TOPIC:

1981 KZ1000... I do realize this is a very open-ended question and diagnosis is not likely possible, but at this point I'm just trying to eliminate whatever I can.

So I got the carburetor bowl fuel level adjusted yesterday (it was off by almost 4mm). So far the butterflies have only been visually synced to where they all closed at exactly the same time, and the air screw has never been touched. I am running the factory airbox, but no filter yet. I just checked the spark plugs -- #4 was slightly wet with oil but also had a visibly too-wide gap. The other three were pretty close but adjusted anyway, and had the expected tan color. My book calls for a gap of .28-.32, so I used feelers at .30.

The symptoms... It simply won't stay running below 3000rpm in neutral, even if I keep it running long enough to get it hot. I've tried with the choke in all three positions. Now that the carb floats are adjusted right, my previous problem of gas flooding into the airbox is fixed so I was able to hook up the fuel petcock to vacuum again, and now have the tank actually sitting on the bike. With the petcock in the 'on' position (which I believe requires the vacuum to allow fuel to flow), I can run the engine for several minutes and the fuel keeps flowing. Usually what happens is if I try to let the RPMs drop below about 2800-3000, the engine will run for a few seconds and then slow down and die. Opening the throttle will not keep it going, and a few times when it was cold it had a mild backfire into the airbox as it died (no explosion, just a sharp puff of exhaust-looking air). And finally, while it doesn't feel or sound like it is missing on any cylinder, it does feel rough. Of course that could just be the speed without having any load, and keep in mind this is the first time I've even seen a KZ1000 running. Also it seems like the engine is getting hot, but my previous experience was with a 650 so maybe this is normal for this size of engine. The heat is noticeable but not worrisome, if that makes sense.

My thoughts so far... As mentioned, it appears to be getting a good flow of fuel. I believe the coils are ok since the plugs look normal and I haven't noticed any misses. When I put the top-end back together, I was careful to count the 44 links on the chain, then turned the engine all the way around and re-counted the links. I'm confident the chain was set right against the marks on the cams. Since I have electronic ignition, I'm unable to check the timing at idle. I did give the springs a squirt of WD40. I'm not sure if there is anything else I can check with the ignition? Honestly if this was an old car I'd be adjusting the timing by a few degrees because it just 'feels' like the spark is coming too late. Next time I start it up I want to spray some ether around the intake side of the manifold and make sure there's no significant air leaks, but those rubber boots may have been replaced by a PO because they looked really clean and didn't have any cracks in them.

All right, I think that about covers everything I can think of. What am I missing? What other likely culprits should I be checking? I have zero funds right now to just randomly throw new parts at it, but I do have some spare parts from another engine to work with (no I don't have another set of working carbs). I'm just out of ideas.

Have you ensured you don't have a vacuum leak? Check those rubber plugs on the carbs to make sure they are not cracked or split.

No eBay APP ID and/or Cert ID defined in Kunena configurationIf you haven't already done so, check and adjust the carb balance with a manometer.
I've had great success using a Carbtune Pro.

See:

IMO, there is no point trying to adjust the carbs before installing the air filter.

all the above plus are the carbs clean? A plugged pilot jet/ pilot circuit won't allow a decent idle. Spray can carb cleaner isn't going to do it either.

2nd on the Carb Tune. Best tool for sync'ing carbs there is.

The vacuum plugs are brand new and seated all the way down. The other two lines going to the emissions device were inspected and seems find. When I sprayed ether across the intakes, I did discover there is a leak on #4 -- hopefully that is the cause of the wet plug but unfortunately it requires removing the carbs again to get to the screws for tightening that rubber boot. Maybe I'll take it off and see if I have another in good shape.

I'll keep the link handy on the carb tuner, but like there said there is absolutely NO money to spend right now. I'd like to get a chuck for the dremel to drill into some locks but I don't even have the $9 for that until the end of the month.

As for the carbs being clean... that is a good question. I completely tore down the carbs a few years back, flushed everything as well as I could, but for some reason the float pins will not come out so I couldn't pull the jets. Visually there was nothing suspicious when I cleaned them, no debris in the bowls or anything like that, but I simply don't know for sure.

The next question could be when was the last time the valves were checked? This will and can effect idle too.

When were the valves checked for what? I did a full tear-down of every engine part before sandblasting and painting, then reassembled with new gaskets. The valves were pulled apart, cleaned and lapped, but the lapping seemed to indicate that PO had the seats ground as the ring from the lapping compound formed a perfect band on each valve.

Here's a shot of how the seats looked before lapping:


And here's what the valves looked like after lapping:


Does that help?

A leak-down test will help determine whether closed valves are leaking due to imperfect interface with seat or insufficient clearance or some other reason.

With insufficient clearance, idle performance often worsens as the engine attains normal operating temperature. For instance, the cold engine might start and idle okay, but then idle poorly or refuse to idle when warm.

A burnt or cracked or bent valve may leak regardless of correct clearance.

When an intake valve fails to fully seal when closed, the combustion that partially escapes through the supposedly closed valve may appear as backfire through the carb.

A leak-down test injects air pressure through the spark plug hole to pressurize the combustion chamber.

Can perform a poor-man's leak-down test by introducing compressed air into a spark plug hole and listening to where it escapes from the combustion clamber. This may be done at TDC or any other cam positions where both valves are fully closed. Top dead center (TDC) is when the piston is at its highest position. An easy way to tell TDC is by alignment of the T mark with the case mark when viewed through the timing window.

May introduce a spurt of compressed air by using a rubber cone-tip blow gun (rubber air nozzle) held into the spark plug hole. And of course keep holding it in position to keep air from coming back out the spark plug hole while listening for escaping air at other places. The air compressor should not be running while listening because the noise will likely drown out any sound of escaping air. Or just use a portable compressed air tank.

Air heard escaping from exhaust port indicates exhaust valve not fully closing (perhaps too tight clearance or damaged valve or valve seat).

Air heard escaping from carb intake indicates intake valve not fully closing (perhaps too tight clearance or damaged valve or valve seat).

Air heard escaping from crankcase breather indicates loss of compression past rings into crankcase (perhaps worn piston rings or cylinders).

Air heard escaping from head gasket area indicates loss of compression past head gasket (perhaps due to a blown head gasket).

A leaking valve may sometimes be resolved by adjusting the clearance to within specs.

A leaking head gasket may sometimes be resolved by torquing the head fasteners when the engine is stone cold (such as after sitting overnight).

Good Fortune!

Hmm that's a good idea to try, thanks! The bike is parked around the side of the garage and I have plenty of hose to reach, so noise from the compressor shouldn't be an issue. Had a long day and won't get to the bike tonight, maybe tomorrow I can get back on it again.

TexasKZ wrote: IMO, there is no point trying to adjust the carbs before installing the air filter.

This

Yeah but shouldn't the engine be able to *idle* without the air filter?