I can't tell if it is running lean or rich

83 KZ750 LTD - it's a belt drive twin.

Though I know I ultimately want way more power and stability in a bike, this is what I have for now so it is my baby for now.

It's hard to start and pipes are blueing, I set a high idle speed to keep it from stalling while idling (1000 rpm's in good weather, 1200 in cold weather) and when I reach higher speeds, throttle response is very, very poor.

My guess is lean, because if it was running rich, it would probably be overheating and stalling more (it doesn't stall that often, mainly when stopping/stopped when the engine speed drops)

Other than that, the basics of the rebuild are complete. I've got a new (working) dash (control lights, speedometer, tachometer), the engine was rebuilt on the top last year. A new, kickass battery, new controls, throttle, a new wiring harness, new headlight, lots of paint. Now I'd like to fix these engine problems and do some customizing.

but before that, I need to fix these engine problems. I refuse to take it on the highway until this, albeit small, instability is rectified.

That and I need to figure out the wiring on the lighting on the new controls, and I don't know what the rear foot peg attachment arrangement was, but a trip to the hardware store can solve that.

Thanks for all your help now and in the past.

PS the site looks amazing, i just feel like a chump because I have a twin.

Salder69 wrote: 83 KZ750 LTD - it's a belt drive twin.

My guess is lean, because if it was running rich, it would probably be overheating and stalling more

Running lean generally makes an engine run hotter than running rich.

How do the plugs look? If rich, they should be black and sooty. If lean, they will be light brown or white.

First thing would be to check for vacuum leaks at the intake manifolds that mount the carbs to the engine.

Are the pipes and airbox all stock?

Have the carbs been cleaned?

I would also check fuel levels with clear tube.

Salder69 wrote: PS the site looks amazing, i just feel like a chump because I have a twin.

I'm pretty fond of my 750 twin. Had it for 34 years now. Never designed to be a street racer, but it's solid and has plenty of power and torque for normal riding.

EDIT to add:

I have found the 750 twin benefits from increasing the pilot jets to size #50. Very easy to do.

Hard starting, stalling at idle sounds very much like a problem in the pilot system. If your carbs are BS-38 Mikuni, the jets are all in the bowl. Take it off and soak it in cleaner and it might fix your problems.

airbox has been removed - When I bought it i searched everywhere I could for the carb-to-box boots - could not find them - so there are pod filters on there - shitty ones.

When I first got it, I did basic cleaning of the carbs, The original tank was rusted and there was tons of rust in the carbs.

When i had the front end rebuilt ( I didn't do it) the guy I took it to said he did all that, but overall I'm not impressed with his work. He chipped off one of the fins/vents on the engine when putting the head back on, and like a month and a half-two months ago, I dumped it because the aftermarket throttle handle he put on either came loose from vibration or just wasn't on tight enough and I accelerated and it it got stuck so I had to dump it to avoid a crash. Luckily it was just a new mirror, headlight bracket and bulb but still...

I'd say the carbs are no doubt what are causing the problems, but I think I may need new diaphragms too, and I might as well replace them if I have to take the carbs off again.

But I'll check the plugs and tell you what they look like then go from there.

TTYS

not to be a smart azz but there is a KILL switch on bike for those reason!
cruise control is great if you know what you are doing sorry my Harley has one
as to the bike its more likely lean with pods on it unless it was rejetted or air leak
twins are a nice bike wished i still had mine was a full dresser that stuffs hard to find now
best of luck

@P21 - I used my kill switch - I had to dump it or crash into a wall. Your choice - Dump it, kill it or kill it and crash.

smartass

I know its already been said but it defitanally sounds like its running lean. That will also cause the pipes to "blue" also the jets should have been changed when going to pod filters same way if going to a aftermarket exhaust or in my opinion removing a baffle.

I have the mikuni 38 carbs.

Here are images of my plugs.

i.imgur.com/dwGy4ai.jpg

i.imgur.com/0sp5aRa.jpg

I vote lean.

Now what do I do?

Salder69 wrote: . . . doesn't stall that often, mainly when stopping/stopped when the engine speed drops . . . .

If not already done, would also double-check the valve clearances to assure being within specs.

Good Fortune!

Salder69 wrote: I have the mikuni 38 carbs.

83 belt drive had BS34 stock
Main jet 115
Pilot jet 45
Starter jet 70

If you still have the stock air box ditch the pods and go back. Search the twins forum for "Moog mod" for a way to connect the carbs to the box easily.

kz400.createforumhosting.com/

I know its already been said but it defitanally sounds like its running lean. That will also cause the pipes to "blue" also the jets should have been changed when going to pod filters same way if going to a aftermarket exhaust or in my opinion removing a baffle.

+1

Pipes bluing are an indication of heat. Lean motors run hot. Sounds like the carbs need some work.

Your plugs are hard to read with the short amount of time they are running. Start up with the choke or enriching circuit on leads to the carbon build up. To read a plug you need to be at highway speeds for awhile, pull over and pull the plug and then see what it looks like.