tuning my cpw oko 28mm

[jayflight]

just got bike used(94 blaster) with fresh top end (supposedly ported, to what degree is unknown). cpw oko 28. fmf fatty w/powercore 2. k&n w/ open airbox. dont know what reeds yet. it had a 152 main and unknown pilot so far. the idle-air was turned all the way in. it was running rich so i switched to a 148 main. it seemed to improve. i turned the air screw out to 2 turns and lowered the idle slide adjuster. it responds fair but doesnt make much diff on the air screw. my instinct tells me to richen the pilot from whatever the size is now. any tips would be greatly appreciated. also the carb is hitting the clutch arm so it has to be slightly tilted and prevents satisfactory bite onto the intake boot. its sealed up but i dont like it.
B)

 

[sicivicdude]

You have to get a reed spacer to fit the larger float bowl of the PWK carburetors. The "tilted" position throws off your jetting because it upsets your float level. It will be more difficult to properly jet like that.

Read the stickies about jetting at the top of this (engine) section, under the title "Most useful posts-everything you need to know about blasters"

The pilot circuit and airscrew are seperate tuning tools from the needle and main jet. If you are running rich at idle and up to 1/8 throttle you need to tinker with the pilot jet and air screw. The only to know what you need to do with the main jet is to get the pilot fairly close in it's range and then do a WOT plug chop.

 

[Blasterr525]

yes, ^ that was a main puepose of the reed spacer. To clear the clutch for larger carburetors.

 

[brianfulcher15]

wishs they woudl have just came out with a new clutch arm design instead of spacer....

 

[Blasterr525]

Exactly. But when u go to buy it, it says it will give you thie power from it. No. All it does it might move your powerband to the lower-end. The power u want from thoes is not noticable.

 

[brianfulcher15]

whats really annoying is that on mine, i still had to go buy new bolts becuase the allen head bolts hit the float bowl too.

 

[cjc3fan]

whats really annoying is that on mine, i still had to go buy new bolts becuase the allen head bolts hit the float bowl too.

Having the same issue here. What type of bolts did you end up getting? Is it possible to properly tune a carb if it's tilted sideways just a bit?

 

[Joey_Stacks]

I got the 28mm OKO and yeah a reed spacer is a must way too much tilt in the carb to get the proper clearance.

 

[jayflight]

from what i understand, if i use the vf3 reed block it will space the carb out far enough. is this true?what about a custom fabricated extension tube between the carb and reeds?(like the tunnel ram theory on my drag car). also i would like to have as much bottom end power as possible for tight trail riding but have a screaming top end for when i run at the oregon dunes. how can i have my cake and eat it too?

 

[jayflight]

whats the scoop on these okos'. in general, the oko 28mm looks good. but i realize looks arent everything. a polished turd is shiny but do you really want one? before i spend too much effort on this carb i would like input from any experienced owners willing to comment. thx! this board rocks!

 

[jayflight]

the richness factor i originally spoke of was top end. i will do a plug chop as soon as i can. funny how the neighbors dont care for a 6th gear w.o.t. pass by their house just so i tune my main jet! lol

 

[Braaaptor]

I ran a 28mm PWK carb (the same as the OKO) with VF3 reeds, and the carb still wouldnt fit perfectly level. The VF3's help, but unless you get a reed spacer, the carb will not sit properly. I had trouble getting my 28PWK tuned properly, even when it was at a slight angle. I'd just go ahead and do a reed spacer. Same effect as the 'tunnel ram' style intake you are describing, without the custom fabbing.

I have nothing against OKO carbs; that being said I have never run one and in general try to avoid Chinese made parts, especially when you can get a genuine Keihin PWK carb in good used shape for under $ 100.00. Other people on here have had good luck with them and they seem to perform fine...

 

[cjc3fan]

from what i understand, if i use the vf3 reed block it will space the carb out far enough. is this true?QUOTE]

Yes it will. I previously had a PWK 35mm and it fit fine; no clearance issues. I went down to a PWK 28mm and that's good to go with clearance as well.

 

[sicivicdude]

The lower left screw had to be changed to a button head on my OKO 30mil carb to clear the float bowl.

It is threoretically possible to properly jet a carburetor when it's tilted but the float is more likely to hang causing an erratic gas level in the float bowl.

Jetting is a balance between the weight of the fuel in the float bowl, the restriction the jets provide, and the vacuum the carburetor throat has in it.

The vacuum and restriction stay the same but the fuel level changes.... not good.

 

[jayflight]

good call on the erratic gas level. the tilt issue made me think of proper emulsion issues but not of a sticky needle and seat due to side pressure from the tilt. i wish yamaha hadnt attached the carb to airbox boot in the manner which they did. it is no fun removing the rear fenders just to clean it out. is there a trick to the attachment thats easier and still retain the airbox for water splash resistance? i live in the pacific northwest and it rains more than it shines here!

 

[jayflight]

has anyone ever tried a long thin tube between the carb and reeds? say 2 inch or so. just curious what it might do. seems simple enough to experiment with

 

[jayflight]

ok, so i just finished reading the page from yellow dog on carb jetting(oops, sould have had that done earlier. it is a very valuable page) it doesnt cover the pilot jet issue as well as i would like tho. it describes symptoms and reactions to air screw adjustments but not to actual pilot jet size differences. anyone have a useful link for pilot jet size characteristics? to date it is the most useful tuning guide thats easy to understand that i have came across. kudos!