Intermittent extremely low power, flat camshaft type feeling

[ThrottleJunky]

I think I fixed my off idle miss which turned out to be a failed o-ring on the #4 carb mixture screw. I had removed it before, but I didn't realize the rubber was brittle. After reinstalling it broke, clogging the pilot and causing that cylinder to run lean intermittently. I replaced all of them.

After getting the carbs back on and the bike started, it appears my off idle miss is gone. When I gently crack the throttle, the rpm steadily rises rather than missing. Excited, I took it for a ride. That quickly turned to disappointment when I found my intermittent low power situation is not fixed.

The bike runs fantastic, then all of a sudden goes into this low power mode where I couldn't even beat a moped. If you've ever ridden in a vehicle with a flat cam, that's what it feels like. When it happens I can open up the throttle and I'm not even really accelerating. I pull the clutch in, give it a few revs, it fixes itself, and I am off like a rocket again.

It's not the petcocks, I've rebuilt those and was running off prime anyway. I'm wondering if maybe it's electrical. I actually got a backfire once, too, which was very odd. It won't do it all the time. When I had the carbs off today, I verified all the floats were absolutely perfect, I'd almost bet my life that they're not sticking. I had that problem before and had fuel coming out the airbox. That's fixed. I have brand new plugs in the bike. I am going to check the wires and coils first thing tomorrow. I don't know what else to look at.

[JeffH]

Have you checked the Pickup Coil wires?
Sounds like a classic broken pickup coil wire.

Hope that's it. A pretty easy fix. Carefully pull on each wire and if you get a mushy spot or the wire pulls apart then that's a likely culprit.

Jeff

[MPittma100]

Pick-up Coils

Check the 4 pick-up coil wires for breakage. Your description indicates that the problem is there. Search the site for the how-to check and repair of those wires.

[motoman]

Check the 4 pick-up coil wires for breakage. Your description indicates that the problem is there. Search the site for the how-to check and repair of those wires.

+2.....rotation of advance causes rotation of pick-up coil wires to loose internal contact from being broken inside insulation. As Jeff suggested, using two hands, pull every inch of each wire. Internal breakage will cause insulation to stretch where broken.

[ThrottleJunky]

Thanks fellas. Will do tomorrow morning. I'm going to go over all the electrical, look for anything suspicious.

[ThrottleJunky]

+2.....rotation of advance causes rotation of pick-up coil wires to loose internal contact from being broken inside insulation. As Jeff suggested, using two hands, pull every inch of each wire. Internal breakage will cause insulation to stretch where broken.

I'm a little confused. I took the cover off and there's barely an inch of each wire exposed, and they all seem perfectly intact?

Edit: OK, I see where I'm supposed to start the bike and then wiggle the wires. Will go do that right now.

2nd edit: Man, you guys ROCK!! I started it up and wiggled the light blue wire, and it stalls out EVERY time. WOOHOOOOOO!!!!

[DiverRay]

When you put it back together, DO NOT crimp the wires in the holders! Leave them a little loose so they can slide back and forth. The crimp is what started this problem. I did try to let Yamaha know back in 1978 with my first XS1100, but as I had not been through "their" school, I wasn't a "real" mechanic and I obviously didn't know what I was talking about....

[skids]

When you put it back together, DO NOT crimp the wires in the holders! Leave them a little loose so they can slide back and forth. The crimp is what started this problem. I did try to let Yamaha know back in 1978 with my first XS1100, but as I had not been through "their" school, I wasn't a "real" mechanic and I obviously didn't know what I was talking about....

On one of my bikes, I provided loops of wire to minimize the "bending factor" as the advance plate rotates. That was probably a decade ago and so far - so good. Knock on wood.

[ThrottleJunky]

Thanks for the comments and information. I have not finished the job because I did not have the supplies I needed. I picked up some heat shrink tube among other things.

This is an extremely poor design by Yamaha. I am not even sure if I've found all the broken wires. I suspect I have another on the upper left side where it enters the pickup area. I will know more tomorrow.

[ThrottleJunky]

How about another WOOOOOHOOOOOOO! She's fixed! That took care of ALL my problems. She purrs like a kitten now, screams up and down the highway like a banshee. I have been chasing my tail on this for weeks. A HUGE thank you to all who helped!

[motoman]

How about another WOOOOOHOOOOOOO! She's fixed! That took care of ALL my problems. She purrs like a kitten now, screams up and down the highway like a banshee. I have been chasing my tail on this for weeks. A HUGE thank you to all who helped!

Glad with our help you were able to solve the running issue TJ!

[ThrottleJunky]

One last comment on this - it was extremely difficult to solder the wires due to their location and such little slack (I did pull a small bit more out). If I did it again, I think I'd use heat shrink butt connectors, then heat shrink over those. They're supposed to only be good to 200 degrees, and I know this is close to the motor, but I think they'd be OK and a heck of a lot easier.

[motoman]

One last comment on this - it was extremely difficult to solder the wires due to their location and such little slack (I did pull a small bit more out). If I did it again, I think I'd use heat shrink butt connectors, then heat shrink over those. They're supposed to only be good to 200 degrees, and I know this is close to the motor, but I think they'd be OK and a heck of a lot easier.

Soldering wires is just, well...... ok. Soldering heat changes composition of the wire copper, and weakens it at that joint. Best option is to shorten up a naked butt connector just so both wire ends still go in each end with a dermal cut-off wheel. Slip tiny piece of shrink tubing over one of the wires. Add connector to each wire and crimp. Slide tiny piece of shrink tubing over connection and heat to shrink.....good to go. Sorry, figured you knew that or I would have included correct procedure of re-attaching those particular wires so they stay that way.