125-200cc four stroking just off idle, nowhere else

[Roon]

I recently bought a 2007 WR125 with the standard Mikuni TMX 38
The bike only had 70kms (58 mins) on it so it is basically new, just 7 years old
Ive gone through everything, fitted a new airfilter, new plug, fresh fuel at 40:1 and I cant get rid of the 4 stroking just off idle.
It came with a 30 pilot and there was tons off sponge all over the pipe, swing arm, rear hub etc To lean off the idle Ive gone down all the steps in 2.5 increments from a 30 and Im now at a 12.5 pilot and it still four strokes "just" off idle, adjusting the airscrew doesnt seem to make much difference, however it does run a bit better with the airscrew out 3 turns on every pilot jet Ive tried
Yes, the carb has been cleaned out with compressed air and the float level is OK
The reeds are OK
The exhaust isn't blocked
The bike starts first kick everytime without choke (Im at sea level and temps are 20C), it always idles perfectly and I can crack the throttle open quickly and it revs clean
Riding is fine, once I get past 1/16 to 1/8 throttle it revs clean and hits band, doesn't bog, doesn't die on deceleration, goes back to steady idle.
I like to ride technical stuff like logs, creeks, rocks, hills, singletrack etc and its frustrating not being able to ride at slow speeds, just off idle
Do I need a #4 slide to lean out the 1/16 to 1/8 throttle opening?
Do I get a Lectron ?
cheers
Cameron
Sydney, Australia
Pic is my daughter and I riding over Easter

 

[sabortooth]

You are still running rich if you can always start without the choke when cold.

 

[huskylove]

What is four stroking??

 

[shrubitup]

What is four stroking just off idle? Lean surge? Does it drip fuel if you tilt bike 30*?

 

[Tentontimmy]

Four stroking means blubbering, in other words, running rich.

 

[Roon]

On the weekend I'll try the smallest pilot available #10 and see if that gets any improvement

 

[Kyle Tarry]

Stop going leaner on the pilot. That bike should run right with a 30-40 pilot jet, something is wrong that isn't going to be solved by just going leaner on the pilot.

 

[Motosportz]

Stop going leaner on the pilot. That bike should run right with a 30-40 pilot jet, something is wrong that isn't going to be solved by just going leaner on the pilot.

Agreed.

Leaky choke circuit? wrong needle?

 

[Roon]

I had pulled the choke apart whilst still fitted to the bike to make sure it was clean to make sure it was not hanging partially open, but I'll remove the carb again (about the 20th time now..) and pull out the choke plunger and check that it blocks the fuel when off because I agree I shouldn't be going down to such a small pilot, something else is bleeding too much fuel.
I'll pull the needle and get my daughter to read the numbers, Ive tried but I need sharper eyes to see those details....If the needle was too rich (too thin) in the straight section do I assume that would let more fuel bleed through the main jet and contribute to the rich idle?

thanks all for the inputs, I really want to get this sorted so I can get rego (licensed) and get out into the bush (woods) and start chainsawing, sorry whippersnipping.....

 

[Kyle Tarry]

This is a dumb question, but are you sure something is wrong with the bike and it's not just normal 2-stroke blubber?

If the needle straight section or the needle jet (the "sleeve" that the needle rides in) is wrong, that gap can definitely cause it to be much too rich.

With a bike that is basically brand new, I don't see how anything would be wrong with the jets themselves, but it might be worth just buying a whole new set to be safe.

 

[R-J van Hulst]

15 minute job will do the trick here.

get in contact with Kelly (motorsportz) and get a lectron.

you bold it on your bike in another 15 minutes and of you go.

Robert-Jan

 

[Dirtdame]

I'm running a 40 pilot in my 125. Its a later model, but has the same carb. I think if you want the slide to be leaner, you will need a #5. It will be a larger cutaway than the 4. Make sure that the O ring on the float needle seat is not dried up or cracked. That can make it leak.

 

[Kyle Tarry]

15 minute job will do the trick here.

get in contact with Kelly (motorsportz) and get a lectron.

you bold it on your bike in another 15 minutes and of you go.

A Lectron might be a good mod, but it's not the solution to a jetting problem. He doesn't need to spend $400 to fix this...

 

[Kyle Tarry]

I'm running a 40 pilot in my 125. Its a later model, but has the same carb. I think if you want the slide to be leaner, you will need a #5. It will be a larger cutaway than the 4. Make sure that the O ring on the float needle seat is not dried up or cracked. That can make it leak.

Do you know which slide your bike has in it, out of curiosity?

 

[Dirtdame]

Do you know which slide your bike has in it, out of curiosity?

Ya know....I looked at it when the bike was new and I was doing all the tweaks and mods to it, but I can't remember. It is supposed to have a #4 in it, and probably does. I was noting the 460 main jet, and that I switched out the 45 pilot for the 40. The bike is jetted and tuned to run really well across the board in fair weather between 3000 and 6000 ft. elevations. I had bought one of those RM needles for it too, but never bothered to install it, since I believe in that saying that if "it ain't busted, don't fix it".

 

[R-J van Hulst]

A Lectron might be a good mod, but it's not the solution to a jetting problem. He doesn't need to spend $400 to fix this...

Agree with you, but after having one for more than a year and did nothing on the carb setting from the beginning is still heaven for me.

2 years ago I was changing needle positions and in some case main jets on the trail.

the mikuni carb you can get good the question mark for me was for how long?

A big thunder storm building up and the setting that was running good an hour before turns in a horrible setting to drive.

Robert-Jan

 

[justpinit]

Drop the needle one clip at a time, It has an effect on small throttle opennings. Go back up to at least a 30 pilot like what was said by kyle tary. If the idle speed surges go richer on the pilot. If the bike starts to run hot go back up on the needle. Hot as in the bike will start to surge really bad like it is running out of gas. Or.. Maybe the crank seal is bad on the trans side, letting oil in. It sat so long that the seals could have drie rotted.