Engine stutter

[leswaller]

My recently acquired ETZ301 Saxon stutters/hesitates when riding on a constant or slightly trailing throttle. No problem when accelerating or on a leading throttle. Any suggestions as to what this might be please?
Many thanks
Les

[den]

hi , to start the ball rolling and to promt others to maybe rubbish my suggestion and offer theres .lol.
A sticking float in the carb springs to mind?
bring it on

[DAVID THOMPSON]

me thinks its bad gas and drain the float bowl time
for that rt125 killer the pop bottle cap size mix of water and ethanol
in the bottom of the float bowl

i never leave the house any more without the long Philips screw driver to drain the float bowl

also some larger 2 strokes due a bit of surging as the mix in the crankcase goes rich then lean
when trying to run slow and steady...
best example of this is the Suzuki T500 titian and the 750cc water buffalo both from the late 1970's
dave

[Linegeist]

........... best example of this is the Suzuki T500 titian ..................
dave

I bet THAT'S no oil painting Dave.

[leswaller]

Thanks for the replies guys.
David - don't think it is bad gas as I drained the float chamber and the tank when I got the bike and refilled with new stuff and we only have 5% ethanol here in the UK

Den - A sticky float is certainly worth investigating, I will try that as the next step

Regards
Les

[Linegeist]

My guess would be a fuel mixture problem and I'd first check the idle jet setting as, if memory serves, this contributes to the fuel/air ratio on light throttle openings.

There's another factor at play too. When a carb throttle's wide open, the sheer volume of air being sucked into the cylinder by the piston will create a sizeable vacuum in the carb's venturi (the narrow part that makes the air speed up and, therefore, the pressure drop). This will usually drag enough burnable fuel into the airstream from the main jet (which is located at the critical point of the venturi of course) to sustain combustion to some degree and, provided there's enough of it to make a decent 'BANG!', most folks won't notice whether it's too rich or too lean.

A light throttle situation, however, is one of the hardest for a carburettor to deal with, especially in a 2-stroke where the mixture charge has to traverse the crankcase before getting burned, as the air moving through the carb venturi is being constrained by the throttle and is thus in a relatively calm state. This means that the depression the airstream creates (to suck fuel up through the main jet) is minimal. This means that not only has enough fuel got to be ready in the main jet to be drawn up, but it must be at a height that's drawable by the minimal vacuum available at the venturi.

This is where float height comes in. The fuel level in the float bowl has to be low enough so as not to overflow and/or drain off into the crankcase/pour out down your leg. But, if it's TOO low, then the fuel won't get drawn off in the correct quantity by the reduced vacuum to create a clean-burning fuel/air mix. The result will be stuttering on a light throttle.

Might be worth a look .......................

[leswaller]

Good points linegeist, I will check the float height
Regards
Les

[Linegeist]

Hey Les! How'd fixing the stutter go? Did you find the problem ............. ????

[leswaller]

Hi
I checked the float height, which was OK, so I am now wondering about mixture control. I have set the tick over air bleed as per the book, and as there is no other adjustment on the carb I am wondering if raising the needle a notch would help or hinder. What do you think? This is my first stroker which I bought for green laneing. Although I understand 4 stroke engines and carbs I have a lot to learn about 2 strokes. I have been on holiday the last two weeks so I havent had a chance to experiment yet
Regards
Les.