bike hiccups under moderate acceleration

[bikerdave79]

Kinda stumped here. Got an 81 xs1100 special I'm working on for a buddy. Idles great, runs great, rips up the highway. Problem I'm having is if your cruising along and give the bike half to 3/4 throttle, it will "hiccup" almost like you loose all power for a half a second then it kicks back in and goes. I you start in first and dump the throttle through all the gears it goes like a rocket with no problem. If you gingerly granny shift through the gears its fine too. Its most predominant when your just cruising a back road at a steady pace and want to just goose the throttle a bit to speed up a little. It will jerk for half a second and then go. Doesn't matter what gear. But seems less likely to do it if you ease into it. If you whack the throttle it pukes for half a second like someone flips the key on and off. No backfiring. No increase in rpm like a slipping clutch. I was thinking coil but I'd think it would act up more under heavy load. Any ideas? Where should I start looking? Bike has been ridden all sumer with no issue this just started.

[motoman]

Kinda stumped here. Got an 81 xs1100 special I'm working on for a buddy. Idles great, runs great, rips up the highway. Problem I'm having is if your cruising along and give the bike half to 3/4 throttle, it will "hiccup" almost like you loose all power for a half a second then it kicks back in and goes. I you start in first and dump the throttle through all the gears it goes like a rocket with no problem. If you gingerly granny shift through the gears its fine too. Its most predominant when your just cruising a back road at a steady pace and want to just goose the throttle a bit to speed up a little. It will jerk for half a second and then go. Doesn't matter what gear. But seems less likely to do it if you ease into it. If you whack the throttle it pukes for half a second like someone flips the key on and off. No backfiring. No increase in rpm like a slipping clutch. I was thinking coil but I'd think it would act up more under heavy load. Any ideas? Where should I start looking? Bike has been ridden all sumer with no issue this just started.

Got an invisible(internal) broke pickup coil wire......likely the white one .... .at this point, keep the hands away from the carbs.......seriously .

[motoman]

Now bet your wonderin' how on God's free earth is that related . Easy-peasy......when throttle backs off to an almost cruisin' rpm, PORTED vacuum to vacuum advance rotates advance assembly moving pickup coil wires, which over decades of that happening weakins wires INTERNALLY, breaking them.....then rotating back makes internal contact when under load(manifold vacuum only).......hope that helped .

[bikerdave79]

Ohhh I hadnt even considered that! Good call, makes a lot of sense. I'll check that tomorrow. Can the wires themselves be replaced or do I need the whole unit?

[MaximPhil]

Ohhh I hadnt even considered that! Good call, makes a lot of sense. I'll check that tomorrow. Can the wires themselves be replaced or do I need the whole unit?

Hi Dave,
Usually enough wire that you just find the break and repair it. Solder and a piece of heatshrink.
Pulling on the wire will reveal the broken spot. test all of them while you are there. Make sure everything is rotating smoothly.
I have seen this done a few times so it can not be too difficult
Phil

[motoman]

Hi Dave,
Usually enough wire that you just find the break and repair it. Solder and a piece of heatshrink.
Pulling on the wire will reveal the broken spot. test all of them while you are there. Make sure everything is rotating smoothly.
I have seen this done a few times so it can not be too difficult
Phil

No soldering allowed......cut a naked butt connector in half(short is better in this case), slip a short piece of shrink over wire...crimp connector to wire ends....then shrink tube it. Heat from soldering weaken wire and raises current resistance.....not good .

[bikerdave79]

Hi Dave,
Usually enough wire that you just find the break and repair it. Solder and a piece of heatshrink.
Pulling on the wire will reveal the broken spot. test all of them while you are there. Make sure everything is rotating smoothly.
I have seen this done a few times so it can not be too difficult
Phil

Awesome. Thanks so much. I'll let you know how I make out!

[bikerdave79]

Boy you guys were right on the money!!!! Pulled the white wire and it was like taffy.

[motoman]

Boy you guys were right on the money!!!! Pulled the white wire and it was like taffy.

Bingo!.........do I get extra points? .

[bikerdave79]

Patched it up with a small crimp connector and heat shrink. Just took it for a spin. Runs like a cat on carpet now!! Thanks so much youb saved me a HUGE headache fellas!

[hamjam]

Motoman wrote :
No soldering allowed......cut a naked butt connector in half(short is better in this case), slip a short piece of shrink over wire...crimp connector to wire ends....then shrink tube it. Heat from soldering weaken wire and raises current resistance.....not good .

I think this only counts if you are joining resistance wire such as found in hair dryers and the like and maybe circuit boards , and cleaning the flux from the joint might help

and how much resistance is generated in a 1/4 or less inch joint in a 12 inch wire ? do you think this really would cause you grief
not trying to be a cactus here just thinking about it

[motoman]

Motoman wrote :
No soldering allowed......cut a naked butt connector in half(short is better in this case), slip a short piece of shrink over wire...crimp connector to wire ends....then shrink tube it. Heat from soldering weaken wire and raises current resistance.....not good .

I think this only counts if you are joining resistance wire such as found in hair dryers and the like and maybe circuit boards , and cleaning the flux from the joint might help

and how much resistance is generated in a 1/4 or less inch joint in a 12 inch wire ? do you think this really would cause you grief
not trying to be a cactus here just thinking about it

Yeppers it can........not experienced it myself in that specific area, since mine was repaired with respect to that happening . Have heard of BOTH happening HERE, just because suggestion of the more experienced fell on 'deaf ears' .

[hamjam]

I am only "hard of hearing " not as much as some other guy on here that had an ST11 but we still speak with each other in ASL
still I think my points are valid the shrink tube prevents movement so if it was a slightly weakened wire it would not matter , this works for the crimped as well and the resistance change would be negligible less than .0001 ohms or maybe 2 so either repair would be ok
and BTW
Here are some values for the materials of interest:
copper - resitivity=1.68E-8 ohm-m (0.0000000168)
typical eutectic PbSn solder (63% lead, 37% tin) - resitivity=1.65E-7 ohm-m

[BA80]

Bingo!.........do I get extra points? .

LOL......you know you can't get away without a comment from the BA.

I've always soldered. But maybe BUTT connectors would work too.

The biggest thing I've found that make repairs fail is the connections or the shrink tubing not flexing enough and it'll break again shortly right at the edge of the repair. If I put the repair inside the little wire clamp (which is normally where the wires break) the repair lasts much longer.

You can pull a little extra wire out of the harness if your careful to give you a little more slack.

[MPittma100]

Yes!

Bingo!.........do I get extra points? .

Yes you do get extra points. You started the week off by getting lots of bonus points just because you came to the state of Georgia. With those points and the ones you get for the pick-up coil wire repair post, you are clearly in the POINTS LEAD!

Most people would be otherwise repairing the electrical problem in their carburetors right now.

MP