Blubber

[Ichmir Vlochlov]

I bought a 98 RM250 with the engine disassembled in a box. The crank was seized. It has a rebuilt crank, new bearings and seals, replated cylinder, new piston, new reeds, stock pipe with a TC2. I figured the PO roasted it with the lean jetting it came with. I set it back to stock. It popped on the first kick after the rebuild, but wouldn't run. After a couple rounds of checking spark, timing, carb cleaning, and ohming electronics, I held it WFO and kicked, and finally got it started. It blubbered really bad, had no power, and wouldnt rev out. I check over everything again including reeds and PV operation. The more I ran it, the better it seemed to run. 

This thing now rips, when there is enough room to open it up. Seemed to me like an abnormally long break in period. I've taken it to the dunes twice since I decided it ran good enough. It runs like it should when pulling hard, but I still have problem of smoking out entire campgrounds, and it takes a while to clear out. No way would I ever get a good start in a race, as it'd blub all the way down the straight till it gets enough heat to clean out. I ended up with the stock main, 2nd clip pos, 35 pilot, blocked power jet. I believe pilots for a PWK go down to 32, 35 was the leanest the shop had. I cant jet it out. It runs lean in the midrange with the clip at the top. I've replaced the jet block o-ring with no improvement. I might check out the reed block again, if I get ambitious. It isn't burning trans oil. Anyone have any suggestions before I slap a new carb on it? I've never dealt with such a thing in 20 years of messing with dirt bikes. 

[CDNSXV]

Clean the carb.  99% of these kinds of problems are carb related.

[kxrob]

isnt 98 a pwm carb not a pwk , choke circuit is an issue with this carb (pwm) , ditch it and get a pwk if this is the case

32-35 pilot and clip in top notch is very lean 

[Ichmir Vlochlov]

On 8/20/2017 at 7:54 PM, kxrob said:

isnt 98 a pwm carb not a pwk , choke circuit is an issue with this carb (pwm) , ditch it and get a pwk if this is the case

32-35 pilot and clip in top notch is very lean 

Looks like you're right about it being a PWM, the screw top threw me off. It has a new choke plunger, it didn't help anything. 

Top notch is definitely lean, I set it back to the 2nd and it runs pretty good from mid-WFO. The problem is all at low speed, partial throttle. 

[kxrob]

Float height ?

[SlowDinoDog]

What do the reeds look like?

[Ichmir Vlochlov]

4 hours ago, kxrob said:

Float height ?

Parallel to the base. I've had it at both extremes. Ran so rich anyway it didn't make a difference. 

[Ichmir Vlochlov]

Nope, I was right. "PWK" stamped on the side of the carb. 

[Ichmir Vlochlov]

Fixed it. Slapped a new airstriker on and ran good for once. Still some tuning left to do. The old carb is going on the wall of shame.