1999 M900 Carb Fuel? Issues

[koko64]

Ignition components can function fine then fail once hot especially coils.

[Howie]

I had one that opened intermittently.  After replacing it (diagnosed bad on the road) I brought it to a boil slowly.  Failed at 180^o.

[Dellikose]

I'm trying to perform a leak down test, but the engine keeps turning. Is there an easy way to lock it into place...2x4 through the wheel and swingarm? I'm trying to apply 100 psi to the cylinder.

After this test checks out, it's on to the ignition system.

[Howie]

If the engine turns over when air is applied the piston is not exactly on top dead center.

[greenohawk69]

Was this issue resolved?

[Dellikose]

Not yet, unfortunately. I am still running lean on the horizontal cylinder.

I did not get much done over the winter, but now that riding season is back I plan on getting some updates with my findings.

[Dellikose]

Well, this problem is still going on. While I have been able to get both cylinders closer to the fuel mix they need to be, but I am still having a problem with the engine cutting out after riding for 30 minutes or so.

I went for a ride today and had the issue. I rode for about 30 minutes with no issues at all, and then the engine began to bog and eventually died. I would let it sit for 10 minutes, start it up and ride for another couple of miles and then the same thing would happen again...rinse and repeat until I got home.

The only thing that I can think of that I did not physically check myself was the pickup clearance...anyone have a good walk-through?

I'm always open to other suggestions

edit: I'll probably just go through the entire ignition system as Koko mentioned.

[koko64]

You'll hate me if it's a carb problem

On these old bikes I just upgrade/refresh the ignition components to get them running smoothly and upgrade everyday performance.

I have seen similar symptoms from ignition pick ups, ignition relays and coils going bad. You may have had more than one issue on an old bike, both fuel and ignition, so that it throws a curve ball re diagnostics. On old vehicles there may be a number of components that have degraded over time to all contribute to rough or unreliable performance.

So, with that in mind I find myself fitting Exactfit coils, new pick ups (if I have any doubt about them), ignition leads, maybe an Ignitech I tune for smoothness (if any doubt about the boxes), manual tap (if it has a vacuum tap), new needle jets, carb service, jet changes if required and tune. You have completed much of this.

[greenmonster]

having a problem with the engine cutting out after riding for 30 minutes or so.

When that happend to me, it was a malfunctioning diaphragm in the fuel pump.

[koko64]

Maybe try a Mikuni Rectangular pump. Economical option.

[Dellikose]

I rebuilt the fuel pump with a Mikuni kit. I tested the pump by pulling a vacuum through the hose and I got some good squirts coming from the outlet hose, so I feel good about it. I will keep it on the list possibilities though.

I'll get out the multimeter and start getting some readings and digging into the ignition. Electronics are not my strength, so time to learn.

[Howie]

When the bike quits on you (you need to be fast) get out your ohmmeter.  The two wire plugs at the ignition modules are from the pick ups.  Each coil should read 95-100 ohms.  The other option, which eliminates operating a faulty bike, is remove the pick ups and boil them with an ohmmeter attached.  If they pass first determine which cylinder is misfiring (if that is the problem, I didn't re read the whole thread) switch modules and see if the misfire moves to the other cylinder.  No change do the same with the coils.

[Dellikose]

Just so I have the nomenclature correct...

Ignition modules are the 2 black boxes...Kokusan. What is their function?

Pick ups are on mounted behind the engine cover, and are mounted to “pick up” the spark timing from the flywheel.

Coils are the 2 black cylinders next to the rear of the air box. They step up the current to be supplied to the spark plugs.

When the bike begins to die, it really feels like it is both cylinders at once. I noticed popping from the exhaust when it was happening - like it was lean. That would lead me to think fuel starvation, but it is dead simple fuel system that I don't see where else to look. No vacuum petcock, new fuel lines with no kinks, and rebuilt fuel pump with new lines to it.

After I check the ignition I will go back to the carb, but I've been in there so many times it makes me wonder what else is left to check.

[Howie]

Re read the thread.  Pick up clearance is .6-.8mm.  You need a non magnetic gauge.  Wow, this has been going on for two years.  My only two suggestions are;  a) check all grounds  b) start from scratch, item by item.  All I can think of is one thing got fixed, one thing got broken.  Part of from scratch is fresh fuel.

[koko64]

Yep, I had to as well.
Might as well start fresh.
Besides trying another fuel pump (little "22" model is 20 odd bucks iirc), a thorough check of the ignition by a pro is in order. If you can't access a pro then slow and carefully considered diagnosis is the key.  It's called electrickery for a reason so follow Howie's guidance very carefully.