Strange Misfire

[Trouble]

Had a strange problem on a bike similar to the symptoms described here. Runs good for a while, then starts to cut out. After checking and double checking everything for half a day, found a strand of wire on the wire-covered oil lines touching the brake light switch connection which would cause the engine to cut out after riding a couple miles, then it would recover for a bit and repeat. The devil is in the details.

[76shuvlinoff]

I have definitely had a worn out dash ignition switch drive me nucking futs before. .

[dwjohnson]

 Customer has bike back right now, had to take a break on it and not enuff time to ride 20-30 miles after each change/check
  It's really not like a switch or wiring short or pinched wire, more like a progressive worsening  type of  issue once it starts. I can hear/feel it beginning ever so slightly and in a matter of 20-30-40 seconds it worsens to a point of what I describe running on one cyl. Almost like a piston is slowly seizing up so to speak.
It does have a braided oil line right up against the sending unit, I'll look into that. I'd also like to disassemble and inspect the tappets soon too, that really seems to fit.
  Thanks for all the replies and tips!!

[One4Tone]

...switch the plugs around see if that makes a difference...what plugs are you using?...even the Harley plugs are old stock for shovels....how is the auto advance?..nice you  don't have to deal with computers...

[a_disalvo]

Had a similar problem, mine would run 12 miles, than shut down. Turned out to be the coil, was a racing 3 ohm and was overheating. What coil did you change to? Frank

[guppymech]

I had a bad carbon core sparkplug wire on a new to me moped, it would run good and then die.  Riding around the block troubleshooting, it would die at about the same distance every time.  Tried a new plug wire, problem cured.  With points ignition you can use solid core wire or some spiral wound conductor wire.

[dwjohnson]

 Spk plugs are new Harley 5RL. Problem did not change any.
Coil was replaced by customer, not sure of the ohm but again no shift or change.
Have not tried different plug wires, didn't think it acted like that would it, but easy enuff to try now.
  So next chance I'm looking to check on the tappets, the plug wires, the flyweights, and I want to look closer at that braided oil line touching the sending unit.
Thanks again

[Burnout]

Better yet remove all the braided lines from that bike to prevent future blood loss and rub spots.

[JW113]

I'll second that. Braided SS lines look great in pictures. Beyond that.....

-JW

[76shuvlinoff]

I've got (Russell?) braided brake line from the front mc that's coated.

[JW113]

OK, I confess I use braided BRAKE lines as well. Bad Johnny. Bad. But have to admit, they sure make the brake lever less squishy.



-JW

[rageglide]

Does the bike still have the VOES?  They can present a vacuum leak and once heated up might be worse.  Is the ignition stock?  '84 shouldn't have mechanical advance.

[dwjohnson]

 Yes bike does have VOES on it but I know it's probably not in use being the customer has replaced ign. with a set of points. I did inspect vacuum lines and all seem to be good. I have had a bike with a bad voes and it acted similar except that bike just kinda scaled back on the "pull" and changed sound a bit while riding down the road when it would happen. I mean you could surely tell when it happened, it just wasn't as extreme as this one.and with the points ign. I don't think it is operational. 

[rageglide]

Ah, yeah VOES would be non-functional with points ignition.  If it's still connected it could be creating a vacuum leak.  The rubber plug dries up and can leak badly.  If it's connected to the carb/manifold still, I'd disconnect it and put a vacuum cap on the fitting.

[dwjohnson]

 Great idea and it is still plumbed so I will address that as well, Thanks

[Hillside Motorcycle]

Hold the phone.....check to insure your gas cap is venting.

[Hossamania]

Hold the phone.....check to insure your gas cap is venting.

Addressed in the op.

[One4Tone]

...how about trying a set of solid lifters...to eliminate the possibility of leaking lifter. I had a situation years ago on a 72 fl (that I still own)..the valve seat loosened up and it would ride up and down with the valve. It eventually bent the push rods once the seat rotated and did not slide back in, if you decide to switch lifters you may want to check push rods for straightness...with the motor running see if the push rod housings have any slight movement

[waltcentral]

Bring a volt/ohm meter with you and when it dies on a ride check to see if the coil is getting 12 volts. Probably help to remove the coil cover to make it easier.
This eliminate the wiring up to the coil.

[david lee]

 the outcome will be interesting