Rattler Carb Tuning

B02S4 · Post by **B02S4** » Sat Apr 25, 2009 9:32 pm

I took a closer look at the carb & airbox today, & here is what I found:

The pilot (low speed) screw was surprisingly easy to access with the correct screwdriver, given all the hoopla I've read about the necessity of seat-removal &/or access hole drilling ...

Mine was actually set too rich (motor is bone-stock) at approx. 1.5 turns out. It is now about 2.25 - 2.5 (I don't recall specifically) out, & runs better.

The airbox had a 10mm thick foam pre-filter covering the paper element. It was just in there by friction fit. I removed it. A quick test after those 2 changes revealed 63MPH indicated (in strong crosswinds, on slight downgrade) bfore I backed off. Not too shabby.

I don't think that drilling out the divots in the outer airbox cover is the way to go. The airbox has a rubber snorkle at the inlet that makes a 90 degree bend into the airbox. It looks overly restrictive. I would like to remove it, however I'm not sure that the Keihin jets that I have on hand will fit this carb. I understand that the stock jet is an 85, is that correct?

Anyone know the actual Keihin series number for the correct jets for these carbs? I preume that removing the airbox & pulling the carb from the manifold (without removing the cables) will make the jet change a bit easier. And there appears to be plenty of room to do it without removing the seat or plastic.

I have plenty of experience tuning Keihin CVK carbs, but none with this thing. The slide is apparently a direct connect to the throttle. Anyone know if the needle has an adjustable clip, or if there is sufficent space to shim it?

nissanman · Post by **nissanman** » Sun Apr 26, 2009 1:07 am

Stock jet is an 85. Wish I had more specific information for you.

B02S4 · Post by **B02S4** » Thu Apr 30, 2009 3:58 am

I pulled the snorkle from the airbox, & with no other changes the bike is running lean @ WOT, & apparently is producing less power. It clearly needs an upjet.

I pulled the airbox & measured the OD of the carb intake; it is approx. 35mm wide x 8mm deep (mounting clamp area).

If I'm going to pull the carb to rejet perhaps I'll ditch the airbox also & run a pod...

killerrabbit · Post by **killerrabbit** » Fri May 01, 2009 12:11 am

I was running a 92 jet with the prima exhaust and it seemed just about prefect. I then pulled the foam pre-filter you were talking about, and boom...it's running too lean with lost power. I'm going to try my 95 next time i tear the rat apart.

Also jets can be found http://www.scooterworks.com/Jet_Keihin_ ... 26C422.cfm<---there.

B02S4 · Post by **B02S4** » Fri May 01, 2009 2:35 am

Thanks for the link K-R, that may be a different model Keihin jet than what I have for the CVK carbs on my Triumph & Suzuki. The Scooterworks image is enlarged to the point where I can't say for sure that the threads are the same, although they are close enough that I'm going to give it a try this weekend. If it works then I'll be able to provide a Sudco parts number that may provide for more choices...

B02S4 · Post by **B02S4** » Sat May 02, 2009 10:58 pm

The Rattler Keihin PB carb definitely uses a different jet than a Keihin CVK carb...

I found it necessary to remove the carb from nthe manifold to drop the float bowl, & also found it necessary to pull the seat tub to get clearance to spin the wrenches on the carb manifold mount bolts (no biggie, 6 bolts & 1 screw, badda-bing, done, tons of access).

BTW the carb manifold inlet is 20mm, so I don't think that a bigger carb on that stock manifold would do much.

Given that I only have the stock 85 jet, I put the snorkle back in the airbox & buttoned it back up. The only change is that the foam pre-filter is out. I then saw 64 indicated with a slight downgrade...

Installation of the new Unifilter pod will have to wait for receipt of the new jets...