1987 V4 140 Idle rev fluctuations

[Roycehg]

My 1987 V4 140 has an idle fluctuation that ranges from 900 to 1100.
Would any one have any suggestions on what could cause this to happen?
Even when I increase the throttle to say 2000 RPM the fluctuations still exist.
Has any Looper experts out there that may have a educated guess as to why this can happen?

Thanks and regards
Roycehg.

[Joe Reeves]

This type problem is normally caused by a improper setting of the linkages between the carburetors.... causing at least one carburetor to have its throttle butterfly at a slightly different setting than the others....... At idle, for example, 3 butterflies completely closed... and one open to .010" (doesn't take much!).

[Roycehg]

Hi Joe,
Thankyou for your response. By eye the butterfly valves looked good but as you say if it only takes .010" then something is not quite right. I will investigate further.
Thanks and regards

[Joe Reeves]

I might add...... Having second thoughts.... You don't say if it is a gradual fluctuation (fuel) or a instantaneous type change in rpms (ignition) which could be due to a intermittent shorting spark plug, a chafing wire rubbing a bare spot on the crankcase, etc. However my experience with the wandering rpms has always led to tension on one of the throttle linkages.

[Roycehg]

If the engine is idling it will range from say 900 and move to 1000 then to 1100 then move back to 900 over a period of 5 - 8 seconds and it seems not to be consistent time wise through the range.
Will investigate..