XT600 Running Rich, missing when warm
 

Hi All

1999 Xt600e in Portugal, 65,000km.

Recently developed an issue with running rich and missing/popping when engine is warm when going slowly at around 2000-2500rpm - possibly around the throttle range of opening the butterfly on 2nd carb. Spark plug was showing a rich condition and also a small build up of black soot, otherwise fine.

Bike makes a fairly audible tapping noice and has done for the last 10,000km. Consumes a good litre of oil for every 3 tanks of fuel (few oil leaks. No idea when or IF the pistons etc have ever been done. Maybe one day I will get it sorted (i use bike for trail riding mostly). New timing chain maybe 6000km ago. Tensioner is good, timing good.

Bike doesnt smoke at startup when cold or warm. Easy startup when both cold and warm, lots of power throughout the range. Bit of white smoke if I give it a quick rev, otherwise nothing noticeable that would be considered abnormal or alarming. Idles nicely when warm, a slight stutter when cold, no hunting or delays in returning to idle.

So few days ago, new air filter, new spark plug, set tappets. Noticed the left side intake tappet adjuster screw is worn unevenly... looks to have been like it for a while but never really paid attention to it before, ground it flat for now, will replace eventually. Rest are fine.

Anyway...

Removed the carb to clean it and found a dark buildup on the airbox side of primary carb, and also black sooty residue on the engine side of secondary carb. A friend of mine informs me I may have a valve that is not seating properly, resulting in the misfire, buildup on carb and (some of the) excessive oil consumption.

As per the condition of the carb itself, its setup currently at 2 turns on the fuel screw, idle roughly at 1200rpm with factory jetting) although the exhaust is a straight through KTM exhaust). Secondary carb is set at full open flap at full throttle). Yet to give it a proper clean as ran out of light but has been a year since it was last out for cleaning, but bike has only really done a maybe 2000km in the last year.

Any opinions on the dark deposits as in pictures?

After cleaning the carb, I will set fuel screw back to its current settings, then lean it out abit maybe to 1.5 turns and play with it. I am hoping the misfiring will be resolved with just this. Also I will adjust the float height. Noticed it isnt set level with the case. An oversight from last clean perhaps?

Any suggestions for carb settings?

https://i.ibb.co/zZHysy1/1.jpg
https://i.ibb.co/ThFCscf/2.jpg

Thanks!

check that the secondary carb CV slide moves up down freely, could be the reason for the transient richness.


other than that, long winded post, not sure i captured the whole plot :)


1ltr of oil x 3 tanks is NOT ok, doesnt sound like a leak..... sounds like top end overhaul time TBH

Had the CV carb apart today. The diaphram thing with spring was very dirty and dusty on the underside.. Slide and diaphram otherwise are in great condition.. Barely a mark on the slide.

Cant clean the jet unfortunately as whoever attempted to remove it previously had basically rounded it out... Hoping I can tap something into the soft metal and twist it out that way.. I have a replacement for it.

Not got round to the primary carb yet. Wasted all my carb cleaner on killing a wasp nest doh.


The current main jet is a 130 and the replacement I got appears to be 135. How will this affect the bike considering it was already running rich at 2 turns?

It does look like an oil residue rather than just running rich. Can you do a compression test?

Wear could be on needle and jet causing rich mixture. But I'm thinking the burning question is the suspected burning oil.

Agree

burning such an big amount of oil is going to prevent the the spark plug from firing well

take a picture of plug and post it

the dark stains in the carb could be related to the oil burning

It is definitely related to oil as I notice that after topping up the oil it misfires a lot more than when the oil is lower.

Cant get a photo of the spark plug atm, but come next weekend I should have time to post one.

Carb is completely clean and have done a few 100km. Apart from running slightly better at idle, it runs about the same as before. All jets are in good condition, as for everything in the carbs really.

Tried leaning and enriching the mixtures via the screw and both jets in the main and secondary carb and never really changed much apart from power. I have set it back to how it was originally being at centre on both jets and 2 turns on the mixture screw where it seems to have most power at least.

I kind of want to remove the head, cleaning up the valves and check the condition of the bore and piston rings etc.. but im worried about the inevitable problem of stripped threads... Its clearly not the original head on the bike as it has 2KF stamped into it and the frame is 4PT.

use a small torque wrench for the M6s, mid size tq. wrench for the head bolts and you should be ok, unless previous owner f$^&d up that is...


with that oil consumption you should really check the top end, might be the reason for your "richness"

Pretty well all XT600/ TT600 heads from 2KF/ 3AJ teneres onwards have letters 2KF cast into head. Same head casting was used through to the end in 04 with only very minor differences over the years. Likely you do have original head.

The blackness on the secondary venturi likely caused by poor sealing of inlet valve so you get small amount of exhaust blowing back into the carb venturi when at light throttle/ no second venturi open. Most engines that have a few miles under the belt will have that.

Have you inspected both carb needles? Both on 3rd clip from top? regardless based on your oil consumption, it is time to rebuild top end and go from there.