Hi

I`ve a Puzey XTR4 which has a Lancin 300cc engine which i am told is a clone of a KLX300 engine with the addition of an electric start.
I`ve a problem with the idle speed going up and down on an inconsistent and random manner despite doing everything i can think of- No air leaks, throttle cable and twistgrip replaced.I`m convinced it`s not mechanical as the revs can be brought down by quickly flicking the kill button without the engine actually stopping.This is a very low mileage bike and i`m getting pretty desperate to sort this out, can anyone help please?Could the ignition system cause this?
It really is as simple as this-

 

No, The ignition system cannot cause large fluctuations in idle RPM - only small ones.

You have an induction system issue - (carb, manifold).. Whatever carb that is, is probably causing the issue.. Firstly, learn all there is to know about its idle fueling circuitry. Certainly learn about any diaphragm driven fueling or air devices within the carb as they can introduce fueling variances "at will" ..

Real KLX300R's will get really hot - too hot - in many riding scenarios. Once overheated, lots of running issues show up..

 

Hi

Thanks for that.
As (i hope) you can see the carb is an `old school` Keihin PWK which is about as simple as it can get- A semi-flat slide hanging off a single cable returned by a spring(no diaphragm).The rev changes are small (i would guess at 200rpm) and are only at(above) idle speeds.I should have said before that `blipping` the throttle will drop the speed back to normal like hitting the kill switch does.This is why i wondered about advance/retard.I`ve had the carb off many times, stripped and blown through any internal fuel/air passages.
It`s not always done it either.Can you see why i am grasping at straws now?

Cheers

 

Possible the throttle return spring is weak allowing the slide to hang up a bit in the carb, it does look a bit like there are marks on the outside of the slide where it may hang up, Your blipping gets the slide to drop back down. I would try stretching the spring out a bit (pull it out) to get a bit more force on the slide and get some 600-1000 grit sandpaper and polish those edges and surfaces that slide in the carb body. If that works, great.

If that does not help consider trying adjusting the idle mix to see if it is running lean. Sometimes that might cause some variation, but usually in the form of a consistent higher or lower idle depending on weather conditions.

 

I assume you have tuned the fuel/air screw?

 

Hi guys.

The slide drops smoothly and readily just under its own weight even before fitting what feels to be quite a strong spring.This is a carb that now only has a couple of hundred miles on it remember.The bright marks on the slide are where i have taken the finest of stones to barely perceptible (possibly imaginary!) high spots in desperation to find a cause!
Have setup the idle mixture on numerous occasions.
Been messing with bikes for over 40 years now and this one is REALLY bugging me!!
Doesn`t momentarily hitting the kill button to bring the revs down suggest it`s NOT the slide?

Cheers

 

I/we are not PWK specialists. Our bikes use CVK's..

A hanging idle, that is carb related, implies a very lean pilot system. Either thru faulty settings on the air screw and idle speed screw relationship, or a fault with the pilot system ( pilot jet, pilot air jet, pilot system circuitry..)

 

Worth a try... I knew sometimes flat slides can stick a bit when the throttle is closed, due to the vacuum in the intake.

I take it you played with the idle circuit. No idea about ignition doing anything. Hope you figure it out.

 

Does the KLX even advance the spark with rpm, I thought it fired twice/cycle~once/rev at the set point.

 

Hi

Thank you all for your input keep it coming!

Cheers