I recently bought a 1979 FLH 80" project. Motor had a rebuild about 1000 miles before I bought it. Not sure exactly what, cause the guy I bought it from didn't know much and I haven't yet talked to the guy that did the work. A reputable place though. The bike had the original butterfly Keihin which displayed a number of issues including it wouldn't idle after it got warmed up. It stumbled, pop back through the exhaust and die if you didn't keep the RPM way up. I had a CV carb that I had taken off my 01 Roadking, so I took it apart and cleaned thoroughly. I installed a 50 slow jet, left in the 190 main that was in it and set the air fuel at about 2-1/2 turns out. The bike runs great when cold and will idle down to a slow lope and sounds great. When it gets fully warmed up it still runs great. No hesitation, good acceleration but once hot the idle problem is still there. When it gets anywhere close to a good idle rpm, it stumbles, backfires through the exhaust and dies.

Any ideas? I have worked on a number of twin cams but have little knowledge in the Shovel. Learning as I go. Any help will be appreciated.

Thanks
Jer

 

Intake manifold leak.

 

I'd guess on an Intake Manifold leak also. It was pretty common for the Shovels to suck air through the manifold where it bolts to the cylinder heads ... also where the "Rubber Bands" connect the manifold to the carburetor. Fire it up and spray some carb cleaner in that area and see if the idle speed increases. If it does you have found your problem. Hope this helps.

 

Thanks, I will check that out. Would that only ahppen when the bike is hot? Someone also suggested a bad coil that was weak when the bike is hot. Does that make any sense?

 

If your ignition is equipped with flyweights, you very well could have a broken spring, or the weights themselves are buggered.
Same/similar symptoms would be witnessed.
Scott

 

I would suspect an intake leak. The 79's had the first electronic ignitions w/o the weights but were non adjustable. The ignition could be the problem but I would start with the intake.

 

'79s are special....no two exactly alike...AMF was dealing with way too many suppliers with varying degrees of quality control and parts availability. Nothing bad to say, they're just all unique....especially in '79.

 

Thanks
I will check out the ignition when I get home as well as leak possibility this weekend. It is an aftermarket electronic, says Dyna on it. I suspect it is a Dyna S.

 

If it is Dyna S equipped, it has flyweights. Pull the breaker plate, and with a 9/16 socket, remove the screw that holds the flyweights.
Inspect them for broken springs, and the flyweight pivot bores for elongation.
VERY negleted area.
Replace them with the best one you can find, if needed.
If you need one, we carry them.
Scott

 

Scott
Thanks, heading for Sturgis tomorrow so the shovel problem will have to wait till I get back. I ordered new rubber bands and clamps although I really couldn't verify that I have a leak. Adjusted timing didn't help. Ordered new coil which isn't here yet. So i will check the advance when I get back next week. If that looks l;ike a problem I'll give you a call to get a replacement.