Villiers, 2stroke, 4 stroking.

I have rebuilt an Allen scythe and it is 4 stroking quite badly.
In thick heavy grass it runs cleanly and pulls well but under light
running it 4 strokes and then when you come to a heavy patch it hasn't
got time to "clean up" and sometimes just bogs down.
The engine has been completely rebuilt (at great expense)so if it will
run cleanly then it can only be an adjustment.
The three things I can adjust are :
mixture, rich/lean
timing, advance/retard
and plug heat, hotter/colder
I had a champion D16 plug to start with and have tried a D14 which I
believe is slightly hotter running and seems slightly better.
Would a NGK plug be any better?
which way should I try adjusting the timing, advance it maybe?
Regards, Kev
Reply to
Kev
Loading thread data ...
Too rich ttfn Roland
Reply to
Roland and Celia Craven
Can you lower the needle ? Villiers and other carbs have needles with five circlip grooves so you can raise or lower the needle in respect of the position of the throttle slide.
Raising it richens the mixture, lowering it weakens it.
Nominally it is normally in the central groove, but worn jets will give over-rich mixture settings, so it's worth a try at taking the needle down by one or more grooves.
Peter
-- Peter & Rita Forbes snipped-for-privacy@easynet.co.uk Engine pages for preservation info:
formatting link
Reply to
Peter A Forbes
New post because it won't let me post follow up. I have weakened the mixture and it seems to be a lot better, though I won't know till the grass dries up and I can try it for real. I had previously tried weakning it but hadn't gone far enough (the needle screws up and down and it only takes 30 seconds to adjust) But what about timing and plug grade? I would still like to get hold of an NGK plug to try as I think they are better. Thanks, Kev.
Reply to
Kev
Check the timing first, preferably with bulb and torch battery.
I'm a great one for fiddling with the plug grade, but without full throttle colour grading, you are running the risk of overheating if you change grades willy nilly.
My first move in this direction would be to get an NGK of the same grade but with an extended nose. Carrying the ignition point out into the combustion chamber changes the flame front progression and will usually result in a cleaner burn. This is especially useful if the mixture is rather rich or weak.
As to carburetion, moving the needle position is a coarse adjustment, but it will certainly demonstrate if you are heading in the right direction!
Check the slide by pushing it towards the engine and away from it when just off its stop. The changes in speed and direction of the induction gas pulse downstream of the carb causes the slide to flap to and fro and this wears both slide and body. If there is much movement here, air will leak around it and you will never get good carburetion whilst it is fitted :o((
Regards,
Kim Siddorn,
Reply to
J K Siddorn
I set the timing to the factory setting using a multimeter so it should be right, But I was wondering if perhaps retarding it slightly would stop the 4 stroking and make it pull better at low revs.
I have tried the local dealers and can't get any sort of NGK plug in 18mm thread off the shelf, but I will maybe widen my search.
My needle is on a screw and infinitly adjustable but I think it is now almost all the way down so I was thinking about a new jet and needle but hadn't considered the slide - maybe get a new slide as well.
Thanks, Kev
Reply to
Kev
Have you checked that the float chamber needle valve is seating properly? If it leaked, it could cause the fuel level to rise when demand is less causing the rich mixture. Just a thought. Rojja r(dot)glover(at)btinternet(dot)com
Reply to
Roger Glover
You won't get NGK's in 18mm, but you should be able to find an adaptor to allow you to use 14mm plugs. 18mm has been obsolete for so long now that all the mid range plugs have long since been used up and all there is to experiment with is plugs that are either too hot or too cold with broad spaces in between.
Further, there are a lot more graduations of grade available these days as combustion is better understood now.
Having got the ignition timing as maker's spec, I'd not fiddle with it other than by adjusting the points gap. It's surprising the difference a couple of thou here can make.
Regards,
Kim Siddorn,
Reply to
J K Siddorn
Unless they have recently discontinued them the NGK A6 and A7 are good 18mm plugs for two strokes. I'd try an A7 first. ttfn Roland - smelling of freshly burnt 2T oil :-)
Reply to
Roland and Celia Craven
I have ordered a Champion D18 from
formatting link
(they seem fairly knowledgable and helpful people) I already have a D14 & D16 so will try them all. I have a lathe so might set about making a bush to step down to 14mm and get loads more choice if my heat trials are conclusive.
Thanks for all the replies,
Kev.
Reply to
Kev

PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.