Ignition coils wired improperly? One cylinder not firing

[mollusc]

Given that it's the simplest and cheapest approach, I would recommend changing the plugs and wires.  It doesn't seem like you have any ignition issues further upstream.  Bob's notion that you could have an intermittent connection is sounding plausible to me.
Compression doesn't seem a likely cause to me.  If there was something going on with the valve train you would probably hear it, and you're getting reasonable numbers so the rings are seated enough for it to run.  I've read of Nighthawks being fine down to 90 psi or so.

[Sterminare]

Your bike likely came with stranded copper wire (not the noise suppressing graphite ones). You can see the ones I ordered from NAPA here https://nighthawkforums.com/index.php?topic=359.msg3054#msg3054

Bob, I'm going to order one of these kits you linked. I saw in your post you mentioned you had to add an adapter to your threaded-top spark plug to get it to fit the aftermarket boot, I can't find these, do you have a link for them or a term I can search for? Better yet did they have them in store at NAPA?

Thanks. They're being shipped to my local NAPA I can pick them up tomorrow so I'll install them this weekend.

[Bob H]

Here's a link (if you are going to NAPA they will have them)

I had some laying around. Here is from that other thread I referenced:

The stock spark plug leads (on my bike) push onto threads on spark plug.
I had to place the thread-on adaptor to the spark plug tip. Same as my lawnmowers and chainsaws.
The plugs were only a few months old and I didn't want to disturb the recently torqued plugs, so I just added the tips and tightened them down with pliers as best I could in place on the bike.



Our bikes came with solid (stranded) copper core wires. In the USA I got these https://www.napaonline.com/en/p/BEL700172
Part #: BEL 700172
Line: Belden

They will come with molded ends to spark plug. They need to be cut to length at the coil end, and re-use your old screw on attachment caps to the coil as I mentioned in that other thread (if your 1984 650 is like my 1993 NH 750).

[Pete in PA]

If it is spark, with the paired cylinder running, where is the spark going?

Try running it in the dark you should see it.

Harbor Freight compression testers for instance are known to read low.
90 psi is on the ragged edge of not running at all.
Sitting that long can cause valves and valve seats to rust giving blow by.

[mollusc]

You won't always see a stray spark if there's no gap small enough for it to jump, but it's worth trying to see whether something is apparent.

[Sterminare]

Pete are you referring to if the spark is jumping through the cable to ground on the block somewhere besides the spark plug itself?
Im installing new leads tomorrow morning but if the issue persists Ill try running in the dark and see what I can see. The leads are packed pretty tight between the coils and the engine so contact with the block is definitely plausible.

[Sterminare]

Update, new spark plug leads and new plugs installed, no change. Measured the ignition coils they're good as far as I can tell. Pickup coils measure good too. Not really sure where to go from here. https://imgur.com/a/LpFb4jk

No change when wiggling the spark plug leads. The air being blown back out the carb feels cool and makes my hand wet with gas so doesn't seem to be exhaust. Confirms it's not combusting at all in addition to the cold header.

[Bob H]

Update, new spark plug leads and new plugs installed, no change.
...Confirms it's not combusting at all in addition to the cold header.

Yuk-O-Rama.
That is frustrating.

It has to be one of 3 things,
Compression (which you ruled out),
Spark (your diagrams look right - and new plugs and leads)
Fuel. The mystery is that starter fluid made no change when sprayed into the "cold" cylinder.

If you didn't separate the carbs, then you likely did not ultrasonic them.
What did the cleaning consist of? Did you pull jets, and pilot screws, ensure that carb-cleaner sprayed through all orifices and out to an opening?

I looked over all your photos, and although the bike only has 5,000 on the clock it looks like it has seen some time outdoors with corrosion on various painted frame parts. I would suspect the contact points on kill switch, kickstand switch, the things that can affect resistance to full amperes going to the coils. But an intermittent or "partial" spark should affect all 4 cylinders equally.

I'm still curious what an infrared thermometer may show for the dead cylinder.
Putting your hand on exhaust headers is risky stuff, and I am curious if it is truly cold or just a mis-fire.
They are pretty cheap, or you may have an AutoZone that will loan one out.

[Sterminare]

If you didn't separate the carbs, then you likely did not ultrasonic them.
What did the cleaning consist of? Did you pull jets, and pilot screws, ensure that carb-cleaner sprayed through all orifices and out

I did not. I pulled them off as a bank, drained them all, and one at a time opened each carb, removed the slide and diaphragm, removed the float, removed all the jets, and sprayed out all the passages I could see with aerosol carb cleaner. The first time, I sprayed out all the jets and made sure they visually looked clear and same size to each others and reinstalled. After this didn't work, I replaced all the jets with new ones from my rebuild kit.

I paid particular attention to the idle passage which is definitely clear.

I reassembled, set mixture screw to 2 5/8 turns out from light seat. And that's how I've been running

I bought a vacuum syncer. But I don't know how well it's going to function if it's alternately sucking and blowing out the vacuum ports. So I'm hesitant to separate them anyway in case I'm unable to vacuum sync afterward- then I go from 1 dead cylinder to 4 

I can call around and see if a local shop has a thermal camera I can borrow. Is there anything specific that I should be looking for? I suspect the exterior of the block would be a similar temperature just because of the thickness and proximity of the cylinders. The headers being separate show a clear temp differential. But I have indeed gotten a couple burns a few minutes into my diagnostics...

Everything I touch on the bike I've been tugging on crimp connections, wire brushing corrosion off connectors, and adding dialetric grease. Painting and restoring things here and there. I want to make a log post showing my stuff once I finally get the bike riding. I keep the bike under a cover. But I've only had it for about 1.5 of its 40 year lifetime. But like you said itd be effecting all 4 cylinders.

I think my next attempt is just trying to clean the carburetors again without separating. I just don't understand how the carburetor fails by ejecting fuel+air mixture back out the intake. That puff of air has to be coming from somewhere??

Engine Is covered in red silicone from previous owners. Valve cover has been off, oil pan, every gasket you can see from the outside basically. Why?? Chasing oil leaks? Messing with valves? I have no idea.

I just repeated testing with starting fluid because last time I only shot it in cylinder 2. I would expect spraying into a running cylinder would increase the revs? But spraying it into any running carb 1,3,4 causes the bike to bog down and almost stall. Spraying up close or far away. But the air box boots are not on the bike right now. I don't know what this means but I figured it might be relevant. In any case sprayig into carb 2 causes no change good or bad

[Sterminare]

Ive just taken a boroscope video down inside cylinders 1 and 2. Cylinder 2 (dead one) is receiving fuel I think. The spark plug is wet and theres a puddle at the bottom of the cylinder. https://youtu.be/Ce2VNu93rF0?si=OMm1ug8JgfjPUoMO

Video sequence: first I lower into cylinder 2. Then I lower into cylinder 1, but it's too high in its stroke so I remove the cam and crank briefly to lower it. Then it goes back into cylinder 1 to show there is no puddle. Spark plug 1 is dry.

Video taken after running the engine for a couple minutes including spraying starting fluid into both these carbs

[Bob H]

I can call around and see if a local shop has a thermal camera I can borrow. Is there anything specific that I should be looking for?

I mentioned thermometer - not camera. Sure, the infrared cameras are amazing. But I got this cheap thermometer from Amazon, below $20 and it works great. If that was my bike, with the tools I have available, I would point my thermometer at each exhaust header. There is a small laser dot to show you where it is reading temperature from. Works great for a vehicle I have that is sensitive to transmission fluid temp relative to marks on dipstick. Once you get one, you find other uses for it. BBQ, etc.

Unless you have a friend at a shop - I wouldn't expect any shop to loan tools to a customer. AutoZone does (in my area).

Everything I touch on the bike I've been tugging on crimp connections, wire brushing corrosion off connectors, and adding dialetric grease.

At this point I think I would run a fused wire directly from the battery to the coil as a diagnostic, and see if it manifests the same issues (be sure to remove that wire).
We often do a "coil mod" where a relay that runs directly from the battery to the coil activates when ignition is on, and kill switch is on. That way the coil gets more juice than it would through aging contact points in the on-off and ignition switch.

How is your battery?? Obviously it has been cranking more than normal, without receiving a charge from a running engine. Weak batteries cause all kinds of grief if the marginal amps are turning the engine over with very little left over for spark.

I think my next attempt is just trying to clean the carburetors again without separating. I just don't understand how the carburetor fails by ejecting fuel+air mixture back out the intake. That puff of air has to be coming from somewhere??

Dead rodent in that one exhaust header...

I just repeated testing with starting fluid because last time I only shot it in cylinder 2. I would expect spraying into a running cylinder would increase the revs? But spraying it into any running carb 1,3,4 causes the bike to bog down and almost stall.

I'm no expert on the different brands, but I do know that over the years I have had the same result you describe (almost like spraying water into the intake and the engine sputters) and other brands with bad-ass ether cause an instant RPM increase.
Playing with flammables is bad advice, so don't listen to me - but if it was my bike and the starter fluid sucked, I would consider squirt a small controlled amount of fuel into the intake (with choke plates open) and try starting the bike. There are videos on YouTube of professional small engine repair techs doing that, and I have done that. I keep a fire extinguisher at arms reach when I do things like that.

Video...

Wow that #2 cylinder is soaked inside. I am assuming that plug is wet and fouled as well. You must have pulled the plug to put the camera down the hole - did you happen to notice if the plug was wet?

I had a chain saw that was temperamental and I would have to put a BRAND NEW plug in each time I did a diagnostic, because if I turned that engine over and it didn't start - that plug would never spark until it was replaced or cleaned in ultrasonic. Combination of weak spark and 2-stroke oil, but the frustration is real.

[Sterminare]

Battery is brand new (maybe 3 weeks old) and has been attached to a tender since I bought it, new gel type battery not fluid filled

Relay mod sounds like a good idea. I might try what you're saying with the temporary wire, but I just don't get why cylinder 3 is operating but cylinder 2 isn't, if there is insufficient current for one wouldnt the pair stop working together. I suppose it couldn't hurt

The dead rodent gave me a good chuckle despite my bad mood right now after a long day of unsuccessful efforts... But for real, I wonder if there could be something blocking the exhaust. It doesn't seem like there's any combustion happening to produce any exhaust in the first place though. Baffles are in place so seems unlikely (unless it's a handful of tiny rodents..)

I'm thinking/hoping the puddle is mostly starting fluid. But regardless of where the fuel came from clealry no combustion is happening in that cylinder.

The plug was indeed wet. I swapped it with cylinder 1 and it runs there anyway.

Fuel/air, compression, ignition; cylinders 1,3,4 run so everything up to the ignition coils is known good. Cylinder 3 shares the coil and runs so the coil is known good. The only things left is the wire and the plug. I swapped wires and plugs between 2/3. So ignition has to be good. I measured compression as good on all cylinders. That just leaves fuel/air. It has to be the carburetor  but I cleaned it twice and I really thought I got everything. It might be time to buy an ultrasonic

[Bob H]

I wonder if there could be something blocking the exhaust.

It is odd that you feel air pushing out of one intake and not the others when you crank the engine.
On the face of it, that would sound like an intake valve stuck open - yet you get acceptable compression readings so it must be closing.

I swear that low mile vehicles that have been stored are more trouble than something that gets ridden frequently. My maintenance these days consists of regular riding, changing oil.

[mollusc]

When you had the carbs apart, did you thoroughly inspect the diaphragms for tears?

[Sterminare]

When you had the carbs apart, did you thoroughly inspect the diaphragms for tears?

Yes, they looked good, they were still soft. The slides drop slowly when pushed and released