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why wont my dr start when the motor is warm?

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I have a '01 DR-z S with 14,000 miles on it. It runs great. When the bike is cold it starts right up and runs great. If you turn it off, stall it, or turn the key off it once the bike has warmed up it will not re-start.

While the motor is warm, it turns over great, just the same as it does when it is cold. If you let the bike sit for an hour or so after its been running, it will start right back up and you can be on your way.

Basically the bike will only start when its cold.

Any ideas? I've researched the forum pretty heavily and cant seem to find anyone having a similar issue. Arrrrgh. :smirk::

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No, I haven't. It has been running great then all of a sudden on Sunday it started doing this.

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+1 on checking the valves. Mine did the exact same thing as yours and it was because of the valves.

You should be able to bump start it when hot if nothing else.

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Check your oil and see if it smells like gas. If the petcock leaks; fuel can get in the oil and give problems like you've described.

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Check your oil and see if it smells like gas. If the petcock leaks; fuel can get in the oil and give problems like you've described.

+2 on this

I thought out of spec valves caused cold start issues hot start issues ususally relate to a leaky petcock and gas in the oil

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I can't believe all the 'starting while warm' issues that have been reported! I spent days trying to trouble-shoot the electrical system and it turned out to be gas in the oil. How the hell would that affect starting while warm!!?? Apparently the gasoline will vaporize and get sucked into the airbox (via the EGR or whatever they call it). The result is an extra rich mixture that prevents the bike from starting! I replaced my oil and problem solved!!

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Changing oil fixed the problem short term. You should also check the petcock if it is vacuum operated to make sure it's not leaking in the on position and make sure you are not leaving it on PRI when sitting. A manual petcock should be turned off when not riding. One other thing to check is the needle/seat in the carb. On the Mikuni carb there is an oring that sometimes fails causing fuel to flow into the motor from the bowl

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that's sdrawkcab....lol

no start cold = tight valves.

valve clearances increase with heat.

If that's the case then why is it necessary to gap/space your valves to a prescribed measurement when the engine is stone cold? If the clearances opened up why not just adjust the valves tight as they would surely open as the motor warmed up? I know nothing is as simple as it appears but being as that metals expand as they heat up I'm trying to figure out how the clearances would open? Different metals percentages of expansion(steel valves versus aluminum cylinder head)? Just looking for a better explanation to your statement as I'm certainly no expert but I've heard that tight valves make for hard warm starts.

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Thanks for the explanation Eddie. I learn new things on here every day.

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why is it necessary to gap/space your valves to a prescribed measurement when the engine is stone cold?

A couple of reasons.

1. Everything is at the same ambient temperature when cold, at it's resting state. On a hot engine, the exhaust side would be hotter than the inlet side. That's also why the exhaust clearance is different to the inlet clearance. At operating temperature, the actual clearance will be the same.

2. The co-efficient of linear expansion of different materials is different, meaning they expand with heat at different rates, and different amounts. The amount of linear expansion is known for each metal or alloy, and sizes are carefully calculated to provide the correct clearance at operating temperature. Working backwards to a cold state allows you to calculate the cold clearances. Otherwise, you would have to measure at operating temperature, which would be impossible, as even getting the engine quickly stripped allows it to cool somewhat.

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I checked and changed the oil last night. The old oil did have the faint smell of gas. However, the oil change hasn't seemed to help my issue.

I guess it's time to check the valves? This will be my first time to tear into a motorcycle engine. I have done moto carb rebuilds and overhauls, and I am pretty mechanically inclined. However, I have never torn a motor down this far. Should I look for help or just tear into with the manual?

What's a reasonable price to pay a "real" mechanic to do it?

Any recommendations for a mechanic in WNC / Asheville, NC?

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I checked and changed the oil last night. The old oil did have the faint smell of gas. However, the oil change hasn't seemed to help my issue.

I guess it's time to check the valves? This will be my first time to tear into a motorcycle engine. I have done moto carb rebuilds and overhauls, and I am pretty mechanically inclined. However, I have never torn a motor down this far. Should I look for help or just tear into with the manual?

What's a reasonable price to pay a "real" mechanic to do it?

Any recommendations for a mechanic in WNC / Asheville, NC?

pulling the valve cover off isn't really tearing into the motor.

real simple procedure to check valves. motor @ tdc on exhaust stroke & slip a feeler gage between the cam lobe & the shim bucket.

clean the bike well before pulling the valve cover. especially the area above & around the valve cover to prevent dirt from getting into the motor.

as mentioned, re-shimming is a little more involved, as the cams need to come out.

should only have to pay 1 hour of the shops hourly rate, shop supplies & shims if adjustment is needed.

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pulling the valve cover off isn't really tearing into the motor.

It really is, it's just no big deal.

The make up of the engine is pretty simple, it's designing the things that takes real expertise.

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