'83 GS750EF, No combustion in #4 cyl.

[Guest]

Tip: Don't let your bike sit for three months because life is too hectic (and its cold), find #4 pipe cold after idling when you finally go to ride it and then pull the carbs to check them out and rejet....over a period of five months.

You'll have problems....

So last fall I had a cold pipe on #4 after idling, spark was there so I assumed a stuck float , needle or something due to improper storage. I wanted to take a look at the carbs anyway since they'd been on for a couple of years and I needed to replace the mains with 122.5s since they had (I'm pretty sure) 117.5s in them.
Bottom line, I pulled the carbs and swapped out the mains. I checked the needle jets while I was in there and everything was pristine, not even sediment in the bowls.

Carbs are now back in, all boots in good condition, clamps tight, fuel in every bowl, good spark, slide in #4 carb moves freely, the rubber skirt is OK and I can feel suction at the test port on the boot (I've got my Carbtune hooked up) but I'm still getting no heat out #4. 1,2&3 all sizzle the spit off of my finger but I can hold my finger on #4 pretty much as long as I want. Its warm but nowhere near hot.

I also "bench synched" the carbs according to the factory manual with the first little bitty bypass port showing and just the slightest hair of the second port. Thats what the drawing looks like so thats how I set them up.

Air jets (or whatever the real name is) are 1.25 turns out and I've tried up to 3 turns out.

I guess my next step is to bring home my compression tester from work and/or buy a leakdown tester.

Am I missing something, any ideas? What would you recheck first...

Thanks in advance.
/\/\acmatic

P.s. Yeah, I'm back. Life got a little hectic there but my new job allows me time to breath.

[80GS750]

do you have spark?

maybe a bad plug or wire....

if spark is good, than it has to be the carb assuming your valves are in check....

[Macmatic]

Yep I've got spark. Not sure how though

I was looking at the bike again after doing some reading here and I found that my 1&4 coil is only getting 5.7 volts! The 2&3 coil is getting 11.2 volts.

I guess I'll be rechecking connections and looking for the voltage loss tomorrow! I want to do the relay mod now that I've read about it but I want to find the fault first. I hope this is the real issue.


So much for inline spark checkers....
/\/\ac

[chef1366]

Is there fuel in the bowl? Switch plug wire 1&4 and see if the problem follows. Did you check the connection on the spark plug boot?

[Macmatic]

Is there fuel in the bowl? Switch plug wire 1&4 and see if the problem follows. Did you check the connection on the spark plug boot?

Chef,

Yep, I've got fuel in all the bowls. I tried a different coil and had the same issue.

Update:

Now I'm trying to figure out where I'm losing voltage. On the Right coil I show 11+volts and on the Left I'm showing 5.5 to 6 volts. Checking Orange to battery negative gives me near full battery voltage and checking White to Batt Pos shows me the same 5.5 volts or so. Just corrosion in the wire right? Well from the coil terminal to the ignitor plug shows something like .003ohm resistance along the white wire.

Any fresh ideas? Electrics aren't really my thing so I might be missing the easy answer here.

/\/\ac

P.s. Can anyone tell me why my "been there" map isn't showing? I saved it and made it a 17.5k file and uploaded it from the control panel... but no icon.

[Outlander]

Something I found on my GS550E was the signal generator. I don't know if your bike has points or not, but when I pulled the cover off of my signal generator, I had found that it was rusty. I used a piece of emery cloth to clean it up, and have found that I got better spark.

Just an idea.

[Nicholaschase29]

If you take your bike for a ride can you feel that cylinder kick on once you get up to a certain RPM? My guess would be you need to clean the #4 carb (or all of them while they're out)

[chef1366]

5.5 to 6 volts won't get it done. Run a wire directly from the battery to the coil and see if it fires.

[Macmatic]

got dem 25 year old wiring blues....

So here is where I stand now.

With all wires off the coils AND plug out of the ignitor I get:

Either O/W coil wire to battery groud = battery voltage minus about .5v

Either O/W coil wire to Bk/Y wire at ignitor plug = batt voltage - @ 0.7volt

Either O/W coil wire to W wire at ignitor plug = just about noting.

Resistance of W wire between coil connection and ignitor box connection = .3 ohm
Resistance of Bk wire between coil connection and ignitor box connection = .4 ohm

Reading between Bk/Y and battery + reads battery voltage -.5v
Reading between W and Battery + reads about nothing, ghosting but never settles.

Those are all with all the connectors at coils and ignitor OFF.

So I'm getting pretty much full voltage at one coil and pretty much no voltage at the other. I WAS getting about 6volts on the bad side but after taking apart and cleaning every connection I can find I've lost that .6v. Grr

This is the same across both ignitor boxes that I have. So both are good or both are bad in the same way. Any values I can read internally or across pins on the ignitor box?

I'm pretty sure my fault is in the W wire but I can't for the life of me figure it out. As I said at the start of this thread electrics are not really my strong area but it seems to me like the W wire SHOULD be fine.

According to my wiring diagram the W wrie goes directly from the ignitor to the coil with no connections between. Since I can read good voltage across either O/W and the Bk/Y wire but nothing across and O/W and the W the W must have a break or high resistance, right? Only when I read the resistance it shows <.3ohm.

Any ideas? Please, please make me look like an idiot so I can start getting some miles on!

/\/\ac

P.s. Anyone know how to get the wires out of the coil connectors? I haven't been able to figure out the release yet.... but now I can take the one I broke off into the house to look at it where the beer is colder.

[Macmatic]

If you take your bike for a ride can you feel that cylinder kick on once you get up to a certain RPM? My guess would be you need to clean the #4 carb (or all of them while they're out)

Can't get it out for a ride now but I just finished putting bigger mains in and checking all the jets and bowls for sediment or gunk, clean as a whistle. Now intake boot o-rings too.

/\/\ac

FYI: Anyone who got o-rings from me a couple of years ago, mine were still round and pliable after about 3 years and 10,000mi of riding. I just changed them out to be on the safe side.

[SPARKSS]

[QUOTE=Macmatic;835189]So here is where I stand now.

With all wires off the coils AND plug out of the ignitor I get:

Either O/W coil wire to battery groud = battery voltage minus about .5v

Either O/W coil wire to Bk/Y wire at ignitor plug = batt voltage - @ 0.7volt

Either O/W coil wire to W wire at ignitor plug = just about noting.

Resistance of W wire between coil connection and ignitor box connection = .3 ohm
Resistance of Bk wire between coil connection and ignitor box connection = .4 ohm

Reading between Bk/Y and battery + reads battery voltage -.5v
Reading between W and Battery + reads about nothing, ghosting but never settles.

Those are all with all the connectors at coils and ignitor OFF.

So I'm getting pretty much full voltage at one coil and pretty much no voltage at the other. I WAS getting about 6volts on the bad side but after taking apart and cleaning every connection I can find I've lost that .6v. Grr

This is the same across both ignitor boxes that I have. So both are good or both are bad in the same way. Any values I can read internally or across pins on the ignitor box?

I'm pretty sure my fault is in the W wire but I can't for the life of me figure it out. As I said at the start of this thread electrics are not really my strong area but it seems to me like the W wire SHOULD be fine.

According to my wiring diagram the W wrie goes directly from the ignitor to the coil with no connections between. Since I can read good voltage across either O/W and the Bk/Y wire but nothing across and O/W and the W the W must have a break or high resistance, right? Only when I read the resistance it shows <.3ohm.

/QUOTE]

Hello Mac. What's missing is just the understanding of what you measured. Without the exact schematic for your bike, I researched diagrams on BassCliff's fine site and looked at the 82 GS1100 one, with electronic ignition which is probably similar (or the same) as yours. I'll assume that when you say you had ALL wires disconnected from the coils you meant all of, the white, black/yellow, and both orange/white wires. With those assumptions made AND with the ignitor plug disconnected, probing the ignitor plug and finding voltage between or/wht and the blk/yel is the problem area Note that the blk/yel and the wht wires are the negative switched leads controlled by the ignitor and should have no connection to ground (or anywhere else). Because you see the blk/yel as ground (voltage seen between or/wht and this), you need to find the short to ground in this wire (also check end-to-end resistance of this wire which should be near zero, indicating it's still intact).

Make sense?

[Macmatic]

Well I DID say to make me look like an idiot....

With the wiring as described above (O/W, Bk/Y, W off at coil. Plug out of ignitor) I have an open circuit between White and ground but some connectivity between Bk/Y and ground. Looking at my wiring diagram I see that the Black/Yellow wire goes to the ignitor AND splits off to the instrument cluster. The diagram says it goes to the Speedo/Tach light but I suspect its really the signal for the tach?

When I probe between the main gauge connector and Batt Neg I get:

(numbers on the left are with the connector out of the gauge panel, right is back probed while connected)

Grn/W = Open 7.3 ohm
Blue = 2ohm 1.7 ohm
Gray = 2ohm 1.1 ohm

Blk/Gray= .5ohm .3 ohm
Grn/Y = 1ohm .8 ohm
LG =1.5ohm 1.3 ohm
B = 1.3ohm 1.2 ohm
B/Y = Open 20.5 Mega Ohm
Yel = Open 7.5ohm
Pnk = 356 ohm (oil temp sender) 356ohm
Y/Bk = Open 49.1 ohm
O/Grn = 2.4ohm 1.3 ohm

I guess my next step is to open up the gauges and start looking some something that looks wrong. Any clue from the wiring diagram if any of the above numbers look out of whack? I'm assuming something is bad/shorted inside the cluster and allowing the 20.5 mOhm between Black/Yellow and ground.

Thanks for putting my on the right track!

/\/\ac

Hello Mac. What's missing is just the understanding of what you measured. Without the exact schematic for your bike, I researched diagrams on BassCliff's fine site and looked at the 82 GS1100 one, with electronic ignition which is probably similar (or the same) as yours. I'll assume that when you say you had ALL wires disconnected from the coils you meant all of, the white, black/yellow, and both orange/white wires. With those assumptions made AND with the ignitor plug disconnected, probing the ignitor plug and finding voltage between or/wht and the blk/yel is the problem area Note that the blk/yel and the wht wires are the negative switched leads controlled by the ignitor and should have no connection to ground (or anywhere else). Because you see the blk/yel as ground (voltage seen between or/wht and this), you need to find the short to ground in this wire (also check end-to-end resistance of this wire which should be near zero, indicating it's still intact).

Make sense?

[SPARKSS]

My thought is that you're correct in assuming the take-off from the BK/YL is electronic tach sig (didn't think of that as it didn't show up in any schematics I have.....and all my GS bikes were mech tachs!). Remove the tach wiring and see if she runs (you didn't mention whether the tach worked......that'd be one clue).

IF this doesn't cause the bike to run right......and if the BK/YL wire still shows a ground connection then you still have a short to find (a short to ground here will merely disable that 1-4 coil.....won't hurt the ignitor because it switches to ground anyway). IF disconnecting the tach causes the BK/YL wire to lose it's apparent ground connection AND the bike doesn't run right AND the BK/YL wire shows good continuity between the associated coil and the ignitor plug THEN you need to see whether the ignitor is switching that coil.

Just to confirm.......that when you first looked at postive voltage at each coil (OR/WHT) wire, you were measuring with respect to battery negative AND confirming to chassis (should read the same or VERY close).

IF the basic positive supply to the suspect coil is ok......and the coil is ok (you said you sub'd a known coil), AND you confirm that the ignitor is or isn't switching the coil then you can get back on track troubleshooting. Suspect coil IS being switched ok = problem with ignition secondary.........Coil ISN'T being switched moves to confirming whether the pickup coil for that cylinder has good input to the ignitor. For this test, I'd run both a continuity test (measuring resistance) at the ignitor plug on BOTH pickups to see if there's a difference AND measure the AC voltage generated by each pickup (if the resistance checked out) - also looking for a difference. If no difference found......and you know already that one coil is being fired.......then the problem is the ignitor.

Make more sense?

[Macmatic]

My thought is that you're correct in assuming the take-off from the BK/YL is electronic tach sig (didn't think of that as it didn't show up in any schematics I have.....and all my GS bikes were mech tachs!). Remove the tach wiring and see if she runs (you didn't mention whether the tach worked......that'd be one clue).

Sparks,
Thats the track I'm on, I'm going to see if I can get the black/yellow wire out of the gauge cluster connector and check the voltage at the Blk/Yel and O/W coil connector. If the fault is in the cluster I should see no voltage just like the other coil set but if I have the same condition then the fault is someplace in the harness.

One thing though, the problem has changed since I started working on this. At first I was getting about 11.5v at one coil and around 6v at the other but now I'm not getting anything at the low coil. So... wait... doesn't that mean that one coil should have not been firing and one should have been firing poorly? The one that was fully grounded wouldn't fire would it? It starts right up within a second or so of cranking but idle is poor and I haven't run it long enough to get off choke. Previously I could cut off the choke after a few seconds if I was just going to be idling for a minute or two and now it really needs it to rev much. I can hold the idle with the choke off but it needs a lot of throttle and is obviously missing on at least one cylinder.

I'll have to hook everything back up tomorrow and try to get a baseline again to verify the voltages. Then I can try pulling the signal(?) wire and see if it changes things.

IF this doesn't cause the bike to run right......and if the BK/YL wire still shows a ground connection then you still have a short to find (a short to ground here will merely disable that 1-4 coil.....won't hurt the ignitor because it switches to ground anyway). IF disconnecting the tach causes the BK/YL wire to lose it's apparent ground connection AND the bike doesn't run right AND the BK/YL wire shows good continuity between the associated coil and the ignitor plug THEN you need to see whether the ignitor is switching that coil.

Just to confirm.......that when you first looked at postive voltage at each coil (OR/WHT) wire, you were measuring with respect to battery negative AND confirming to chassis (should read the same or VERY close).

When I first looked at the coil voltage I measured between the two coil connectors for each coil, the o/w and the switched ground for each coil. This is where I had "good" voltage of about 11.5 volts and "bad" voltage of 5.5 or so volts. (overall voltages have dropped slightly because the charge is down to about 12.0 volts now.)
I also checked from the O/W lead for each coil and the battery ground and got about .5v below battery voltage. I didn't check to frame ground but the battery is triple grounded with one to the case, one to the frame and one to the R/R.

IF the basic positive supply to the suspect coil is ok......and the coil is ok (you said you sub'd a known coil), AND you confirm that the ignitor is or isn't switching the coil then you can get back on track troubleshooting. Suspect coil IS being switched ok = problem with ignition secondary.

The part below seems pretty clear but I'm missing something on the paragraph above. If the 12v+is good to each coil and the ignitor IS switching each coil as it should then there isn't a problem, right? Unless secondary means its the HT wires or caps. I haven't checked that value yet... Man... if this is all over a corroded or loose terminal in a plug cap....I'm actually going to be pretty happy about it.

. Coil ISN'T being switched moves to confirming whether the pickup coil for that cylinder has good input to the ignitor. For this test, I'd run both a continuity test (measuring resistance) at the ignitor plug on BOTH pickups to see if there's a difference AND measure the AC voltage generated by each pickup (if the resistance checked out) - also looking for a difference. If no difference found......and you know already that one coil is being fired.......then the problem is the ignitor.

Make more sense?

Thanks for the help, I'll post again tomorrow night after I do some testing.

/\/\ac

[SPARKSS]

Sparks,
The part below seems pretty clear but I'm missing something on the paragraph above. If the 12v+is good to each coil and the ignitor IS switching each coil as it should then there isn't a problem, right? Unless secondary means its the HT wires or caps. I haven't checked that value yet... Man... if this is all over a corroded or loose terminal in a plug cap....I'm actually going to be pretty happy about it.
/\/\ac

Howdy Mac. "Secondary" does mean the HT side of things here (refers to the secondary side or HV winding of the transformer or ignition coil versus the LV [low voltage] primary side which is switched). Many times I've seen people chasing electronic and other electrical issues, assuming that the HT (HV) side must be good....because well.....it looks good.

A GOOD STRATEGY FOR TROUBLESHOOTING ELECTRICAL/ELECTRONIC CIRCUITS: !. Know what the circuit is supposed to do. 2. Verify power supply. 3. Troubleshoot from output back to input to see where the process has failed.

In your case, you noticed that part of the circuit didn't work (you had 2 cylinders not firing). At this point I'd want to pull each associated spark plug and look at it to determine probable firing efficiency.....then, with it outside the head and touching it, see if it fires with a healthy blue spark (you've now verified output) You didn't quite check power supply next (that would have been to check O/W to ground....at battery and at the coil mounting where it has to be). You did back up from the output (spark and HT side) but weren't looking to see if the coils were being switched with good voltage - this can be as simple as placing a test light from coil negative to ground and cranking the bike.....a bright light winking on and off while cranking indicates probable good switching (and verifies coil primary is intact). It was here that I answered your post thinking you may have had one coil negative terminal permanently pulled to ground (not switching). From there it depends on your results as to whether you'd then go back up the chain to HT or down the chain to see whether the ignitor was being triggered.....the results here will determine where the problem lies.

If I haven't put you to sleep, I hope it helps

P.S. If you think about this strategy....you'll see that you can troubleshoot many types of electrical/mechanical problems the same way.