#1 and #4 are not firing

[legaleli]

My problem started in #4... it was working intermittently. I pulled the top and checked valve clearances, pulled the carbs and took #4 apart to see if there was an issue, ensured all seals are good from carbs to intake as well as seals in the airbox and carbs to airbox. Plugs were replaced.

Here's the thing... there is spark across all four plugs. #2 and #3 fire fine. The non firing plugs get wet with gas. Occasionally a non firing plug will backfire.

I know little to nothing about electrical.

 

[gearhead13]

check voltage at one coil and compare it to to voltage at the other coil, then compare it to battery voltage. Maybe a coil relay mod is needed.
Two wires go to each coil, one is the trigger from the ignition, the other is always hot when the key is on.

 

[tom203]

My problem started in #4... it was working intermittently. I pulled the top and checked valve clearances, pulled the carbs and took #4 apart to see if there was an issue, ensured all seals are good from carbs to intake as well as seals in the airbox and carbs to airbox. Plugs were replaced.

Here's the thing... there is spark across all four plugs. #2 and #3 fire fine. The non firing plugs get wet with gas. Occasionally a non firing plug will backfire.

I know little to nothing about electrical.

Refering back to other forum, you said you replaced coils. Why don't you switch coil positions to see if problem moves from 1 and 4 to 2 and 3? If it doesn't move, then problem is not the coil. You then need to check wiring from signal generator to ignitor to coil ( head off to Basscliff's house). You might just have a bad connection or your ignitor might be bad. But in the other forum, you were talking about running to redline, so I don't grasp how with misfiring two cylinders you could do this.

 

[legaleli]

Refering back to other forum, you said you replaced coils. Why don't you switch coil positions to see if problem moves from 1 and 4 to 2 and 3? If it doesn't move, then problem is not the coil. You then need to check wiring from signal generator to ignitor to coil ( head off to Basscliff's house). You might just have a bad connection or your ignitor might be bad. But in the other forum, you were talking about running to redline, so I don't grasp how with misfiring two cylinders you could do this.

It's getting more interesting... on the non-electrical side I made an error when I put the carbs back in... I turned all the mixture screws all the way in so 1 and 4 (and 2 and 3) were WAY lean... I put them all out 2.5 turns and #1 came back and #4 was still bad. For an experiment I turned #4 mixture all the way out 7 or 8 turns and now it is back to working intermittently. There seems to be a sweet spot in the amount of throttle that gets #4 cylinder firing... you can actually feel the change in the bike when the cylinder comes to life... it might be a mechanical issue after all.

THAT SAID... I checked the voltage across the coils... the LEFT coil (1 and 4) has 10.3 volts across the wire on the top, and the wire on the bottom, of the coil. So the issue with #4 is probably not from the back of the coil back into the electronics... BUT #2 coil (2 and 3) has 10.2 volts across the top and 1.3 volts across the bottom. That said, #2 and #3 cylinders seem to be firing fine...

What does it mean that coil #2 has 1.3 volts across the bottom wire?

Also, it may be time for a compression test...

 

[gearhead13]

It's getting more interesting... on the non-electrical side I made an error when I put the carbs back in... I turned all the mixture screws all the way in so 1 and 4 (and 2 and 3) were WAY lean... I put them all out 2.5 turns and #1 came back and #4 was still bad. For an experiment I turned #4 mixture all the way out 7 or 8 turns and now it is back to working intermittently. There seems to be a sweet spot in the amount of throttle that gets #4 cylinder firing... you can actually feel the change in the bike when the cylinder comes to life... it might be a mechanical issue after all.

THAT SAID... I checked the voltage across the coils... the LEFT coil (1 and 4) has 10.3 volts across the wire on the top, and the wire on the bottom, of the coil. So the issue with #4 is probably not from the back of the coil back into the electronics... BUT #2 coil (2 and 3) has 10.2 volts across the top and 1.3 volts across the bottom. That said, #2 and #3 cylinders seem to be firing fine...

What does it mean that coil #2 has 1.3 volts across the bottom wire?

Also, it may be time for a compression test...

Ok, I take it those voltages were checked with the key on and the engine off, did you compare that to what voltage you have at the battery? Coils work better with full battery voltage at the coils. While you are at it check the voltage with the engine running to see how you are charging, rev it up a bit it should go up to ~14v or so.
Sounds to me like you have a clogged idle circuit on #4 carb So, the misfire on #4 is just at idle.

 

[legaleli]

Ok, I take it those voltages were checked with the key on and the engine off, did you compare that to what voltage you have at the battery? Coils work better with full battery voltage at the coils. While you are at it check the voltage with the engine running to see how you are charging, rev it up a bit it should go up to ~14v or so.
Sounds to me like you have a clogged idle circuit on #4 carb So, the misfire on #4 is just at idle.

The engine was off but the battery is fully charged and shows 12.25 volts (it's new).

I thought it might be the idle circuit but the bike still misses at full throttle... in fact the missing cylinder fires best when I am lightly on the throttle... not REALLY lightly...but gentle accelleration causes the cylinder to come back... when it's back if I roll on it starts to miss again...

Regarding the right coil (cylinder 2 and 3) what would cause the lower wire to read 1.3 volts?

 

[tracktune]

Hi did you check float level and plug caps ,ET droped a cylinder and all it was was a cap fault
Cheers

 

[gearhead13]

The engine was off but the battery is fully charged and shows 12.25 volts (it's new).

I thought it might be the idle circuit but the bike still misses at full throttle... in fact the missing cylinder fires best when I am lightly on the throttle... not REALLY lightly...but gentle accelleration causes the cylinder to come back... when it's back if I roll on it starts to miss again...

Regarding the right coil (cylinder 2 and 3) what would cause the lower wire to read 1.3 volts?

You only need to concern yourself with the one with steady voltage, the other one will only show voltage at certain times in the combustion cycle. You have a 2 volt drop at your coils That is bad. Doesnt help your situation. Look into doing a coil relay mod.
I would check your #4 plug, wire and cap for resistance and continuity. Check your plug gap as well.

 

[Billy Ricks]

If you're 7 or 8 turns out on the mixture screws you're completely off the jet and running full rich down low. The circuit is bound to be clogged to even let you get 4 turns out without being rich. 4 turns is just about where you are off the jet. Time to go through the carbs and clean them. You may have already done it but they aren't right. Float levels may be wrong too as already mentioned. Carb synch could be way off too.

 

[legaleli]

This would be the right time to take her down to little bits and put her back together right... I am certain the carbs are clean... but something may have ended up in the #4 carb somehow...

The wiring IS a mess and I was looking forward to taking the bike down to her frame in any event...

She's got 61,000 on her now... time for rings and she needs her gaskets changed too.

I think, like a lot of issues... it's a combination of things mechanical and electrical that come with age and a mis-spent youth .

Without the people here I'd never know that. I am so freaking glad this forum is here.

This bike is going to be amazing... some day!

It's a good thing I've got another GS coming in 8 days!

 

[850 Combat]

If you're 7 or 8 turns out on the mixture screws you're completely off the jet and running full rich down low. The circuit is bound to be clogged to even let you get 4 turns out without being rich. 4 turns is just about where you are off the jet. Time to go through the carbs and clean them. You may have already done it but they aren't right. Float levels may be wrong too as already mentioned. Carb synch could be way off too.

This is correct.

 

[legaleli]

This is so freaking weird - but it is a happy ending.

I took the carbs off... broke #4 down to her little bits... they were clean... but I blew compressed air through the entire body in case there was an obstruction...

I bench synced the carbs the best I could, put it all back together and still there was an issue with #4. I pulled out the plugs and notice that 2 and 3 were fine but 1 and 4 were not.

I then followed the advice of Tom203 and switched the position of the coils. I also moved around the plug wires at the same time (which was dumb because if there was a difference then I would not know why).

There WAS a difference... 1 and 4 and 2 were fine and 3 was bad...

I then took the coils off again, re-cut the plug wires, cleaned the connections to the coils... installed the coils in a different fashion (better grounding and a more convenient position on the frame), and put it all back together...

Now all is fine...1,2,3,4 are all good. The power is off a but though... sluggish through the mid range. I did oil the air filter and might have it a bit too greasy.

In any event she is definitely drivable now.