Flatslide carb tuning instructions

For those who lost the instruction sheet. Tuning instructions for PWK flatslide carbs are now available online at:

http://www.jsmotorsport.com/technical_carb_inst.asp

Find this link by going to jsmotorsport.com
Go to the technical section under “Flatlside Carbs”
Look for the “carb tuning” link

Hi Jim, I noticed that my fuel consumption was quite a lot higher than when I first put these carbs on, also I had always had a flat spot from the time of installation at 4800 to 5200 rpm when opening the throttle quickly and always after leaning the bike over in long uphill sweepers, it would always falter when stood back up again. The flat spot wasnt there if i slowly increased throttle. Anyway as I was off on a long ride for a weekend that involved some drag racing on an airstrip as a fund raiser, put the bike on the dyno prior to the long ride(bike is std 850 Roadster with 25,000 mls on it, your 32mm flatslides and Pazon Surefire ignition,std un balanced headers ) and found that it was way to rich and showing 40 rwhp, removed the small supplied aircleaners, made 45 rwhp straight away , but still to rich, and ended up coming down 2 x main jet sizes. Checked the old air cleaners to make sure they were not clogged,which they weren't, so all good there. Now running a couple of UNI filters that I got with a couple of 32 mm Premiers from a forum member, I used the boots from the air filters you supplied, removed the stainless gauze from the front chrome base and glued the UNI filter into the chrome base, now it all fits.
Fuel comsumption is very good and no falter in the 5000 rpm rev range, managed to take 1st in the pre Hinckley Twin cylinder Class 14.0 sec f for 1/4 mile
Regards Mike

Its always best to start rich and then lean it out. No one wants to damage a motor from too lean a mixture. I am working on getting better air filters that aren't too expensive. Did you oil the aircleaners I supplied? They are not designed for oil and that will choke them off.

I am looking into an aircleaner with more filter element.

Is this a stocker? Describe cam, pipes etc and tell me what size main jets were too rich and what you are using now.

Congrats on your drag race win.

Hi Jim, stock standard motor, clean and un oiled filters, as soon as I removed them with same jets and settings , I gained 5 rwhp indicated by the dyno.
It just didnt pull enough air with them on. Thats why I doubled checked to make sure they weren't blocked with road grime or dust.
I then modified the UNI filters as explained while still at dyno shop, ran again on the dyno to see that the 5 rwhp was still there, then started going down on jet sizes. I wen t from 150 as supplied and ended up with 130, flat spot gone and fuel economy great and plugs a better colour, running 98 pump fuel.
I realised at the time going down 2 x sizes was a big step, didn't change the needle at all.
Headers are standard diameter and length, mufflers are an after market set that I also use on the race bike, as the other two so called originals sets I have give me a big dip in my midrange, as per the dyno readouts I posted on the forum and copies i sent you from my race bike with your internals.
Hope this helps.
All this close to sealevel as well.
Regards Mike

I have a ported 750 with free flow exhaust and I use 160 mains, it loads up with 180s. I jet by richening till it loads up and then drop down two sizes (180 to 160).

I usually send out carbs for 750s with 142 jets (carbs come supplied with 142s) and 150s for the 850s. I don't want to hear from anyone about a piston damaged from lean burn. And some bikes need them that rich or richer depending on tune.

Better Filters are coming. The filter below look similar but it is a different brand and alk proof with more filter element hanging downward.



K&N makes some nice ones (see below - part # K&N RC-2330 with 2-3/4 length) but they are about 1/8" too long to fit inside the original aircleaner backing plate. I would have to raise my price for the carb kit.



UNI makes some short socks that should work but I'm worried that they may be too short to breath. I use a longer 6" UNI sock part #U-603 on my Atlas with modified oil tank (the aircleaners I sell won't fit my Atlas). I don't use the internal spring and I made a press on PVC collar to fit on the carb bell mouth and clamp the filter onto the collar. It works but its impractical to sell.



To fit within the stock Commando air cleaner backing plate the aircleaner must be no longer than 3-1/4" OVERALL and short free breathing aircleaners are rare. A uni U-403 cut to length and clamped directly onto the carb bell should work but the clamp might cut through the foam sock.