My kawasaki is sick, can you help me nurse her back to health?
February 17, 2008 4:56 PM   Subscribe

Help me figure out what is wrong with my motorcycle! I think it's simple, but I'm confused...[long and technical, yay!]

So hi. I've got a 1982 Kawasaki KZ750 I picked up last year for an obscenely low price. It's in amazing, amazing condition. Think "show room" condition. Anyway, when I purchased it, it wouldn't start. The kid had just gotten it back from the shop and was wanting to get rid of it. The shop told him it needed a new head gasket, and he didn't want to pay for it.

I brought it home, and the fuel lines weren't connected. Connected them and BLAMMO, bike ran great, but was leaking a little oil out of the head. I ordered a new one, and started the teardown. The bolts were, I thought, a little loose, but I didn't think much of it. Got down to the head gasket, and it looks perfectly fine. I went ahead and replaced it. I think the shop loosened the bolts so that it would leak so he'd pay to have it fixed. W/e. It doesn't leak now.

So, as I'm putting the bike back together, I have a DEVIL of a time reseating the carbs. Total nightmare. I get it back together, fire it up, and it runs fine, but ramps to 3500 rpm's and holds there. The only way to get it down was to back out the idle adjust screw all the way, at which point it would die.

Talked to another shop, and they said it sounded like a leaky vacuum tube to them, but to check the carbs again. So I pulled the carbs again, checked all the floats and diaphragms and pins, cleaned 'em, and then hoseclamped all the vacuum lines in place, and put everything back together.

Now, it will fire up in the first 5 seconds of cranking when it's completely cold, run for about 20-40 seconds, and die. At that point, no amount of begging will make it start back up again.

Fuel lines are fine, carbs seem to be working. They aren't vaporlocked. I can look in from the air cleaner and see they're getting gas. I can occasionally get a backfire when trying to start, but that's rare and seemingly random.

Today I decided to check plugs and wires, and pulled off the wire on the number 1 cylinder and pressed the start button---a spark came THROUGH the boot and zapped me. Weird. So I put the plug in the boot and held it to the cylinder cover and pressed the start button again. That time it zapped me through the boot cover AND at the start button. Owwie.

I tried the number 4 cylinder too, pressing start to see if it would spark from inside the wire boot to a screwdriver---it did, and no zapping of me. Have not tried 2 and 3.

So, it seems to me that it's getting gas, and it's getting air, but I'm not sure about spark. I'm assuming that getting zapped through the boot isn't a good thing, and the spark plug was NOT zapping to itself when I tried to fire it up, it only zapped me through the boot.

I thought perhaps I had put the wires back on in the wrong order, but I don't think it would fire at all if I had done that, and also I was very careful to do it correctly.

Today I also rechecked all the vacuum lines, no leaks and no collapses, but there comes a point where I can no longer blow (or suck) air through the line---and I honesly don't know what the piece is. The cylinder cover has 2 hoses going to some sort of a diaphragm, which also has a smaller line going back to the carbs (to pull the vacuum, I think) and also a larger line going back to the airbox. No idea what that does. I can't move air between that diaphragm and anything, sucking or blowing.

I intend to call the shop tomorrow, but I know it will be weeks before they can get her in. I sort of feel like this is something easy and stupid.

It's getting gas. It's getting air. Does NOT seem to be pulling gas into the cylinder, and/or it can't ignite it when it's there.

Hit me with your best shot!
BTW, this is a KZ750 LTD, the 4 carb, 4 cylinder, 4 into 2 exhaust system. It's weird that it will start and run for 20 seconds and die for hours. I think this is a telltale sign of something, I just don't know what. BTW it dies instantly while running if I try to give it any throttle at all.
posted by TomMelee to Sports, Hobbies, & Recreation (11 answers total) 1 user marked this as a favorite
Sounds carb-related. If the wires or plugs were out of whack, I don't think you'd be seeing it fire up initially. Do you have a factory manual that tells you how to initially set up the carb?
posted by bprater at 5:20 PM on February 17, 2008

Not sure what you mean by "initially set up the carb". I've got a haynes manual, but it's close to useless regarding the carbs.
posted by TomMelee at 5:25 PM on February 17, 2008

a spark came THROUGH the boot and zapped me. Weird.

Not weird, high voltage. I wouldn't assume that's the problem, and I would handle plug wires with caution.
posted by knave at 5:35 PM on February 17, 2008

The tech forums here are really good. Register (it's free), fill out your profile, and ask away.
posted by Forktine at 5:43 PM on February 17, 2008

That is, in fact, very odd. A good sign that the insulation isn't doing it's job. Replace the wires.
posted by IronLizard at 5:50 PM on February 17, 2008

Ignition wires conduct thousands of volts. It's very likely that you'll get shocked if you do anything but ground the threads and watch the gap while you're kicking it over. Anyway, if you weren't getting spark, it wouldn't run, and if it did, it'd idle really lumpily, but the quality of the idle wouldn't change much with time, only revs. Forget about the spark.

My guess, and it is just a guess, is that you've got two problems - you've got a leak between the carb and the intake valve, and you're running far too rich. The fact that you can back the idle adjust all the way out and it'll still run nearly confirms the air leak. The fact that it'll run with a leak indicates that it's still getting some fuel. I bet that you richened it up to get it to run, and then started playing with the idle to get it normal. Currently the mixture is right to get it to run cold, but once it starts to build some heat in the cylinder, it dies and won't start again until it gets cold.

I'd recommend pulling the carbs again, as much as I know you don't want to. Then reset the main jets to where they were when you pulled them the first time, and set the throttle to factory spec - there should be a spec somewhere, but if not, just back it all the way out (i.e. closed) and turn it back in two full turns.

If you really don't want to pull the carbs again, get some starting spray or some carb cleaner, start it up, and start spraying. You'll know when you hit the leak, because it'll rev up, cough, or die. Something will change, anyway. Good luck.
posted by TheNewWazoo at 6:45 PM on February 17, 2008

Clarification for TheNewWazoo:
I wasn't getting a spark across the gap, only through myself, even when insulated there was no apparent gap spark in the number 1 cylinder.

It doesn't run now. The running w/ the idle adjust out was before the last carb pull and vacuum line securing. At that point it didn't run, it would die, but in just a little bit it would wind up. I thought air leak at that point too---but now it runs somewhat normally for 20 or so seconds and then dies.

I didn't change any of the jet adjustments when I pulled them the last time (or ever), but I was somewhat suspecting that air/fuel ratio might be to blame. (for whatever reason.) Realisitically, that's a little outside my technical ability/the limits of my tools and space w/o some guided supervision, and I also don't have technical recommendations for these settings---they're NOT in the Haynes manual.

Someone else advised spraying wd-40/carb cleaner/ether around the carb boots and waiting for a rev to show the leak. Is that what you're suggesting?

I'm seriously afraid of pulling the carbs any more than I have to---they're easy to get out but so damn hard to get back in without excessive force.
posted by TomMelee at 8:04 PM on February 17, 2008

Doh that was clear as mud. Second paragraph from last post: when it would wind up, backing out the screw all the way would cause it to die, at which point I could give it two or three turns and it would start right back up again....and rev up high again. As of right now though, it doesn't *run* for more than about 30 seconds.
posted by TomMelee at 8:07 PM on February 17, 2008

The sparkplug should arc across its electrodes when its metal is against the cylinder. That it doesn't is proof there's something wrong there. Replace the plugs, and probably the wires as well.

The engine racing does sound like an air leak, but it's also possible the choke is stuck on, or the slides are hanging up and not dropping when the throttle is released.
posted by Kirth Gerson at 4:06 AM on February 18, 2008

Are the carbs properly balanced? The can be assembled properly and run rough because they're not all sync'd up. It can be done yourself, but it's easier to have a shop do it.
posted by electroboy at 7:26 AM on February 18, 2008

All right, just got off the phone with the garage. It's going to be at least a month before they can get it in, SO we're back to the races.
posted by TomMelee at 7:26 AM on February 18, 2008

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