Posts
27442
Joined
7/22/2007
Location
St Helens, OR
US
Edited Date/Time
4/11/2019 5:40pm
I sent an email to Derek today about picking up another STIC metering block from him , as I plan on switching over to a PWK 38. I'll be changing to a rad valve , changing the exhaust and milling the head to around "0.045 ( stock is around "0.065" + )
My goal here is , to be able to run the same fuel in my 125 and 250. Right now I'm running 40:1 / 927 with 1/2 and 1/2 Clean fuel and VP 110. I'm thinking of possibly changing both these bikes to a 36:1 ratio instead? I really don't want to run that synthetic stuff in my 250 , but with the stock carb / jetting I didn't really have a choice.
I guess I need to wait to hear from Derek on this , but if I make these changes , shouldn't I be able to make the switch to 927? In my 06' RM250 , i have been running 40:1 / 927 and she ran perfect.....but she also has a PWK 38 on it.
My goal here is , to be able to run the same fuel in my 125 and 250. Right now I'm running 40:1 / 927 with 1/2 and 1/2 Clean fuel and VP 110. I'm thinking of possibly changing both these bikes to a 36:1 ratio instead? I really don't want to run that synthetic stuff in my 250 , but with the stock carb / jetting I didn't really have a choice.
I guess I need to wait to hear from Derek on this , but if I make these changes , shouldn't I be able to make the switch to 927? In my 06' RM250 , i have been running 40:1 / 927 and she ran perfect.....but she also has a PWK 38 on it.
I run 32:1 in my '14 KTM 150SX and '17 Husky TC250; 93 octane (with 10% ethanol) and Lucas Oil semi-synthetic.
I installed a STIC metering block on my '14 KTM 150SX a few months ago. The bike was stock except for a slightly thinner base gasket (to tighten the squish). Never had any issues due to the compression ratio or fuel mixture. Performance-wise, it improved roll on/low end some and really improved midrange and top end/over-rev.
Recently, I swapped the carb from the 150 (PWK) to my 250 (TMX) for some testing. On my TC250, I only have a slightly thinner base gasket, again to reduce squish. Compression is very close to stock. With the STIC equipped PWK on my TC250, I had some pinging when I rode on a softer track that put a higher load on the engine. Performance wise, it was similar to the 150SX but a bigger change: much better roll-on/low end, more midrange, and much better top end/over-rev. But, I was unable to richen the jetting enough to not have pinging in the range I was having it (1/4 to 2/3ish).
Later, put the stock metering block back in and tested the PWK on the TC250 and the TMX on the 150SX. Both were actually better for me in this configuration. The roll on power is still better with the TC250, but without the benefit of the overrev added by the STIC. I do have a PC pipe and silencer on it and they make it better than the stock setup anyways. Also, the midrange and up on the 150SX with the TMX now feels better to me than the PWK. And since less time is spent at smaller throttle openings, the roll on isn't as much of a problem.
All that being said, with your race gas mix you should be fine. I had pinging that was unacceptable and I'm not buying race gas. But, you might ask your buddy with the 150SX to try out your TMX and you could try out the PWK on your TC at the same time.
Just pick a middle of the road oil-ratio like 40:1 or 36:1 and jet around that for both bikes. Or buy two gas cans and a sharpie if that help you sleep better.
TMX or PWK can work well 20:1 to 100:1. Obviously you'll need to jet for those ratios.
My buddy has a 2017 KTM 250. He went through some major testing on the Mikuni ( actually read a lot of what AJ595 on here has written ). He tried 40;1 with 1/2 and 1/2 race gas on 927 and the bike ran like complete crap. He then switched to Synthetic at 45:1....still ran like crap , tried 50:1 and it got better , and then finally settled on the 60:1 synthetic blend and his bike runs well with the Mikuni. But still has issues with small temp changes / jetting changes.
So I already know my bike won't run well at all ( no matter the jetting ) on 40:1 - 927 with this carb. Even has the JD jetting jet kit installed on his Mikuni , and it still wouldn't run right. Up here in Oregon , we deal with cold 35 degree days to 105 degree's and dry as a bone. The 125 / mikuni setup for me was a nightmare. I don't want to go through that same bullshit with my 250......so I'm getting the PWK. I honestly don't know if it's the absorbent amount of squish these bikes have , the crappy carb or bad reeds. I don't know what makes them want / need to run at 60:1 synthetic , which is way to lean for 927 and I won't run that.
@Erik....let me digest some of the stuff you wrote above , as I'm dead tired from work and my brain isn't functioning right.
I have a 5.5 cut slide that I can send you if you'd like to try it. You'd have to get the needle, needle jet, PJ and MJ to go along with it, but the slide is whats the expensive part that nobody likes to buy. It's slightly richer than the 5.75 I run, But much leaner than the stock 4.0.
The Shop
I have previously ran my TC250 with a head cut down by 0.020". It ran great on pump gas even with the TMX. Then ran a 300 kit for about 10 hours and when I reinstalled the 250 cylinder, installed the stock cylinder head to remind myself how it ran. It is time for a new top end and I plan to install the cut head again and dial in the jetting with the PWK.
Will probably test again eventually and report back.
The PWK is definitely easy mode. My first attempt at jetting and it ran great with only a tweak on the air screw (175 MJ, N3EW 3rd clip, 45 PJ, 1.25 out on AS). It is a bit rich, but it ran good enough to not even worry about it.
@BR8ES.....totally agree! I can understand Husky's and KTM's thought process on these bikes , as far as making them pretty mellow right of the floor. But at least the full on race motor is sitting inside these thing's , with a little tweaking. Which I don't mind at all , since I can never leave a stock bike alone anyways haha.
I have ridden a 300XC with a shaved head and Keihin carb (do not think it had the STIC mod though) and it was not much different than my bike. Maybe a bit more torque down low? But his powervalve was set up more aggressive.
If you take some time with the Mikuni you can get them to run very well, save you quite a bit of $ too.
I put a PWK on my 18 TC 250 last year. It has V-Force reeds, Pro Circuit pipe & silencer. Stock motor otherwise. Plan on running 40/1 with 50% VP110 & non-ethanol 90 octane pump gas. I also have the STIC to throw at it, but I would rather jet it in without it for starters.
I did buy the JD kit for the PWK. It has been so long ago I forgot the brass I installed. Bike has not been started with the above mods done almost a year ago due to health issues, which have been corrected & the doc says I am good to go. I just pulled the TC out of mothballs and would like to hit the local tracks again.
I will find out tonight what brass I installed.
EDIT: 172-42-1 turn out-slide 65 (6.5?)-needle JD red middle clip
Questions being, anybody have some jetting specs I can start with with the PWK? Might save me a bit of time changing brass.
What about with the STIC? What is your jetting & impressions with it installed?
My STIC came with a 190 main & a 48 pilot from Derek.
Thanks bunches in advance!!
Also have a Thunder Products Torque Wing for sale $50 shipped.
And a clean stock take off PWK 38 carb from a my 2006 RM project bike for $160 shipped.
Email me at gforcecoatings@gmail.com or text 608-556-5877
(payment via paypal and shipped next day via fedex)
Post a reply to: Harris STIC mod / PWK 38 for my 18' TC 250.......fuel mix?