1983 250r tuning help?

[drhill]

Hi everyone - finally got my 83 250r back out on the trails after 6 months out of commission...just did a top end rebuild and the recommended break in for wiseco piston. I had the bike jetted rich and it fouled 2 plugs during about 4-5 hours of riding...one of them to the point that it stalled the bike on a uphill climb. plugs were very sooty and the bike slowly lost it's "crispness" as I rode longer on each plug. The bike ran PERFECTLY with a new plug until I did a few long hills, fouled plugs more quickly with the throttle open and load on the bike (uphills). I know I need to lean it out but can you geys help me know how much to drop the main jet?

Bike is stock except for old aftermarket silencer and air filter (both in good shape). We were riding at about 5000-5500 ft elevation. manual says 128 main jet for above 4500 ft, stock is 130. I have a 132 in there. Everything else in the carb is stock settings/jets. Is going from 132 to 128 a really big drop? or should I just try a 130 first?

[harryredtrike]

put what you had in it before the rebuild.

[drhill]

I only rode it once before the rebuild and it burned the piston up(later found that the carb was still gummed up a bit)...previous owner had it sitting with occassional start ups for over 20 years. He had a 48 slow jet and a 132 main jet. I put the slow jet back to stock (50) and kept the 132 main for break in...I have a 130, just dont know if going down to 128 is risky for high altitude riding? Bike runs spectacularly...until the plug starts to foul

[HoldOnTrike84]

Same happened with my 84 R after complete motor rebulid. Check to be sure the air adjustment screw is 1 1/2 turns out, needle jet clip is 3rd notch from the top, and might try dropping the slow jet one size at a time till you get the sweet spot...my 84 has a 40 slow right now, and a 132 main (0 - 5,000 ft.) . I could prolly go back to a 42 slow, but 45, 48 and 50 would not let it idle right and fouled the plugs constantly.

What fuel mix you using to break in the motor?

[drhill]

interesting...I am running a 32 to 1 mix for break in... so you kept the 132 main jet and just kept dropping the slow jet size?

[HoldOnTrike84]

I originally had the 130 main and the 50 slow (PE 30A carb), with that set up it would not idle and would cut out mid to high throttle. Also, it would continually foul plugs. I started with the slow jet to get it to idle, one size smaller at a time till the idle started working and the throttle response instantly improved. Next, to clean up the top end throttle I went up a size (132) main jet. When I went to a 135 main it started cutting out again, so I stuck with the 132 main and the 40 slow...since I jetted it I haven't fouled out and its running excellent.

A little background on what was done to my 84 R...the motor was completely gone thru and bored .20 over, ported head, Boyesen power reeds, K&N with a drilled lid, DG expansion tube with silencer and running a 50:1 mix of racing fuel 110 leaded octane with royal purple racing 2 cycle oil. Compression is currently at 210 psi on this 5 year old build.

Just to confirm, other than your jets everything else on this carb is at their original settings as per the manual?

[drhill]

Intersting...thanks for the info 84...yes all else in my carb is at stock settings...mine seems to run much better than yours at stock carb settings...I have a good idle (when the plug's not fouled) and good midrange and even top end on a clean plug. I'm guessing I'm just a bit rich somewhere...I could drop to the 48 slow and 130 main that I have and see what happens...I'm just always scared of running lean and don't know how drastic of a change this would be...

[HoldOnTrike84]

With that said maybe keep the 50 slow for now and go to 130 main, see how it does on a fresh plug check and if still rich go to the 128 per the manual for that elevation your riding at. Keep an eye on your plug till you know it's the right color and I'd be interested to know the results.

[drhill]

got back to messing around with the 250r again, going riding tomorrow. dropped to 130 main...ran good, but still darkened the plug really fast just drusing around at sea level where I live.. Threw in the 48 slow jet...better tan color after cruising around. Can't see a definite smoke ring on my short plug chop attempts...but not much load on the motor on the street and I don't have a lot or room to hang it out in 4th or 5th...if I was riding at sea level I'd put back in the 132 main and leave the 48 slow I think (gee, just like the previous owner had it...

I going to 5500 ft to ride tomorrow - bringing tools, fatter and leaner jets and plenty of plugs...should be interesting...

[drhill]

Ok rode the bike today about 10 miles or so...trails but I was on it hard when I could...hitting hill climbs hard etc...plug was better...not blackened but a dark brown...dried on there so not oil but rich mixture...by the end of the ride idle was racing low end power was weak...still started up. ran good at high rpm...I'm thinking of dropping the slow jet another size or two...maybe keeping the main at 130 for altitude riding and 132 for sea level. light tan at the bottom of the porcelin...so i think that's about right for main jet? Should I be meeing with the needle clip at all???


Thanks for the help!!

[drhill]

was playing with the air fuel screw today - warmed up bike, new plug, higher idle speed...bike needed 4 turns out to idle at it's highest...that means the pilot jet is too rich, right? That seems way off and maybe why I'm still fouling plugs? I'm at a 48 pilot right now...

Thanks!

[Dirtcrasher]

Be careful, I've seen a couple dozen AC 2 strokes seize up, usually due to jetting or cylinder/piston clearance. I'd have about .007 clearance on those motors, but some of the shops don't know that...........

Hopefully your AOK.