No.2 Cylinder not firing

[Lbrown311]

No.2 cylinder doesn't seem like its firing. What are some issues that would cause this and how do I go about checking if it is or not? Header seems like it is hot, but when wire cap is unplugged from spark plug it causes no difference in idle, where the other 3 do significantly. Is it coils, could it just be a bad cap? Runs fine on other 3. Compression check and Volt meter check coming tomorrow. O-Reily's rents them for free. Can't beat that price.

[BA80]

Probably just a carb adjustment thing. If the exhaust tube is hot it's firing. Might be just a little weak because of fuel.

Have you ridden it enough for a good color check on the plugs?

[L0rdexpectati0n]

the exhaust on cylinder will still get hot from the surrounding cylinders just not as considerable hot. id check a few things gas, air, and spark before i started looking in to compression. if it comes to that, do a leak down. when i was having issues with mine it ended up being weak gas in the float bowl. pull the wire and put a spare plug into it and ground it to the engine and check for spark if no spark check the ignition coils for cracks.

[Lbrown311]

Well would it be an idle mixture screw adjustment, because the carbs are sync'd very well. My shop has a Volt meter I can borrow just to check the electrical for good measure, and like I said O'Reily's has a compression tester they rent for free so why not. Might as well see what is goin on in there. Just so I have an idea. I am ordering a Colortune within the next week, but I have some issues I need to deal with in the mean time so hopefully I can resolve this issue while not actually driving it. I did check a couple plugs. The one I thought might not be firing was very white. The other one i checked was brownish grey, which from what I have read it is about right. I will check the other side tomorrow when I get home from work. I think they were close to what the side I checked was.

[James England]

Stick to the easiest thing first. Remove all the plugs. Cut a small piece of the end of the number 2 lead and reattach the cap. Put plugs in the caps and make sure they're all grounded on the head. Turn the engine over and check that you have a spark on 2 (and the others, of course, although you know that you have sparks on them already). If sparks on the other three but none at 2, swap 2's plug for one off another cylinder. If spark, it's the plug that was on 2 that's no good. If no spark on 2, try swapping an entire cap + plug. If spark, the cap that was on 2 is no good. If no spark, it's the lead or the coil.

Are you using OEM coils? Or coils with removable HT leads? If the latter, after doing the above and still no spark on 2, swap an entire lead + cap + plug from one of the other three and see if spark on 2. If so, the lead that was on 2 is dodgy. If no spark, then it's your coil. It will not be the pickups, because you are getting a spark on 3 and 2 uses the same pickup.

In general, given the simplicity of checking for a spark and working backwards as per above, you're better doing that first. If you do have a spark at all four plugs after doing the above, then move onto the carbs. The mechanical stage of things should, IMO, be left until last unless it's plainly obvious that something is wrong (eg no compression, hole in piston, horrifying noises etc)

As I've mentioned before here, there is a tendency to go for the shotgun approach to fault diagnosis and jump around from one thing to another, creating faults and uncertainty as you go. The engine has three distinct systems 1. electrical 2. fuel 3. mechanical

You need to work logically through one system until you've either nailed the fault or not found it. Then move to the next system. It's no good saying "my header pipe's cold on 2, I'll check the valve gaps" or "must be the carbs" or just plain guessing. Or doing several things at once. Work on the easiest bit first ie as per above. You may find it's just a bad end on a lead or a faulty HT cap........ That's better than unnecessarily stripping your carbs (and possibly creating problems) or taking the head off (and causing even more)......etc.

Number 4 header was cold after fitting my Dyna coils. Did I think "Mmm...better check the compression" or "Must be the valve gaps"? No... I did the above tests and found ......idiot that I am.... that I hadn't plugged the nice new silicone sheathed, graphite cored HT lead into the coil!

[DGXSER]

If your plug was just wet, I would agree with James to look at spark, and that methodical fashion. But your coil has to be good since 3 is firing well. The coil fires 2 and 3 at the same time every time. If it were bad you would lose both cylinders.

You stated the plug is white, assuming you mean the electrodes are coated in white not just the insulator, then it is running very lean. If you have the mixture screws all about the same, then it seems you got some crap in the idle circuit of that carb.

[James England]

The coil fires 2 and 3 at the same time every time. If it were bad you would lose both cylinders

Yes, but not if it's the lead on the OEM coils where they're moulded in with a rubber sheath on top too. Or a non-OEM coil with plug in leads. Just because plug 3 sparks is no reason to assume that plug 2 doesn't have a problem caused somewhere up the line......... The point is, the spark test takes only a few minutes and you can then rule it out/in as a possible cause.

The very first test to do on any apparently non-firing cylinder is to check the spark and rule it in/out as a cause...It's quick and easy to do and has an immediately noticeable test result that's either pass or fail. Then start messing with carbs, which contain loads of bits, can be sensitive, full of dirt, holed diaphragms, blocked hemisphere filters, stuck float valves, incorrect float tangs etc etc. It makes sense to spend 10 minutes establishing whether there's a spark or not. If I ever get a dead cylinder, I'm always hoping it's a plug, or cap or lead, or coil..... cos it's a lot easier than taking carbs off. Hence starting with the easy stuff first.... surely you're not advising doing any fuel line investigation before checking for a spark at all the plugs?