81LH Sputters Between 5k and 6k

[thibtyson]

Hi everyone, I've got an 81LH that sputters under load between 5k and 6k rpms. It doesn't do it when I rev the bike in neutral, just under a load and if I get over the 6k - 6.5k mark it goes away and revs smoothly through the rest of the rpm range. I just pulled the carbs and cleaned them this weekend. I get a little better throttle response, but the sputter is still there. Any thoughts on where to begin?

[TopCatGr58]

Hey there,

Okay, a few questions about the bike. OEM intake/exhaust or mods?

If it were an earlier model, I would be saying to check your pickup coil wires, but being an 81, the PU wires don't flex as much because the cent. adv. curve is programmed into the TCI. It still uses a mech. vac. adv. but it doesn't flex the wires as much as the early models.

You were just inside the carbs, what size pilots and mains?

T.C.

[3Phase]

Thibtyson, T.C.,

It could be the pickup coil wires.

The '81 still has the vacuum advance so the pickup coil plate moves just as much as the '78 to '80s. In '81 the mechanical advance was eliminated but that only turned the reluctor. The 4RO TCI has pre-mapped electronic RPM based advance curves so it doesn't need the mechanical advance.

In '82 the XJ11 replaced the vacuum advance and its movable pickup plate with the boost sensor. The 10M TCI has pre-mapped electronic RPM and engine load (vacuum) based advance curves. The XJ11 shouldn't have the pickup coil wire problem unless someone accidentally broke 'em while checking the timing or something... or installed a TCI and the timing guts from an XS11.

[skids]

Thibtyson, T.C.,

It could be the pickup coil wires.

The '81 still has the vacuum advance so the pickup coil plate moves just as much as the '78 to '80s. In '81 the mechanical advance was eliminated but that only turned the reluctor. The 4RO TCI has pre-mapped electronic RPM based advance curves so it doesn't need the mechanical advance.

.

I agree, the wires do flex and can break. Check 'em.

[thibtyson]

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.

[3Phase]

Thibtyson,

I don't think you want to mess with the pickup coil wires while the bike's in gear and under load.

Have you read the Tutorials in the Tech Tips section here on the site?

Here ya go!:-

Pick-up Coil Wire Repair


The Coil Pick-Up Fix

Ignition Problems - Cylinders Misfiring

[motoman]

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.

Try to seperate every half inch lightly tugging every half inch.......specificly the white wire,DAMHIK.

[BA80]

Try to seperate every half inch lightly tugging every half inch.......specificly the white wire,DAMHIK.

RACIST!

[motoman]

RACIST!

If the all important smoke is kept in the wires, these ole' motors get a bit racey again......

[thibtyson]

I'll try the pick-up coil wire check again and see if I missed a spot last time. I'll let you know what I find.

[thibtyson]

OK, now that the family vacation is complete, I took a minute to do the pickup wire check and everything seems fine. There isn't any spots with shrink tubing on the wires, so I don't think there has been a break in the past, or if there was the PO replaced the wires completely. Where to go from here?

[BA80]

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.

[trbig]

Pinhole in a slide diaphragm?

[thibtyson]

I was installing new clutch springs and noticed a leak in a fuel line just below the right hand petcock. I didn't see it until the bike was running but it spits a reasonable amount of fuel and puts an air bubble in the line. I wonder if the air bubble is causing my stutter? I'm trying to wrap my head around it, the air bubble would enter the octopus and then split out to the 2 right hand carbs, then I guess it would cause those two carbs to run lean for a second. But why would it be around the same rpm every time? I need to fix the lines and see if it helps. Any suggestions on fuel line and where to get 'em?

[BA80]

1/4" Tygon line. You should be able to get it at any parts house.

BTW, air bubbles are common and won't cause any problem.

I'm fairly certain what your experiencing is ignition related.