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3rd cylinder wont fire...

  • Thread starter Thread starter Johnny K
  • Start date Start date
J

Johnny K

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My sig is my bike. I had adjusted the valves last month to about .06-.09. I started my bike up one day about 2 weeks ago. Started fine and let it idle for about 5 min. Shut it off, got my helmet and went to start it again but all it did was click every time I hit the starter button. It wouldn't turn, but only click how ever many times I hit the button. I did the test to make sure it was the starter and I thought it was. I ordered and got a new starter the other day. Put it on and the same thing happened. Just would click every time I hit the button. Well I hit the button a bunch of times and then held it in where it was trying to turn but couldn't keep it idle without full choke. Well it was idleing really bad and I took each plug boot off to see if the idle dropped. Clynder's 1,2 & 4 almost stalled the bike whereas #3 did not affect the idle. Which is the same pipe that has no colour coming off of the head. I have a compression guage, but haven't used it yet. When I do the compression test it will be cold. What numbers should I be looking at? What else should I be worried about? Not sure how serious this is yet.
 
Compresssion would have to be real bad, like non-exsistent compression, catastrophic failure of something, before that cyclinder will not fire.

I suggest you look more towards the ignition relative to that #3 cyclinder, maybe swap the spark plug cap with #2.
Or maybe pull out the plug and lay on cyclinder head to visually check for spark.

.
 
Yeah, I'm sure it has spark. But now it has really just into crap after a short amount of time. What would switching the plug boots tell me? I will def. know more when I do compression numbers, but I know this isn't good the way that it sounds.
 
I took cold compression numbers. From left to right: 95, 70, 80, 90. After that I switched plug boots 2 and 3, started it up and as it began to run with the choke on, tiny but really strong backfires were coming out of the pipe. Ive had backfiring in the past due to carbs, but this felt and sounded stronger. So I shut it off and switched the boots back and started it up. Weirdest thing is that it started as if nothing ever happened in the first place. In the beginning of the normal start up it did back fire just a tiny bit, but after about 15 seconds, it stopped. I couldn't believe it and had it on choke for about 5-10 min to warm it up. Took the choke off and it idled great around 1100 rpm. I shut it off and on a bunch of times wondering if it would do what it did last week. Having the new starter in, I can hear a tiny but good whine noise as I hit the starter button. It starts quicker without any throttle once it is warmed up. I haven't taken the boots off again while the bike is running to see if that 3rd boot has any affect on idle. If there is no drop in idle again when I take the 3rd boot off while the bike is running, what does that mean? I will do compression numbers again when the bike is warmed and see what they are.
 
The suggestion you start by checking the ignition is right on and the place you should start troubleshooting. If #2 is firing and #3 isn't and you switch the plug leads over (not just the boots) and #3 fires and #2 doesn't, you know you have a bad plug lead or boot or connection. You switch #2&3 because they share the same coil.. The coil is good if one of the plugs is firing but it can have a problem where the other lead comes out of the coil.

Don't worry about the compression. It isn't perfect but it's not your problem. It's also typical for the two inside cylinders to be lower than the outside. That's a result of being less efficient at cooling.

If you put the plug of the cylinder that isn't firing on top of the engine, still connected to the coil, and crank the engine you should see spark. If you have spark and the cylinder doesn't fire you need to look for a fuel problem with the cylinder.
 
It sounds like you're going okay, that's good. Further, you can also tell which cylinder isn't firing because the exhaust pipe coming out of that cylinder will be cold while the others will get real hot, real fast. My 1000 always backfires when cold. I can start shutting off the choke after 10-15 seconds and have it shut off within 1 minute. It won't be backfiring by then but might have the odd little fart until up to temp.
A good rule when figuring out bike problems is to start with the simplest tests first. They tell me that computers are better than humans because they start with the simplest solutions and we humans jump to the worst conclusions right iff the bat.
 
Hey ryder, what are the plug leads? I know the plug boots but not sure what the plug leads are?
If you put the plug of the cylinder that isn't firing on top of the engine, still connected to the coil, and crank the engine you should see spark. If you have spark and the cylinder doesn't fire you need to look for a fuel problem with the cylinder.
​
Do you mean take the plug boot off and spark plug out? Just a little confusing for me. Thanks.
 
Johnny K said:
I took cold compression numbers. From left to right: 95, 70, 80, 90. After that I switched plug boots 2 and 3, started it up and as it began to run with the choke on, tiny but really strong backfires were coming out of the pipe. Ive had backfiring in the past due to carbs, but this felt and sounded stronger. So I shut it off and switched the boots back and started it up. Weirdest thing is that it started as if nothing ever happened in the first place. In the beginning of the normal start up it did back fire just a tiny bit, but after about 15 seconds, it stopped. I couldn't believe it and had it on choke for about 5-10 min to warm it up. Took the choke off and it idled great around 1100 rpm. I shut it off and on a bunch of times wondering if it would do what it did last week. Having the new starter in, I can hear a tiny but good whine noise as I hit the starter button. It starts quicker without any throttle once it is warmed up. I haven't taken the boots off again while the bike is running to see if that 3rd boot has any affect on idle. If there is no drop in idle again when I take the 3rd boot off while the bike is running, what does that mean? I will do compression numbers again when the bike is warmed and see what they are.
Click to expand...

I am pretty sure you do compression checks after the bikes warmed up. Did you test the compression wot? That will affect your numbers as well.

Rick
 
Johnny K said:
Hey ryder, what are the plug leads? I know the plug boots but not sure what the plug leads are?
If you put the plug of the cylinder that isn't firing on top of the engine, still connected to the coil, and crank the engine you should see spark. If you have spark and the cylinder doesn't fire you need to look for a fuel problem with the cylinder.
​
Do you mean take the plug boot off and spark plug out? Just a little confusing for me. Thanks.
Click to expand...
Uhh, ... the leads are the wires that go from the coils to the boots.
The boots are the hard, angled thingies that actually snap on to the ends of the spark plugs.

For quick troubleshooting, just pull the whole boot/wire assembly off plugs 2 and 3 and swap them, leave the plugs where they are. Just take the wire off 3 and stick it on 2, take the one that was on 2 and stick it on 3. There is no problem with spark timing as they both fire at the same time. If you have a problem with one of the wires, the problem will move to the other cylinder. If the problem is with the plug or valves, or rings, it will stay with the cylinder.

.
 
I had switched the boot plugs 2 and 3. When I did that, there was a lot of backfiring out of the exhaust. Really short strong backfires. So I switched them back and fired it up and it runs normal and good like before. I did take the cylinder 3 spark plug and boot off and stuck the plug into the boot while off the engine. I fired it up and put the spark plug next to one of the bolts of the engine and saw little electric sparks like it should. But that is the weird thing. Cylinder 3 has compression and now it does have spark. But when I take each boot off, the engine basically stalls until I put the boot back on. But cylinder 3, I could leave the boot off or on and it still does not affect the idle at all. The pipe of that cylinder does not have any color as the other 3 do. I did check the valves about 3 weeks ago, and all are pretty much .06-.09. Any ideas?
 
Carb #3 needs to have an attitude check. :-k

Sounds like a fuel related problem (shortage) to me.

If you have spark, and air, you're missing the go juice.
 
Dave8338 said:
Carb #3 needs to have an attitude check. :-k

Sounds like a fuel related problem (shortage) to me.

If you have spark, and air, you're missing the go juice.
Click to expand...

I am with Dave on this one. Some how, you are not getting the "juice".

I am assuming that your carbs are super clean, right? Or not?

I bought a 78 750 and cylinder #3 was not firing (pipe was very cool--never really warming up). So I super cleaned the carbs, soaking the bodies overnight, spraying carb cleaner through every hole and blasting air through it.

Guess what? Cylinder #3 sprang to life and I was back to running on all four:D!

Just a thought.

Rick
 
Yeah the carbs were dipped with Berrymans, sprayed with carbs cleaner, compressed air through every jet and crevice throughout each carb body, then re-sprayed and new o-rings for the whole carbs. I did that about 2 months ago. The pipe gets real hot, but not as hot as the others because of the color of the pipes.
 
I did a warm compression test today. They were:
85; 75; 70; 90.

I then added some oil to each cylinder and the numbers were:
110; 130; 125; 130.

After that my exhaust is blowing white smoke which is probably normal because of the oil. How do the numbers look?
 
Johnny K said:
I did a warm compression test today. They were:
85; 75; 70; 90.

I then added some oil to each cylinder and the numbers were:
110; 130; 125; 130.

After that my exhaust is blowing white smoke which is probably normal because of the oil. How do the numbers look?
Click to expand...


#1 is a bit low, but, it probably just needs a long ride.

The smoke is normal

I'd be looking at the coil, as you had a negative change when you switched plug wires between #2 and #3
 
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