[Rune Skiaker]

Hello. Maybe I should post in the mecahanic forum; IDK. I'll try here.

This is a US GPZ600R; the first "Ninja" model, as I understand.... 1986 steel frame. Imported to Norway, and sold used here.

Okay. After some troubling times, I got hold of a new fueltank last year. After cleaning the carbs, but still experiencing some low speed (under 3500 rpm) stumbling, I get hold of new PILOT SCREWS. Unfortunately, I forgot to count numbers of turns out, but after reading up, it seems 1 7/8 of a turn should be OK. They are right now out only 1/2 turns.

The Pilot screws wer about 1 1/2 turn out, and I was experiencing RPM not going down to idle when i released the throttle. Freed the cables and mechanically the carbs closed fully, but it took some time befor RPM's went down to normal. I suspected TOO MUCH FUEL, and therefore closed the pilot screws and tok the 1/2 turn out, only.

Now I'm experiencing an idle problem; need to open the blades to "full" with the idle adjustment screw. And then, randomly- the rpm suddenly rises to 4000 rpm or more, then slowly goes back to the normal 1300 rpm or so.

This also happens when starting (the warm) engine; rises to 4-5000 rpm. If I then turn the idle speed screw to lower RPM, the engine will stall, and I have to turn it to the max setting, where it idles somwhat steady- for a while.... Until it rises once again....
Today I checked the (large) fuel filter I have on. It's clean. But I noticed the filter compartment is NOT fully filled with fuel. I have no fuel starvation on higher RPM's either. So; I'm a bit stuck here.....

If you have a clue to whatever faults my carbs can have- I'd love to hear it...
Thank you very much
Rune

 

[Hugojose]

The pilot screws add fuel to the IDLE mix, thus I doubt they have to do with stumble when moving.... There are tiny holes under the butterfly for idle, and the screws tips control another tiny hole slightly ahead to get a bit more fuel...but this is only significant at idle or very low speed.

It does sound like you have vacuum leak, on rubber boots or vacuum hoses. That would cause idle to rise, or not wanting to go down as the engine can get extra air bypassing the carbs.

 

[Rune Skiaker]

Hello, Jose.. Yes, I checked the vacuum hoses as my first idea was some fault there, and they seem not leaking, Rubber boots. Hmm you mean the diaphragms?

If we forget the stumbling sub 3500 rpm running for now... And talk about the idle.
If the idle adjusting screw is turned to "Full open" I have a idle at around 1300. And suddenly the idle can rise to almost 5000....Close the idle adjustment, and RPM goes down, and it stalls. Need to get fully opened again to idle.....My thought was the fuel supply is not steady. IDK.


The bike runs well, and all I need is a reliable, steady idle.....

Thanks for input!

 

[Kawasakian]

Did you check for air leaks with some starter fluid, running through one of those tiny tubes, to look for a rise in rpm's? The fuel the idle circuit provides does figure into the total amount of fuel the bike is getting. It sounds from your description that you're getting an air leak after the bike gets warm. That would be the time to check the bike for air leaks using very directed squirts of fluid with a spray tube (the tiny thin long Red one that fit into the spray nozzle). Watch where you spray and if you have an air leak, you will get a rise in rpms. The other thing to check is to make sure the valves are adjusted properly and aren't too tight. That can cause all kinds of problems. Check for fuel flow out of the petcock. If it is vacuum controlled, that could be causing problems, if the vacuum mechanism is stuck. A place to start anyways. IMHO

 

[Hugojose]

......your description of the action of Idle Screw...almost sounds like the action of opening the enrichening circuit ("choke"). No offense, but are we talking about same thing??

There is no much science on the Idle Screw...it is just a stop to the butterflies, keeping them a crack opened, and adjusting it does same as moving throttle with a very, very lightly touch. ....

Have you checked the fuel level in the bowls?

 

[Kawasakian]

My Suzuki has an enrichening circuit for the choke. I think that design stinks personally. It makes the bike very cold blooded, your adjustments are limited, and the dissimilar metal causes them to bind up. Float bowl level check is a good idea. They can drop and are easy to adjust. Shake them when you have them out to make sure they still float.

 

[WFO-KZ]

I agree with what has been said so far about it being a vacuum leak. Just to be clear, the leak is likely between your carbs and the cylinder head. Check tightness of those clamps and use spray or an unlit propane torch to try to identify the source of the leak. Do this outside for safety.

You may need to purchase new rubber boots and clamps in order to get a leak-free connection.

 

[Davey H]

Hello. Maybe I should post in the mecahanic forum; IDK. I'll try here.

This is a US GPZ600R; the first "Ninja" model, as I understand.... 1986 steel frame. Imported to Norway, and sold used here.

Okay. After some troubling times, I got hold of a new fueltank last year. After cleaning the carbs, but still experiencing some low speed (under 3500 rpm) stumbling, I get hold of new PILOT SCREWS. Unfortunately, I forgot to count numbers of turns out, but after reading up, it seems 1 7/8 of a turn should be OK. They are right now out only 1/2 turns.

The Pilot screws wer about 1 1/2 turn out, and I was experiencing RPM not going down to idle when i released the throttle. Freed the cables and mechanically the carbs closed fully, but it took some time befor RPM's went down to normal. I suspected TOO MUCH FUEL, and therefore closed the pilot screws and tok the 1/2 turn out, only.

Now I'm experiencing an idle problem; need to open the blades to "full" with the idle adjustment screw. And then, randomly- the rpm suddenly rises to 4000 rpm or more, then slowly goes back to the normal 1300 rpm or so.

This also happens when starting (the warm) engine; rises to 4-5000 rpm. If I then turn the idle speed screw to lower RPM, the engine will stall, and I have to turn it to the max setting, where it idles somwhat steady- for a while.... Until it rises once again....
Today I checked the (large) fuel filter I have on. It's clean. But I noticed the filter compartment is NOT fully filled with fuel. I have no fuel starvation on higher RPM's either. So; I'm a bit stuck here.....

If you have a clue to whatever faults my carbs can have- I'd love to hear it...
Thank you very much
Rune

Yes this sounds like a vacuum issue. Check the carb diaphragms very carefully as well as the rubber components immediately before and after the carbs. The idle screw setting should be according to the manual if everything is standard in the carbs. Changing the setting to correct the issue isn't the best longterm fix. Check valves very carefully when the engine is properly cold. Petcock diaphragm and take off vacuum hose should be checked and replaced if necessary. Make sure your air filter is really clean as well. Hope this helps.

 

[Kawasakian]

Bikes these old can develop air leaks, the air filters get mois and close up, the check with a Propane Torch (no one obviously) is a new one for me, I like it. It does sound like a lean condition. I owas over zealous on a valve adjustment one, and I had adjusted the valves a bit too tight. I couldn't rev the bike over 500 rpm's. I waited till the bike got real cold and checked the adjustments, I was shocked at the crappy job I had done. After I finished I went for a snort and the bike was up to "blow up the engine" rpm's again. I don't know why Suzuki does not govern their engines?