Just took the jets off of my 88 trx250r, she was bogging in 1st and 2nd, then every other gear pulled flawlessly, recently bored the jug and went from a 66.5mm piston to a 68mm piston, the clip is on the 2nd position (for my elevation) I have a 152 main and a 42 pilot, I believe it's my pilot jet, my mind tells me go up a size, because it's a bigger motor, am I right? My elevation is 100ft from sea level and I run 40:1 castor 927 with non ethanol gas, the carb is a 36mm kiehin
If everything remained equal except the over bore I suspect the over bore would not be enough of a change to go from running great to running so lean it “boggs” now. (That’s not to say you don’t need a bigger pilot but I don’t think an over bore all by itself would have that significant of an effect on pilot size) I suspect your pilot jet is plugged. The simplest way to eliminate things As problems is to start with a brand new pilot, same size as current set up, and see what happens. I have had countless pilot jets that look good but are plugged in some fashion.
This will give you a baseline to start adjusting things. While you are at the store buy the next 5 jets in size.
If the new 42 does the exact same thing as the old, jump a size or two and reevaluate did the bigger pilot make it better?
Also, make sure your airscrew starts at a base line position usually 1.5-2 turns out. Don’t mess with the air screw until you have it “close” with the correct pilot.
For me the most important thing is start from a known position and only change 1 variable at a time. It’s the only way I can deduce what helped and what didn’t. If moving up in pilot does not change the problem, then you Likely have a different problem.
If everything remained equal except the over bore I suspect the over bore would not be enough of a change to go from running great to running so lean it “boggs” now. (That’s not to say you don’t need a bigger pilot but I don’t think an over bore all by itself would have that significant of an effect on pilot size) I suspect your pilot jet is plugged. The simplest way to eliminate things As problems is to start with a brand new pilot, same size as current set up, and see what happens. I have had countless pilot jets that look good but are plugged in some fashion.
This will give you a baseline to start adjusting things. While you are at the store buy the next 5 jets in size.
If the new 42 does the exact same thing as the old, jump a size or two and reevaluate did the bigger pilot make it better?
Also, make sure your airscrew starts at a base line position usually 1.5-2 turns out. Don’t mess with the air screw until you have it “close” with the correct pilot.
For me the most important thing is start from a known position and only change 1 variable at a time. It’s the only way I can deduce what helped and what didn’t. If moving up in pilot does not change the problem, then you Likely have a different problem.
Okay, I'll try a new pilot jet, I just got my jets in today, and I have 10 pilots and 10 mains just in case, there all genuine kiehin jets so fingers crossed it's just a plugged jet, the air screw is 1.5 turns out and I believe the idle is 2 1/4
IMO; way to lean on idle to 1/2 throttle...will be most noticeable in the circuits you detailed. Below is closer jetting per your description at basicly Sea Level, Try:
158-166 Main (I would start at 160)
46-50 Pilot (I would start at 48)
3rd Clip on Needle (DGH)
#6 Slide (Important to be a #5 or #6 for a 250R)
1 1/2 at AS
2 1/4 at BPS
No, I just jetted it, and when I started it, it would idle fine, and then all of a sudden it high revs, i also found out my oils gray, idk what's wrong with it
Could pressure test coolant system. My oil used to turn grey, it was from my wore out clutch and basket. After a full bdt rebuild it’s clean and get serviced every couple rides. I’m using maxima mtl. 🍻
How would I do that? I have a feeling it's the ceramic seal, so just to be on the safe side In going to buy a water pump rebuild kit, and I'm going to buy the BDT collar set for the kickstart spindle so I can use my chrome clutch cover that doesnt have JB weld covering a hole
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