4 not firing, even with #1 wire attached

[knitt31]

Hi all, first, is someone knows of a thread to point me to, please do, I've looked high and low.

Cylinder #4 is not firing, or will fire for a bit occasionally.
I had spark, so I figured it was the carbs. Full clean of carbs and no luck.
Figuring it was possibly a bad #4 wire, I brought the #1 wire over and started the bike up. Still no fire on #4.
Thoughts on where to go next?
Thanks!

 

[Brendan W]

Compression ? You have spark and fuel so there is only one left. When were the valves last done. What state is the plug in , sooty, oily, wet ? Have you tried swapping plugs with #1
Compression tester is a useful and relatively cheap tool.

 

[Call Me Ahab]

Hey there, I'm actually in the exact same boat.

Same story - mine started out with #1 with no ignition and migrated to #2 no ignition, but #1 now ignites.

My plug comes out wet, like it's fouled, compression is around 96-100 psi, and swapping plugs and wires achieves nothing. I have checked carbs and resynced, reset idle mix.

I'm calling it for tonight, but I'll be back at it tomorrow. I'm going to keep an eye on this thread and I'll post anything if I can find a cause and solution for this - it's driving me insane. Spent about six hours today wrenching on the bike testing everything I could think of.

Good look, this one's a major pita.

 

[knitt31]

Sorry to hear that.. but glad we're going after it together!
I just bought a compression tester tonight. Probably won't get to play with it until Friday though.

 

[Call Me Ahab]

I'm at a loss.

I took my battery off and charged overnight. Took the valve cover off, checked all my valve shims, swapped 4 of them around, now they're all in acceptable tolerance or have no measureable tolerance (I have no bloody idea why!!!!!). Timing was perfect. I was getting angry and just wanted to see if there was any change in... freaking anything. All my cylinders are up to 140 - 150psi. What in the name of flying spaghetti monster.

I have no idea where to go from here, I'm just sitting around and waiting until my new intake boots arrive sometime tomorrow. If they fix the problem I'll let you know.... Until such time as one of us can figure this out, good luck... to both of us

 

[Guest]

Do you mean you tried to measure valve shim clearance and on 4 you couldn't? so you mean they were so tight you couldn't even get a feeler gauge in there? if so, you need to fix that. If you don't you could, or might already have, burn valves.

 

[kdo58]

i had a similar problem if the spark plug is bad you will not get any spark, mine problem was when i bought the plugs and took off the little cap thinging that unscrews it broke loose the stud inside the spark plug.

 

[koolaid_kid]

If the plug is wet, it means one of two things (or both).
First, it could mean that the spark, even if present, is not hot enough to fire the fuel/air mixture.
Second, it could mean too much fuel is being supplied. Being as it is cylinder#2, this could mean one of two things (or both).
One, the fuel bowl is overflowing. This could be caused by one of two things (or both) (Like the way this is going? )
a) The float is stuck or the needle and seat have issues.
b) Float level is too high
Two, the petcock is allowing fuel down the vacuum line. Usually caused by diaphragm failure in the petcock.

 

[Call Me Ahab]

Do you mean you tried to measure valve shim clearance and on 4 you couldn't? so you mean they were so tight you couldn't even get a feeler gauge in there? if so, you need to fix that. If you don't you could, or might already have, burn valves.

Oh. Well, crap. That answers my question then...

Yes, there was no clearance between the lobe and the shim. I am unsure as to why or how - they have not been replaced by myself or the previous owner, and he had the bike for 7-ish years before he sold it to me. So this one's really odd.

When I had the valves out a couple months back, no damage, no warping, no evidence of overheating. I just lapped the seats and replaced one guide - replaced oil seals and went on down the road, nothing looked out of the ordinary. I carefully labeled each and every bucket as I removed it (oil base sharpie) so I know they went back in right. I see on one shim only where it looks like it's making... excessive contact? It's worn shiny at the apex of the stroke in a very small (about .5-ish mm wide) measured w/ calipers.

 

[tkent02]

Yes, there was no clearance between the lobe and the shim. I am unsure as to why or how - they have not been replaced by myself or the previous owner, and he had the bike for 7-ish years before he sold it to me. So this one's really odd.

Not odd at all, that's what they do. As the valves wear, they usually recede into the seats, so the stem on the other end gets longer, the clearance goes away. When you lapped the valves, you speeded this process up a little, moved them even further into the head. There is a reason they should be checked routinely.

Set the clearances correctly before doing anything else.

 

[Call Me Ahab]

Not odd at all, that's what they do. As the valves wear, they usually recede into the seats, so the stem on the other end gets longer, the clearance goes away. When you lapped the valves, you speeded this process up a little, moved them even further into the head. There is a reason they should be checked routinely.

Set the clearances correctly before doing anything else.

Aha! That's the bit that eluded me then, I was assuming the shims were replaced due to wear on the engine, requiring me to make up for greater tolerances. I kept looking over my manual's shim chart, wondering why in the hell they made something as thin as a 2.00... Well, now I know

Thanks for clearing that up!

 

[knitt31]

Update: I checked compression:
120 100 110 120
When I put a bit of oil in cylinder 2, the compression shot back up. (Opened another can of worms there)
I cleaned the plugs, restarted, and let run for ten minutes.
Pulled the plugs. Plug 1 and 2 were fine. 3 was black...already (ANOTHER can of worms)
And 4 was dry!
Does that send me back to my carbs??

 

[Call Me Ahab]

Update: I checked compression:
120 100 110 120
When I put a bit of oil in cylinder 2, the compression shot back up. (Opened another can of worms there)
I cleaned the plugs, restarted, and let run for ten minutes.
Pulled the plugs. Plug 1 and 2 were fine. 3 was black...already (ANOTHER can of worms)
And 4 was dry!
Does that send me back to my carbs??

Hmm... As Koolaid Man was saying, have you tweaked your idle mixture lately - or before this happened? When you cleaned your carbs, did you ensure that the springs and orings went back on each needle, and that the mixture was set appropriately? Have you checked the engine-side of the carb, feel for a broken point from one of these needles? That's a possibility if one was over-tightened and broke off.

What condition are your intake boots in, and have you tested for intake leaks?

Was the bike running recently?

If your compression is fine, your spark is fine, there's not a great deal else I know to check outside carbs... Check for intake leaks at the airbox and at the engine. When I first got my bike I replaced the o-rings on the intake boots, if they've never been replaced they're almost guaranteed to be dried up or split. An intake leak could be contributing to this problem.

You say the #3 plug is black - if the plug is fouled it could be over-rich, if it's getting fuel. If that's oil on the plug... another can of worms indeed.

One thing you can check - using a voltmeter check your voltage at the coils where the 2 blade connectors (or bullets, based on your year and model) connect to the coil. Check this while the engine is running. If it's too low, your coils will produce a weak spark like Koolaid was saying. Within .5v of 12v is considered to be healthy (So I've been told. Mine read 11.9~12)

Have the spark plug wires and caps ever been replaced?

Has Basscliff been by with his mega-welcome?
If not, take a look @ http://members.dslextreme.com/users/bikecliff/images/GSR_Greeting.html
A LOT of helpful information here.

Look @ number 19 specifically here http://members.dslextreme.com/users/storagecliff/images/electrical_odd-n-ends.html#A17

EDIT:

I'm still kinda new at all this, but this draws from the experience of men wiser than I. Hopefully one of them will pick out anything incorrect I may have said

 

[Brendan W]

Update: I checked compression:
120 100 110 120
When I put a bit of oil in cylinder 2, the compression shot back up. (Opened another can of worms there)
I cleaned the plugs, restarted, and let run for ten minutes.
Pulled the plugs. Plug 1 and 2 were fine. 3 was black...already (ANOTHER can of worms)
And 4 was dry!
Does that send me back to my carbs??

Going back to your original post, swapping the wires would not tell a lot unless the #4 plug had been cleaned as intermittant spark will lead to fouled plugs.
1 and 2 are fine running 120/100 compression. 3 and four should run also so compression is out off the frame for the moment. #3 , black and dry is too much fuel/insufficient air, wet is generally weak or intermittant spark.When you say #4 was dry what colour was the dryness
When you ran it for the ten minutes were all four firing? Any header cooler than the rest

 

[knitt31]

Going to do my best to respond to everyone's thoughts here..
The bike had been running great for the last year. It would intermittently drop to three cylinders now and again, but the 4th would come back seemingly for no good reason. This summer, it dropped to three, and the starter went out, so it sat for a few months before I had time to work on it. Starter replaced, so now on to getting that cylinder back up.

Something else worth considering: When I changed the started, I had the carbs off so i sprayed them really good with cleaner without disassembling. Put it back together and I had all 4 cylinders! Rode about two miles, parked the bike.
Next day, starts up, and back down to three. I figured that meant I had a temporary blockage in the carb, so i pulled them off and tore them apart.
When I say apart, I mean I pulled the jets, soaked the bowls/ jets, checked the holes with a needle etc. I never actually pulled the carbs APART and off of the rail. I didn't want to have to retune them.
No such luck there.

I played with the idle mixture today. No luck there. However, I believe the plug actually did come out wet, AND I have good spark. I'm entirely lost now. 4 just won't fire!
My boots and wires are original, but if i'm getting good spark, should that be a problem? Going to go test the coil now..

 

[Call Me Ahab]

I played with the idle mixture today. No luck there. However, I believe the plug actually did come out wet, AND I have good spark. I'm entirely lost now. 4 just won't fire!
My boots and wires are original, but if i'm getting good spark, should that be a problem? Going to go test the coil now..

A way to test for an intake leak is to use starter fluid and spray a little bit around the boots. If it pops, revs up or otherwise reacts to the fluid, you've got a leak.

I'm not terribly sure what else to do, myself. I'm still working through a checklist of things that may / may not be wrong. I'll let you know if I learn something new. Good luck, and most of all, keep calm. Don't lose your nerve like me and get impatient... It's likely something terribly simple.

I'll post back again tonight if my next round of tests show anything new. I'm also in the middle of a valve job, so I'm just poking around looking for trouble at the moment.

EDIT: misinformed about an intake leak, removed suspect info while I research the claim

 

[Killer2600]

I have to ask either of you, has a brand new plug been put in? How old are the plugs on the bike?

A dry plug that isn't contributing is a no-fuel issue.

A wet plug is either a no/weak-spark or too much fuel.

 

[Call Me Ahab]

I have to ask either of you, has a brand new plug been put in? How old are the plugs on the bike?

For myself, that's a yes - new plug from advance auto. Current plugs are 2 years old. Gap was set accurately. Plug comes out wet / black. Not oily though, as the piston crown looks wet too - but does return to the flat appearance after leaving the plug out foa bit.

 

[knitt31]

New plugs here also. I checked that first hoping it was the answer. All of my plugs have about two miles on them.

 

[adam]

wow i have the same issue on my 82 gs1100g. I had it in the shop and ended up paying the guy almost $400 and all he did was the rear brakes, replaced the regulator/rectifier, installed a new oil pan gasket and spent some time trying to figure out the misfire in number one. He never did figure out the misfire but charged me anyway. Oh well payed him for his time I guess. Any way I do plan on getting out the multimeter and check the generator as well as the cdi box and coils. Have you guys did any of those checks yet? I do have spark on the plug but don't know if it is good spark. I have rebuilt the carbs, according the step by step found here http://members.dslextreme.com/users/...rb_rebuild.pdf so I know its not the carbs. It was running great after the carb rebuild then all of a sudden the misfire started. I will let you know what I find.