OK - re my GL1100 - but greater knowledge needed.

[WingNutJC]

Decided to run my 1100 hard thru the gears to the red-line.

1st - 8k rpm. OK
2nd - 8k rpm - almost - but OK
3rd - nothing over 4-5k. Like it had lost a plug.

Felt like something had just broken in that instant. Grrr.

After that - could not rev beyond 4k under any sort of load.
Starts and idles like a sewing machine, and is good to 3k rpm. After that - lots of blubbing (that's a technical term ...).

Changed out everything ignition related. No improvement. Valve clearances all good.

Hoping to hear of a fault diagnosis re our GL engine wizards.
(Not holding my breath ...)

Cheers.

WingNutJC

[julimike54]

If you want my guess, it's fuel delivery problems, pump, filter/screens, carbs. That and some money would buy a cup of joe

[WingAdmin]

Missing that starts suddenly at a specific RPM is almost always spark-related.

[WingNutJC]

Thanks guys. Will keep you posted.

[Kurt J]

May be the diaframes stuck open in the carbs......

[cwatts9929]

Actually, sounds like you might have busted a diaphragm in one of the carburetors.

[Old Fogey]

Actually, sounds like you might have busted a diaphragm in one of the carburetors.

There are no diaphragms in the 1100 carbs.
If it runs sweet up to 3k, my money is on blocked main jet(s). The idle/slow running circuits will let it rev to that level easily, but then you transition onto the main jets.

[indianakid]

OK....... "There are no diaphragms in the 1100 carbs." ............. That is incorrect. There are four Idle Air Cut Off diaphragms (one for each carb). When the diaphragms fail it will expose the idle circuit to direct manifold vacuum.

[Old Fogey]

Yes, I stand corrected. I was thinking you meant Slide control diaphragms as in the 1200 carbs. But damaged air cut-off valves wouldn't cause his higher revs problems. I have seen bikes running well without any diaphragms fitted at all, and his idling sounds like it's ok.

[indianakid]

if one was to intentionally eliminate the idle air cut off diaphragms the passage from the manifold side of the carb throat would be also be intentionally blocked. if it wasn't (or in the case of a damaged / defective diaphragm) the manifold vacuum would draw in air from the idle air jets causing an effect similar to a vacuum leak and fuel from the idle jet in the float bowl chamber causing a rich condition to further compound the problem.

[ekvh]

WAG suggestion: check the vacuum advance. Maybe the tube fell off, was blown off. Or you have a leak in the canister on the back of the motor. I say this because you say it runs good to 3-4K, right where the advance should be moving/ moved.

Kind of a pain because of its location but, if the tube looks okay, you should be able to use the human vacuum pump (mouth) or mechanical if you have one, to apply and watch for visible movement of the arm in the advance mechanism.

[f1xrupr]

You dont supose a loose timing belt jumped a knotch do ya?

[WingNutJC]

Hi Guys.

I think it's a coil breaking down.
New coil arrived today. Will fit tomorrow.

The sudden way in which the problem came on, for me, was the clue.
On the way home I thought of every possible disaster, including a valve touch. Errrk.
Bike had been running to 6k rpm without the slightest hiccup.
Would idle smooth as a sewing machine - so bent valve? Unlikely.
Sudden fuel blockage? Mmmm ok - but tank, carbs and passages previously back flushed. (Believe me - if I had a $$$ for each time I've had them out and in pieces ....) New fuel filter.

Will take very light throttle up to 4k, but any more throttle = misfiring.
BUT - at 2-3k rpm, WFO throttle = same misfiring.

Back when the problem began, all I can surmise is that when rpm was held for longer at 8k rpm, it was enough time for that sustained high voltage to punch through coil insulation.

Anyway - will know tomorrow.

Watch this space.

Cheers.

JC.

[purgeraptor]

I suddenly had a high rev misfire on my GL, turned out to be a cracked spark plug cap.
It still revved out though, but badly.....

[DenverWinger]

I got a couple cylinders cutting out on my 1100 over 5k RPM on hard acceleration, otherwise she runs wonderfully.

Initial thought was carburetors since they haven't been touched except for synchronizing since 2005, rebuilt them when I first put the bike on the road. But since it's TWO cylinders cutting out in unison that's a pretty good clue it's a coil breaking down instead. 'Nuther project for when things get warm.

Replaced sparkplug caps several years ago, had a couple that would start snapping sparks to the head in the rain, and then one finally gave out to where it wouldn't even fire the plug in dry weather, just sparking from the cap to the head.

[WingNutJC]

Thanks DenverWinger. Sounds just like what mine is doing.

Finished fitting new coil into the LHS about 10 minutes ago; about to get helmet and go for a ride.
Had it in the RHS last night but problem persisted.
Taking a BIG breaths right now.

Back soon.

[WingNutJC]

Hmmmm - only marginal improvement.
Both original coils failed? Not beyond bounds of possibility but thought it unlikely.
Screwdriver between plug caps and heads. All good.
Revved it in a dark garage: no sparklies.
All new plugs btw.

Hmmmm.
Time for second new coil.

Mumble grumble ....

[WingNutJC]

PROBLEM SOLVED.

Looks like it was the earthing of the CDI units.

Had reached the point where I was completely out of ideas, and just to feel like I was doing something I unscrewed the CDI units in case any corrosion between the heat-sink bodies and frame could be causing problems.

Nothing unusual looking, but I brightened everything up and re-fitted (with a coating of copper grease). Didn't disconnect the units.

Engine now revs cleanly past 4000 rpm.

Looks like the heat-sink earth must form an active part of the electronics, despite there being a green earth wire exiting each unit.

However, something in the back of my mind is not 100% convinced, yet I can't think of anything else I've done (or disturbed).
Time will tell.

Cheers.

[WingNutJC]

Problem found.

After replacing plugs and wires with no result, I bit the $$$ bullet and replaced both coils.

Well .... O.M.G. ....

Not only was the misfire gone, but the extra performance ...

Seat of Pants dyno says 15-20%.

Not just feeling a little sharper. Nope. It got the chemically sharpened, laser polished, Samurai sword treatment.
And from 4000rpm up it just goes!!!

In hindsight, the original coils must have been struggling for years.

Huge object lesson regarding ignition performance.

[WingNutJC]

PROBLEM SOLVED.

Looks like it was the earthing of the CDI units.

snip

However, something in the back of my mind is not 100% convinced, yet I can't think of anything else I've done (or disturbed).
Time will tell.

Well that fix didn't last.
I'm sure there was also discussion about the incorrect use of the term "CDI", as well as the bodies of these units not needing to be earthed.
Posts removed?

[WingNutJC]

Oh wait.
Just found all that.

viewtopic.php?f=4&t=41427