I have a stock 86 250R engine. I'm switching from an FMF fatty (junk!) to an ESR TRX6 for strong lowend and midrange. Topend isn't a big concern. Now, I'm at the intake and carb. A guy at ESR suggests a Mikuni TMX36 w/ a stock CR250 reed cage. He says that combo will improve all around power and Throttle response (<VERY important!) better than just about any other comparable mod like a RAD valve, RAM valve or PWK35 or 36 etc. etc.

My friend, today over the phone, said he doesn't feel that ANY bigger carb w/ that CR250 reed valve is going to help unless porting and head mods for for lowend and midrange are done along with it. he said port if I'm gonna do the Mikuni/CR250 Reed combo otherwise just put a RAD valve and stop there because the RAD is the best reed cage for low RPM torque and power>> I've heard that before too so I'll assume that of the RAD valve. Anyone disagree?

Now, I'm no mechanic. Everything I know is from reading and theory...not practice. So, with that in mind, I've ALWAYS read that a bigger carb is, without exception, a mod that favors upper mid and top end and actually WEAKENS throttle response because the velocity is lower in a bigger carb. That is, unless the head and ports are modified to handle the bigger carb. I know it gets tricky when you start combining different mods so I'm not sure what to make of all this.

I've also considered weights for the flywheel to make the power more tractable. Good idea or not? I also read on another "2 stroke expert" site that reed spacers (between head and reed cage) are bad for what I'm trying to accomplish for some a air-related reason and thast they are a gimmick

So, any mechanically knowledgeable people are more than welcome to shed some light on this project. I'd really appreciate it! Based on EVERTHING that I've taken the time to explain, what do you all think would be the best thing? Remember: Lowend, midrange and zappy throttle and strong acceleration. The hell with a 50 HP at 11,000 RPM screaming revver....not fun for the woods!

 

The TMX carb is a very good choice. They have great throttle response and are easy to tune. I would prefer the 38mm over the 36mm. Once the carb is tuned right the 38 will respond awesome as well and add to the top end too. If money is an issue stock carbs work just fine. Rad valves work well for low-mid power as well. I've never used the cr reed cage buy my guess it goes with their engine designs and they are probably just trying to sell you something. Raising compression will also help on the low end too. I used to run a 38 mm tmx, rad valve, high compression with some mid/top porting. It had good low end (better than stock) and was very fast on top too.

 

machwon,

Do you think adding the TMX36 or 38 w/out doing any porting or compression change will be worth the money (my friend says no)?

 

The best money spent for bottom end would be raising the compression then the rad valve while staying with a stock carb. Any carb larger than stock will help the mid/high and upper rpm ranges in a ported motor. The tmx will be one of the best responsive carbs you will find but it doesn't mean it will make more power than the other ones.

You could also help the stock carbs response out by change the slide to one with a larger cutaway. I think stock is a 40 and changing to a 60 would help the throttle response. Also by further tapering out the bell side of the carb would help the intake velocity.

 

I'd save your money and buy a power valve cylinder, alot smoother power band.

 

for low end power, i don't think you will find a better combo than the fatty pipe and rad valves. a friend of minehas this combo with a stock 246 cc cylinder and a 36pj carb and it has great bottom end and revs well. i also have a 310 pro-x cylinder. i had a fatty pioe and rad vavles on it with a 39 pwk cark. it was a pure trque monster. only problem was it ran out of power quick. i switched to a sparks mx pipe and lost a lot of low end power and gained a lot of mid range and upper rpm power. the sparks pipe is faster and makes more power but the fatty pipe had a lot more torque. i just rebuilt my motor and added the sparks reed cage. just broke it in and haven't had a chance to see if it makes a difference or not. my pro-x cylinder is slightly ported (really just a good smoothing out of everything) so a ported cylinder for low end power might help more. my other friend has a full curtis sparks 350 and it has monster torque and a rediculous amount of mid range and top end power. has anyone tried the new sst fmf pipe?