GPX250RR Problem

[gamgee]

not sure if this is the right place to post this but anyway...
The problem seems to happen more on cold mornings and nights, but what happens is the bike starts up fine, idles fine, but as soon as i let the clutch out to go and take off, the revs drop and it either stalls, or i jam the clutch in and stop it from stalling, give it a bit longer to warm up and it eventually takes off and rides as if nothing is wrong
choke doesn't make a difference, it doesn't seem to be the kickstand sensor as it 'fixes' itself without me touching the kickstand, so has anyone got any ideas?

[Ixion]

You're in Dunedin. it's winter. Let the poor bugger get warm first. sorted

[Buster]

Yep, warm it up before you take off and dont ask too much from it for the first few kays.

[gamgee]

yeah but should i just be putting it down to the cold when it does it even when i try and take off at 5krpm and it still just drops off the revs and does the same thing
it's also done it a couple of times when i've turned it off to unlock the garage, so it shouldn't have cooled down much in the 30 seconds it takes me to unlock that

[gamgee]

and yeah i usually give it a good 2 minutes of warming up before riding and real easy on it even when it has reached optimal temp, i don't want to kill another 250

[Ixion]

It's winter! In Dunedin! Remember that bike carbs are not as sophisticated as car ones. (Even bike FI likewise, except may be BMW).

Carbs have a special fuel passage for idling.Which is normally pretty rich. So they'll idle even if it's cold. But as soon as you open the throttle you are off the idle circuit. That cold petrol in a cold carb won't vaporise easily.

Warm it up. Even in Auckland I need to warm Ratty up for a bit these mornings.

One other possibility is that you have the idle mix REAL rich for starting on cold mornings and it's fouling a plug, cos the plug is cold. I assume you are using the choke judiciously?

[gamgee]

i stopped using the choke at all as it wasn't making any difference

[skidMark]

maybe the choke is jammed?

if all else fails take it to a mechanic

[Ixion]

So maybe your idle IS too rich? They fit the choke for a reason.

[gamgee]

nah choke works lifts the idle a bit higher, it just doesn't make a difference to this problem, i'll get dad (mechanic) to have a look at it, but he's a car mechanic and doesn't really seem to know a lot about bike specific problems

[gamgee]

and i'll check the plugs but last time i checked them a few months ago (yeah i know they probably are dirty now) they were clean as

[Ixion]

It's not really bike specific. Cars used to have the same issues back in the days when they had simple carbs. Things like the old SUs and Solexs. If you Dad was wrenching back in the 50s or 60s he'll remember .

EDIT: the plug will clean itself once the engine heats up. You'd have to whip the plug out immediately after it stalled to tell. Just gets a bit of fluffy carbon on it, that burns off once the plug reaches full heat.

[gamgee]

so there is absolutely nothing else i should check?
haha and he was only born in the 60's

[Ixion]

Well, yeah, there's a bazillion things you COULD check.

Zorst could be blocked. Or air filter. Oil may be too thick for winter (that's actually not a bad one). Ignition timing could be out. Valve timing might have slipped. CDI unit could be on the fritz. Coil could be bad. Carb could be worn or dirty. Carb could be icing up. Water in the fuel or fuel lines . Blocked tank vent (ice?) Heaps of oddball stuff.

But odds are 100 to 1 it's the carb . May just be normal. Is this the first winter you've had the bike?

EDIT: We used to put hot water bottles on the carb overnight when cars did this back in the day. You could try that. Some folk used blankets. (Yes, I am serious)

[gamgee]

yeah first winter, and it does mainly seem to be when it's cold, except those odd times, after i've just got home, so the bike is warmed up, i turn it off while unlocking the garage, start it up again... stall, start it up, fine off we go.
oil is 5/40 sinthetic is due for a change in about a month, but it was as clean as when it went in last time i changed and did filter, so yeah maybe i will just put it down to friggen cold dunedin winters, brrr, i'm going to bed where it's warm, will report back if dad finds anything wrong