Ignition coils wired improperly? One cylinder not firing

[Sterminare]

I've pulled the exhaust off. After the dead rat comment I can't help but think about exhaust blockage. It makes sense doesn't it? If the exhaust is blocked, combustion occurs but the cylinder doesn't depressurize during exhaust so it remains pressurized until the intake valve opens, blowing air and fuel back out the carb. Leading to occasional irregular combustion followed by several misses which I think is what I'm seeing, still makes good compression because the valves are operating as they should. In fact that piston makes 5psi more (125 v 120 in the other 3).

So I wanted to stick my boroscope down the header and see what I can find- probably not a dead rat but maybe degraded heat shield material, or something of that nature I'm not too familiar with exhaust systems.

First thing I noticed: all the acorn nuts on the exhaust headers are only finger tight. I didn't even need my ratchet to spin them off. I guess that's better than seized? But all the headers are/have been completely loose this entire time.

Second: looking into the exhaust ports on the block, cylinders 1,3,4 are bone dry, cylinder 2 is absolutely soaked. Check out the images of cylinder 1 and 2. I stuck my scope in to try and look at the back of the valves but a) it doesn't focus well that close and b) I'm not sure what I'm looking at. It looks like the backside of two valves to me but I expected only one? https://imgur.com/a/6QWlYAi

Third, I stuck the scope down header 1. Not super easy to see anything, the scope does have a little light on it. Basically looks like a lightly rusted pipe until I hit something flat and metal, presumably the baffle in the muffler (?). Then I stuck it down header 2, this time it looked similar until it just went black. Confused I pulled out the scope and the lens is covered in black goop. So as you can imagine all the unburnt fuel is going straight down the header and collecting at the low point.

I poked out the drain holes but the bike is/has been on the center stand and not much drained out just a few drops of clear liquid. Bike is under a watertight cover but is outside. I don't think it's rainwater, probably condensation from not fully warming up every time I test it it only runs a minute or two.

I think I'm going to try hosing out the exhaust pipes and see what comes out, and then see if I can get a clearer view with the scope. Unless I'm ending up at the meeting point in the center, I should be able to get to that same flat plate I found in header 1. But right now I can't see anything the lens gets obscured.

[mollusc]

I'm not sure what I'm looking at. It looks like the backside of two valves to me but I expected only one?

There are four valves per cylinder, so you should see two exhaust.

[Sterminare]

I still get blowback through the carbs with the headers removed, just cranking with the Killswitch off. I feel air being ejected from all four exhaust ports. So I think the exhaust blockage theory is out.

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Carburetors removed, exhaust headers removed; so literally just the head. Valves and pistons. While cranking I get puffs of air coming out of cylinder 2 intake. With all else removed this has to be a valve issue?

[Bob H]

Carburetors removed, exhaust headers removed; so literally just the head. Valves and pistons.

Valve cover still in place?

While cranking I get puffs of air coming out of cylinder 2 intake. With all else removed this has to be a valve issue?

With valve cover off you could see if the intake valves on #2 are closing fully.
My borescope only has one camera lens, but they have some affordable ones with multiple lenses, on side, that can show more detail on valve position and condition.

[Sterminare]

Valve cover still in place. Right now I'm removing carb boots to see what I can see without taking the cover off. But then the cover is coming off. Nervous, I've never done this stuff before. But I've never done any of it before and I've gotten this far so we'll see how it goes 

[Sterminare]

I'm not really sure how to confirm that it is coming all the way up. Best I can tell by just watching the rocker and valvestem, it doesn't appear to be sticking it moves up in a smooth motion.

I do see more wear on the lobes, at least some of them, than I was expecting. https://imgur.com/a/xkdPoEk

[Larry Fine]

Have you tried swapping the #2 and #3 spark plugs themselves?

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Yes, all the plugs are new but I've tried swapping them in several combinations.

I'm not seeing anything obviously/visually wrong in the head. I may end up pulling the head to inspect the valves/bleed the tappets. I'm not sure what else to do at this point

[draser]

With all else removed this has to be a valve issue?

If you have 120 psi in that cylinder there's nothing wrong with the valves. You may get some valve overlap, hence the blowback. Also the head should be okay.

I've read about getting the fat spark on problem cylinder, and also same cylinder being soaked with gas, is that still correct?

Because if it is... it sounds like a carb issue, carb 2 flooding... have you checked for that?

[Sterminare]

Yes that's correct all these problems are the same cylinder 2. But how can it be receiving fuel if it's blowing back out the carburetor? Don't I need to fix that valve overlap before I can get that cylinder to run again? With the timing being non adjustable id think that it would be caused maybe by air in the tappets or similar

[draser]

I'd recommend checking the fuel level - float height - in carb 2... it sounds like the level is high and gas gets pulled in via main jet and floods the plug, hence no spark inside.

[Bob H]

I'd recommend checking the fuel level - float height - in carb 2... it sounds like the level is high and gas gets pulled in via main jet and floods the plug, hence no spark inside.

yeah, I suggested that on Pg 1 of this thread. Here was the OP reply (Post #4) "The carbs are all getting fuel. I've had them off the bike twice now and drained a similar amount from the bowls across all the carbs."

[Bob H]

I'm not seeing anything obviously/visually wrong in the head. I may end up pulling the head to inspect the valves/bleed the tappets.

The reason I asked if you had the valve cover off - is because that is the opportunity to slowly turn the engine over by hand (plugs removed) and watch the movement of valves in #2 compared to the other cylinders.

That suggestion was just a big picture view of why you feel air pushing back toward the carbs only on cylinder #2, like maybe the valve stem was bent and the valve not fully closing.

If nothing visually wrong when slowly rotating the engine, if you still suspect there is excess air that "should" be halted by closed intake valves, you could do a "leak down" compression test (watch YouTube videos). However that is typically done when you already have confirmed low compression, and just diagnosing if it is rings-piston or if it is valves. You say the compression is 120psi equal across all cylinders so the leak-down test is kind of a shot in the dark.

There is no need to pull the head at this point. You wouldn't go that deep just for diagnosis.

Are you certain this bike had only 5,000 miles? Your cams aren't terrible or anything but they show more wear than my 750 when I changed my valve cover at 40,000 miles

[draser]

I've had them off the bike twice now and drained a similar amount from the bowls across all the carbs.

Being as it may, it seems that cylinder 2 (still) gets more fuel than the rest. The first "culprit" is usually float level, however it may be other things as well... such as wrong jet/emulsion tube/needle in that carb or even wrong slow jet. I'd do a close review of the carbs to ensure all components are identical and match Partzilla's parts list.
Somehow fuel gets past the slow jet at start up, question is how?

Also, levels need to be the same but according to the specified millimeter height for that year bike.