Weird stalling issue

[geek]

Alrighty, I just picked up a 1990 750 Kat three weeks ago.

The past week I've been plagued with a wierd stalling problem.

I've been riding along(mostly 50-60kph and less) when the motor cuts out as if I'd hit the kill switch. Sometimes I can quickly pull the clutch in, go up a couple of gears and release to bump start it. Often though, it's pull over to the side of the road and wait 20 minutes or so before it'll start again.

If I try to start it immediately after it stalls, you can hear at least one cylinder firing and the bike trying to start. As soon as I release the starter button it stalls out.

My suspicions are a heat related failure of some sort. The majority of the time it's happend I've been slowing down using engine braking with the RPM's hovering around 3500 - 4000 RPM. It usually happens at stop lights after slowing down and stopping. The bike idles fine at the red light, but as soon as I give it some gas to pull away it stalls dead. The last time it stalled I was coming down a somewhat steep hill in heavy traffic and using the engine to maintain speed. Once I got to the bottom I tried to accelerate and stalled out. Thankfully I was on my way to my mechanics to get a new rear tire and brakes installed, so they came to pick me up.

It's going into the shop today, but would appreciate any insight anyone here might have. The mechanic suspected that it may have been the kick stand kill switch so we disconnected that but the stalling problem persists.

The previous owner did mention that it did this very occasionally and would only do it for a few revolutions but start up immediately again. It's also had a few times in the mornings that it wouldn't immediately start, no spark. Wait 10 minutes or try to bump start it and away it goes. This certainly does sound like it's related.

[trinc]

cdi or coil(s). you could lift the tank, put a fan on the bike to keep it from overheating, start the bike - then use a hair dryer and a can of freeze spray to isolate which part is failing.

tim

[geek]

Well, I now know it isn't the carbs...

I took it into the dealership near my place, the tech there suspected it was the carbs and not electrical.

So, they did a major tune up on it, Valves adjusted, cleand and synced the carbs, new plugs, oil change, etc.

Take it out, purrs beautifully, more responsive and much smoother feeling.

Sure enough, 20 minutes later she stalls again.

Call the dealership, they've closed by this time and no one would be there by the time I got the bike back to drop it off. Fine, I'll get it home eventually.

Wait 20 minutes and sure enough it starts up again.

I ride home all nice and slow, leave an intersection and part way through it stalls and restarts, surges ahead and stalls again(in first gear, this wasn't smooth) The sudden surge caused me to lose my balance(didn't help that the road was quite rough and slanted in several directions) so down I go.

Thankfully the only physical damage was my left mirror broke off. No damage to me, so that was a good thing. Couple of pedestrians helped me get the bike upright and pushed to the side of the road.

After a few minutes of calming my nerves(this was my first time falling), try to start the bike. Nada.. nothing. totally dead, the starter won't even click.

So the fall jarred something loose and it won't even turn over now.

Of course this had to happen in a bad section of town, so there was no way I was going to leave it parked there over night. A tow home and it goes back to the shop tomorrow.

ARGH!

[Guest]

I'm going to agree with Trinc and say coils. Mine did the exact same thing... It would get hot, then start to run bad and die. Let it sit for a few minutes, it would fire back up and run til it got hot again, then dead.

[geek]

I'm going to agree with Trinc and say coils. Mine did the exact same thing... It would get hot, then start to run bad and die. Let it sit for a few minutes, it would fire back up and run til it got hot again, then dead.

That's what I'm going to insist they check out when the bike get's picked up today.

Frustrating though, the previous owner kept really good maintenance records. But he did it all himself, I now know he's no mechanic. Even said the valves were done last season, the mechanic said they were waaaayyy out of adjustment. He also rebuilt the carbs last year, but they were in rough shape as well. Oh well, it is a 15 year old bike, bought used, can't expect perfection right? Well I suppose I could, but I'd be bound for some big disapointments.

...now to go search ebay for a new mirror....

[geek]

PROBLEM SOLVED!!!

Well, the problem was finally solved.

I finally got a chance to speak directly to the head mechanic about this and bypass the service writer(owners son) of the shop(Suzuki dealership).

He suspected that perhaps the carbs were running too lean as when he took the bike out he could get it to stall but it would start up immediately afterwards(not what was happening to me). Anyhow, since the bike had a K&N Filter he thought that maybe changing it to a stock filter would fix the problem, it did, but only for him. I picked it up, started making my way back to work and it stalled again. Managed to get it within a few blocks of the shop before it stalled once more and ended up pushing it the rest of the way.

The bike wouldn't start once it was back at the shop and the owner overheard what was going on and suggested the mechanic use (and I may be wrong on the terminology here) a "pulse detector" to see if there was a signal coming off the pickup coil that hangs off the end of the crankshaft.

Dead! once the bike cooled down it started up again.

What's weird is the intermittent behavior with this failure. Usually when this goes the bike will stall as soon as it heats up and not start again til it's completely cool.

The part he removed definitely had some problems. The wiring was really stiff and brittle, plus the wires in the harness had all the colour bleached out of them. It looks like the bike had overheated in the past and this caused the problem.

It was replaced with a used one out of a GSXR and the bike has been totally reliable and smooth running ever since. YAY!

[The CyberPoet]

Re: PROBLEM SOLVED!!!

The part he removed definitely had some problems. The wiring was really stiff and brittle, plus the wires in the harness had all the colour bleached out of them. It looks like the bike had overheated in the past and this caused the problem.

It was replaced with a used one out of a GSXR and the bike has been totally reliable and smooth running ever since. YAY!

Q: Do you know which parts of the wiring harness were replaced? Was it the plug wires, or other parts?

Curious
=-= The CyberPoet

[geek]

The mechanic labelled it on the invoice as "pickup coil".

It actually lives in the oil bath as a plate that surrounds the end of the crankshaft. There is a small magnetic(?) sensor with 4 wires attached to it that sends signals to the ignition system as to position of the crank and allowing the system to fire.

The coil and wiring harness, including a rubber plug that keeps the oil in, are replaced as one. To do the job, the right fairing and gas tank have to be removed as the tail of the harness is located under the seat/tank area.

[The CyberPoet]

Thanks geek -- I know exactly which parts you are talking about. Glad to hear it was resolved.

Cheers
=-= The CyberPoet

[Markchouinard]

Hmm. First things first.. The SEARCH Option on this forum is the best thing since sliced bread. I have an 89' Kat 750 with what I believe to be exact symptoms and found a realistic solution in 30 Seconds!

Thanks for Pushing the issue further CP, and thanks for the Updates, Geek!