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Dead cylinder...coil?

  • Thread starter Thread starter adamgagne
  • Start date Start date
A

adamgagne

Guest
Before I describe my problem this is what I've done to the bike this year.

'83 GS850 (No points)
1.Cleaned all grounds and all ignition related electrical connections.
2.Carbs soaked and cleaned as per GSResource instructions...new o-rings from whatshisname
4. New fuel hoses
3.Petcock cleaned and checked.
4.Intake o-rings changed, and boots leak checked
5.airbox sealed
6. valve clearance checked and adjusted
7. Compression check.
8. Coil resistance check ok, voltages wierd...see below.

The bike runs really rough at idle and the cyl#3 exhaust is quite cold (can hold hand on it indefinately) when plug #3 is removed when bike is running, no change in RPM occurs. So I switched the plug wires from 1 and 3, now when I do this neither 1 or 3 runs (bike running REALLY rough and 1 and 3 exhaust cold).
when I check the voltages on the coil they are both 12+, however when I turn the ignition on and check the pos voltage is 10.3 and slowly decreases as I leave the ign on, is that normal? It's doing it on both coils and 2 and 4 run good...
It seems to me that it is either a bad coil, or the coil isn't getting the timing signal to send spark for the #3 cyl. Is there a way to check and determine if is a COIL, IGNITOR UNIT, or PICK UP COIL?

Also when I accellerate above around 4,000RPM all 4 cyl seem to kick in and I get a Surge of power.
 
Sync your carbs and charge your battery. Spray electronic cleaner on your ignition trigger ends and coil connections. Flip flop the entire coil (switch connections and plug boots) and see if issue follows. Unscrew your plug boots and trim wire till you see good wire ends to grab on to.
 
Did you actually visually verify spark on the plugs in question? This will reveal a lot.
1 & 4 fire simultaneously from one coil, and 2 & 3 fire simultaneously from the other coil. So switching 1 & 3 really messes things up (unless you meant that you swapped the wires and reattached to appropriate coils).
Anyway, the bottom line is that if you're using the original coils and wires there's a strong likelihood that the coil is in its "intermittently-failing-soon-to-die-altogether" stage.
 
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oops, I was thinking one coil fired 1,3 and the other fired 2,4...thats wierd, I just checked the leads and they are labeled 1-3 for one set and 2-4 on the other...stupid labels...
 
ok, now that I've got the 1-4, 2-3 thing figured out...
I cleaned the ignition pickups w/ contact cleaner (although already very clean)
I swapped the wires going into the coils and then used the 2-3 coil to supply the 1-4 plugs, and vice versa...however 1 and 4 still run good, and 2 and 3 aren't so hot, 3 exhaust pretty cold to the touch....
All plugs show spark outside of the cyl, not super strong but bluish white.

So I guess the coils are good (even though 23 years old)

Shasta, so I guess it's not electrical?

Any other ideas?
Float levels are good, carbs are good (pretty sure, been through them 3 times already), elec seems to be good, valves timing good...
I guess the next thing to do is carb balancing, although I don't think that is the big problem.
It does this even with a fresh charge on the battery and I've been riding the bike a lot, so that should be charged well.
 
Did you clean the screen and journal under the funky little plastic float thingy in the bowl.

Mine ran the same way until I cleaned the carb for the 3rd time!!
 
Carb syncing

Carb syncing

My next step is going to be syncing the carbs...
I am planning on making my own manometer, I ordered the 5mm port adapters from motionpro.com,

Mymanual says that I am supposed to set the vacuum on the outside cylinders "a half ball above the centerline" how am I supposed to do this with a DIY manometer?
Also, I have my air screws set to 2- 3/4 turns out. Is setting those to highest idle a vital step in carb syncing? I'm afraid I'll mess things up adjusting those.
Thanks
Adam
 
You verified compression (and they were within spec), SO:
The problem you describe could only be carb-synch related if your carbs are very severely out-of-synch. If the butterfly valves all look to be in the same position then the synch can't be the problem.
You verified it's not a coil problem by swapping 1&4 with 2&3.
You verified that the plugs are actually firing so all your plugs are good.
The only thing left is that there's a problem with carb #3. It's either too lean or too rich. Is the plug color significantly different that the others?
 
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