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Topic-icon Elevated Engine Idle RPM

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1 month 1 week ago #5191 by 895
Elevated Engine Idle RPM was created by 895
The motorcycle is a 1982 BMW R65. It has 30,000 miles and had not been operated for several years. Once it has warmed up, the engine idle RPM is elevated. If the clutch is let out with transmission in gear, then engine RPM is dragged down to normal and stays there. What causes this?

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1 month 6 days ago #5196 by Wobbly
Replied by Wobbly on topic Elevated Engine Idle RPM
Pin hole air leaks in the diaphragm or intake hose. Both hoses ought to be replaced, then check both diaphragms.

You'll also want to be using a Top Tier Fuel with cleansers in it.

Don't hide 'em, Ride 'em !!
#15150

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1 month 5 days ago - 1 month 5 days ago #5202 by 895
Replied by 895 on topic Elevated Engine Idle RPM
The choke and throttle cables and were too tight on the right cylinder. That fixed the elevated engine idle RPM.

Now working to resolve an engine vibration problem. My understanding is the R65 engine is notorious for vibration between 4300 - 4700 RPM.
Last edit: 1 month 5 days ago by Wobbly.

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1 month 5 days ago - 1 month 5 days ago #5205 by Wobbly
Replied by Wobbly on topic Elevated Engine Idle RPM

895 wrote: The choke and throttle cables and were too tight on the right cylinder. That fixed the elevated engine idle RPM.


If the throttle cables did not have the same slack on both sides, then it is clear that both throttles are not opening the same amount at running speed. That will lead to lots of vibration.

Using some type of gauge, you need to sync the throttles at idle using the idle speed screws. THEN you need to sync the throttles at 1500-2000 RPM using the cable adjusters.

Also check the ignition timing using a strobe lamp at very high RPM (full ignition advance) and the flywheel 'F' mark.

Don't hide 'em, Ride 'em !!
#15150
Last edit: 1 month 5 days ago by Wobbly.

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1 month 4 days ago - 1 month 4 days ago #5206 by 895
Replied by 895 on topic Elevated Engine Idle RPM
All of the motor mounting threaded fastener's as-found torque was below spec. Re-torqued and most vibration is eliminated save for handlebar vibration. After valves adjusted and carbs synchronized, we'll add some bar-end weights if needed.
Last edit: 1 month 4 days ago by 895.

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1 month 3 days ago #5208 by 895
Replied by 895 on topic Elevated Engine Idle RPM
We adjusted the valves and synchronized the carburetors. Engine mounts were torqued to ~45 ft-lbs. Most of the engine vibration is gone The handlebars are still buzzing however.

When the throttle is briefly cracked open, the engine revs but is slow to return to idle. It hovers at 2000 RPM for several seconds before settling to 1400 RPM. This bike has a bean can. I'm thinking the centrifucal spark advance flyweights are sticking open or the return springs are weak.

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