81LH Sputters Between 5k and 6k

[thibtyson]

Fuel lines replaced, and I did the plastidip mod to the slide diaphragm's because I had a couple spots that looked like they may have holes. Still have a stutter, but I put almost 600 miles on it the last couple days. I went through Yellowstone park and over the Bear Tooth Pass. Amazing ride. I just had to shift a lot to keep the bike between 3k and 4.5k rpms to avoid the stutter. The bike would run up to the 5k-6k range if I slowly creep up past 4.5k. If I tried to accelerate past the 4.5k quickly it would act like it was out of gas or choking. Once I got to 5K plus range it would hold there and be reasonably fine as long as I didn't try to accelerate. On one stretch I was holding @ about 5k and the bike surged about 7 or 8 times then settled down. It felt like it was starving for fuel, aside from an ignition issue, could a sticky or improperly adjusted float be causing my problem? Also, when I get a chance I'm going to test my coils and see if they are putting out the proper spark.

[motoman]

Fuel lines replaced, and I did the plastidip mod to the slide diaphragm's because I had a couple spots that looked like they may have holes. Still have a stutter, but I put almost 600 miles on it the last couple days. I went through Yellowstone park and over the Bear Tooth Pass. Amazing ride. I just had to shift a lot to keep the bike between 3k and 4.5k rpms to avoid the stutter. The bike would run up to the 5k-6k range if I slowly creep up past 4.5k. If I tried to accelerate past the 4.5k quickly it would act like it was out of gas or choking. Once I got to 5K plus range it would hold there and be reasonably fine as long as I didn't try to accelerate. On one stretch I was holding @ about 5k and the bike surged about 7 or 8 times then settled down. It felt like it was starving for fuel, aside from an ignition issue, could a sticky or improperly adjusted float be causing my problem? Also, when I get a chance I'm going to test my coils and see if they are putting out the proper spark.

As BA80 stated, ignition before fueling when diagnosing. Ohm's check on coils becomes a moot point at times, unless it can be done when their still hot. Heated up, one can still have an 'open' that won't rear its ugly head till hot.

[thibtyson]

I'm beginning to think I'm having a TCI issue. It's an 81 Midnight special and I've been told that it uses a different module than the others. I'll look at it later to determine which module I have. Does anyone know by chance which one it would be and would anyone be willing to loan me one to plug it in and see if that's my issue?

[bikerphil]

Your TCI should be the 4R0 type, they usually work or they don't work. Module is probably OK if you have spark on all 4. Try switching it if you want, sorry don't have one for you though.

[thibtyson]

I believe it's the 4RO TCI unit.

[BA80]

Sent you a pm yesterday thibtyson. Did you see it?

[trbig]

A pinhole in one of your slide diaphragms could cause this also. You can check it by lifting the slide, covering the air inlet port, and letting it go. If the slide quickly drops, instead of sliding down very very slowly or staying up, you have a hole in the rubber diaphragm.

[Bonz]

Be sure the vacuum advance rotates easily/freely. You can see where the vac adv circular assembly rotates in the "housing". Take a good dose of silicon spray lube and rotate the unit by hand, spraying really good where the base is rotatiing in the housing. That will clean gunk out and leave the lube behind.

I would spend my time there. Every so often (every year or so) I get a st-t-t-t-t-tutter at a random rpm and it sits there, not wanting to gain rpm. I clutch it, quick blip to get a few rpm, then re-engage the clutch and keep motoring along just fine. Everytime the bike does this, I go in there with some slicon lube and the problem resolves.

Later!

[thibtyson]

BA80: I saw it and thank you! I've got a friend who rebuilds TCI modules and if that's the case I'll have him do it. So if anyone needs a TCI rebuilt I can get you his information.

trbig: I've checked for pinholes and diaphragms are good.

Bonz: I've played with the vacuum advance, but never lubricated it. I'll give it a try.

[Bonz]

Yeah, give a good lubing to that stuff down there...

[donebysunday]

Topcat, Intake is stock and the exhaust is 4-1. I didn't really pay attention to the jet sizes. I assume they are stock. As to the pickup coil wires, I wiggled them earlier in the riding season and it didn't seem to make much difference. Maybe I'll try them again and see if I can get something to happen while the bike is in gear and under load.

How long have you had that 4-1 on the bike ?
Did this just start happening, was the bike running just fine with this 4-1 previously ?
I went for 1 1/2 seasons after putting a Mac 2-2 on a XS650 with a stumble at 6000 rpm. Everyone said you need bigger jetting. I tried all kinds of pilot, main, air jet and shimmed main needle ( 82 SK ) combos and still the same. I thought about it for some time and figured I had tried all the bigger pilots and mains as well as Blaine Hoops suggestion of different sized air jets. I put all back to stock but installed 1 size smaller mains ,,,, problem solved. Probably could have played some more with the needles and jets but running it up it would shoot right past red line still pulling.

[thibtyson]

The 4-1 has been on the bike since before I bought it and the jetting is still stock.

I ran down and bought a can of silicone lubricant from the local hardware store and haphazardly sprayed a little in there. It's not completely fixed, but there is a significant difference. I think I'm going to see if I can clean it up a little in there and replace my vacuum line. Hopefully, with a little luck that's all it is a mucked up vacuum advance.

[Bonz]

I know someone will come in and slap my hand for this one... I sprayed contact cleaner into the vacuum advance elbow to clean out any crap in there, if there could be anything in there at all. Also sprayed where the linkage goes into the cannister with the same thing, to clean it.

That stuff evaoporates so quick I don't think there is any chance of something negative happening to any components.

Then put a spurt of silicon spray on the bottom where the linkage goes into the cannister, and a quick shot into the elbow as well for the heck of it.

When you described the problem, it sounded familiar...

In any case, the fact that what you did has made it better, you should continue with your cleaning as that is probably where most, if not all, of the problem lies.

[James England]

This just crossed my mind. Just before one of my ignition coils went out I had a little sputter when cruising not really noticeable any other time except for occasionally it would misfire just once when idling. Then, one day it just dropped 2 cylinders all of a sudden.

JAT.

just what I was going to say. Failing coils can be weird and give splutters and misfires, I found. Replacing my OEM coils with Dyna coils cue my irritating splutter...

[TopCatGr58]

I've got a friend who rebuilds TCI modules and if that's the case I'll have him do it. So if anyone needs a TCI rebuilt I can get you his information.

Hey there, looks like others have got you on the right track to fixing your problem, but what you said above caught my eye. We used to have a fellow (Randy/Davinci) that repaired them, but he's since moved on to a newer machine, and doesn't do it anymore. But also, our 81 4RO and 82 10M TCI's are a bit more complicated because they have eprom chips and circuits that provide electronic centrifugal advance and also Vac. curves that are programmed into the TCI's. SO...Randy could not fix them because they couldn't work on the eproms and such.

So...I would just like to ask if your friend has the ability to examine, extract the data from the Eprom chips, as well as being to reprogram them, etc.?

If so...then I/we could provide a working 4RO unit, as well as possibly a 10M that he could examine, and possibly extract the Eprom data and save/store it for future unit repairs.

T.C.