Jerking on overun

[leswaller]

I still haven't been able to solve the problem of my ETZ 301 continuously jerking on overrun on a closed throttle. I have:

checked and cleaned the float chamber valve
checked the float level
checked for free movement and position of the float
ensured the rubbers on the throttle and choke cable connectors are on securely and in good condition
checked the needle valve - on middle position
ensured the slide isn't sticking
checked quality of spark
changed plug
checked mixture/colour of plug
adjusted the tension in the drive chain

I am running out of ideas, any other suggestions please??
Les

[DAVID THOMPSON]

large 2 strokes suffer from surging as the mixture in the crank case goes rich then lean
the 500cc suzuki t 500 i had was bad about it
adjusting the carb leaner but not to lean may help
a higher idle speed may help
do check for air leaks and a proper float level
is the exhaust in good order and not full of soot
dave

[leswaller]

Dave
Thanks for your suggestions, the etz is of course a 300cc machine so I was not expecting large engine problems. The mixture (according to the plug colour) seems slightly on the lean side if anything. I have adjusted the idle air mixture to be both rich and lean without it making any difference. The float level is correct and the tick over is higher than recommended in the book. There are no apparent air leaks (hence my comment about the rubber boots on the throttle and choke cables) and the silencer is not restricted.
Someone else has suggested lifting the needle by one notch, but this would of course make the mixture richer - what are your thoughts on this suggestion?
All other suggestions will be gratefully received and tested, I am determined not to let this beat me.
Les

[Skorpion]

Hi leswaller.

To overcome the lurching you must adjust the carburetor until you get a reliable tickover at or below 1000 RPM,
usually you have to set the air screw slightly richer to be able to do this.

If when you blip the throttle the engine is slow to return to tickover, the mixture is too weak.

[therealche]

My solution was to get rid of the tickover altogether and get very good at pulling the clutch in and blipping the throttle when I came to a halt. Seem to remember someone suggesting drilling out the pilot jet helps but for the life of me I can't remember the details. Can someone else help?

[Skorpion]

[quote="therealche My solution was to get rid of the tick over altogether and get very good at pulling the clutch in and blipping the throttle when I came to a halt. Seem to remember someone suggesting drilling out the pilot jet helps but for the life of me I can't remember the details. Can someone else help?[/quote]

If I remember correctly, drilling the pilot jet was to create a tick over on the TS250/1, and maybe earlier models that came I think with a 35 size pilot jet, you can replace these with the later ETZ 250, 45 size pilot jet.

Although none of this will help the OP if he has the Bing carb fitted to his 301.

[leswaller]

Yes I have got a Bing carb on my 301. I have changed the tickover so that it is below 1000 rpm and leaned out the idle mixture. The engine slows down much more quickly now when closing the throttle and without popping. However this has all been done in the garage as I haven't had chance to ride it yet. Once I can take it out on the road I will report back
Les

[ericetz301]

this is a `feature` MZs, 2 strokes dont realy have engine braking, especialy going down hill, I thought something bad had happened the first time it happened to me (Sazon tour 301).
lowering the slide stop to almost nothing helps, but ,then tick over can be a problem.