Rising Idle on an older DR600

[CrunchyProd]

I've had a nagging problem on my DR600 sled ('86) with the engine idling up when it's warm. Bike runs fine, starts fine, but when it gets warm it wants to turn up the idle speed. Usually I just pop the clutch to pull it back down but there's got to be a reason.

Without pulling the carb out to do a full check, any troubleshooting steps I can take? Seems to me like a vacuum issue somewhere.

Thanks for the feedback.

 

[Sparkle]

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Hi CP:

Here's some wild shots:

Your bike uses a vacuum fuel tap I think. At idle there is not much vacuum to hold it open and it could be shutting off which would cause a lean fast idle as the float bowl runs low. Then when you gas it the fuel valveopens and all is normal for a bit. Make sure the vacuum line to the fuel tapisn't leaking and the valve is staying open at idle. The diaphram in the fuel valve could be leaking or it could be hardened.

Could bean air leak too...Check all the vacuum lines, the ends get hard and leak....cut them off and re-attach. Make sure the intake rubbers (from the carb to the engine) are good, tighten the bands and check by squirting a little oil around the joints

Sparkle

 

[CrunchyProd]

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Thanks Sparkle. Good starting point and makes sense to me.

 

[Cedartree]

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There is actually a significant amount of vacuum at idle. The throttle slide or plate is closed and the engine is trying to ingest air pastit.Open the slide and vacuum drops, due to less restriction in the intake tract. An engine running at WOT has very littlevacuum. Any old hot rodder or person whois familiar with carbs will tell you the same.

The hanging idle could be a number of issues. Too lean an idle mixture. Possiblevacuum leaks causing that or it is just too lean to begin with, could be blocked fuel passages in the carb.Elevation changes affect jetting, was your bikejetted for a PO's elevation? My DRZ had that high idle issue until I went up one size on the pilot jet while doing the 3X3 mod.

 

[Sparkle]

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Cedartree wrote:

There is actually a significant amount of vacuum at idle. The throttle slide or plate is closed and the engine is trying to ingest air pastit.Open the slide and vacuum drops, due to less restriction in the intake tract. An engine running at WOT has very littlevacuum. Any old hot rodder or person whois familiar with carbs will tell you the same.

Of course Cedartreeis right CP....oh well.....it was a wild shot...:shoot:

Sparkle