Engine misfires

[suzukizone]

1981 GS850G, 77k miles +/- Full Vetter fairing with lowers.

Posting here as not sure if fuel or electrical issue.

Roadkill having issues. Will do my best to describe as hoping someone might be able to point me in best direx.

Rode about 150 miles a few weeks back with the ole girl was running so sweetly and kept it up until about a week ago. Didn't touch anything since then but she began "breaking up" but erratically, that is on a ride the problem can come & go. Also it is not a steady misfire but irregular unlike a cylinder dropping off the job & bike running as a triple. Of course significant power drop as this goes on.

Seems to occur mostly on acceleration whether very gentle or slightly brisk (I rarely twist the throttle vigorously although had to pass a slow farm vehicle last week and it pulled ok up to about 6k). Most of the problem seems to start between about 2800 to just over 4200 RPM or so. Once misfire kicks in, seems to affect the RPM range a bit below that and definitely as high as I can push the engine speed.(5k or so) Throttling off a bit has at times let her recuperate but soon problem is back. Other times throttling back has no effect. Does not seem to misfire when I do throttle back until I reapply throttle. Attempts to accelerate harder usually much worse but I rarely go there normally. Up until the last few miles, the idle has been nice and steady and blipping the throttle has yielded crisp & immediate response. Better than it has been in years but just before I put her away last ride, was a little rough on the last few minutes of the ride.

Thought it was fuel starving but with the fuel tap in the on position allowing full flow there is still the misfire. The vent for the tank is not pinched.

Not 100% sure if just one cylinder or 2 but really feels like one as still has a bit of power in spite of missing.

Not sure if fuel or electical/ignition. Plugs burning very evenly across. Drained gas into glass jar (about a quart and then thru a coffee filter into jug. No sign of dirt/water.
Had tried using both reserve and then "ON" positions on the fuel tap during the "sputtering) to see if there was any restriction. No effect.

Made sure the plug caps (especially #s 2 & 3) were securely on the plugs & free from any dirt or corrosion. Plugs have 500 miles or so on them.

Have just cleaned the low tension connectors that trigger the coils and applied di-electric grease but not tried running the bike as they didn't look like the problem and a hassle to put together & break open for each step.

Am going over all ignition wiring and HT leads to plugs. Do not so far see any issue that would cause shorting.

Hoping it is not failure of the Ignitor box as do not believe there is a test. Will test coils with info from The GS Resources but not sure this would show anything that would create this erratic problem. Sorry if word, just trying to put in as much info to save asking questions back that I could have told you initially.

That's where I am, any idears not matter how off the wall will help me run through checking.

Thanks for any tips & guidance.

DH

[fastbysuzuki]

Do you have a prime on your fuel tap if so try to run using that to test as on and reserve both use the vacuum side on the tap where as prime bypasses the vac side. After test turn it back to run.
there is an ignition and igniter test http://members.dslextreme.com/users/...-ends.html#A11
what voltage are you getting at the coils?
test the resistance across the plug caps as they each have a resister within the cap. Between the two HT plug caps of the same coil, secondary HT winding, approximately 30 - 35 K ohm

[suzukizone]

Do you have a prime on your fuel tap if so try to run using that to test as on and reserve both use the vacuum side on the tap where as prime bypasses the vac side. After test turn it back to run.
there is an ignition and igniter test http://members.dslextreme.com/users/...-ends.html#A11
what voltage are you getting at the coils?
test the resistance across the plug caps as they each have a resister within the cap. Between the two HT plug caps of the same coil, secondary HT winding, approximately 30 - 35 K ohm

Hi, Thanks, as stated did try switching to both RES & PRIME during events,.....no effect.

Will test voltage at coils & get back. Is this read at the primary leads? Ohms there BTW were 4.0 & 4
Cannot get any readings across the HT leads. I had put Dyna Coil leads/caps on years back & remember now that this was done cannot get a read on the secondary coils. really don't want to dig them out & read across the pins in the coils unless that is a last desperate measure.

Did see some slight tears in the plug cap area on #2 & #3, probably from using the wrong tools to be sure the plug caps were pushed onto the plugs securely. With the Fairing, it is murder to get my fat arthritic hands to push those two on without removing tank each time I am looking at the 2 inner plugs but guess I have to do it. Have sealed up all damage with "Liquid Electrical Tape" stuff, triple layer so should not be an issue. Have cleaned out the plug boots w/ Contact Cleaner and pipe cleaners. Am going to use Di-Electoral grease in the plug caps to get better connex and keep any corrosion from forming. Hoping I got lucky & stumbled onto a cure,.....

But keep those cards & letters coming.

Read the bit on the ignitor test. Would that spot an erratic problem like this or just a dead out on the unit? Will read it again & try if no success on test run tomorrow.

Thanks again!!!!

DH

[tom203]

Yes try the petcock in "PR" spot..and while you're fiddling with petcock, maybe its vacuum line to #2 carb is leaking, causing # 2 to misfire,so do this test..

Try this... remove both lines from petcock: get some clear vinyl tubing that fits snugly on petcock vacuum fitting. In "on" and "res" fuel,show flow when you suck on this tubing- otherwise it should not. Any signs of fuel in the vacuum tubing means the petcock diaphragm is likely leaking.maybe just when bike is running but maybe at alltimes.

[suzukizone]

Yes try the petcock in "PR" spot..and while you're fiddling with petcock, maybe its vacuum line to #2 carb is leaking, causing # 2 to misfire,so do this test..

Try this... remove both lines from petcock: get some clear vinyl tubing that fits snugly on petcock vacuum fitting. In "on" and "res" fuel,show flow when you suck on this tubing- otherwise it should not. Any signs of fuel in the vacuum tubing means the petcock diaphragm is likely leaking.maybe just when bike is running but maybe at alltimes.

Since I don't know the answer, I will try this too. Not sure this is what is up. # 2 plug does not show any signs of running rich but I can see this test would show a leak so worth a crack. A 37+ year old diaphragm can always be a suspect. Years back I tried to replace it with an aftermarket diaphragm as OEM no longer available. Just as preventative measure. Tried 2 of them, I forgot if they didn't fit or leaked but, I put the original 1981 OEM item back in it's still in there. Never found an issue. I have done this test a few times but never a sign of leakage

Until it is corrected, like the great Brit detectives on TV, I will pursue all avenues of investigation.

The game is on Watson!

Thanks for your input.

DH

[scratch]

How old is the battery? Have you checked it and the bike's charging performance from idle to the idle where it starts to falter in the rpm range?
The bike has 77k on it... with 77K a compression check makes good sense.
Did to check the air-filter box for obstructions?
Did you try to run it with the gas cap off? (Tank venting issue is a possibility that is easy to test then cross off the list)
Can you see anything funky happening with your bowl vent tubes?
Is there really no test for the ignitor box?
There may be a blocked main jet, pick-up tube clogged, failed float, loose linkage...
Was it crazy hot and humid when this happened? (just taking notes)

"any idears not matter how off the wall will help me run through checking"
Two insane "act-of-mother nature" relatable incidents:
1. A rodent made a nest in my airbox once when I left a bike alone for a weekend... took me a month to figure out.
2. Found a wierd moth cocoon in a left handlebar switch that fouled my directionals with some sort of short, supose that could happen in a right handlebar switch and drain some ignition voltage?

Good hunting and hope you get it figured!

[tom203]

We need to rule out the simple stuff first..like the petcock. (driving around on a 37 yearold petcock is asking for trouble). Testing the charging system is a simple one....in case voltage drops off randomly and interferes with ignitor.
checking the ignition system is needed: you must inspect /test the small signal coils and their connection to ignitor box - go here for some ideas. Fairings make for fun during troubleshooting!

http://members.dslextreme.com/users/storagecliff/images/electrical_odd-n-ends.html#A17

[Steve]

I just went back and re-read the original post. The thing that caught my eye was the "erratic", "intermittent" and "occasional" aspect.

Fuel problems related to a petcock would not make the bike "run like a triple", they would affect all four cylinders. It sounds considerably more electrical to me.

One thing I would try is to remove the spark plug caps from the wires, trim about 1/2" from the end of the wires and put the caps back on. Yes, they are screwed on for more mechanical integrity, but even those connections can get dirty and corroded. Snipping the ends of the wires will get you into fresh wire and better contact.

.

[suzukizone]

I just went back and re-read the original post. The thing that caught my eye was the "erratic", "intermittent" and "occasional" aspect.

Fuel problems related to a petcock would not make the bike "run like a triple", they would affect all four cylinders. It sounds considerably more electrical to me.

One thing I would try is to remove the spark plug caps from the wires, trim about 1/2" from the end of the wires and put the caps back on. Yes, they are screwed on for more mechanical integrity, but even those connections can get dirty and corroded. Snipping the ends of the wires will get you into fresh wire and better contact.

.

Thanks Steve, I am sort of one with you on the fuel (at least as to flow from fuel cock to all 4 carbs) as being unlikely. There could be some issue with an individual carb as Scratch had in his multi checkpont list (Thanks Scratch, printed that up & taking it into the surgery with me to go over all points).

As to cutting off the ends of the HT leads, the spark plug ends are set into the leads. Not sure I can cut them off as how would I then effectively replace the ends that look to be accurately crimped on by machine. These are not the stock NGK style caps but the "snap fit" as are installed on the Dynatek wires. Can send image if necessary. These are the fittings used when you leave on the little screw on tips on the spark plug ends.

I have cleaned out the insides of those metal "clips". I was going to apply di-electric grease to the caps/plug tips BUT- IS THIS WISE WITH THE AMOUNT OF HEAT THERE???? Can the Di-Elec grease hold up to that heat or would it bake and create its own problem??? Any ideas? Haven't done it yet & won't until I get some consensus.

Thanks again, off to work!

DH

[suzukizone]

How old is the battery? Have you checked it and the bike's charging performance from idle to the idle where it starts to falter in the rpm range?
The bike has 77k on it... with 77K a compression check makes good sense.
Did to check the air-filter box for obstructions?
Did you try to run it with the gas cap off? (Tank venting issue is a possibility that is easy to test then cross off the list)
Can you see anything funky happening with your bowl vent tubes?
Is there really no test for the ignitor box?
There may be a blocked main jet, pick-up tube clogged, failed float, loose linkage...
Was it crazy hot and humid when this happened? (just taking notes)

"any idears not matter how off the wall will help me run through checking"
Two insane "act-of-mother nature" relatable incidents:
1. A rodent made a nest in my airbox once when I left a bike alone for a weekend... took me a month to figure out.
2. Found a wierd moth cocoon in a left handlebar switch that fouled my directionals with some sort of short, supose that could happen in a right handlebar switch and drain some ignition voltage?

Good hunting and hope you get it figured!

Thanks Scratch, gave me lots to do.

1. Battery less than 2 years old, Yuasa AGM kept on Battery Tender Jr. whenever not on the road. Will test Batt voltage & charging sys to be sure but do not suspect there is a problem here.
Top end rebuild about 20k ago w/new pistons/rings/valves lapped/regular checking of clearances. Will check compression cold & again when get eng warm.
3. Will check airbox, all boots & manifolds look OK w/good fit.
4. Can try running w/gas cap popped but the air relief to the tank is via a hose that presents outside air pressure to vent opening just under the cap on the model. Don't think that would be the seat of the prob. Also will go over all carb related info. Won't go into carbs until I complete some of this & try a test run. Could be something there on one of the carbs?????
5. Tom203 sent link for a lengthy test of ignition. I just printed this 5 pager up and taking it out with me. Includes test of ignitor as well.

Weather was hot but not as bad as it could have been. Up into the 90s but some riding where this happened was in the lower 80s. BTW I do NOT ride in rain so that's out as a poss. Nicht, Nyet, Nein No No No.

Thanks so much.

DH

[suzukizone]

We need to rule out the simple stuff first..like the petcock. (driving around on a 37 yearold petcock is asking for trouble). Testing the charging system is a simple one....in case voltage drops off randomly and interferes with ignitor.
checking the ignition system is needed: you must inspect /test the small signal coils and their connection to ignitor box - go here for some ideas. Fairings make for fun during troubleshooting!

http://members.dslextreme.com/users/...-ends.html#A17

Thanks for that link. I must have missed finding it. Printed all 5 pages & heading out to the shed before wife finds me to do something.

Still don't seem to be able to get a reading across the HT leads & see in DynaTek's website that these leads are some sort of fiber rather than metal conductor. My notes from past indicate I never have gotten a reading tho did with stock leads & caps. Yet bike ran approx 20k miles using them. I think you can't get a reading with them.

DH