125-200cc One Strong 150!

I’ve been modifying my 150 for a while now trying to get the power just right and I am happy to say “mission accomplished”. The power is just amazing now! It pulls so much harder than it did as a stock WR150. The throttle response is instant and it will get singing on demand with no clutch work. It will still chug when needed but the mid is so broad and easy to stay in that I usually just keep it in the meat of the power. It might be a bit too quick and strong for a beginner but I am loving it and it is just so much more fun to ride now. I let a guy from TT on a CRF450 ride it and in a mile all he had to say was “I’m buying one”. Anyway, I know others are tuning the same bike so I want to list what I have done in case anyone finds it useful.

09 WR 125 with factory 150 kit.
CR ignition advanced 1-2 degrees.
Stock carb with RB Designs divider plate, air screw, and low speed mods. Jetting was perfect in the morning (37 degrees) with 30 pilot, chy16-61 needle at 3.5(I had a half clip spacer in it), 460 main, #5 slide. It still worked well at 65 degrees in the afternoon so I know the carb will not be too picky. I took out the half clip needle spacer though and gave the air screw a turn and it was perfect again.
Head squish set at .9mm by RB Designs
Walts power valves which I set as close to the piston as I dared.
FMF Fatty with TC2 silencer
Straight AV-Gas with Lucus premix at 32:1

Good job NWRider!

Just got done with mine and I feel the same way!

What is your gearing?

Gearing is currently 12/50 and way too low with the way it is running. I think I will try 13/50 again. If that does not work does anyone know if the stock chain will work with 13/52 and if it does how close does the tire get to the swingarm and does it make a handling difference?

poynedexter on here ran the 13/52 on his new CR with stock chain. Good job on the tuning! Is the plug tough to read with the avgas?

Plug is very hard to read with avgas. I always go by feel anyway. With these small bikes if they are a little lean or a little rich it usually makes it hard to get on the pipe. The CR ignition mask some of the difficulty but not all of it. I would just run pump and back off the ignition but it all has alcohol in it, also I sometimes have a few weeks between rides and avgas does not go bad. In theary it should have poor throttle response but I have never been able to get any better response with race gas, and I have instant response now anyway.

Interesting about the AvGas. I would think that it would cost you some on the top more than throttle response but what do I know about fuels. I expect that advancing the timing helped that. I do like the idea of mixing the avgas with non-ethanol pump gas. In Montana there are a number of distributers that supply guaranteed ethanol free fuel. I have 1000 gal of it at the course. I am now mixing 113 oct. with 87 ethanol free pump gas with fantastic results. My 210 psi compression 144 was an absolute rocket with instantaneous throttle response. I am in search for a CR125 rolling chassis now so I can mount my spare motor in 144 form. I want to be able to chose either the 167 or the 144 depending on where I am riding. The Hi comp 144 ate up the worst of the rocky stuff at Pipestone Pass with 13X49 gearing.

i think i would like to own that bike when you are ready for your next one!dan

what s the verdict on less flywheel weight - does it still lug ?
I am riding the TE 250 now but would swap in a heartbeat

I have no desire to add any FWW on mine. I like it to spin up fast and the bike is still hard to stall.

Wally - What did you do to your 144 head to get 210 psi? I have .3mm shaved off by RB Designs but he left the bowl alone. I need to have the bowl redone to get any more compression. I think it is just at 185 now.

Mark,

I use a different piston. There are two designs to chose from and depending on what you want your final compression figure to be you go that direction. One is a domed piston and really works a trick for the higher compression, the other is a flat top piston but with a raised dome. That way you don't have to do any creative machining of the bowl. When you wear out your stock piston lets talk and I can tell you what to get. You will need to re-cut the squish band of your head to match. Going this direction you don't have to mill anything off the deck of the head. Very easy and you get a really nice squish surface. 240 psi is possible without machining of the deck by just setting the squish to .032" but that is asking for trouble that high considering the rev range. I was at 215+ psi with .040" of squish. I have looped the 144 in the field twice screwing around not paying attention and that instantaneous throttle response in the mid range below the power valves opening got me.

Walt,
what would you do with my bone stock 09? Moto and woods.
Pretty happy with how it runs as is, but I wouldn't refuse some more oomph.

Just finished going through 3 heat cycles breaking in the 144.With the top end still being tight I didn't notice a huge increase in low end,got a wake up call when I hit the midrange,then was almost caught off guard when I flirted with the top end as it exploded with front wheel launches....quite a difference from 125 standard.
Yet to get into the woods as we have had nothing but rain,will have to stay in the open grass to get more break in time before race day next weekend.
Hoping to get a little smoother transition from low to mid range when it loosens up a bit,at any rate I see a overall positive difference going with the 144.More to come as I'm looking forward to get some real saddle time in shortly.

@Walt, I'm getting excited.

As you should be. David you're gonna be a very happy rider. My 144 is a rocket thanks to Walt.