Idling issue (79 kz400)

I'll try to keep this simple. So let me start from the beginning so you have all the facts:

First, about 2 weeks ago I finally got the bike to start. BUT it was idling really high, the idle screw wasn't working real well and only 1 cylinder was firing consistently. It was also noted that my intake boots were not sealing 100%.

Since I am running open headers and k&n style intake rejetting was the next step. I upped the size on my main just 1 size but could not find the secondary jet or pilot jets anywhere in town. So I left them for the time being.

After installing new jets and tweaking carbs for about 2 hours it started running very well. Only problem was that when revving the idle would sometimes remain high. Wouldn't drop back down. I am pretty sure my throttle cables were adjusted correctly.

Remembering that my intake boots weren't sealing, and wondering if that could be the cause here I went ahead and sealed them last night.

NOW it is back to only firing consistently on ONE cylinder and will hardly even idle with the choke on.

I am confused because this is the opposite of how it was running before, and the opposite of what I would have expected sealing a intake leak to do. It appears it WAS running rich but is NOW running lean.

ADVICE!?

treitz wrote:

I'll try to keep this simple. So let me start from the beginning so you have all the facts:

Good! :laugh:

First, about 2 weeks ago I finally got the bike to start. BUT it was idling really high, the idle screw wasn't working real well and only 1 cylinder was firing consistently. It was also noted that my intake boots were not sealing 100%.

Boots not seated 100% - yep, thats the result.

Since I am running open headers and k&n style intake rejetting was the next step. I upped the size on my main just 1 size but could not find the secondary jet or pilot jets anywhere in town. So I left them for the time being.

That sucks... cause that just wont work right for actual riding power. Maybe revving on a stand ok, but not riding. You need to install new pilots, possibly new needles (usually just a change of position is fine), and of course the mains, and you deffinately need to go up more than one size, I guarantee.

After installing new jets and tweaking carbs for about 2 hours it started running very well. Only problem was that when revving the idle would sometimes remain high. Wouldn't drop back down. I am pretty sure my throttle cables were adjusted correctly.

Not necessarily the result of an air leak. It could just be too little idle mixture due to incorrect jetting.

Remembering that my intake boots weren't sealing, and wondering if that could be the cause here I went ahead and sealed them last night.

NOW it is back to only firing consistently on ONE cylinder and will hardly even idle with the choke on.

Is this a twin? 4? Each carburetor represents a seperate fueling system. 1 can be clogged, 1 have an air leak, 1 rich, all out of sync...

I am confused because this is the opposite of how it was running before, and the opposite of what I would have expected sealing a intake leak to do. It appears it WAS running rich but is NOW running lean.

ADVICE!?

Purchase the service manual for your model.

Check valve to shim clearances as per regular maintenence.

Some compression check numbers would really help... you can turn the engine over with starter, (NO plugs in) holding your thumb over the plug hole. It should pop your thumb off the hole every time, no matter how hard you try to seal it. Its actually kinda fun

Fresh gas, oil, and plugs.

Pull the carbs and clean them properly. By proper, I mean aside from a regular thorough cleaning: spray cleaner through pilot system from the bottom of the carb, and look down the carb bore, to make sure that the spray is in fact squirting out of all the small holes into the bore.

once your carbs are good and sparkling inside, peform a bench sync on them. make sure the slides are open the same amount, and that they move up and down smoothly, correctly.

Repair all possible places for air leaks. Exhaust header clamps? Carb boots? Air filter connections? there should be no uncapped holes/nipples on the outside of the carbs, except for your bowl vent tubes.

Install everything air tight, and set mixture screws to stock positions. When starting the bike, DO NOT USE THE THROTTLE. It bypasses the starting circuit built into the carbs. Just use choke, and the starter.

Best of luck.

Thanks for the input.

I have ridden it twice, and you are right. Riding power does not feel right.

However, it should be noted that I AM going to install mufflers. Just need some parts to do it. Hopefully this will help? :dry:

It is a twin and I did completely clean the carbs. However I did not conduct a bench test.

Maybe that should be next on my list...

treitz wrote:

Thanks for the input.

I have ridden it twice, and you are right. Riding power does not feel right.

However, it should be noted that I AM going to install mufflers. Just need some parts to do it. Hopefully this will help? :dry:

It is a twin and I did completely clean the carbs. However I did not conduct a bench test.

Maybe that should be next on my list...

Right on.

Power will be funny till jetted right.

The muffler will help your ears more than the jetting. The effect of muffling/baffling doesnt usually require a jetting change from a correctly jetted open header bike.

Good hunting.

Alright, thanks to timing adjustment I was able to get it idling again like it was before.

However it is still doing the rev thing (revving up and staying there) like I explained before.

Hopefully mufflers will fix it. If not, on to pilot and secondary main jet.

Put the mufflers on and it is idling A TON better but is still running a little lean. I believe.

I like the sound too. And I think my neighbors will too:cheer:

s629.photobucket.com/albums/uu13/treitz2...current=09ba0034.mp4

Nice, very good. It sounds better, but like its still rev hanging in the video. It should return immediately to idle and stay there upon letting the throttle go.

Just tune the mixture screws as I suggested previously, and you should be OK on the idle/pilot circuit.

The other circuits will need more fine tuning...

Peace.

I am currently at about 2 full turns out on my pilot screws. 3/4 of a turn past stock. Should I keep going and see if it helps?

treitz wrote:

I am currently at about 2 full turns out on my pilot screws. 3/4 of a turn past stock. Should I keep going and see if it helps?

Any possibility that the pilot screws are being turned toward leaner instead of toward richer?

Good Fortune!

treitz wrote:

I am currently at about 2 full turns out on my pilot screws. 3/4 of a turn past stock. Should I keep going and see if it helps?

:laugh: YES! :laugh: You can go as far as you like. You will find the spot that the idle drops/engine stumbles (which is what you want to find), or you will completely remove the screw - in which case the pilot system is either dirty, or you need to increase your pilot jet size.

Just do like I said: Turn out the one till you hear it stumble, then turn it back in a small amount, just till the idle smooths back up nice. Then repeat the process with the other. They will both be at different positions.

Then turn them both in an equal amount - say 1/4 turn, and listen. If the idle goes up, continue turning both in till the idle stops rising. If the idle drops, then return the screws to the last position - thats it.

Enjoy.

When people put pod filters on there bike, the cheap pods will make the mix screws end up all over the darn place, this is normal/proper setup.

Patton wrote:

treitz wrote:

I am currently at about 2 full turns out on my pilot screws. 3/4 of a turn past stock. Should I keep going and see if it helps?

Any possibility that the pilot screws are being turned toward leaner instead of toward richer?

Good Fortune!

I think he meant to say toward - leaner instead of outward - richer :laugh:

Okay I will play with it some more.

I have k&n style filters that shouldn't allow much more airflown than stock, so I am hoping I can get it running right without rejetting the pilots. They seam to be hard to find and expensive