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Runs a bit rough/doesnt rev up when cold

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Hi Guys

My 2008 DRZ has a problem that seems to be manifest more the longer it is sat in the garage. If I leave it for a few weeks, come to it, start it and just let it idle on the choke it fires up no problems. If I leave it to sit idle, the revs gradually drop til it sounds like it's only firing every other stroke (?)

If I take the choke off at this point, it'll cut out. It will restart with a touch of throttle but struggles to rev past 2000, maybe 2500 rpm. If I let it sit and warm a bit longer, rev it a few times it gradually seems to clear up and behave normally..

If I then ride it to work (few miles), let it sit most of the day, come to it in the evening it'll start without choke, but doesnt rev up too well.. it clears faster than before though.

The puzzling thing for me is that it *used* to start on the button without any choke at all, if it had been used within say 48 hours, and it would rev up well more or less from the start. Nowadays it seems to require choke for longer. The ambient air temperature is higher than it used to be (bought in winter, good running, now it's summer, this rough patch while not warmed up has developed).

There was one event that may be relevant - the problem seems to be worse since I had it out in a very waterlogged field. Riding all day, as it came to the end of the day I hammered it through a few puddles and shortly after it cut out and wouldnt restart. I thought it was just fuel level, so i didnt pay much attention. It may or may not be relevant, but the RPM indication from the Vapor computer is less reliable these days- often it shows ----RPM, or the reported value is half what the engine RPM truly is..

Only other thing to mention: it needed a new sprag and torque limiter so I did the loctite fixes at the same time. Didnt notice any obvious decay of the coils/windings etc.

Can anyone suggest a list of things to be trying, or is it the case that the behaviour before (could start without choke, or come off choke very quickly) was unusual, and this "new" behaviour, where it seems to need choke for a long time/needs to idle for a while then revving to clear up its running, is actually the expected behaviour for these engines? (All the suzuki 4bangers I've had don't really seem to need choke if they are regularly used)

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In warm weather you should need choke at most for a couple seconds. I usually don't, but I remember reading somewhere here that if the fuel screw is set perfectly the choke should be needed for cold (as in room temp) engine starts otherwise it is a bit rich.

Hmmm. Usual checks, does the oil smell like gas? How is the oil level. Any vent hoses on the carb plugged? Muck in the spark plug hole?

Track down a manual or search google or thumpertalk for one if you are in a rush and go through the signal and trigger coil tests.

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You poor running on cold start after sitting could well be fuel related.

First, next time, put the petcock on 'pri' for a few seconds before you go to start it, once running, switch to 'on'. If that makes no difference, new time the bike is going to sit several + weeks, drain the tank and carb. The day you are going to ride, buy new fuel and fill it. Put the petcok on 'pri' and start it as above.

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