U-4 vs U-2

[2strok4fun]

besides the spec sheet offered by VP, does anyone know what the O2 level of the Ultimate-4 and Ultimate-2 fuels are?

I dont know if I did the right thing, but I mixed in 30% U-4 into C-12 and liked the response on my 250 2-stroke. I think my jetting for straight C-12 is still too rich on mid to WOT ( I didnt change jetting for the extra O2 the U-4 put in)

 

[steve125]

The U4 and U2 have 6% 02. My favorite mix in my YZ144 is 50/50 U4 and U2, that gives me close to a 95 MON. On my 4 banger it's straight U4 and it works great! On a std. 2 stroke that runs well on pump, the U4 straight would be a great choice.

 

[elf]

Steve why did you mix u2 and u4 why not straight u2? is your mix better than mr2 with u4 that you have tried previously?

 

[steve125]

Elf I don't run the U2 straight because I feel it's MON is a bit high for my motor. 95MON seems to be the magic number that works for me on the modified 2 stroke. I prefer the crisper "hit" of the lower octane mix. I always strive to not go any higher than the motor requires. Oh! and yes this mix is the best I've tested to date, I don't use the MR-2 anymore.

 

[elf]

Blast! I just picked up some mr2 and u4 last week. I have been using c12 and since reading through older posts thought I was on track. I have come to realize my 144 doesent need 110 octane. Oh well thanks for the info it is much apreciated!

 

[2strok4fun]

Well, my bike was jetted well for 3200 ft and 40 deg on C-12, being lazy I didnt dial in for 4200 and 60+ deg. I think the additional U-4 hit the spot, or close enough. My 2-stroke is set up for 100 so the C-12/U-4 is OK. For some reason I thought there was a difference on the O2 level tho. Ill stick with the 33/66 of U-4/C-12 as the C-12 is still more economical.

Thanx for the info.

 

[steve125]

Blast! I just picked up some mr2 and u4 last week. I have been using c12 and since reading through older posts thought I was on track. I have come to realize my 144 doesent need 110 octane. Oh well thanks for the info it is much apreciated!

Don't worry elf, the MR2/U4 combo is an awesome mix. Next time go U2 /U4.

 

[bclapham]

my YZ144

what happened steve, i thought you had left us for greener pastures over on thumper talk????

 

[steve125]

Have ya missed me BruceO? :joke:

 

[bclapham]

Have ya missed me BruceO? :joke:

Of course, young stevie. :worship:

but dont tell me you traded that CRF in for YZ??? :| :ohmy:

 

[steve125]

Nope on the YZF, I 'm back on the KXF. I couldn't get the CRF to turn the way I like, that bike rides high and pushes. I like a bike that has a bit of oversteer and thats the KXF, it carves compared to the CRF. The YZ 144 is not for sale, that motor is the best Ive ever ridden!

 

[bclapham]

when did you get a yz 2 stroke? i thought you had a kx and a cr139 lasst year?

 

[steve125]

After I sold the KX and CR I found a good deal on the 03 YZ. It's all done up, suspension, motor is a EG144. Pete re-worked the head, 36mm carby, 00pv spring, FMF factory fatty and a special Rad valve set up! I need to dyno it sometime. It will pull the 250f's on the straights.

 

[bclapham]

Steve, that RM144 is running great now- that PWK 38mm wouldnt work without the #4 slide!!! i will stick with that carb since i hope to go 155 in the summer.

back on topic, i found a mix of premium and C12 worked better than straight C12- sounds odd i know- ive really cut back on $$$ spent on gas recently- we had some U2 locally but i steered clear, LOL

 

[steve125]

back on topic, i found a mix of premium and C12 worked better than straight C12- sounds odd i know

Thats not odd, I've been telling Rich something to that effect for years now. :debil: Ever since the U4/U2 has been offered, there's no need for me to use pump fuel. C12 straight has always made my motors feel too smooth and a bit lazy.

 

[elf]

Steve I have some questions about the 36mm carb. I noticed its alittle shorter from side to side. Did you have any problems hooking up to the airbox? Also would I just use all the jets out of my 39 including the slide? Does the smaller carb run richer or leaner with the same jets? Also where does the 36 change the power compared to the stock carb.Sorry for all the questions, this is somthing I might try in the future once I get my jetting sorted out with the new gas mix.

 

[bclapham]

Thats not odd, I've been telling Rich something to that effect for years now. :debil:

yes, but dont forget my testing has got more holes than a lump of Swiss cheese! :eek:

i will butt :moon: in on the carby Q though.

Elf: what carb are you thinking of getting? the PWK on your KTM is a good one IMO, but very big at 39.5mm- maybe not as good as that new OEM TMX but its pros and cons and the PWK is easier to work with IMO since you can figure the needles out.

also the PWK 39.5, 38 and 36 are the same fit and should be a direct replacement on the KTM. if you go smaller, the 38 can be bought real cheap ~$150 from service honda (CR250 2000 carb), but the 36mm will have to be had from carbparts etc for more bling. when you go smaller, the velocity increases so it will pull more fuel and you will need smaller jets.

theory dictates that you get more bottom from the smaller carb and loose top, but listening to Steve and Marcus thats either debatable or negligable with tuning. they might know the best one to try.

 

[elf]

theory dictates that you get more bottom from the smaller carb and loose top, but listening to Steve and Marcus thats either debatable or negligable with tuning. they might know the best one to try.

Ya I dont know about that theory, most 250s have 38s and they make lots of power. I dont know what carb to try just wanted some input from steve on the 36. Whats the deal on those stroker cranks Bruce? Is Eric going to make them for all the 125s?

 

[bclapham]

better ask Eric, i dont think there are many things he cant do. i think you have to send the whole engine though since all sorts of things need machining

 

[elf]

A 155 would be fun. Are you going to do it on your bike?