Motorcycle no go vroom!

[jmerlino]

1982 R100RT

Just had it into Max BMW for a service. New plugs, fluids, etc. Rode it to work a couple of times. One morning, I had just gotten out of my driveway when it just stopped. No warning, no nothing. Now it won't start at all.

The battery and starter are fine. It cranks like crazy. Lights come on and everything. There's just no action when it's cranking. My first instinct was the ignition control unit, so I replaced it, but it didn't help.

Anybody have any ideas?

[20774]

Twin coils? Check the small jumper wire between the two coils...

[jmerlino]

Will do!

[manitou_commando]

As you say it cranks, you may want to narrow your search to 2 likely areas: Have you checked for spark and have you checked for fuel delivery to the carbs?

[Rod Sheridan]

Joe, your motorcycle isn't meant to go VROOM, it's an airhead.

The closest I can come to describing the sound, is that it's similar to a corduroy snake, it makes WHIFF WHIFF sounds. (At least my R90 does)

If it goes VROOM you've accidentally purchased a Japanese sport bike.


That said, you obviously have either no spark or no fuel, probably no spark. Start checking the standard suspects...........Rod.

[jmerlino]

As you say it cranks, you may want to narrow your search to 2 likely areas: Have you checked for spark and have you checked for fuel delivery to the carbs?

Carbs are getting fuel. It's clearly a spark problem. I assume it's not the plugs as they were just replaced (although I will check that). What else should I check?

[20774]

I assumed you checked the jumper wire between the coils...

If you think it's spark, remove each plug and stick them back into the high tension leads. Then ground the threads for each plug to the fins of the cylinders. Make sure they are positively grounded...you want a path to ground for the spark, just as if it were screwed into the spark plug hole; no path to ground and the added resistance could cause a problem with the coils. Then hit the starter...you should see sparks and they should be bluish...a weak spark will be yellowish. Of course, no spark and you'll need to follow things backward.

I've not see this happen, but people say that plugs will spark outside the compression chamber but sometimes will not fire under compression. It's not clear to me how that can happen, but plugs can misbehave. You said they are new plugs...probably they're OK. Just a note that sometimes they could be bad out of the box.

[jmerlino]

I assumed you checked the jumper wire between the coils...
The jumper wire is there, but I can't tell if it's good or not. I need to find my multimeter and do a continuity check.

I think I may just turn it back over to Max and let them figure it out. I don't really have time to be futzing around with it.

[Bill Burke]

With minimal futzing, you can perform one simple check:
1. Find your multimeter (and make sure it is functional);
2. Put the meter setting on "ohms";
3. Pull both spark plug caps off their respective plugs;
4. Insert one meter probe into one cap (making full contact in the top of the cap) and insert the other probe into the other cap; and
5. Read the meter.

Your resistance should be in the neighborhood of 20K ohms. 18 is fine and 23 is fine. Way more and way less is not fine.

This simple test is a handy way of pretty much eliminating a spark plug cap, plug wire, and coil failure.

[Mongo]

OMG it's Joe!
:wave Hi Joe