For Mr Nick and kwackboy ?

[Joe Rocket]

Since I put the GPX back together it has always had carb problems, probably only one though. It starts fine and runs well. However it over-runs on shut down when changing gears, put simply it revs too high. If I back off the idle setting it will shut down properly but won't hold tick over. I'm looking to increase the pilot screw settings (petrol) to provide a more rich idle. I've gone up half a turn on each carb from standard and it still isn't happy. Standard setting is 2 turns out so I'm now on + half a turn. I can try another half turn. After that it's off the known scale.

It's a total removal of the carbs just to reset the pilot screws as they're under the assembly. I've got dismantle/reassemble time down to 90 minutes to restart.

BTW, the carbs are already synch'd and valves properly adjusted so I don't need to go there.

Very technical and old school but any help would be appreciated.

[MartinW]

I was going to tell you how to fix this but you seem to only want help from people who know what they are talking about.

[Joe Rocket]

Your ramblings are always welcome MartinW. 

So...........

[kwackboy]

From what you describe suggests an air leak of some kind.
Are the diaphragms sealed and In good condition and do the slides move up and down free and evenly .. ?

Sometimes if a slide is sticking it can hold the airflow which can hold the rpm a little longer than normal.

[Joe Rocket]

Thanks kwackboy. I've gone down the leak side already. Kawasaki don't make new carb/engine rubbers so I've replaced them with the best I could find, perhaps wasted money but no change there. I've inspected the diaphragms and no issues there either and all slides are functioning correctly.

I'm sure this is an idle/pilot screw issue.

[TLPower]

Air leak or sticking slide/throttle plate.

Being out of balance can also lead to throttle holding.

Either way it's unwanted air.

[Mr Nick]

Yup, I can only agree with what's been said already. A similar issue on the V50 was cured by replacing the idle air screws and o-rings as there must have been air getting by at least one of them. Have you tried spraying brake cleaner or similar at various points to see if you hear a difference in the engine?

[Joe Rocket]

How good do pilot screws have to be? Haynes asks to check the tapered end for damage and replace if necessary but mine seem to be OK.

I'm expecting to hear a difference in engine noise by tweaking the pilot screws but as they're underneath I can't do them with the engine running, just remove carbs, change the screw settings and put them back......then run the engine to see if anything changes, like run faster or slower without touching the idle adjuster. It's time consuming.

[kwackboy]

Do you have a remote petrol tank ?

With troublesome carbs I find it best to remove both tank and airbox so you can run the bike and tinker with ease.

[Mr Nick]

I could see no discernible difference between the old & new so the wear that made the difference wasn't easily identifiable. Try the solvent spray method at various places on the carbs & inlet and it may point you to an area to check - easier than taking them in & out all the time.

[Joe Rocket]

Thanks for your suggestions.

I'd have to concoct something kwackboy as a remote tank, albeit only as small as necessary, and therefore easier to fiddle. However I still have to remove the carbs to get the airbox out of the way!

I'll try the spray around the carbs too. I'm fairly sure (shouldn't have said that....) there's no air issue on the inlet rubbers. I had a problem with a Yamaha there and the symptoms weren't the same at at. The engine ticks over at 1100 rpm comfortably, it's just it doesn't fall back properly when revved over 3k. When I reduce the idle to 800 it will shut off but not sustain the tick-over.

BTW the carbs are synch'd and valves set correctly.

[kwackboy]

It'll save you work in the long run .. 

Have you striped the carbs.... By that, I mean, really striped them so they are all separate ..?

The connector tubes have seals on them and being that they're quite old they may have perished.   

[Joe Rocket]

Yes and thanks for the big tip kwackboy.

Separating carbs is not my objective but I see why you suggest it. It's the old 'If it's not broken then don't fix it' argument. I'll be obliged to replace things that aren't necessary .......... but then again I won't know for sure!

Kawasaki parts are not always available and extremely expensive if they are. One step at a time I reckon. 

[kwackboy]

Back in my courier days I had two Kawasaki GT550'S,  great bikes but almost every weekend I was dabbling with the carbs, glueing diaphragms to get me out of trouble, balancing and making sure the airbox was seated correctly ... 

I've still got my balancing gauges, nearly 30years old now, I've only had them calibrated once after I dropped them accidentally. 

[Joe Rocket]

Solvent sprayed around the carbs showed no change hence suspect rubbers or seals appear to be OK. It's a confined zone so if anything was wrong it might have shown up.

I've now set the pilot screws to 2.75 turns out, factory is 2 turns. That's lean as a base setting due to niggling emission rules as far back as the 80's. American bikes had the pilot screw heads plugged.

The throttle shut off is now mastered but the engine idles around 900 rpm and it's not really happy. You feel you have to keep your hand on the throttle when idling.

I'm not prepared to spend another £13 per pilot screw (plus vat, post and exchange rate). Happily it doesn't attract Brexit tax/customs tarif!