2-Stroke card question (250r)

[roostu]

I did a search but i was unable to find a post with simular mods. I am looking to get a new carb, I do some minor trail riding but I primarly ride the dunes. All sugestions would be apreciated.

~Roost-U

[airheadedduner]

The 38mm Airstryker is probly the most commonly used carb out there. It may not be the best but it gets the job done and is priced reasonably well.

[holeshot19]

gives you somemore top end with out suffering trailrideing:D

[speedjunkie]

Whatever Man, you know you ride 99.999999999% on the trail and 0.000000001 in the dunes. Just kidding. :devil

[MX26]

I have a 38mm PWK and my R has more low end than any other I've ever ridden. If I had it to do over again, I'd get an Air Stryker though.

[deathman53]

I have a 38 a/s on my r and it doesn't have much low end, but the mid and top screams, the stock carb had alot better low end, and good mix might be a 36mm, I had that on my tecate and it gave it low end, but didn't kill top.

[airheadedduner]

The AS is designed to give big flow without looseing low-end. It has fins in the bore witch trick the motor into thinking it is a smaller carb. Kinda like how a torque stuffer works.

[nuttynewt]

torque stuffer

That sounds like the name of a cheap porn movie. You gotta fill me in on what this is... lol

[roostu]

Thanks for the replys. So let me see if i got it straight, a bigger bore card will give me more top end but i will lose out on low end? But if i get a better carb with the same size bore (close to stock size) it will give me more all around power because it is just a better design?


~Roost-U

[airheadedduner]

A torque stuffer is something they put in the headpipe of a thumper and some 2 stroke pipes. What it does is it tricks the motor into thinking that it is a smaller pipe then it is giving you a boost in low end. Same as what the fins do in the AS carb.

Yes roostu, smaller carb=low end, big carb=top end but...............
Let me try to explain again, I am not really sure how to put it. Good low-mid acceleration is very dependend on intake and exhuast velocity. A smaller carb carb has better intake velocity because the vaccum produced by the motor can better and more efficently pull the fuel through the carb and to the cylinder. Bigger carbs have enough volume that it can overcome the engine vaccum to a point and does not flow as well till the revs rise enough. The AS has fins in the carb partialy blocking the bore.
(Fins look kinda like this \ / but flatter angle inside the bore on the bottom)
So at low RPM's it is mostly pulling through the area above the fins and acting like a smaller diameter carb. But as the revs rise and more flow is needed it will start to pull fuel/air using the entire carb bore and making it act like a bigger carb. So for low rpms the AS actully flows like a 34-36mm carb but at mid-high flows like the 38mm it is. Make better sense??:ermm: I can't really explain it that well, I am sure I missed or goofed up some points but I hope you get the idea:p

[roostu]

airheadedduner that makes perfect sense, thanks alot!!! I just talked to Jason at LRD and he suggested that for the mods i have a 38mm AS would be best, and that I need to have my RAD valve flow matched. So you guys were right on!! Thanks!

~Roost-U

[nuttynewt]

Originally posted by roostu
airheadedduner that makes perfect sense, thanks alot!!! I just talked to Jason at LRD and he suggested that for the mods i have a 38mm AS would be best, and that I need to have my RAD valve flow matched. So you guys were right on!! Thanks!

~Roost-U

What do you mean by having to have your RAD valve flow matched? Do you have to put a different boot on it? Do they actually machine part of the RAD valve? I'm curious...

[roostu]

nuttynewt when you order a RAD valve you order it for a specific type of bike. I was told that the RAD valve is flow matched from the factory to flow the amount of air that the factory carb flows. Hence all there products are specific to the bike. If i get a bigger carb i can still use the same RAD valve without having it flow matched but then it will be the bottle neck of the intake system.

~Roost-U

[AndrewRRR]

Yeah, i have a Rad Valve that LRD ported to match my 330 cylinder (also from LRD).

[airheadedduner]

Jason@lrd is really helpful.

From what I have read the area of the reed block( I am guessing where the boot goes into the block) should not be more then 110-115% of the carb bore. What they are probly doing is just milling away to bring the block up to thoose numbers.

If you guys really wanna get the dirt on 2 strokes I highly recomend you BUY, not check out, rent, borrow, but BUY the book Two Stroke: Performance Tunning By A. Graham Bell. I got it for under $30 shipped to my house from amazon.com. It is a must have.

[Evan]

Actually your partially right.

The AS is has fins to control the air going in the carb. When the throttle on a carb is wicked open, it sucks alot of air into the carb at once, causing a swirl. This may sound stupid but it does have an effect on the carb. When the air is swirling, it starts bumping into things and slows down the velocity of the air. What these fins do is stop the swirl and cause the air to be sucked straight in therefore increasing velocity. Hope I explained it good enough. If you want more reason to buy the 38mmAS, look at nearly every MX dirtbike (CR KTM YZ etc) they use the 38mm AS. As do the pros that still race the 2 stroke motors in quads. WHY? because it works the best, simple as that, if they didnt work, they wouldnt use em.

One thing I plan on doing to my 38mm AS is put one of those mass airflow sensor things in it, what it does is smooths out the flow of air even more giving better throttle response. More on that later tho.

[airheadedduner]

I knew I was missing something:rolleyes:

Thanks, x-rider:D

[nuttynewt]

I am guessing here, but is the reasoning behind running a CR250 RAD valve in a 250R the same as having your RAD valve flow-matched, since you would assume the CR250 pulls more air/fuel since it is a higher HP engine?

[AndrewRRR]

Originally posted by nuttynewt
I am guessing here, but is the reasoning behind running a CR250 RAD valve in a 250R the same as having your RAD valve flow-matched, since you would assume the CR250 pulls more air/fuel since it is a higher HP engine?

Mine was a CR250 rad valve (02B), it still got ported. I have a picture somewhere I took of them sitting side by side (the CR and the TRX rad valve), I'll try to find it. If I remember right they were the same size. The CR has a shorter neck on it.