airbox and OKO carb.

[sicivicdude]

So I bought a OKO 30mm carburetor direct from the manufacturer. It ran me $138 for the 30mm carburetor, a selection of 10 pilot jets, a selection of 10 main jets, and a plexi float bowl

I was aware that the airbox boot would have to be stretched to fit over the inlet but I was unaware of the difference between the factory Mikuni carb inlet size and the new carb inlet size. It's rediculous how much bigger it is, like 3/4" difference in inlet size for only 4mm difference in height of the throat and only 2mm in the width of the throat.

Anyway, I had seen someone stretch their airbox boot with a socket with success so I figured I could bring out the big guns and use a heat gun and tail pipe stretcher to really work that thing out. I worked for THREE DAYS with a tail pipe stretcher, heat gun, ice cubes, and several deep well axle nut sockets preheated with a propane torch. Each time I removed the heat, cool, or stretcher it returned to its previous size (or really close) and I never could get the boot over the inlet to the carb.

After farting with it for three days, I took a hacksaw to the rear plastics and cut the stock airbox completely out of the rear plastics.

I'm far too cheap to purchase an airbox proper, I enjoy working on junk AND I have a welder so here goes!

I have a mig welder (man I wish I had a tig but no dice for now) so it's all steel for me although I bought thin stuff to keep down the weight. I'm going to compare the stock airbox's AUW to my box's AUW when I'm all done to see how it compares.

I bought a thin sheet of weldable steel from Ace hardware

part #- 5081187 24" x 24" x 22 ga. $19.99 <---is about twice the sheet I need but it's all they had.

I bought a radiator hose and an exhaust pipe from Advance Auto Parts.

part #- 548623 2" tailpipe 18" long $6.89

part #- C71216 Dayco molded rubber hose with two slight bends in it. $11.99

I'm also using a UNI filter I already had sitting on the shelf and a few standard band clamps.

I'll be working on the box tomorrow night so more good pictures then but I already cut the radiator hose to fit the carb and out past the side of the shock. If you look real close you can see the black hose coming out of there

 

[Whitty21]

i am intersted in this man!!!! keeps us updated, link to where you bought the carb?

 

[scotj77]

thanks for the pics keep em comin. can't wait to see the finished product. someguys just cut the airbox boot back and use metal or pvc tubing with somesort of reducer to make it work. but kinda late for that lol

 

[Zwiser]

looks good!
151515151515

 

[scotj77]

do you want some dimentions from my factory 7 airbox to help you out?

 

[sicivicdude]

I actually worked a deal with the guy off of Ebay, spcglobal. He's out of Taiwan and shipped from the company. I ordered it on a Tuesday and it was here that Saturday. Super fast shipping and so far, a decent product. Oh, did I mention that $138 was including shipping?

I know slickerthanyou had an issue with the OKO chrome slide flaking but mine looks pretty good and hopefully will be fine running like that.

Well, cutting back the tube only adapts that silly stock airbox tube to the aftermarket carb... I have the capability to replace the airbox all togetherso I figure, why not?

 

[Whitty21]

i am seeing a lot on ebay for 60-70 bucks.........

 

[sicivicdude]

The OKO 30mm carb is a keihin pwk 28mm knockoff which has been bored up to 30mm tall.

So far, it's actually idling better than the factory Mikuni carb. I had my stock carburetor jetted up and set up VERY nice and it still didn't idle as smooth as this carburetor. I can't attest to the top end because I don't have an airbox yet! LOL.

 

[brandoz28]

love mine too. can't wait to see how this comes out!

 

[slickerthanyou]

You are right about my slide but i think that was an isolated issue as the replacement sent i've had no issues with. I'm happy with it! Getting it jetted was a pain for me, but now i know what to listen for and how it is suppose to sound , i have no problems, and you will be pleased with top end too!

 

[sicivicdude]

So I got home about 4PM to a series of messages on my answering machine. My parent's well pump had locked up and they needed help pulling 285 feet of plastic pipe out of the ground.

When I got home, I traced out the airbox on the steel plate and welded the pipe up to get a rough idea of the shape I am going to cut it.

I'm going to cut the steel and weld the corners hopefully tomorrow. More pics when I get more done!

 

[sicivicdude]

I went over to their house last night and reinstalled their well pump. They were pleased...they had water!

I went out to the garage last night and worked on the airbox proper. I cut the sheet of steel out to shape and began bending it. I had a hellova time cutting as the aviation shears I was using were really working my forearm which was already sore from pulling 285 feet of pipe out of the ground...

I used the vise, deadblow hammer, and a few body spoons to work it as smooth as possible and then welded up all four corners. The box is now square! I'm going to get some picture this afternoon after I cut the hole in the front corner for the pipe...

 

[sicivicdude]

The finished product:

Sitting mounted under the plastics:

The carburetor:

The clear plastic float bowl:

 

[brandoz28]

looks good man. that box should be a little better than stock

 

[sicivicdude]

Thanks, I still have to do a little jetting on that OKO carb and as this is the first real time I've played with lots of jetting it should be fun. I mean I used the vito's jet kit for the factory Mikuni carb but it was simple to set up in there. 290 on the third clip with the stock pilot isn't really complicated...but with a set of 10 pilot jets and 10 mains I have a lot more choices to figure out...

The only thing I'm really bummed about on that OKO carb is the lack of instructions and tuning help after installation. It seems to be a solid unit and is running beautifully even without having the jetting dialed in perfectly yet.

 

[Whitty21]

looks awesome dude, hopefully i will have an oko soon, gotta do a stupid build though....

 

[brandoz28]

yeah, oconnor may be able to help with jetting, i know slickerthanyou is running this carb too.

 

[sicivicdude]

Alright, after about 3 hours of playing with jetting and chasing my tail I finally figured out something.

I decided to get the idle spot on and then play with the needle as I lack an area large enough for a plug chop at my house for the main...

The OKO carb comes factory with a 48 pilot and 138 main with a N80F (I don't know what that means because OKO doesn't provide a chart and that's not the same numbering system keihin uses) needle on the third clip. I bought 10 spare pilot jets ranged 42-60 and 10 spare mains from 130-150

The idle was choppy with the air needle any less than 2.5 turns out so I decided to drop the pilot to a 42 to try to dial the idle in. When I did that, the engine started idling smoother but applying any throttle at all started chopping up real bad and sputtered as it took off with random sputter and bog...

I then took to the needle setting trying to work the sputter out of it. Sputtering is usually rich so I moved the clip up a notch and it went to hell. It started sputtering at an idle and the bogging/sputtering while taking off didn't get any better. I move the clip to the top position and it wouldn't idle at all and bogged totally out when I tried to take off. Stumped as to what in the world was going on I took the needle out the other way to the 4th clip position and the idle was spitting but the off idle was better (still not perfect) I moved the clip down to the 5th and it began to spit splooge out between the head and the cylinder... and the pilot jet and air screw were not effective at stopping that.

Each change of the needle clip I'd also try to chase the idle around with the pilot jet and air screw to no avail...

I finally broke down and pulled the needle out and looked at it. I slid it down the needle jet holder and wiggled it around! I pulled it back out and looked at it carefully. The 80R needle has a step in it down below the clip area that does not fit tight inside the needle jet holder...

I found a replacement needle that did not have a step to it. I put it on the 3rd clip position and fiddled around with pilot jet until I finally settled on the 48 pilot jet back in it.

You'll never guess where I found the needle which has my blaster zinging around my yard on the back two wheels with even the slightest application of throttle...

The vito's replacement needle for the stock Mikuni 26mm carb without airbox is now sitting in my OKO 30mm carb and running BEAUTIFULLY!

 

[Whitty21]

nice job being one of the original trailblazers with the oko, i am sure i will be using this when i get mine, have some rep man

 

[sicivicdude]

Alright, After some careful measuring (and deciphering of keihin's needle chart) I have determined that I have a N427-46HLJ needle for a PWK28 carburetor. Which is totally screwed up for my application apparently as it made it run like dog poop...

The mikuni needle is a might too short for this carburetor (like 1mm shorter than the keihin needle so I'm afraid it's going to come out of the needle jet and hang the throttle open one time) but it's running like a scalded dog in mid-throttle. Anything above 1/8 throttle in 1st or 2nd gear is on the back wheels which I think is about where it should be

I'm still getting a TINY bit of pop and flat sound out of it at less than 1/8th throttle. I believe the 48 pilot is a bit too fat but I'm idling smooth at 1 1/2 turns out on the air screw. Anyone advise on that?

I'm going to call around to some tuning shops in my area today and see if anyone stocks an assortment of Keihin needles. I'm looking for one in the JJM, JJL, or maybe HKL region. Maybe that'll get my needle setup right for the low RPM without changing the pilot smaller and airscrew farther in.