couple of times when releasing the throttle I found that the engine would still rev ( a bit weirdly - and quite similiar to the rising revs you get when about to run out of gas.. )

this turned my plug chop from a brown to partly white

is that a jetting issue? ( but its hands off gas? )

Mart - You're running a bit lean. Richen up as you've reached the limit. What is your current jetting .

ps this would happen releasing throttle at medium high RPM..

Yes. If you have been using full throttle before you shut off then you need to go up on the main jet NOW . You are flirting with disaster . Unfortunately this is when 2 storkes run at their most powerful so you will loose a bit of performance.

Karts run so close to the wind with jetting that they put their hands over the entrance to the carb when they lay off the thottle, this stops the engine seizing.

cheers Steve .. current jettiing is 142 -

I will go back to 145 as there wasnt much diff in power..

still need to fix the pilot I think... ( still burping in 4th 5th... )

I would say I was at 2/3rd throttle...

low end power could perhaps increase.. I will play with air screw some more.. currently is on 1 - 1.5 turns out..

Drop the needle back down.........................NOW

That is drop the need down a groove (up physically)

^^^^+1, 145 main +1, have you oiled the filter?
Mike

Possibly an air leak as well.
Mike

Difficult splitting this post between here and - viewtopic.php?f=1&t=8404

One of the more interesting posts, keeps the site active......., it seems the bike wants to give up and die peacefully having been abused for many years.

But against all odds somebody is trying to give it the kiss of life, and we are trying to help him resuscitate it.

Somebody send him a carb, it must be worn out changing jets and the like.

thanks Mark - but carbs is in reasonable condition.. changed recently - and it has much improved things.. and its true the bike has needed a lot of love!!! its still been a lot cheaper than giving up and getting an orange un! and I've enjoyed new challenges!

apologies for creating a too many threads! was trying to get a better understanding of pre-ignition - as my top end rebuild seems to have been almost successful ( jus need to try instagasket on the leaky thermostat when I get out there take a look shortly.. )

preignition from the bits I was read - is from spark plugs glowing hot? or crud in the chamber acting like a glow plug... but this could have been caused by running too lean from your replies.. so will back off a notch...

but the air leak theory might hold water I was fumbling around in the reed box... replaced reeds but re-used the gasket that had been on there a month or so,,, and that was my dodgy cutting out- so I will try the air leak test ( spray around there when the bike is running - ) ( that'll learn me tryin to take short cuts!!! )

so perhaps I should fix that first and see if thats the cause of lean burn, then take another look at the jets... altho I dont think there was much if any diff between the 142 and 145 -


cheers guys- feel sure I would have scrapped the bike without the support of this site

felt really good to rip up some filthy hills yesterday tho!

[quote="knackeredMk1"]
Karts run so close to the wind with jetting that they put their hands over the entrance to the carb when they lay off the thottle, this stops the engine seizing.[/quote]

I always wondered why they did that! That's a little mystery solved for me :)

I have just experienced the same with my MK1. It gets to the point where it starts to rev on it's own and will not respond to the kill switch and ignition so it has to be stalled. Off with the carb then and check the jets and for air leaks