Idles fine - then dies

[George Ryals]

Clean (again maybe) the air and fuel passages associated with the idle circuit in the right carb., including the idle jet.

[Manfred]

Clean (again maybe) the air and fuel passages associated with the idle circuit in the right carb., including the idle jet.

Thanks for your patience with me.

I cleaned (again) the right card air & fuel passages. Will find out tomorrow how she goes.

[Garnet]

I had a quick look in my Bing handbook and it shows all R80s haveing a base setting of 1/2 turn out on the idle mixture screw. If all is correct the bike won't even run at 1 turn out as that is too rich. If you are at 1 and a half to two turns there is some blockage or the wrong idle jets, or you idle stops are too far open and the carbs arn't even sucking through the idle circut.

Did you have the throttle plates out? If so they are not back in the right place and air is getting past them.

[Manfred]

Hmmm. I have a Bing book as well - but have been using a carb synch process to set my idle mix screws. ~1.5 turns out provides the fastest idle, which is then set right by the idle set screws. She started fine this morning and ran much better. I will find out on the way home this afternoon if she dies at idle.

[Garnet]

I'm glad you have a Bing book. Check your carb numbers to make sure they the right ones for your bike. Then set the needle position and idle mixture screws to the stock base settings for those carbs. Make sure your jet sizes are correct. Make sure the float level is correct.

Start the bike and take it for a ride. It should run OK at base settings. The idle mixture adjustment should be very close and only need a small tweek to make it perfect on each carb. If you need to turn the screw more than about a quarter of a turn there is something blocked or wrong inside the carb, or the method you are useing is suspect. I have never had any luck useing the shorting out a plug method, but that is just me.

[Manfred]

On my way home this afternoon - she started with a little more cranking than normal, but not bad or worrisome. Runs very smooth - better than last week by a large margin. While at idle - hot day, hot bike - nearly vibration free at ~1,100 rpm. And I felt the catch in the giddy-up and gave a little throttle before she died. When I do this - she stumbles off idle; this does not happen when she doesn't try to die at idle. About 2,500 or 3,000 rpm, smooth again.

I am in my air conditioned living room and will read up on the Bing book. No plans for tomorrow, so I should be able to spend some time tinkering.

[Manfred]

The numbers on my carbs are:

Right: 64/32/358
Left: 64/32/357

I find in the chart on page 2 what you've said - idle mix screws starting position 1/2 turn out from soft bottom. I will make this adjustment and sync the carbs according to the procedure on page 13.

[Manfred]

OK. At 1/2 turn out, she wold not start. At 3/4 turns out, starts good, idles fine and is very smooth. I will take her out tomorrow and see how she behaves when she gets good and hot.

Many thanks to the folks who have patiently helped me figure out what's going on with my airhead. It's my first beemer

[Manfred]

Amazing difference. Firm idle, crept up as she got hot - settling in ~1,250. When I got home, turned the fan on, restarted the bike, and adjusted the mixture screws in another "notch" and used the idle screws to get the hot idle to 1,000.

No surging or stumbling, no sign of the "catch in the giddy-up" that has preceded a sudden stop of the engine.

Never did know what that chart on page 2 of the Bing book was! Many thanks to all for helping me out.

[Ken in Oklahoma]

Amazing difference. Firm idle, crept up as she got hot - settling in ~1,250. When I got home, turned the fan on, restarted the bike, and adjusted the mixture screws in another "notch" and used the idle screws to get the hot idle to 1,000.

No surging or stumbling, no sign of the "catch in the giddy-up" that has preceded a sudden stop of the engine.

Manfred, I don't think you should have necessarily used the used the "mixture" screw to bring the idle down. If your bike was idling well, albeit fast, at 1,250 rpm, your mixture was likely already in the ball park. The throttle stop screw (what you're calling the "idle" screw) would have been the one to start with.

Your bike was probably not idling fast because your mixture was wrong. What happens with a lot of these old airheads, including one or two of mine is that the centrifugal advance springs may be a bit on the week side. So at idling rpms the bob weights are already wanting to swing out and advance the timing. The advanced timing is what probably brought your idle up.

I would only use the mixture screw to "touch up" the idle after you've got it where you want it rpm wise.



Ken