CARB UPGRADE PAGE. 

Here's another upgrade that I've done to The Fire Drake. The swapping of a 30mm OKO carb instead of the stock 25mm one. They're both the same, but this isn't an easy swap for sure. There are more hoses and things on this engine than any other I've seen. The swap is not impossible as you can see, but it does take a long time from start to finish. With the prepping and the tapping, removal of this, fabricating that, it took me a good 5 hours- no joke.

Here's the original carb, a Keihin 25mm CVK. It's a regular CV type carb, but the K designation is for Kawasaki. The jets are 102 for the main and 35 for the pilot. Don't forget that this is a water-cooled engine so they don't have to be as large even though it is a 171.2cc motor. When I previously added the MRP exhaust, I was running leaner, so I adjusted the A/F screw a good full 1 turns. That was about as rich as I was going to get until I'd have to re-jet the carb. It was enough, but I did sense a little popping on occasion after the enrichener shut off and while I was engine braking. Mostly it was at speeds above 60 mph and letting off the gas fully. The new carb has the original ones that Mitch (mx5tc in scootdawg) and I probed using drill bits since the jets weren't marked. After the conversions we believe they are a 132-142 main and 34-38 pilot. 

 

This is the new air intake, filter. It's an Emgo 48mm filter. I bought two of them off eBay for 12.00 shipped. The flex-tube assembly is a length of good ole-fashioned choke tube for a carbureted cage air horn. This will mount directly on the carb's inlet as shown below. 

 

 

 

Here's a picture of the intake assembly that was removed. Sixteen inches and over 3 pounds of restrictive bulk. There are breathers plugged in all over the place here. The top snorkel is the fresh air inlet.

 

 

 

Problem number one... The cooling exchanger won't fit the new 30mm OKO. Big problem for me because that exchanger is tied directly into the thermostat. In other words, if you just cap it off or otherwise bypass it, I'd say you're going to run into a few problems with temperature control on this engine. S.O.B. :) 

 

 

 

Now you can see the problem with the cooler mounting. The original carb on the left has been machined and ready for the cooler. The OKO on the right has the same dimensions externally on the cooler hole, but its inner recess is  not milled and is "stock." Time to go to work...

 

 

The finished product. I used different sizes to emulate the bevel effect  that is needed on the bottom. When I drilled it out I first used a 21/64ths to bore the main hole. Afterwards I finished it off with a 23/64ths to create the bevel effect like the stock one. I went very, very slow and used 3 in 1 oil for lubricant. It's soft cast aluminum alloy so the drilling was easy, but it's real easy to screw up if you're not careful. I taped masking tape around the bits and used those as a depth guide.

 

 

The new carb is on the right in this photo.           The new carb is on the left in this photo.

 

Above are a few photos of the old carb and the new one. most noticeable is the addition of a accelerator pump on the new OKO. That proves to be pain-in-the-arse number 2. It won't clear the frame normally and to install it; I had to attach it at a 90 degree angle and twist it and finagle it to mount under the frame instead of on top of it and then align it to the intake manifold which is part of the block on this motor. It's going to be another pain in the butt to remove the actual rubber intake when I have to. Take a look at the pictures below and you'll see the "lock-nut" on the right side. That's gonna be fun. Simple jet swapping on this new carb is not so simple and will take 30-45 minutes just to remove it.

 

 

 

 

The exchanger has been mounted on the new carb.

 

 

The cable mounting on the carb has got to be 99% compatible with any scoot. the 30mm OKO carb has mounting holes and brackets everywhere and I actually took one off as you can see to the left.

 

 

Mounted and ready, here are pictures.

The red area is where I'm fabricating a mount  for the intake pipe instead of the temporary wire tie. The blue X is the  some of the PAIR that was removed after I fabricated a cap-off.

 

I still haven't made the mount yet for the air filter, but in this photo, the PAIR is gone. The cropped photo shows  where I capped it. I left the metal tube on the block and capped the end to the valve instead. The extra metal tube will help in heat dissipation better than if I just capped it at the block. Even if the cap blows off, there's nothing around that it could hurt before it was fixed.

Here's the filter peeking out a bit. I kept it underneath and shielded by the splashguard. I could retract it even further in or out if needed. If you notice in the upper right of the photo; You'll see an unused support for the splashguard that I'm going to make a bracket for also. On the one below it, I had to add a lock washer to keep it from flapping around. The bottom one has a spacer in it and I had to lock it up otherwise it would hit the wheel.

Summary:

With the addition of the bigger carb and free-flow filter, it is almost twice as loud as it was before and you can hear the whoosh-whoosh at idle. Under normal acceleration it's louder, but open it up and it sounds like a freakin' jet. It may not be as pronounced on a 2 valve head, but since this is a 4 valve head, it may be louder still. I'll be constructing a shroud of sorts if it becomes too bothersome. Space is extremely limited and I couldn't mount it directly on the carb. Hell, I was lucky to even get it in there in the first place:) With the MRP and the free flow carb system, it's open in and open out. It sounds like a mini Harley with the deepness in tone and not like a racing bike. I don't mind the exhaust aspect, but the intake roar is a bit much.

Performance wise I still haven't tuned it and our cold dense air at this time of year isn't helping. Did I mention it's freakin' in the teens???

 

 

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Revised: July 06, 2010