hard to start and wont idle when warm - Kawasaki Ninja 250R Forum
 
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post #1 of 6 (permalink) Old 06-16-2013, 10:04 AM Thread Starter
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hard to start and wont idle when warm

my 95 gpx250 will start and idle no problem when cold but take it for a 5-10 mins run i have to work at the throttle to keep it running at traffic lights ect.then when i stop it,its hard to start it again.turns over for a good while until it starts.whats the first thing i should look at?valve clearance?carb?any ideas?
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post #2 of 6 (permalink) Old 06-17-2013, 12:58 PM
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Probably a dumb question but when you first start off, do you ride with the choke like halfway on briefly? I have to on my bike is the reason I ask. (These is the most cold-natured bikes I have ever seen)
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post #3 of 6 (permalink) Old 06-17-2013, 01:27 PM Thread Starter
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Quote:
Originally Posted by deeptekkie View Post
Probably a dumb question but when you first start off, do you ride with the choke like halfway on briefly? I have to on my bike is the reason I ask. (These is the most cold-natured bikes I have ever seen)
i ride with choke off.bike starts first time with choke full on.by the time i have cloves and helmet on choke off and ride away.goes great for about 10 mins.must mention the temp gauge went way up one time but came down again
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post #4 of 6 (permalink) Old 08-24-2013, 07:50 PM
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Hi skikman,

You're on the right track with your ideas of the problem.

I'd probably discount carburetors as the problem though, as generally they would cause the bike to run crappy at cold as well as hot.

My guess is it sounds more like valve clearances need adjusting. This is generally presented by the fact that it gets worse as the bike warms up.

When cold, all the metal parts of the bike have "shrunk" as their material cools, allowing the clearance between your valve cap and cam-shaft to widen. As the bike warms, and the valves and other parts warm up, they all expand slightly.

This causes the gap between your valve cap and cam to close up, often to no gap at all. The effect of this is that your cam begins holding your valve open slightly all the time, instead of creating a good seal against the head.

This allows fuel and air to escape at low revs, lowering compression and causing mis-firing. When you hold the revs up, you're giving the gasses less time to escape, hence why it still runs at higher revs.

If you're mechanically inclined, you can check your valve clearances by removing your fuel tank and rocker cover, and checking the clearances with feeler gauges. Each cylinder should be at top dead center when you check its valves, and the cam lobes pointing upwards or outwards from the head.

You're measuring the distance under the cam lobe, between it and the valve cap.

Normal clearance is usually accepted as Inlet - 0.003" to 0.005" (Thou) and exhaust as 0.005" to 0.008". Any smaller and you're going to have problems, any wider and they just get a bit noisy.

I'd suggest taking the bike to a mechanic to have shims swapped, unless you are familiar with removing cam-shafts yourself, and re-setting up timing.

Hope this helps.

Cheers!
-Matt
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post #5 of 6 (permalink) Old 08-24-2013, 07:52 PM
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I should mention too that close valve clearances will also make a bike hard to start...

Good Luck!
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post #6 of 6 (permalink) Old 09-01-2013, 10:23 AM
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Then there is always that bane of not enough air to displace the amount of gasoline burned from the tank. Many riders have had problems with their gas caps not venting air into the tank properly.
The next time that you have trouble pull over somewhere safe and open the gas cap with the bike level. After you shut it see if it runs fine for a few moments again since it's not having to suck gasoline into the carbs. Just a thought...
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