One cylinder not firing...tips

OK, I'm almost positive that I saw kind of a breakdown on how to ferret out what was the cause of a cylinder not firing, but try as I might, I can't find it today. So, here's my question. I went to ride my 82 XJ650 the other day and for some insane reason decided I should touch the header pipes (actually, after reading about it a lot on line, wondered if perhaps my bike wasn't firing on all cylinders). Low and behold, but cylinder number three just did not seem to be kicking out the kind of heat you'd expect. So, what is the recommended procedure for figuring out the issue? I seem to remember starting with something as simple as checking the plugs, but I'm not sure. I also seem to remember mention of the coils, but again, not sure.

Also, while I've got your attention, any suggestion on a set of coils? I know the Dyna 3ohm are the most popular, but they are a bit outta my budget right now, so, any other suggestions? Accel??

Thanks in advance.
Beardking

 

I would check the plugs first. One of the keys to trouble shooting is to check the simple things first. If that’s not the problem see if its getting spark if it is I would think that is a fuel problem but remember that even if it has spark when something’s under compression it takes more power to make that gap.

 

Sometimes it's something as simple as the tightness of the Plug Cap on the end of the Spark Plug wire. Insert the strands of some ignition wire into where the Plug Cap screws-on and cut them off even.

Add an inch of tight-fitting shrink-wrap to the plug wire's end and shrink it ... followed by a second application of shrink-wrap for strength.

Screw the Plug Cap back into the end for a "Sure Fire" solution to loose ends.

 

I had one heck of a time, I think after I did my valve shims. Was running on 1 cylinder, which means barely running.

Pulled plug, base up against head. No spark. Kept messing around. Tried to start again. Plug fell off head - nice hot spark when it was ungrounded by 1/4 inch.

Plugs didn't look bad - but clearly fouled. Probably all those trips back and forth to the barn this winter not really getting them cooked clean. Also, idle might be a bit rich.

Cleaned the insulators off and it purred like a kitten.

 

Are you talking about the end that connects to the plug or the end that connects to the coil? If it's the end that connects to the plug, that's a pretty secure connection currently.

I took my plugs out today and they were all a bit black and sooty, except the 3rd cylinder. It was black and a bit wet (like fuel). Just for the heck of it, I took the spare set of plugs that I have from before doing my carb work and put those in, as they were fairly clean. Took the bike for about 1/2 a mile ride and checked them and they are getting black and sooty again, except #3, it's black and a bit wet. To me, it seems like all are running a little rich and #3 is REALLY rich. Thoughts?

Oh, and I checked the spark (pulled plug, grounded it on the cylinder, hit start button) and it was getting fire.

I'm trying to get this thing completely ready for riding as I'd like to start riding it to work every once in a while.

 

Did the wet on that plug smell like gas?

I recomend hooking the clear tubing to check float bowl levels and see if the floats are set just right.

 

Hvnbnd, yep, smelled just like gas. As did my air filter (was checking to see if it was clogged, which it wasn't).

I'm going to have to do the float bowls tomorrow after I get off work.

 

Are your mixture screws accessible? Sounds like you might have an overly rich idle...look at this thread for more info...

http://xjbikes.com/Forums/viewtopic/t=2 ... crews.html

I'd go ahead and screw the #3 mixture screw down a couple turns, take the plug out and clean it off with an old toothbrush and then run it a bit and see what the plug looks like. I had the same problem on my bike.

If you happen to have a colortune, then colortune it. :wink:

 

Man, you'd think they would have made those freaking mixture screws more accessible. I just filled up the tank this evening, so it's going to be a pain in the butt to take it off and go at it with the colortune again. ;-) Oh well, you do whatcha gots ta do, right.

 

You can do it with the tank on...I can on my bike, anyways.

Use a 2" long hexagonal slot bit (the kind you'd put into a cordless drill or one of those quick-change bit holders), and you should be able to reach in there and turn it with not a lot of finger pressure.

 

air filter with gas smell and runs rich......I'd suspect float level.

Try the clear tubing to check float bowl level.

 

Well, I just checked the float levels (literally, my hands still smell like gas) and they are all within spec. So, tomorrow (hopefully) I'll pull out the colortune and see what I can find out with it.

One question, I know that the exhaust for the non-firing cylinder will warm up from the general heat around it, but I noticed that after letting the bike warm up for a good 5-10 minutes, it seemed to be up to about the same temp as the other 3. Is it a possibility that once it gets warmed up that 3rd cylinder kicks in? If so, any suggestions on that? I'm sure it's not supposed to do that.

 

I've seen this symptom before......plugged pilot jet. Not saying this is your problem, but if you've got the bowls off, it's easy enough to check.

 

The fouling of the #3 cylinder means something. That is where the vacuum line for the petcock attaches. I would check the petcock for leaking. This would produce a reich mixture for all cylinders but mostly for #3. Remove the fuel line and see if it leaks fuel with it set on "ON".
If you have already colortuned by the time you read this then I suspect you will have found it hard to eliminate the orange flame if I am correct.

 

Blue Maxim, actually, there is no line going from the #3 cylinder to the petcock. I have dumped the failure of a petcock that needed the vacuum line and I have installed a nice little cap over the vacuum port.

I did colortune tonight and no matter how much I turned the adjustment screw on #3, I didn't get any change in color. Any suggestions on this one?

Man, I really need a local person that knows about this and will work for beer or pizza. ;-)

 

Only thing I can think of is that you're turning the mixture screw the wrong way...turn it in to lean it out. If you've got it turned all the way in and that cylinder is still running rich, then it's possible you might have an obstruction of some kind somewhere in the number 3 exhaust pipe.

Ok, I can think of one more thing...your idle jet is way too big. Maybe a PO did a little modifying in there. :x

 

Well, I guess I'll have to look at the exhaust and see if there is anything there and if not, I'll be taking the carbs off Sunday when it's raining and check the idle jet because I turned the screw all the way in (carefully) and out and it didn't change color at all. The other 3 I could easily get yellow flame showing and backed it back down to a nice bunson blue.

 

So was the colortune orange?
If so it is rich on that hole?!

Why is another story...... Have you tried the tapping on the carbs?
I use about a 1/2" - 6" extension and tap on it with a ratchet (you have to be very careful not to break anything)

So what led up to this trouble again?
Did you go thru the carbs?
Remove any jets and change them or perhaps put a couple in the wrong place (say in the #3 carb?)
I'm grasping here...

 

Actually, no the color was a fairly decent blue on #3, just not adjustable. As for how it came about, for some wild reason I decided to check the exhaust pipes to see if the were around the same temp, and #3 was a lot cooler than the others. It ended up getting up to the same temp as the others, but the cooler part at first worried me.

I'm wondering if maybe I'm making a big deal out of nothing since after only a couple of minutes of warming up, #3 seems to get in line with the rest.

As for going through the carbs, the only thing I've done on that front was I pulled the float bowls off and cleaned them. I'm pretty new to the carb thing, so I was a little hesitant to break them down any further. I bench synced them and then put them back on the bike and colortuned them. Then it got cold and I didn't mess with it for around a month or so. Now I'm trying to get it prepared for the oncoming nice weather.

 

I just had another thought....(yeah, that happens occasionally :wink: ).

You might have something wrong with your actual mixture screw on the #3. It's got a tiny tip on it that could easily be busted off by a ham-handed PO. If the tiny (and I mean tiny) tip is gone, it won't be sealing the hole at the bottom like it's supposed to. I'd pull it out and have a gander, unless you've already had it apart and know for sure it's ok.

You might want to wait and see if any of the gurus chime in, as well. :wink:

I just read your latest post....maybe it's something you can live with if the flame is a proper shade of blue? If it's not fouling the plug, then I'd just leave it. I was assuming you had an orange flame in the #3.