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Maybe one of you can tell me what I'm hearing for the first time? I've done a bit of work on my bikes before, but I've never experienced this problem.

I have a parts bike for my beloved '92 CB750 Nighthawk. It was a running parts bike, when I bought it years ago when I had a really good job, I checked it out and test-rode it plenty, then put it up for long-term storage. Well, things are such that I need to sell the parts bike. My own Nighthawk is running just fine, at least, and I don't need any parts for it.

When I put the parts bike away, I removed the tank, drained the float bowls, ran it till it quit from lack of fuel, put just a little oil in each cylinder, and put it up on blocks. It had a cheap rusty aftermarket exhaust on it that was absolutely terrible, it had been dropped and pretty much ruined. I removed the exhaust and put rags in the exhaust ports. Then I rolled it into the corner of the garage, jacked up the bike and put it on blocks so the tires would stay good, and never needed a part except for a stripped bolt and a brake lever. This bike has less than 15k miles.

The Nighthawk 750 is the same from '92-'03, air-cooled inline four, chain drive, four valves per cylinder, with hydraulically adjusted valves.

Fast-forward 2+ years to today. Pulled the bike out of storage, fresh fuel in the empty tank, bolted on a stock used exhaust that was in good shape, borrowed the battery from my other bike and hooked everything up. It finally started, and I finally got fire on all four (I had spark but no fire on cylinder 1 for a while). It's smoking a lot, even after running for a good five minutes, longer than I think it should smoke. Rings?

It's popping a lot too and sounds like it's not firing regularly. Condensation in the tank that I thought was empty?

And it's tapping, it sounds like a car with a bad valve. If one of the hydraulic lifters is stuck, am I doing damage to run it? Will it come loose with time? Does this happen often and what do I do about it?

The PO told me that the bike had not been rejetted for the aftermarket exhaust but that may or may not be true.

Thanks for any info you folks have...I sure hate to jump into the top end, I was pretty sure I'd done a good job of putting the bike away in such a condition that it would be good to run when I needed it. I hope it's a simple fix, looks like over a hundred bucks just for new rings....

Sounds like it may be a stuck/sticky tappet, alright. You could take it for a run and it may work itself free, you may need to give it a shot of Mystery Oil or other lifter treatment chemical to do it. Possibly pull the valve cover and valve train to get at and clean or replace the bad one, but I would guess not. All the usual 'careful what additives you dump in the sump/clutch' warnings apply.....

Just idling won't put enough load or temp on the cylinders to burn off storage oil for a very long time, it is always best to warm it up, then ride it to put proper load on the engine. It will also really increase the chances of that tappet coming free with a load. The tricky part is knowing when the noise it makes is just the cricks getting worked out after storage or something eating itself to death in the motor.

Tick, tick, tick....... clack, clack, clack...... grind, grind, grind...... whiiirrr, bang, tinkle, tinkle..... some of these noises are acceptable for a short period, some ain't. Where that line is drawn is up to your own comfort level.

If you have any real doubt, best yank the V/C and have a look.....

Thanks Buzz,
your advice coincides with what some pretty knowledgeable folks at the nearest shop are telling me. They reccomend either some Marvel oil or some ATF in the crankcase, run it just a bit to get it all up in the lifters, then dump that oil (it's old oil and needs to be changed anyway. It was brand new oil when the bike was put away, it's still clear.)

I put in a new plug on the #1 cylinder, now it's firing very well and no more coughing and missing. Still smoking like a freight train, though. I haven't ridden it yet, I need another rider to come along in case something is bad wrong.

Wish I could keep this bike, I really really love the later Nighthawks. Not the fastest, not the flashiest, but real tough, good-handling machines that don't need much care or money to run.

I'm with Buzz. Do a little riding to loosen it up. The engine has to generate some horsepower in order to get the cylinder temps and pressures to their normal operating values. The smoke could be left over storage oil, or it could be that you have a sticky ring or two.

I'm not much on snake oils, but this would be the time to pour some Marvel Mystery Oil into the crankcase. I don't have much of an opinion about using that stuff on a regular basis, but I've seen it work wonders on air cooled aircraft engines that had been in long term storage.

To finish this little story:

Threw a cup of Marvel Mystery in the crankcase and ran it up and down the street. Valve quieted right down, and it's done smoking too!

Thanks folks!