koso 28mm -setup

[Torco225]

Hello all you tuning guru's .... I've just fitted a Koso 28mm (open mouth) to a standard 200 sil barrel with a sterling pipe on. It is a great little carb for being cheap and cheerful but not sure where to start with jetting . I'm nearly there with a 125main jet but the 38 pilot that came with it seems a little small maybe.
It will not start with out choke and is flat at bottom end , the 125 main works fine at top end (or at between 4,000-5,000 revs running in) . If I take the choke off it won't tick over , and have to blip the throttle to keep running . When I leave the choke on it seems to run ok but a little tickover fiddling is needed.
My problem is finding jets for it , a friend has told me that jettex main jets fit (which is the 125 in at the minute) . The pilot's are not found many places , they are like the Keihin type (round not hex like the PWK) .

Found sets at Readspeed so if no one has any other info might have to dig in my wallet for them .

cheers all

Rich

[shocky]

i used a 42 and i reamed the chock jet out till i was happy look on epay for jets

[ForemanBob]

The PWK mains are HEX shaped, the pilots are as follows...



MB are a good source for these, as the price for the BGM set = what you pay in some tuning places for a single item.

Send me a PM with what you're after if these are the right shape as I have a few duplicates could let you have gratis...

I ran a suzuki 190 on a sterling and was 138 on the main and 42 on Pilot with a JJH needle. The needle can have an influence on the pilot sizes too, as you get bleed through... I have recently come down on the pilot having changed the needle to a HFG to richen up a week spot that I had at 1/4 throttle.

[wack 63]

Try this Rich, http://scootrs.com/tech.cfm?tip=tunecarb

[Torco225]

Cheers guys much appreciated , had another tinker today. Got the tickover right with adjustment on the slide and throttle today , bit of a waste of time thou as it was with the choke on .

Spotted a set of pilots being sold by Readspeed but yours sound much better deal heeee heeeee.

thanks again , it's nearly there but the pilot is the problem I think just not sure whether to go bigger or smaller .

thanks Rich

[dapper]

Running a 24mm on my scoot and found I had to go as small as a 32 pilot. There is a list of other owners settings with PWK/OKO carbs on the ScootRS website if that helps

http://scootrs.com/tech.cfm?tip=jetpwk

[Torco225]

Had a look at that Dapper and tried both ends of the scale (well 32-42) but even using the air screw it makes no difference whatsever.

Thanks must go to Forman Bob for the special delivery

Tonight I've made sure the floats are all set correctly ( again) , but no luck . fuel getting in ok , runs great with the choke on but soon as its off the scoot dies when the throttle is anywhere around 1/4 throttle to stop .

Went out for a little spin on it in the village and choke on starts and runs ok (for running in) but as soon as the flip choke is off lurchs like a good un under 1/4 throttle ????

plug is wet , spark nice and blue , timing spot on , can't see any tel tale signs of leaks anywhere, so wait for a reply off who I bought it off for a little help now.....

will try another carb thou to eliminate the possiblity it's my crap engine building heee heeee.

[Chris in Margate]

Been running a KOSO for about 3000 miles now.
Plug chopped and all changes recorded for reference points.

225 iron barrell ported and casings matched.
ScootRS exhaust
Electronic Ignition Timing 18 degrees BTDC
Running open mouthed with home made tea strainer filter.

JJH Needle
110 Main........ yes 110
32 Pilot.

Runs pretty sweet.
Will not run with breath easy filter fitted.
Starts easily. Not a lot of torque low down (exhaust) but lots of power and driveability when in the power band.
Gurgles and 4 strokes like mad on anything above 115 Main or 36 Pilot.
Plug nice colour

PS: Use choke so start first thing in morning and let it off almost immediately. If turned on when cruising it induces 4 stroking due to over rich mixture.

[shocky]

Had a look at that Dapper and tried both ends of the scale (well 32-42) but even using the air screw it makes no difference whatsever.

Thanks must go to Forman Bob for the special delivery

Tonight I've made sure the floats are all set correctly ( again) , but no luck . fuel getting in ok , runs great with the choke on but soon as its off the scoot dies when the throttle is anywhere around 1/4 throttle to stop .

Went out for a little spin on it in the village and choke on starts and runs ok (for running in) but as soon as the flip choke is off lurchs like a good un under 1/4 throttle ????

plug is wet , spark nice and blue , timing spot on , can't see any tel tale signs of leaks anywhere, so wait for a reply off who I bought it off for a little help now.....

will try another carb thou to eliminate the possiblity it's my crap engine building heee heeee.

if it has an oil injection pipe on it check its blanked of there may be a hole behind the main body that takes the pipe just a thoughtn

[chris2470]

I have run a scootrs one of these for years, I'd recommend 118 main and 40 pilot on a standard 200. Needle will be a JJK 2nd clip.