250-500cc 2013 WR300 High RPM MISFIRE at small throttle openings

Hi , I wonder if you guys can offer advice?. I have a lovely 2013 WR300 with Pro circuit Racing exhaust, 6 speed gearbox, Keihin PWK38 carb.

Some issues:
I notice lately that at HIGH RPM it has a severe splutter / misfire-the last time it did this was when the Base gasket leaked coolant into the crank case. The coolant level seems OK this time. And there is no white smoke.
It is not pulling like it should at all.
Could it be jetting, air leak, power valve etc?. Plug seems OK as well.
I did find one of the breather pipes on the carb (It has many!) blocked with mud, and cleared it-still same.
Could it be ignition unit?.

I love the Bike, but it is certainly hard to start with the headlight ON!..(I have to turn off the headlight and blip the throttle)

The Clutch-Oh boy!.. I have NEW fiber plates fitted, the FREE PLAY is OK, I can physically see the clutch HUB pull away from the basket. But it STILL DRAGS!.. I am using Motul Gearbox oil-10W40.

any advice?.
Cheers,
COYOTE

How's your spark? It weak? Doesn't sound good that the bike can't be started with the headlight on. Is that a new development?

What about the push rod coming across the engine case from the clutch arm? Sounds like it may need adjustment after the clutch rebuild.

Heath

Sounds like you'll have to go through the process of eliminating the obvious possibilities first: air leak! I'm on my 3rd intake boot in 1 1/2 year; new plug?; reeds?; how many hours on the rings?; good fuel flow?; dirty carb?; check all the connections under the tank and make sure the earth/ground is solid.

Terminator cable and Moose EZ clutch lever helps. Mine came with a Rekluse, so haven't dealt with stock clutch issues.

Others have posted about starting with headlight and Ducati ignition. I think LED lights help to cure the issue, but you'll need to add a rectifier to run DC lights.

the title says small throttle openings..is that the only time it acts up? how small?

Small throttle opening but high rpm......sure it's not just normal 2t operation? How does it run with more throttle at same rpm? If ign is breaking down at light load then it would definitely breakdown at high load. Is this a new development?

was curious myself..not many times a two stroke likes or wants little throttle and high rpm..

do the basics, spray carb cleaner around anywhere you think you might have a leak
change the plug as they are cheap
put a switch on the headlight had a similar problem right before my ignition failed (sorry see you have one)
the clutch rod freeplay needs to be set according to the manual
check the power valve adjustment according to the manual
these are all basic maintenance procedures (do 1 at a time except the clutch check it first)
in the end put on a Lectern and say goodbye to jetting problems

Hi Guys, Thanks for the excellent replies!.
Clutch First--I have done the push rod and free play adjustment, with the side cover off, I can physically see the clutch hub move away from the fibers and plates-(BIG GAP)-the only thing locking them up seems to be the oil. So I would guess a different oil could be used?.
We live at a high altitude with cool temps, I run waterless coolant so the bike never boils or gets hot.
So I guess the clutch pack does not really warm up as well.
When the fibers were new , the clutch worked fine for ONE ride.

I recently Installed a full pro-circuit racing exhaust, but did not notice the misfire immediately.
This is the current carb setup: @ 1600m above sea level:

Keihin PWK-38 Air Striker Carb, (same as Yamahas), not the original Mikuni.
Carb jetting is 45 pilot and 175 main. Needle is 2nd groove from the top. ( Johannesburg Altitude)
At sea level pilot jet is 50. Main jet is 178.
Still I feel it should be more CRISP. I Have a WR250 as well and that is super crisp and responsive.
One of the A/S carb. vent pipes were blocked, but is now clear.
What I mean by high RPM low throttle openings--Top Gear, flat terrain, throttle less than quarter open-this is when the splutter is very noticeable. Guess it is still there with higher openings to Full Throttle.
As I previously stated , the last time it misfired like this was when the cylinder base gasket leaked coolant into the crank case, but this time no coolant loss.
Start loading the engine at lower rpm climbing a hill and she is normal.

I am away from home at the moment, but the reeds and intake boot is worth checking.
I wonder if one can get a spark enhancer or replace the CDI with a better unit, the Bike Does NOT start with the headlight on, and it is apparently a common complaint.
Maybe a battery powering the CDI?.
I half expect it could be spark related.

Top end is NEW, no scratches in cylinder, compression--WOW, this thing will break your leg!.. Never had a 2T with this much compression!. That FRONT FORWARD kick starter--!..(I am tall)

LOVE the suspension on this machine-the Showa forks are great!..
Just the small niggles like stalling due to clutch drag and then kicking like mad when everyone else has pressed their happy buttons and disappeared over the hill.

Sounds poss rich on needle straight section or pilot jet. What needle are you using? What setting is the airscrew at? Does screwing the air screw out (leaner) another 1/4 turn improve things? An ign base misfire under the conditions you've described would be very unusual.

if you are having the issue with the light switch it sounds like there is an issue with the ignition - I had a similar issue on my 125 but it didn't break up at high revs
carbs normally cause issues at low to mid range - plug is ok and settings sound ok so id say its something else like the stator? ... been through water ?

Thanks for the replies!.. I'll have to strip the carb when I get home-then inspect the needle.
Could well be carb still, I think the headlight when on loads the supply to the CDI and weakens the spark.
Maybe I'll disconnect all plugs, spray them with lubricating contact cleaner, will inspect stator housing as well. Could well be water from a previous wash-I see they say in the manual you should not spray water directly at the CDI unit?.
Guess the only way forward is slowly, one step at a time. I could always 'BORROW' my 250's CDI unit for a comparison.
DO you guys use the original NGK spec. plug (B8EG) or another type?.
When I removed the plug it was a little more black than brown..(Tan.)

Cheers,
COYOTE

The only time my 300 felt "crisp" is after installing the race head. I regret selling the head. As others stated, I would check your reeds and see if you have a crack or chip.

I was convinced at some point that original CDI on my 300 was faulty because of weak spark, hard starting, stuttering I couldn't tune out, etc. Replaced it to the tune of $180 and noticed no improvement yet. Just did rings, checked everything and replaced all gaskets I could without splitting the cases. We'll see....
Recommended plug is BR8EG, not B8EG. Your plug sounds a little rich which should be fine depending on your riding. If you're riding slow, technical stuff with little or no WO throttle, you could probably lean it out a little. Otherwise I would leave it unless it's pure black and wet or fouling.

A while back on here a guy on a 125 had spluttering and he tried everything and It turned out to be the stator . It made a sound that was different to carb spluttering - more metalic - tinny - had a definite electrical sound

Aaah, thanks guys!-more points to ponder!..
As I said I can 'borrow" the CDI off the WR250 to compare as a last resort, but will go through the motions first to check carb, reeds, intake rubber etc.
Lovely bikes but it seems they can be moody!..
I like the Showa forks-mine has been valved and shortened by 15mm, so this bike is an offroad technical beast!. (Much better than 4CS I think...)

Cheers,
COYOTE

Showa forks?! Not kyb?

You are right of course -KAYABA--typo on my part-.. The are still very good!..haha..
Only thing I find because they are shortened, the front wheel rubs on mudguard during big drop offs.