KZ1000 popps... ALOT

This is kind of an exhaust and carburetor issue so i just put it on this part of the forum.. i recently installed a Kerker 4 into 1 on my 1981 KZ1000LTD. the bike runs like a monster. But, no matter what gear or RPM your at, when you let off the throttle it popps a whole bunch as the RPMs decrease. when you pull out the choke to the halfway mark, it doesnt pop at all. I know its running lean and i have made the conclusion that i have to jet up since messing w/ the pilot circuit screws didnt help. Im just wondering if i ride it with half choke as a bandaid till i get a jet kit, can i screw anything up by doing that? Also, the insulator on the spark plug for cylinder 4 is totally white and it looks like its got really hot before.. i also have loose valve clearances because you can hear them chattering on that side of the motor. i plan on getting these things fixed soon but in your guys' opinion, should i stop riding it until then?

Thanks guys,
KT

Kitten Tooth wrote: This is kind of an exhaust and carburetor issue so i just put it on this part of the forum.. i recently installed a Kerker 4 into 1 on my 1981 KZ1000LTD. the bike runs like a monster. But, no matter what gear or RPM your at, when you let off the throttle it popps a whole bunch as the RPMs decrease. when you pull out the choke to the halfway mark, it doesnt pop at all. I know its running lean and i have made the conclusion that i have to jet up since messing w/ the pilot circuit screws didnt help. Im just wondering if i ride it with half choke as a bandaid till i get a jet kit, can i screw anything up by doing that? Also, the insulator on the spark plug for cylinder 4 is totally white and it looks like its got really hot before.. i also have loose valve clearances because you can hear them chattering on that side of the motor. i plan on getting these things fixed soon but in your guys' opinion, should i stop riding it until then?

Thanks guys,
KT

So those are all symptoms of running lean. Makes sense as the 4-into-1 flows better than the stock exhaust. I remember my exhaust was popping quite a bit on downshifts due to a lean condition caused by worn out carb to head intake boots. Next time you have your carbs off, wouldn't hurt to check them out as well.

You won't kill the bike running with a little choke, might foul a spark plug but might not. If it pops on decel with throttle closed, you need richer pilot jets. Did you get a good seal with the exhaust gaskets? If you have a leak they will sound like firecrackers going off.

Pull pilot jetts,call Z1E,order two sizes up. They will be there in three days and you will be good to go. Less than 20 bucks. Roy

Here you go Tim, to go along with Roy's reply...
Possibly will give you some insight...

NOTE: Do one jetting at a time, run & test before going to the others.... Best to start with Main, then pilot then needles...

Once Main and pilots are pretty much dialed in, for needles run at 65mph, she surge a tad, or... @ 65mph let go of the throttle, she back fire/pop.... If so, still too lean... Change clip position or needle pending your configurations.





Also, keep in mind with summer temps, humidity etc....

Sorry guys... but DO NOT change your pilot jet until you make sure that your problem is NOT a basic air leak. Remember - if your mix screws have no effect at all - they are either clogged - or an air leak - or your idle is way high to compensate for another problem.

If you have the CV style carbs associated with the 81 year bikes, then all you have to do is add a little fuel the the idle circuit via your good ol' mixture screws.
Turn them richer by 1/4 turn and test - AS LONG AS THERE AR NO AIR LEAKS PRESENT ANYWHERE, the popping will decrease quickly with each turn. When the popping has ceased completely, add an additional 1/4 turn - and your done.

If you change the pilot on those carbs, the cruise position will become very narrow and jerky with a 4-1 header.

If you have slide carbs, well usually an air/mix screw adjustment will suffice - but MAYBE 1 pilot up would be required - and never more.

I've done this on japs and hardleys for years when aftermarket pipes are added.

Good luck friend.

Just my 2 cents! PEACE.

I believe that i have a good seal with the exhaust gaskets.. If there is a leak its totally not obvious. Whats a good way to test for an exhaust leak? also, i put brand new plugs in my bike and have gone for a few rides since then. I didn't do the plug chop test but i checked the color of them a few nights ago and cylinder 4's plug was white.. bone white. and it looked like it has gotten really hot before. as you go inward from cylinder 4, they seem to get darker. When i got to cylinder 1, the plug was tan like they're supposed to be. Im at stock 122.5 main jets. not sure about the pilots, i never looked. I think i have a damn good seal on the manifold boots between the carbs and the motor. im going to test that by spraying carb cleaner on them while the bikes running in a second here..

Thanks for all the help so far guys,
KT

Right... I forgot about that bone white plug...

Are the valve clearances all good? Good compression?

Could be poor throttle body/slide balance - pull the carbs and do a bench sync at least if you havnt.

Fuel height is ok on all carbs? Carbs have been thoroughly cleaned by verifying the flow of cleaner through all the passages/pilot holes into the bores?

Neeeeed more info :laugh: Tried swapping/new plug???

Sad thing is really... if you dont do ALL of these things, then it will run poorly. You cant skip a single step of a real good carburetor tune and setup.

valves are loose.. You can hear them chattering, especially above cylinders 3 and 4. cylinder 1- 145PSI
cylinder 2- 125PSI
cylinder 3- 125PSI
cylinder 4- 135PSI

Thats what i got for compression. im thinking that the inner cylinders are a wee bit low considering these bikes come off the line with like 170psi compression... hopefully thats due to my bad valve adjustments.

oh.. and did i mention that this bike is the fastest thing in town? no but it does scare the hell out of me just about every time i ride it. its VERY fast and VERY powerful. front end comes up without a problem:)

And thank you OMR for that chart, i already saved it on my computer:)

Pull on each header pipe at the port and see if you can move one.

Light a ligher and hold it in front of each pipe.

How much did you turn the pilots out?

The motor is going to need them opened about a full turn more to get rid of that pop.

With the cams and pipe it's not getting enough gas.

The lean factory settings are out the window.

If you aren't running a baffle it's gonna need more fuel for idle.

You can look forward to alot more snap once you richen up the pilot circuit with the screws.