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Pilot Jet Change? or other Issue?

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I have a 2006 WR250F. I ride mostly at about 4000 ft.

Bike is very derestricted. It has:

High flow air filter w/o backfire screen

Snorkel removed

Holes in side of airbox following mold line pattern

FMF Ti Powebomb Header

FMF Factory 4.1 muffler and midpipe

AIS blocked / removed

Engine vented like YZ, not returned to airbox

Grey wire cut, YZ throttle stop

I bought the JD Jetting Kit. Currently running:

Red needle

175 main

Needle clip in position 3

Seems like the bike idles and runs best with idle mixture screw less than one turn out (~1/2 to 3/4 turns). Idle does not speed up or slow down as I change it from 1/4 turn to 2 turns out. If idle is high enough, it will run with the idle mixture screw closed for a little while.:bonk:

So, I researched the Jetting Sticky. Seems like some folks, but not all, that ride at higher elevation have "leaned" the pilot circuit with a smaller pilot jet by using a #40 instead of the stock #42.

I'm going to try this, if it makes sense. Does this make sense? Any other thoughts or ideas on what to change / check???

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Yes makes sense. Try the 40 and it should die or feel like its going to die when all the way in. If the 42 doesn't die when all the way in then go down. If it does die when all the way in but works best at .5 to .75 turns out I would leave the 42 in there. That's just me tho and I'm lazy!!

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You can change a pilot or a mainjet in about 2 minutes through the drain plug port.

I use a make up mirror on top of the cases and a small screwdriver.

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hey beezer. I haven't "mastered" that technique, yet.:banana:

Here's the method I use:

Remove seat and tank. (need to do that anyway to change needle clip position)

Drain the gas from the carb

Unhook hot-start plunger, throttle cables, and TPS sensor

Loosen screws on front and rear boots.

Then, I can rotate the carb in both directions to get access to the main, pilot and leak jet from the bottom, and the needle jet from the top.:bonk:

It does take longer, but I can see what I'm doing better. Also, it helps me inspect and remove the o-ring from the idle adj screw.:smirk:

DSCN0444.jpg

and then rotate it...

DSCN0446.jpg

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Replaced pilot jet with #40

Checked carb boots - sealed and tight

Checked hot start plunger - working and tight

Bike started up with choke on and it idled. Shut it down because it's late. I'll test ride it tomorrow.

Also, put clip back in nominal #3 position. I think my pilot jetting issues may have been affecting my clip position decisions. I'll try positions #2 and #4 again after I'm happy with pilot jet.

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Seems like the change from a #42 to #40 pilot jet didn't make much difference.

Bike starts/idles/runs cleanest with idle mixture screw still at ~1/2 turn out

I have a #38 pilot jet that I can try.:bonk:

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Seems like the change from a #42 to #40 pilot jet didn't make much difference.

Bike starts/idles/runs cleanest with idle mixture screw still at ~1/2 turn out

I have a #38 pilot jet that I can try.:bonk:

When I went to CO high altitude on an 02 wr250, I had a 38PJ working best and i was 2 MJ sizes down vs here at 600' ASL.

"There are no right or wrong jet sizes, the bike either runs great or it doesn't " is my jetting motto.

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Thx.

I'm assuming you meant 6000', not 600'.

I agree. The temptation is to run big jets because it's some type of badge of honor to run bigger jets than the next guy.

However, in Southern AZ, I ride at 4000 ft. That's not as high as in CO at 5000 - 6000 ft, but we often have riding conditions where it is 100F at 4000 ft. My testing has shown that my bike runs best with smaller jets than typically recommended for sea-level guys.

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So... the only way I could get the bike to run at 1/8 to 1/4 throttle without missing was to really lean out the pilot to ~1/2 turn out and to run the needle clip a couple of positions richer. Stange combination to me. Still stumbled a little and seem to backfire too much. Turning the pilot from 1/2 turn to 3 turns out didn't seem to make a difference.

Couldn't find any intake or exhaust leaks. Finally, checked valve clearance. Two intake were slightly out of spec. Re-shimmed them into spec and now the bike jets much easier. Was able to back out the idle mixture screw #38 to 2 1/2 turns out and getting clean firing between 1/8 and 1/4 throttle. I'm going to go back and check less rich clip positions, now that the pilot circuit seems to be working again.

Does this make sense? Can two intake valves slightly outof spec cause these effects?

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Going to re-set the jetting and test ride.

Currently running JD Jetting kit. I'm riding at 4000 ft with temps from 50F to 100F.

They recommend #175 main for 3000 ft to 6000 ft with the red needle and the clip is the third position.

They recommend 005 larger on the main and one clip position lower on the needle for a free flowing exhaust. I have the FMF Factory 4.1 with a Powerbomb header, a No-toil Superflow filter, and a derestricted airbox.

I'll go with a #180 main and clip in #4 position, to start. Right now, fuel screw is 2 1/2 turns out with a #38 (small) pilot.

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Have you checked your float level? FCR carbs are very sensitive to float level. sounds like yours might be set a little too high. Float level should be set @8mm

Another problem may be the needle diameter is too small (the straight part, before the taper starts. If the needle diameter is way off it can allow some fuel flow through the needle jet, even at idle.

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thx. I'll check the float level. I also bought a replacement float valve needle to ensure it's sealing well. Should be here in a couple of days. :bonk:

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So... the only way I could get the bike to run at 1/8 to 1/4 throttle without missing was to really lean out the pilot to ~1/2 turn out and to run the needle clip a couple of positions richer. Stange combination to me. Still stumbled a little and seem to backfire too much. Turning the pilot from 1/2 turn to 3 turns out didn't seem to make a difference.

Couldn't find any intake or exhaust leaks. Finally, checked valve clearance. Two intake were slightly out of spec. Re-shimmed them into spec and now the bike jets much easier. Was able to back out the idle mixture screw #38 to 2 1/2 turns out and getting clean firing between 1/8 and 1/4 throttle. I'm going to go back and check less rich clip positions, now that the pilot circuit seems to be working again.

Does this make sense? Can two intake valves slightly outof spec cause these effects?

It sounds right to me. After I leaned out my PJ I needed to richen the Leak jet as a whack on the throttle would yield a stumble. I also had to raise the clip 1 or 2 just as you did. IMO, if you don't have a bog then you're there.

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Thx.

I'm assuming you meant 6000', not 600'.

QUOTE]

I did mean 600' as I'm in Austin TX. i was referring to the difference in altitude between my CO ride and my home base.

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Going to re-set the jetting and test ride.

Currently running JD Jetting kit. I'm riding at 4000 ft with temps from 50F to 100F.

They recommend #175 main for 3000 ft to 6000 ft with the red needle and the clip is the third position.

They recommend 005 larger on the main and one clip position lower on the needle for a free flowing exhaust. I have the FMF Factory 4.1 with a Powerbomb header, a No-toil Superflow filter, and a derestricted airbox.

I'll go with a #180 main and clip in #4 position, to start. Right now, fuel screw is 2 1/2 turns out with a #38 (small) pilot.

Test rode with the above settings at 60F. Richened the needle to clip position from #4 to #5. It was an improvement (ran slightly cleaner) at 1/4 throttle position.:bonk:

Idle mixture is still behaving well. It's at 2 1/2 turns out.:smirk:

Goint to test ride again today, get the bike warmed up, and then re-adjust idle mixture.:busted:

Once I get it running as clean as I can, I'll check float level and condition of seal on float valve.

If adjusting intake valves a small amount really cleared up the jetting issue, I may go in and re-shim one of the intakes that was borderline that I left alone.:banana:

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It sounds right to me. After I leaned out my PJ I needed to richen the Leak jet as a whack on the throttle would yield a stumble. I also had to raise the clip 1 or 2 just as you did. IMO, if you don't have a bog then you're there.

My case was a little different. After leaning the PJ's way out (1/2 turn), and it didn't seem to matter if it was a #42, 40, or 38, Then I had to richen the needle (raise the needle, drop the clip) to minimize the stumble at 1/8 to 1/4 throttle. Still missed a little and backfired with the throttle off under decomprssion braking conditions.:bonk:

Once I adjusted two sligtly out-of-spec intakes, the issue seems to have gone away. PJ is now at 2 1/2 turns out.

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Thx.

I'm assuming you meant 6000', not 600'.

QUOTE]

I did mean 600' as I'm in Austin TX. i was referring to the difference in altitude between my CO ride and my home base.

Thx. I re-read your post and understand what you mean, now. Thx for the help. I lived in Austin from '76 to '80. Nice town. I went to UT.

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My case was a little different. After leaning the PJ's way out (1/2 turn), and it didn't seem to matter if it was a #42, 40, or 38, Then I had to richen the needle (raise the needle, drop the clip) to minimize the stumble at 1/8 to 1/4 throttle. Still missed a little and backfired with the throttle off under decomprssion braking conditions.:bonk:

Once I adjusted two sligtly out-of-spec intakes, the issue seems to have gone away. PJ is now at 2 1/2 turns out.

It REALLY sounds like you have a problem with float level or needle diameter. Trust me....I had bloody knuckels from this issue the first time I encountered this type of problem 8 years ago.

I have never seen a valve adjustment make that much change in jetting requirements.

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Took the carb off today. I usually pull the tank, seat, and raise the subframe to make it easy.

DSCN0466.jpg

DSCN0467.jpg

Checked the float level per the manual. Not sure I completely understand the measurement. However, it measured to the spec level. Had the carb tilted like shown in the manual and the distance to the top of the float was near the spec number. Also, removed and inspected the float valve and seat. Looked good, no wear. Looks like the floats should close the valve okay.

DSCN0469.jpg

Pulled out the carb slide valve, Cleaned it and cleaned the seal. No real issues. Since the tank and seat were off, went ahead and re-shimmed the marginal intake valve. It went from the low side of the spec limit to the high side. Here's a pic showing the new shim installed.

DSCN0472.jpg

Thx for your inputs. The bike is running well. Now, it's tough to find a spot where the bike has a miss. I can hold it at partial throttle (1/8th to 1/4 throttle) now and let it rev out on the street and it doesn't miss.

I was wondering if out of spec intakes cause a slight miss at high RPM at partial throttle? Seems like mine did. I couldn't jet it out. Of course, it's subtle. Didn't really notice it on the trails. Have to be on the street to find and hold the spot.

So, enough wrenching for now. Going to get it out and ride it this week to see if the changes are good enough.

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I was curious to estimate the amount of time on the top end. It's a 2006 and I'm the third owner. Fortunately, the original owner kept a ride log and maintenance log and passed it on to the second owner, along with the manual and some spare parts. I spent some time with the second owner to understand how much he rode it. I've kept a ride log (in miles) since I have had it. I can use and average riding time per mile and estimate the hours I have put on it. These are not "dual-sport" street miles. These are "technical trail" miles and generalized goofing around roostin' and trying wheelies miles. :smirk:

Original Owner: 30 hrs (3/06 - 10/08)

2nd Owner: (less than a year): 20 hrs

Me: (6/09 to present): 250 hrs (:bonk:)

So, I believe the bike has roughly 300 hrs on it. From what I can tell, the previous owners maintained it well. It still has original plastic and decals, except for the tank decal. It still has the original (slightly bent) radiators and they still work well. Anyway, the bike has been ridden hard and needs some rebuilding. Worst problem now is the upper steering stem bearing needs to be replaced. When the steering stem is tightened, the steering is notchy. Bearing was rusty and pitted. I took it apart and cleaned it and regreased it, but it still needs to be replaced.

DSCN0449.jpg

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