GS850 bogging down originally but now won't start

[Bob Gibson]

Now, I can?t get the bike to start very easily. It is appears that it?s either not getting proper spark or fuel. I can eventually get the bike started after about 5 minutes of cranking and adjusting the carb idle screws and yes, charging the battery. I?m not sure the carb adjustments are the reason I?m getting it started. Once it starts, it appears to run poorly in neutral, especially at low end revs, yet once I put it in gear and gently start to let out the clutch it instantly dies and then won?t start for another long bout of cranking. So here?s what I?ve done since taking it around the block after the valve adjustment a few weeks ago. As a reminder, this bike was the one that bogged down at high speeds. After adjusting the valves the bike still started instantly but ran poorly.

Ignition/Spark: When I did the valve job a few weeks ago, I noticed that the signal rotor tabs were pretty rusty, so I very lightly polished the tips of these rotor tabs. Less than .002 inch was removed (gapped before and gapped after), and I adjusted the signal pick-ups inward slightly to get close to original gap. I also noticed that my 2 signal pick-ups did not consist of 4 wires as the manual states (Blue, Green, Yellow & Black), but 3. A blue wire goes to one pick-up, a Green wire goes to the other pick-up, with a Red wire attaching from 1 pick-up to the other pick-up. I checked the resistance across the Blue and Green wires with a multi-meter, near the ignitor box, and got 320 ohms. Dividing in half gets me 160ohms, so does that indicate I?m within range? And does this ignition system seem to be an ?after market? or for a later model, since it has the wrong wiring? I?m asking that since my ignitor box has only 6 wires out, not the 8 described in the manual. The colors of my 6 ignitor wires match 6 in the manual, but I don?t have the solid Yellow and the solid Black wire. The ignitor unit also indicates it?s a 12volt system, but about 8.5 volts is the most I get checking across any wire combination (Orange/white stripe across Black/white stripe). The ignitor unit number is 32900-45110/131100-1901. Now I?ve checked for spark at the plugs and I do have a spark. I expected a stronger visual spark, but that may be due to my auto background, however I do have a spark to all plugs.

Carburetors: I also took the complete carb 4 pack off the bike and thanks to Mario Padilla supplying me with 4 viton o-rings, I replaced in the intake o-rings as suggested. Inspecting the inlet ducts did not indicate any rubber cracking or poor seating. Now, while I had the carbs off I adjusted the butterfly gaps with a drill bit as the article suggested. They were not off by much. I could have left them as is, but trying to be a perfectionist? I also blew filtered compressed air all around each carb, above the idle screws and through each air jet. I then adjusted the idle screws to 3 turns out, reassembled the carbs onto the bike, checked the petcock (functions properly), added the new air box (it?s properly sealed and with a new air filter) and started cranking the bike over, but to no avail. Then adjusting the idle screws out by 2, then 4 then in 3, then 5 and then it started, ran poorly then died as mentioned above. I then took the airbox off, reinstalled the air pods and the result was the same. I can?t believe that a very slight butterfly adjustment or air in the idle screw or into the air jet could cause such a calamity, and that?s why I started verifying I had a spark, but there?s spark.

Help once again!
Bob Gibson

 

[Skyboy8950]

Always check the obvious. Is there gas? My 850 runs poorly on little gas in the tank since it is gravity fed. It does just that when low on gas.

 

[Big T]

You either have a bad igniter or need to supply 12V to the igniter and coils.

Also, what is the state of your carb cleanliness??

Why don't you post up a picture of your ignition for others to inspect?

 

[almarconi]

What year is your bike?

 

[Bob Gibson]

My bike is a 1981 GS850G, but it appears to be more like a GS850GZ. No points.
I've got about a half a tank of gas and I've verified the fuel flow is good to the carbs.

As for the ignitor, that also bothers me. I'm only getting 8.5 volts MAX across any combo of wires, and there are only 6 wires out of the box, not 8. Note that I do have a spark to all plugs, so I would suspect some type of starting though maybe a rough start and idling.

I tried to post Pics once before but failed. The memory usage was too large. I'll work on this today. I already have the Pics of the ignitor pick-up area and the ignitor box.

Carbs appear visually clean, but I bought the cleaner kit per the carb clean tutorial to eliminate this possibility. Carb clean and rebuild will be my weekend project. This way I'll know if blowing compressed all around and in the carbs damaged something.
Thanks again for your ideas.

 

[rustybronco]

http://members.dslextreme.com/users/bikecliff/images/80GS850GT_wiring_color.gif
you should have at or near battery voltage at the coils, and the same for the igniter.

 

[LarryA_Texas]

http://members.dslextreme.com/users/bikecliff/images/80GS850GT_wiring_color.gif
you should have at or near battery voltage at the coils, and the same for the igniter.

Simple test: Run a wire from the + battery to the positive side of each coil, try to start it. Make sure the coil negative is grounded. If battery voltage directly from the battery helps it start, you have a voltage problem that has to be addressed. If it doesn't make a difference, look at your carbs again. Something went wrong there. It sounds like one or more cylinders isn't firing at all.

As for wires from the SG; if you have an earlier model ('81 or '82) you have a mechanical advance and the blue and green are appropriate. The black and yellow wires should be on a wiring diagram supplement in your manual and apply to later models with an electronic advance. If the 2 wires connect to a proper two wire connector in your ignitor box then you're good.

8 volts at the coil still is extremely low. You need to fix that anyway.

If you ever get it running at all, check the temp on all 4 pipes and make sure they are all getting warm. That will at least tell you if you're hitting on all 4. It could also tell you which is not firing.

 

[nisom512]

check your compression as well. I had starting problems on my 550 did everything, valve adjustment, coil relay mod, carbs with o-rings, and intake o-rings. and still bad cold starts, finally checked the compression and bam bad compression and put some mystery oil in the cylanders and it went up and now she runs great.

Good luck
Jake

 

[LarryA_Texas]

grounded

grounded

Make sure the coil negative is grounded.
.

Someone pointed out to me that the line above is misleading. 'Grounded' meaning properly connected to the ignitor box with secure, clean connections. Sorry for the confusion.

 

[Bob Gibson]

Bizarre ignition voltage! Battery voltage is at 12.7volts. Coil leads1-4 has 8.1v across the 2 wires (Orange-yellow and White), while coil leads 2-3 (Orange-yellow and Black-Yellow) has zero volts across the 2 wires. But Wait, hand turning the rotor to get rotor tab aligned with the Green pick-up produced 8.3v to coil leads 2-3, but then coil leads 1-4 register zero volts. Turning key off then rotating rotor tab away from either pick-up and power back on gets me back to leads 1-4 has 8.1v and leads 2-3 has zero. Cranking for about 10 seconds with multimeter in leads 2-3 and I?m back to leads 2-3 having 8.3volts, while 1-4 is back to zero volts, and rotor tab is away from either pick-up. Now, adding wires from Battery Positive to both Orange-yellow wires produces 12v across both coil lead sets. Excellent. Tank on, all 4 carb idle screws set at 3 turns out (previous request), bike starts quickly and runs rough, but at least it?s running again. Choke full out is only way to keep bike running. Bike will not rev at all without dying (whether choke is in or out), BUT now engine stays idling when in 1st gear and clutch released! Excellent. Check pipe temps after about a minute of running. Pipe 4 is cold! But spark is good and bright. Remove extra positive battery wires to coil leads and check for coil voltages again. Coil leads 1-4 now has 9.6 volts (not 8.1 volts) and leads 2-3 has zero. Sounds like an intermittent ignitor unit, if I understand these correctly. Do you agree? Now, I?ve read that many of you stated that the after market ignition system is better and cheaper than the OEM. Comments?

Now being that I?ve got good spark to chamber #4 but no combustion (cold pipe), it appears I damaged carb #4 with my compressed air spraying and now it?s not feeding any fuel to the chamber. I tried to turn the idle screw in and out, but no change. So, I?ll start the carb tear downs, clean and rebuilds tomorrow (need to help a friend on house issue today) and then start searching for a new ignitor assy.


By-the-way, the bike does have mechanical advance, so I guess my pick-up 3-wiring system (Blue, Green, Red) is OK. Thanks for that info.

I checked compression again, since I?m still shocked on the increase after the valve adjustment and since one of you suggested it. All four chambers are between ~130 to 140psia, so all?s good there. Seems impressively good. I'm still shocked with a 30 to 40psia improvement in each chamber.


[FONT=&quot]The ignitor unit is very bothersome. I wonder if the ignitor box has been slowly failing since before I bought it. If that is logical, that would explain my slow erosion of power at the higher RPMs over the last year, but I thought these devices just failed and not eroded toward failure. Comments to get me smarter?[/FONT]

 

[almarconi]

The ignitor unit is very bothersome. I wonder if the ignitor box has been slowly failing since before I bought it.

These units usually work or they don't. Before spending money on another one, the service manual has a test procedure to test the ignitor. It's easy to do.. I can't remember the specifics but look in the manual. If the tests confirm that the ignitor is bad, you may want to upgrade to a dyna unit instead of an oem ignitor.

 

[Bob Gibson]

Actually I've looked through the manual and they only define two tests. The test if you have points and the test if you have the 8-wire ignitor. Since I only have 6 wires on my ignitor (no solid Black or solid Yellow) I don't know how to verify my ohm reading or do the conductivity spark test. They both require using the solid Black and Yellow wires. Now when I check the resistance across the Blue and Green wires I get 320 ohms. Since the manual states that testing across the "Green" and Black should result in 160 ohms and then the resistance across the "Blue" and Yellow should also be 160ohms, is it plausible that 320 across the blue and green is OK and does that mean my ignitor is OK?
So if the 320 ohms is indicative of a good ignitor, how come I get voltage across only one coil lead at a time?
Thanks for any incite.

 

[almarconi]

I don't have the wiring diagram for your bike but the 650,750 and 1100 only has 6 wires from the ignitor. The 1100G has 8 wires. That being said try the procedure for the 750 ignitor test and see what happens.

Here it is...
Remove each spark plug of #3 and #4 cylinders, fit it
to the plug caps and place it on the cylinder head.

Remove the frame cover on the right side and disconnect the lead
wire from the signal generator.

Connect + lead of voltmeter (set on ohms) with blue lead
wire on the ignitor side and - lead on the voltmeter with the green
lead wire.
The moment the test pins are connected the spark plug of #4 sparks
and the moment the tester pins are disconnected the spark plug of
#3 cylinder sparks.

 

[Bob Gibson]

Thanks for the information below about the 750. So I tried it ... Multimeter positive wire connected to Blue wire through a connector port while all wires were still connected, then touching negative multimeter wire to Green wire, nothing happened. So I removed all of the plugs and plug wires and tried again thinking that just maybe it might be sparking plugs 1 and 2. Still nothing, but I did get 1000 ohms across the Blue and Green wires (note previously I got 320 ohms consistenly, so what's going on?). I tried cranking over the bike (all plugs exposed) and all plugs had spark. Now I noticed that by connecting and disconnecting the Blue and Green wires at the connector port, I could sometimes get #4 plug to spark and less often #3 plug would spark. The connector appears clean and I do get a resistance across Blue and Green wires as mentioned above, so I'm getting conductivity across the lines and connector port. After trying the multimeter approach a few more times I can sometimes/inconsistently get #4 and #3 to spark, but there's no consistency. Sometimes plug 4 sparks when I touch the multimeter line to the Green line, sometimes it's #3 when I touch the multimeter line to the Green line. I expected that the sparking would be obvious . . . touch the Green line and #4 would spark, remove and #3 sparks. Actually sometimes they both spark when touching the neg and Green together.
Comments?
The inconsistency of active voltage across the two coil sets bothers me. I'm not certain my ignitor is bad nor do I have confidence it's good. But the bike ran a month ago. I just couldn't get high end power (55mph was my max and for an 81 GS850, that's sad), so I started repairing back to stock status to search for more consistent operation.