erratic idle

[wayner]

I have a 79 650 2F, been shedded for years. When I got it running I set the idle at about 1200. After a short run it would idle too slow, raised the idle to around 1200 again, then after another run it idled too fast. I cleaned carbs and installed new carb kits, including needle jets and needles. Still runs the same, any ideas?
Thanks Wayner.

 

[xsjohn]

They all speed up a bit at operating temp from a cold start......(considering all else is correct)..... the mix screws need to be set at operating temperature.............run it along for a few miles at low throttle and check the plugs..........just a "very" tiny amount of soot on the end of your finger from the plug is what you are looking for.......set each side "independently"......no soot and light color porcelain turn it out a bit ....lots of soot turn it in a bit....listen to the engine.....ect......new plugs are harder to read this way......and if it is too sooty it should clean after another few miles after adjustment...........then check it again...

xsjohn

 

[wayner]

This happens at operating temp, i'm talking 100-150 rpm's. I have to turn the stop screw in or out at just about every stop. Seems to run fine otherwise, everything is stock on bike. Was thinking vacuum leak but that doesn't come and go like that?

 

[xsjohn]

If it were mine I would work on the mix screws like I said earlier (above).....run along at low throttle.....40 miles an hour is ok......you are mostly on the mix screws at low throttle......and check.....again each side independently...avoid new plugs because it takes a couple of hundered for them to even begin to show running color and soot..........xsjohn

Might as well show some body parts if anyone wants to really get fingered....and it's from the plug not the arse.....

 

[retiredgentleman]

As xsjohn mentioned, its normal for the idle speed to increase as the engine warms up.

I start on choke, within about 15 seconds I take the choke off and turn the throttle stop screw up enough to keep the rpm at 1200 to 1400 rpm. As the engine warms up over the next 10 minutes or 15 minutes, I keep decreasing the stop screw to keep the idle at 1200 rpm. Thats just how they work.

You probably need to adjust the pilot screws (mixture screws) using the dead cylinder method. Warm engine fully. Use a fan to cool the engine. Connect one cylinder spark plug lead to a third spark plug that is grounded( to prevent ignition coil damage) , so that the engine only runs on one cylinder. Adjust the rpm down to only 300 or 400 rpm with the stop screw. Adjust the mixture screw for the fastest, smoothest idle. Repeat for other cylinder.

Also good idea to sync the carbs.....................make your own U tube manometer from plastic tubing, fill halfway with a coloured liquid.