#4 Cylinder Dead - Can't find Cause

[Brendan W]

Hey guys, in an attempt to stir up an old thread I'm having basically the same issues with #4 cylinder except that regardless of which boot I use #1 or #4 it does the same thing. With the boot fully on #4 doesnt fire, if I pull the boot off and just place it on top of the spark plug the cylinder starts to fire! It's almost like something is shorting out my ignition coil??? Any thoughts?

Run it in the dark with the boot in both positions. You are looking for spark escaping from the boot to the cylinder head.

[Mutashio]

Sorry, I have very limited knowledge on this, just something struck me about your issue that made me think of reading about spark plugs, caps, and wires, any of the 3 can have resistors, but you only want it in one of the three, and that could potentially be an issue for you. It may not be. Just thought it was worth exploring the idea. Take a look at this thread, the knowledgeable people like Nessism and Steve know what they're talking about. See if any of that info seems to make sense with your issue.

You may want to start your own thread on this.

Tip on using this sites search function.
Always used advanced
Type in your keyword(s) and change to search titles only. It's the only way to get any meaningful results.
Good luck.

Thanks for the info! I'll try to dive further into this!

[Rich82GS750TZ]

Sorry, I have very limited knowledge on this, just something struck me about your issue that made me think of reading about spark plugs, caps, and wires, any of the 3 can have resistors, but you only want it in one of the three, and that could potentially be an issue for you. It may not be. Just thought it was worth exploring the idea. Take a look at this thread, the knowledgeable people like Nessism and Steve know what they're talking about. See if any of that info seems to make sense with your issue.

You may want to start your own thread on this.

Tip on using this sites search function.
Always used advanced
Type in your keyword(s) and change to search titles only. It's the only way to get any meaningful results.
Good luck.

[Mutashio]

Spitballing hear based on what I’ve read. Bike originally had resistor caps (I think). Original spark plugs were non-resistor. If you’ve replaced plugs with the more commonly available these days resistor type, you could have 1 too many resistor on a given line?

I'm not sure if i follow you...So a little background, the bike had the original ignition coils on when i got it, which i have had issues with over the last 2 years. So last year i did the coil relay mod and now get a full 12v to the coils. Then a couple weeks ago i picked up a new set of coils off amazon, i know someone is going to give me grief about it but yes they are cheapies from china...although it doesnt seem like its a coil issue, as yesterday i went ahead and swapped the 1-4 coil back to the original and it does the exact same thing! I'm very confused how that could even happen unless its a spark plug issue, is that what your referring too @Rich82GS750TZ ?

[Rich82GS750TZ]

Spitballing hear based on what I’ve read. Bike originally had resistor caps (I think). Original spark plugs were non-resistor. If you’ve replaced plugs with the more commonly available these days resistor type, you could have 1 too many resistor on a given line?

[Mutashio]

Hey guys, in an attempt to stir up an old thread I'm having basically the same issues with #4 cylinder except that regardless of which boot I use #1 or #4 it does the same thing. With the boot fully on #4 doesnt fire, if I pull the boot off and just place it on top of the spark plug the cylinder starts to fire! It's almost like something is shorting out my ignition coil??? Any thoughts?

awesome! I've had a number of carbs stay dry after a refresh.. dunno why it happens but it does... once they get gas , all is well!!
CONGRATS.. hope the valves are right on baby!!

Nice! Glad to hear it!

[bellucci]

Big smiles all over the forum...
Curt

#4 is alive ! ! !

#4 cylinder is ALIVE ! ! !

As suggested a number of times, I swapped the #4 and #1 plug wires.

As soon as I fired it up I knew something was different since I was getting some blue smoke out of the right side exhaust that I had not seen before. (I had squirted some engine oil into the cylinders through the spark plug holes before trying to start the bike the first time.)

So, I figured that with #4 running, #1 cylinder now had to be dead (if it was a spark problem). But no, #1 cylinder was also firing, WHICH MADE NO SENSE AT ALL.

The only thing I can figure is that the last time I ran the bike I used the old carb mechanic's trick of tapping on the side of the fuel bowl with a plastic screwdriver handle in an attempt to loosen a stuck float and/or needle valve.

The only thing I can figure is that the needle valve in #4 was stuck from sitting dry so long after the rebuild and the tapping finally freed it.

I still need to get the valves adjusted, but for now I think I've got all 4 cylinders running.

Thanks everyone for all the help and advice chasing down this dead cylinder.

***

[tkent02]

Something like this?

The plug wires are long enough, you don't have to take anything apart. Just pull it through to the other side, just wire #1 to the #4 plug and wire #4 going to the #1 spark plug. This takes less than a minute, and will tell you once and for all if it is an ignition or a fuel problem. If the problem goes over to #1 it's ignition. If it stays in #4 it's not.

Did not realize that they were long enough to pull across to the other side.

If so, that makes it easy.

Thanks!

[Brendan W]

Something like this?

I just thought about something...I use a propane enricher tool for vac leaks. you could try propane too as an aid to finding out if #4 is LEAN/no fuel....but discaimer here . I have the right tool but have also used a burn-zo-matic torch on occasions.. but using a torch you can not turn it all the way on.. just crack it open UNLIT to get a small flow.. then maybe let it suck into the sync hole? just another idea here...don't blow yourself up...
I always suspect carbs first but in your case.. ??? if that does nothing, after eliminating spark, get a compression gage!

I have seen plugs that fired in the open but wouldn't in the cylinder but it wasn't the plugs fault. Generally it's down to a weak spark.You could try pulling #1 and comparing the strenght of the spark - it should be 'fat'. I'd try running it in the dark with the tank off looking for escaping sparks along the ht lead. I don't know if it's possible to swap the ht leads on that coil but you should be able to get the longer one to the short side and see if it still runs on three if you get my drift.

Brendan,

I haven't yet, but I intend to swap the #4 and #1 spark plug wires and see if the symptom moves over to #1 cylinder. If so, bad plug wire.

Thanks.