1982 KZ750 Spectre won't hold speed/cruise

Hello! This is my first post, and I'm pretty new to technical forums as well, so sorry in advance for any ridiculous errors I make.

Ok here's the story with the bike, a 1982 KZ750 Spectre/N1. I bought it about 2 months ago as a project bike, PO said it runs and drives, so I drove 100 miles to get the bike and drove the bike 100 miles back to my house. Bike was dropped on the right side and the right side muffler leaks. I think the bike has around 10,500-11,000 miles, not going to go into that, the PO replaced the original tach(which might have broken when it was dropped, no idea). The bike has some K&N pods, still had stock exhaust, and later on, I found out it had stock jetting. Anyway, about 3 days after I bought it, I took her out to go to work and show her off to some work buddies. On the way back, she would not rev over 4,000-4,500. I think this was caused due to the carbs slipping out of the intake manifold boots(when I went to take off the carbs they were pretty loose). The next day after that, I began the process of the build. I'm not going to go into all the cosmetic stuff, just give a list of what I did so far that might affect how the bike runs.

-Rebuilt Fuel Petcock

-Cleaned Carbs and rebuilt carbs. Oh, btw, the carbs are Keihin CV34's.( I didn't dip them like I wanted, just ended up using a bunch of carb cleaner and an air compressor to blow it clean. The carbs were amazingly clean, barely any build up at all.) Also, on a forethought, when I was rebuilding the carbs, the pilot jets had this plastic plug inserted, i broke them when trying to remove them to clean the pilot jets. I immediately panicked and turned to the internet, read somewhere that they weren't necessary, said something about being related to emissions, so I chucked them. They were these little polyester caps with o-rings in them. As I reflect, probably not the best idea...

-Re-jetted carbs using Dyno-Jets stage 3 main jets.

-Took off mufflers. As of right now, it still has none.

-Synced carbs

That's all I did so far, now the bike accelerates great, but as soon as I let off to hold speed, it sounds almost like a cylinder cuts out, like 1 piston is doing all the work. I don't know how else to explain it. She will sometimes hold speed, but it sounds terrible, like a playing card being vibrated by a spinning rubber tire. Other than this main issue, she gets terrible gas mileage and doesn't idle. I can adjust the idle knob to get her to idle, but then she has a hanging idle, give her gas and she stays at 4,000 rpm. As for gas mileage, I rode around 50 miles and had to go on reserve the way there, topped off on gas, and again hit reserve the way back. I'm completely flabbergasted by this, as I'm pretty sure she's running lean; she pops and backfires when i let off completely, has a hanging idle, and the plugs didn't suggest a rich condition. Also, I blew the main fuse like 3 times, always the main 30A one. I think it's because the leads that attach to the fuse is dirty and not allowing a firm connection, but I have no idea, electrical stuff isn't my forte. The main problem I want to address here is the cruising problem, I can fix the other issues, but maybe these symptoms can help lead to a solution to the cruising problem? So that's why I explained them as well. Any suggestions??

First thing, the carb mounts must be tight on the carbs, and have no vacuum leaks anywhere. No part is unimportant, those little plastic plugs are necessary as well.

DGA wrote: First thing, the carb mounts must be tight on the carbs, and have no vacuum leaks anywhere. No part is unimportant, those little plastic plugs are necessary as well.

They aren't, They were required for US import to prevent owners from adjusting them from the factory lean condition required for emissions standards.

Gas formulation is completely different now and the pilot jets need to be adjusted as well, like everywhere else in the world.

Between the damage to your pipes, the factory jetting and the pods it's not surprising you were having issues. If you have vacuum leaks that will contribute as well.

Be sure not to confuse the non-essential externally visible "non-tamper" plug (covering the pilot adjustment screw) with the required internal plug that prevents fuel entry into the otherwise exposed end of the pilot jet.

Non-tamper plug over pilot screw


Required internal plug over pilot jet




Good Fortune!

By GPzMOD750: They aren't, They were required for US import to prevent owners from adjusting them from the factory lean condition required for emissions standards.....

He's talking about the polyester caps over the pilot jets on the underside of the carburetors.
I think they're necessary for the proper uptake of fuel thru the pilot jets.

Although the pod lifestyle does seem alluring, I would put the stock airbox back on.

Airbox and muffler. Mostly the muffler, for the sanity of everyone that lives within 5 miles of your bike.

Nessism, do you know if the polyester caps are still available anywhere. I'm too lazy right now to search. :blush:

martin_csr wrote: Nessism, do you know if the polyester caps are still available anywhere. I'm too lazy right now to search. :blush:

I believe those caps are obsolete martin.

Someone with a lathe could carve up a set. It's pretty fiddly work though because of the size. Ebay may be another option.

The Mikuni carbs of the same era came with rubber plugs over the pilot jets. Those may be a possible substitute although I'm not sure because the float bowl holds the Mikuni plugs in place and keeps them from falling out. I'm not sure if the Keihin carbs have a similar feature.

Could do an ebay search for 11012-1128 which should include some listings -- un-cheap of course .

Good Fortune!

By Nessism: I believe those caps are obsolete martin. ....

Thanks. Anybody got a 3D printer? Those caps seem like a good candidate for the process.

One of the members here had made some nice looking ones. Not sure if he is still active.
See www.kzrider.com/forum/3-carburetor/37944...able?start=20#686026
you might have to scroll up to the top

A few years back I tried some rubber plugs I got from Z1 Enterprises designed for a Honda or Suzuki but they fell out after a week and the bike wouldnt even start without them. The CV34 float bowl wont hold them in place

I also remember someone else here who reported a pretty radical and possibly dangerous solution involving wedging some fuel line in place and setting it on fire until it melted into place. :ohmy:

There are a few pricey ones on ebay at the moment

Wow, thank you all so much, I wasn't expecting this many replies. So off with the pods? Man, they look so cool... Oh well, the bike came with the stock airbox but no filter element, so I'll need one of those. I think the local auto parts store carries some. The mufflers will go back on as well. In the future, thinking of getting these shorty mufflers and fabbing some mounts to get them to fit... www.dimecitycycles.com/satin-black-16-in...lashcut-muffler.html I did have trouble with the carbs sliding off the intake boots, the stock clamps weren't tightened enough and stripped out. So I bought some regular hose clamps and tightened them down really good. I will double check when I have time and spray some WD-40 to make sure nothing is leaking.

As for the polyester pilot plugs... I say no to evilbay, had too many bad experiences with that website. I looked up the part number on bike bandit and actually found some.
www.bikebandit.com/oem-parts/detail/kawasaki/11012-1128/b752106
Just now put in the order for 4 of them.

The carbs still have the dynojet upgraded jets in them, would I need to put the stock jets back in for the airbox and mufflers? Or can I leave them the dynojets in?