TOPIC:

Hey all,

I have a 1984 KZ700 with 10,100 miles on the clock. Stock exhaust with K&N pods and 125 main jets.

This problem isn't completely consistant; sometimes all of the cylinders will fire just fine. However, even in this case, I think the bike is down on power as it was dyno'ed at 38 RWHP and it should be 79 HP to the flywheel.

But the main problem is when a cylinder drops out. Sometimes when the bike is cold it will be troublesome to start, often backfire, and finally start -- but on 3 cylinders. Strangest thing is, its not always the same cylinder. I feel the exhaust pipes moments after it starts and one is often cold.

After a few minutes of slow riding, the sleeping cylinder wakes up and the bike runs fine.

Anyone know what this could be? Other symptoms my bike has: Valvetrain noise (lots of ticking from the cylinder head, although not entirely consistent), and gasoline has been getting in my oil.

I had service done to my bike in the spring and the bike has only seen probably 500 miles since then. They said they did a valve adjustment.

Thanks all for the help.
-J

There is an interesting thread in the carb section started by KB02 you might want to look at. I suspect that if you start going through the same troubleshooting steps as he has undertaken, you will figure out your problem. If the bike has been "serviced" how much do you trust the place that did the service? Sounds like you may not trust them 100 percent.

Also, your jetting is lean for K&N pods. Should be a bit richer set of mains. What pilot jets are in there? If they are the stockers, the bike will be really hard to start and warm up real slowly. The BS carbs really like larger pilot jets when you remove the stock airbox and add pods. Which pipes do you have? Anyway, I am going to move this thread based on your answer.

Post edited by: wiredgeorge, at: 2006/10/13 07:51

del

Thanks for the replies.

wiredgeorge: I don't trust the shop much at all, actually. I went back there after I heard tapping from the cylinder head and they said "Roy [the previous mechanic] probably just didn't tighten things up. Sorry, better luck next time" and then refused to work on the bike. It also took them 2 1/2 weeks to figure out that the compression on the bike was good.

But the mains need to be even larger? The stocks were only 105's. Unfortunately I think the pilots are stock b/c one had its head stripped off (not by me...seriously) so I can't really get it out...the bike seems to warm up pretty quickly though. I have stock pipes on it.

I'm debating switching back to the stock airbox but getting those airbox hoses on are such a pain. What main / pilot sizes would you recommend?

JMKHI: Will try that. Thanks for the tip.

Update: The bike fired right up this morning no problem and its the coldest its been for a while, about 50 degrees.

One thing I forgot to mention, the ticking noise from the head only happens when the bike is idling or at low RPM...under acceleration or just revving it up, the ticking goes away.

del

The fact that it only ticks at low rev sounds like you have a problem with the oil feed to the head. When idling the oil pressure may not be great enough to push the oil past a nackered oilway, but at high revs it will be.

usually valves would be a constact rattle, not just at idle. It could also be the sound of one cylinder not firing, as mine often does that on a cold morning!

Jon.

wiredgeorge wrote:

There is an interesting thread in the carb section started by KB02 you might want to look at. I suspect that if you start going through the same troubleshooting steps as he has undertaken, you will figure out your problem. If the bike has been "serviced" how much do you trust the place that did the service? Sounds like you may not trust them 100 percent.

Also, your jetting is lean for K&N pods. Should be a bit richer set of mains. What pilot jets are in there? If they are the stockers, the bike will be really hard to start and warm up real slowly. The BS carbs really like larger pilot jets when you remove the stock airbox and add pods. Which pipes do you have? Anyway, I am going to move this thread based on your answer.<br><br>Post edited by: wiredgeorge, at: 2006/10/13 07:51

If you have the correct needle, you shouldn't need anything larger than maybe 1 over for the pilot.

Anyway, since the dead cylinder seems to be a moving target, it's harder to diagnose the problem.

Your ignition is paired 1-4 and 2-3. Which cylinders are dropping? Is it always one of the ignition pairs?

Simple things you can easily check would be.

1 - unscrew the plug caps and look for corrosion in the wire where the caps scew on. Trim them if you have enough length. Check them at the coil as well.

2 - Check the plug cap resistances with an ohm meter.

3- Check the spark plugs.

4 - Check compression. Low values could indicate a tight valve.

Those 700 motors could be rather noisey in the valve train from brand new. Things that contribute to the noisey top end are.

1 - valve clearance
2 - carb synch
3 - cam chain tensioner [often problematic]

How many miles on the engine? How hard of a life has it lived?

Down-N-Dirty plug wire check (most probably from somewhere deep in the archive bowels): With motor running in dark pitch black garage, zap with mist from trusty handspray water bottle and maybe get to enjoy a free fireworks show.

Cheers

JMKZHI: No, it didn't require anything to start that morning...the annoying thing about this problem is that it isn't consistant. I was thinking it may be a valve problem as well because the carbs have been looked at already, the tapping noise, and the 38 RWHP dyno.

Crowson_punk: sounds reasonable. This isn't the sound of a dropped cylinder b/c it does it when all four are firing (although I do know what noise you are talking about because I do get it when i'm only running on 3 as well). How would I go about checking oil pressure? Can I add anything or use a different weight of oil that might help?

larrycavan: The dead cylinders aren't matching with the coil, unfortunately...the other day cylinders 1&2 were both dead, 3&4 fine. What is the procedure for checking coil resistances? I have a Clymer manual but it is worthless and i'm not sure how to do it.

Will check for corrosion & recheck compression, the shop said compression was uniformly good. Not sure if the shop did a carb synch or not. Is there a way to perform this myself without a special tool?

I'm not entirely sure how tough of a life the bike has had, I've only had it for about a year. Has 10,300 miles on the clock.

Patton: Thanks, will try ASAP.

Post edited by: masospaghetti, at: 2006/10/17 23:30

Which piston is it that is problematic?

Yeah, like Wired George said, check out my post , It's crazy but I think we're getting somewhere now. (start on page two where George jumps in. Some really good diagnostics in there.)

As for your bike, it does sound like an electrical issue. As for the noise, when was that last time your cam chain was tightened?

As for syncing the carbs, you really do need a special tool for the job to get it right. You can bench sync the carbs with just a 1/8" drill bit, Laying it on its side in the venturi on the carb and adjusting the slider to rest right on top of it. This will get you close, but you need the syncer to get it exact. Doing this, mine were WAY off, but at least closer then they were. Your clymers manual should have a diagram of how to make a synching tool from common household materials. I've never tried it, but they say it works.

Hope this helps.

Post edited by: KB02, at: 2006/10/18 20:37