TOPIC:

What would be the best way to check the electric system to see if it is the cause for a bike to sputter and cough when hot?

I haven't ridden it myself so I don't know how it feels but it clearly won't pull and letting it cool for as little as half a minute is enough for it to run fine again. Sparkplugs look okay, a bit on the hot side maybe but neither with soot, oil or bright white.

TheForumTroll wrote: ... the best way

"best way" is to use a Kawasaki Factory Service Manual, go through all the recommended maintenance and then diagnose the problem.

Ignition problems generated by heat typically is coil related or bad wiring. Pull the coils off and test them to spec OHM, use a heat gun or hair dryer on the bench to simulate a running engine, careful not to melt the casing. If the OHM rises out of spec you found your problem. When it comes to wiring you should as maintenance check/clean/replace all connections and wires. With your problem start where engine heat and wiring meet. Good luck.

How's the valve clearances look? Being too "Tight" is not good, possibly leading to valve and valve seat burning. Metal expands when hot, having you chase problems, that really are not there. I'd check the clearances on a cold engine, and adjust if required first.

First suspect would be coil. Guess how I learned that.

1) Do all the maintenance in the factory service manual
2) See 1



Unless you just bought it or are in need of a quick fix against having money it is pretty bad advice. Maintenance is for maintenance, not repair or troubleshooting (throwing parts at a problem is not fixing things imho)

The bike was maintained after the manual this summer. The valves are in spec, voltage drop, wires and connections, etc. has been checked. If it was an old car I would have guessed on boiling fuel. I'll test the coils.

TheForumTroll wrote: I'll test the coils.

High voltage breakdown won't show up on a bench test but it's the most common failure mode.

bountyhunter wrote:

TheForumTroll wrote: I'll test the coils.

High voltage breakdown won't show up on a bench test but it's the most common failure mode.

So I can't test them without having some replacements on hand?

yes, unless you can 'drop test' them with a megger, not a tool much used by auto electricians. Probably best to eliminate other causes and replace the coil last -probably just one of the pair out.

If the coil and pick up resistances are a small amount out of spec don't worry about it, also check carefully the femal blade connectors on the coil low tension wires. Does the electronic tacho bounce about ever?

If it is an ignition fault you might be able to use a spark tester to try to see which of the pots isn't firing to trace it further.

More info in the description would be useful, is it spluttering when off the choke or only when really hot, where is it spluttering in the rpm range?

The ATU mechanical ignition advancers can get sticky casing similar problems.

A megger?

The tacho doesn't bounce, but it might not show up as the needle is very sticky and moves very slowly.

Not sure what info is needed, but a bit of history etc.: The bike has been in a barn for 4 years. After it was bought it was fixed up following a factory service manual. New filters, oil and brakefluid changed, new sparkplugs, tank and petcock cleaned, carbs cleaned and synched, wires and connectors cleaned, new battery, valves adjusted, rusted parts exchanged with new and so on. The bike runs great now except when it gets hot it... well it doesn't die or stall completely but it doesn't pull at all and nearly crawls to a halt. Turning it off for a very little pause -like less than a minute- and it runs just fine again for awhile. It runs a bit too lean but not by much as far as I can tell. The sparkplugs looks like the last OK or the Slightly Hot in the chart below depending on where in the RPM range it is tested.




By the way, it is a twin -not my four- in case I didn't mention it

TheForumTroll wrote: 1) Maintenance is for maintenance

AGREED, but without knowing what you later posted, most owners should start there and make sure the basics are in place. Coils were pointed out.

I test my coils on the bench with a heat gun to simulate under the tank conditions (not load). If the OHMs spike above spec, the coil needs to be replaced. Just don't apply direct heat and melt the casing. I have only tested 1 out of 4 original coils to fail.

Good Luck