A year ago I bought a TTR 600 2001. I hadnt touched a bike before so Im no expert. It had done 27 000 km. I had issues starting it from the start and sometimes I had to kick it for maybe 30 min before it started. While running it was fine. Never a problem to start it when hot/recently used.

I went on a 20 000 km trip and the same characteristics continued, but since I rode the bike every day it usually started "ok". Sometimes I started the day sweaty from kicking and if it stopped before getting hot I needed to let it rest or get someone to push-start (yes, a PITA but I managed). After about 10 000 km it wouldnt start, the plug was fouled and a new plug fixed it. At that time I was on 3k+ altitude and soon I had to change plug again. Then once more. So 3 changes in a short time. After that I was on lower altitude and it lasted the remaining maybe 5000 km.

After getting home it rested for a few months. Then it was hard to start but again.. after 30 min it did. After a bit more it wouldnt start. Another spark plug change and it started well. I hardly drove it and after a week I tried again and it was hard to start again... (i.e. I had bike on for maybe 10 min with new spark plug, left it for a week then hard to start. So potential oil leaks should not have had time to foul plug?).

Spark plugs have always looked the same when fouled. Sooty, like pictures shown for "too rich mixture". I attach a photo of it.

I dont think that the carb is dirty. It was cleaned (it didnt look dirty) once during all this and nothing changed. During that cleaning I also got help to "lean" the mix by a half or one turn (cant remember for sure). I didnt notice any change.

Easy answer would be "too rich" and maybe it is. But shouldnt a "too rich" mix be easy to start with a spark plug that ran for ~10 min? Although the fouling looks like rich mix, it doesnt make sense to me that an almost new plug is hard to start cold due to rich mix (because then it wants richer mix?).

Attaching photo of latest fouled spark plug.

Also, I got help checking valves by some mechanic who seemed a bit sloppy. He did change 1 or 2 of the valves which were out of spec, but the bike didnt behave any different after that.


Any ideas?

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Does the motor use oil ? It looks more like oil fouled than fuel fouled. You are fully correct, if it was over rich in gas, it would actually be opposite in hard starting issue, easier to start cold, but hard to start once hot. I had one messed up carb that made the bike miss and run real bad, any hard throttle and black smoke blew out the exhaust, still the plug never fouled, it takes a lot of gas to do that, enough to be very bad running at all times that you would have noticed.

You need to check the spark condition, is it a sharp, big blue spark or tiny weak orange. Then a compression check and leak down test to see where any comp loss is from. Valve clearance should also be verified correct if any concerns about previous work.

I suspect weak spark topped with some oil burning. Ignition coil may be weak or a poor grounding of the motor. Can you get an Iradium plug to try? I use Denso IX24B , splug fouling issues and weak spark is where iradium plugs are a big help , otherwise not a real benifit for the cost.


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It does use some oil. It has since purchase (used). Maybe 2-3dl on an 800km trip. Fuel consumption seems unchanged for 20 000km+ but I havent done any serious testing.

If its not black from gas I guess it has to be oil (the fouling doesnt seem "oily" though). However I dont look forward to all the job and money (in relation to the total value of the bike) that I probably have to put in to test compression, find problem and then fix cylinder if its broken. Feeling a little disheartened to be honest Leaving it at a shop for fixing would probably cost as much as I could sell it for.

I will check the spark again, but Im pretty sure its ok.

Thanks a lot for your help!

EDIT:
btw since I got home it started puffing out white smoke when I start it. It goes away after maybe 15 seconds of enginge running. I heard it could be ok and climate has been cold, but ofc it could be related to this (oil seeping into cylinder while bike rests?)

That would be a sign of a bad valve seal, oil leaks down into cylinder when cooling down. The smoke should be blueish, white smoke is water and unless your dumping gas in the pipe it shouldn't be that. Excess burning fuel is black smoke. I'd say it is from that seal, just enough oil is fouling the plug, but I wouldn't doubt if the sparks a bit weak also to foul that easily plus the hard starting, I've seen a plug that was a ball of sludge yet still the motor ran (smoked like hell though).

An Iradium should cure it as it is for now to get by.

Pull the plug and spin it over to have a quick look at the spark.

I will def check the plug spark and try iridium plug. Im planning on buying some other spare parts so I might throw in a valve seal or two just in case.

I have not noticed any blue smoke but I havent specifically looked for it either.

Thanks again!

Update. Today I went for the year's first longer ride. Total about 2-3hours.

Bike started after ~10 kicks with the "new" plug that had only been run twice shortly.

As usual nowadays white smoke. I was outside and it was a little windy, but I could only see white (i.e. not blue) smoke.

After running the bike for a while I stopped for ~20 min. After that started first kick.

Rode some more. Stopped for ~2h. It started after ~3-4 kicks.

Rode home and checked spark plug again (first time I check without having problems).

See spark plug in attached photo (slightly white on tip. Some black soot near threads.

The smoking only occured right after first start of the day, after resting a week.

Amateur diagnosis:

Hard to start + a little white spark plug = Slightly lean mix (I did lean it out a little a while ago).

Last 4 spark plugs were fouled pretty quick and they were very black (see prev photo). Also white (not really blue) smoke when I start after ~1week rest). I guess this could be oil burning. But the black is really more like soot than oily. Not especially wet, although I could quite easily get it off with my thumb.

Would anyone make a different diagnosis? Maybe the plug doesnt look so bad..? It could ofc just be bad valve clearances or leaking valves/piston ring. Or even weak spark. I checked spark on plug but didnt see. Its a little tricky to do alone though, so probably just me doing a bad test.

I ordered iridium spark plug Monday this week but it didnt arrive yet... I also bought shims to test valves. Have not invested in a compression tester... Might do that if other things wont solve.

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Did you figure out the problem?

Thanks for asking. Not really. But I went on a ~3500km trip and brought 5 spark plugs. I actually didn't have to change a single one...

However during my 20k+ km trip I changed 4 (I think) and during the recent 3500km trip the bike used 0,5l oil and smoked a lot during cold starts so something is definitely not right.

One strange detail I noticed was that one cold morning (almost 0 degrees C) I couldn't see any smoke at all when I started. Usually it comes instantaneously or after a few seconds. I later started other cold mornings with smoke. I thought it might be related to oil levels (too much oil leads to "overflow" or something), but I got smoke other mornings after that (and no oil refill). The only "unique" thing about the morning without smoke was that I had first ridden all day, then left it cold, then started it again during the afternoon (with smoke) and just riding it shortly (2km?) before it rested for the night (and the subsequent morning was the one without smoke). This indicated that maybe the engine needs to get really hot and then cool down in order to cause subsequent smoke.

Another reflection is that since the smoke comes only after the bike has rested, maybe leaking from the valves is more likely than anything wrong in the cylinder. Leaking seals in the cylinder shouldn't build up oil during rest (I think?). Not sure though. I have been trying to get in touch with a mechanic who can help me. One mechanics instant reaction to one of my spark plug photos in this thread was "too rich fuel mix".