 2005 machine! reeds, timing, crank seals (sucking oil, ask how I know this), loss of compression, rings, piston slop, PV issue, clogged exhaust, weak ignition, bad plug, bad coil, bad plug wire, , carb slop, worn carb body, worn out slide, worn needle,--or basically worn out carb parts, Rock you need to baseline your machine man, so you don't get to chasing cascade issues. Best of luck these bikes are basically bullet proof.
Its definitely the carb .As ive said "I tried the other RB designs carb again and it works well - " . I think I have it solved just need to check out needle sleeve location - If that's not it I will just run the other carb Even though it was running rich generally down low it was possibly leaning out at high revs - like its on a rev limiter This is now clear to me its an restriction of some kind - not a minor adjustment of mixture or slight wear somewhere .
Still not revving out. The needle seat is sealing ok . Tried re aligning as per other carb . Ive noticed that the choke doesn't seem to do anything . It seems to be working but not changing the idle. I will readjust the idle screw / slide down - must be too high Anyway I am getting a plate made for the inlet manifold so I can run the newer/shorter Mikuni
Yes I think is a rich condition but I am not sure whats causing it . The plug is very wet . Its not the jetting - ive tried very lean settings - inc needle. Older carb jetting (that is problem) Ive dropped to 370 main 30 pilot . Newer carb which does run richer settings runs well with 440 main 35 pilot Ive tried changing from needle on top clip to bottom and it doesn't affect it at all So it seems like something is blocking air getting in on this carb ? The slide seems to open fully . The needle seems firmly secured . The cable has a slight kink / bend so I will change the cable to another one I have
Yes, I see that you've got one carb that seems to work and one that doesn't. Good detective work, and that does point toward the carb itself. I mean, I guess it's possible, just as an example, the the reeds are chewed up and one carb cares and the other doesn't... but that's not very likely. So, assuming it's the carb, I'd be doing exactly what you are: Verifying the jet sizes, checking floats, needles, O-rings. What about the floats... could they be soggy and heavy, sinking into the fuel and allowing the running fuel level to be too high? Also, there is a replaceable needle jet in the Mikuni and they do wear out (get larger) over time and the carbs run richer. I found that problem on a used PWK that I once purchased... pretty clear why it was for sale, as it was essentially impossible to jet lean enough to run. Also, there is a jet-block gasket in both the Mik and the Keihin, and they do fail, and they do cause all sorts of weirdities. Worth checking into.
I ve pulled the air box out so I can see the slide operating when running Ive never really watched this before but it looks like a hell of a lot of fuel coming through around needle The needle jet is a new JD one but it was running the same with the original I might put original it back in though - a bit leaner I think Ive tested float in water Jet-block gasket ? Not sure where this is The choke doesn't seem to do anything but Im guess this is because its rich anyway But it doent feel rich when riding until 1/3 throttle
This is not just a feeling of rich - it feels its hitting a rev limiter at 5000 but there is heaps of overrev if that makes sense
I changed the float needle for one off a spare carb , changed the needle jet back to original and changed the needle height to leaner Seems to be revving fairly normally now . I need to take it for a run
Played with bike on the trails for a couple of hours . Original carb is working great now with needle 2nd slot . Just a bit of fine tuning on pilot and main now thats all . Not sure if it was the float needle or possibly changing float height or a combination of things . I know it wasn't just chaging the needle height that fixed it but it certainly doesn't like being on the middle or lower setting Liking the old WR250 motor a lot - I prefer it to the 300 I will still be getting a spacer plate made for my shorter 39mm TMXX as I have already drawn it up in CAD for a router . It should give some better results
Float levels raise over time as parts wear. TMX carbs are float height sensitive. High float levels also dump gas all over the ground as you ride and fuel mileage drops. Also, as the compression drops the motor feels like it is running rich. They run smoother with Keihen carbs but you loose some top end power.
