Main jets and two-stroke tuning

[badlydamaged]

Hey there, as some of you may know I have a KH100, which I am intending to uprate a little for buzzing about on . Recently I brought a 22mm carbuerttor, not much bigger than the standard 19mm one for reliability's sake. I have also just picked up an Allspeed exhaust for it (rocking horse **** rare!) which I intend to fit with the carb and leave it at that.

So, I was wondering what sort of size main jet would it be worth trying for this set up. Standard jet size is 80, any ideas?

Also, I have a 125cc top end from a KH125 knocking about which will fit, although it needs honing and a new piston before I can fit it. Would it be worth slapping this on as well, I was thinking about it but with the added costs of sorting it and then all the paperwork to keep the DVLA happy I'm not sure If I will bother. To be honest I'm only looking for enough power to cope with when I change the sprokets so it will keep up with traffic doing 70mph on the dual carridge way, and I would imagine the allspeed and slightly larger carbuerettor should cope. Or do you guys think I should go the whole hog and get the new top end on (bearing in mind the current engine was rebuild just 1500 miles ago).

Any thoughts? Like I say Im not planning on being able to reach silly speeds, a genuine cruising speed of 70mph would be ideal (currently 55mph due to the fact it red lines at 65, although it will do 65 all day long on the flat in dry / calm conditions). Im sure some scally has fiddled with it before (due to the fact that it had "Remus, Sport Exhaust" stickers all over it, and that it runs incredibly rich, choking at high revs and only running on 3 grade hotter than standard spark plugs without fouling) so theres a chance it all ready has the right main jet fitted in the standard carb, but I just wanted to run it by the experts here that have had more experiance with this sort of thing.

Thanks, Jonathan
____________________
My bike: 1988 Kawasaki KH100 Status: Polluting Devon with two stroke smog and noise pollution!
"Its not your engine size that matters!, It's what you do with it that counts"
Add me to MSN if you want! badlydamaged@hotmail.com.

[stinkwheel]

If it were mine, I would be inclined to 'suck it and see', fit the plug temperature you intend to use (use a new one, it is easier). Get it warm and do a quick blast (maybe 1/2 mile to a mile) on the standard jets. Do a plug chop and see what it looks like, if it is lean as hell, ride home on half choke, fit a bigger one and start again.

If it ain't, give it a bit longer on full chat and do another chop from flat-out. Use this as your basis for selecting your new jet or leaving the current one in. Carry on until you get a nice, light brown deposit.

Now do some chops at 1/2 to 3/4 revs and raise or lower the needle jet until it you get the magic colour.

That is my old fashioned way of doing it, there is doubtless some other way.

I reckon it'll blow up pretty quick if you manage to tune it for cruising for a long period at 70 though. Remeber this bike was first sold in the UK thirty five years ago, and it is air cooled! They do bloody well for what they are. Race tuned bikes will go faster...but race bikes get their engines rebuilt every couple of races
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[Kickstart]

Hi

You might gain a bit but not that much. The old Allspeed / Micron exhausts mainly sold to people with restricted 125s which tended to gain 50% + power wheold restricted exhausts were replaced. Yes you will probably gain a bit of power, but bear in mind that a sporty 70s air coole 125 twin would only manage a top speed of 80~85mph.

The carb you have got is from what model of bike?

All the best

Keith
____________________
Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[badlydamaged]

Ta very much for your replies, will look into it Stinkywheely