Can't answer, but the engine is a double overhead cam 4 valve. It seems you can't realize it with the original carb. I think either TM will work great. Look back at the photo of the business end of the two. The original carb has a butterfly in the middle of the air stream. Either TM has a "sliding barn door" with nothing interrupting the air flow except the needle. My Idea from the start is go big or go home. And to get the most performance for the dollar. I did the 351 first because I knew it would be worth it.

Now I can't stop New damper valves for the forks on their way.

It got up to 30*f today, roads are sort of bare. Its a long winter.

David

 

My 351 with the 36 mm carb does use more fuel then the smaller carb. It gets about 45-50 MPG around town and a little better on the highway when ridden conservatly. I installed a 15 tooth front sprocket which helps. The off road mannors are great. 1st gear is only used when trials riding up a steep rocky hill. In normal trail riding 1st is only used to take off from stop. I do not use the air box snorkle and installed a unifilter. I'm 68 and plan to ride it in some cross country races this year, after I install some tires.

 

For what? I'd guess the 36 is better on the street or racing because you're reving it up a lot more. And in thoery, the TM33 should be better for putting along in the woods.

Now keep in mind I used to run 1 30mm carb on a 1967 Triumph 650 twin and it never really ran out of carb. I went to 2 30mm carbs and it made a real little difference. My friend put 2 36mm Amal square bodies side by side on his 1969 Triumph 500 and he had a little problem with over carboration but at the top end it really screamed....until he blew it up and rebuilt it twice. I think it's in a basket in his garage now. What do 250 motocross bikes run for carbs?

I don't think the difference between 33 to 34 to 36 is enough to make any real difference. The nice thing about the TM36 is it's $275 and it fits while using both cables. The TM33 is $285 and you have to turn up the spigot adapters in the lathe and hack and weld the throttle cable bracket to get it to work. Then you have to grind on your frame and all that fun crap to get it to fit. If I had to do it again, I'd be doing the TM36 hands down. We just need to come up with some general jetting recipes to get new guys close.

 

Nice job! Great pictures too. Oh and just for the record...I HATE SNOW!!!!!!!!!!!!!!!

 

Feral Donkey touches on a real issue. While we may look at the DOHC, 4-valve KLX motor as some high zoot, whizbang technology, there's really nothing special about in light of todays technology. The concept of upping the carb size because of increased displacement is somewhat logical, but FD's observation about the smaller carb size being more suitable to off road power has some merit. I recall most 250cc, single cylinder, 4-valve, 4-stroke, off road engines having cable-pull slide carbs in the 28-32mm range. Our 250's come with a 34mm carb...but...it's a CV carb. This does make a difference. You can generally run a larger CV carb because of its vacuum design. If you run a 34mm cable-pull slide carb, I'd contend that you already have increased carb potential. With an engine like the KLX, going to a 36mm carb doesn't seem as logical. A modern, pure race, Honda CRF250 used a 37mm carb, but this engine revs to the moon, and mileage isn't as much of a concern.

Now, I'm not dissin' those who are trying the bigger carb, and I'm not saying that it won't be capable of getting it to run on the KLX. I love projects like this, and I'm one who putzed with the EI Magnum and various other off beat carb applications on my off road 4-stroke singles since '79...XR250R's and even the old 2-valve KLX250. I would bet, however, that off road performance will not improve except at the extreme end of the top speed spectrum. And in fact I'll bet some traction, power delivery, and fuel economy will suffer. The KLX has an amazingly tractable power delivery. I don't care how wimpy we think it is, it is able to stick that measly power to the ground on some goshawful loose climbs like you can't believe. Overcarbureting the engine will cause one to lose this ability.

Now, I also understand that those who don't off road their KLX's, and especially those with the SF model, won't care as much about low end torque and traction. But I tend to think that the 36mm carb is somewhat of an overkill for a KLX intended primarily for off road use. The BB 34 carb or maybe even another 34mm cable-pull carb might be the best match to a big bore KLX. I salute those who are pursuing the biggest possible carb. As Tim the Toolman used to say on his show..."More Power!" It's a fun and often rewarding pursuit and also one that can cause premature gray hair, but always a great learning exercise regardless of the results. I only throw this out there so that so that some who aren't well versed in carb putzing won't think that bigger is always the panacea that it appears to be. For most folks who want more power, it might be better to go after one of the more modern racing 4-strokes...but...they aren't that great for any real pavement use, are they.

 

I agree with you TNC, Bigger is not always better especially in carbs. A smaller bore may give more control in the lower end especially in the dirt. Think of it as a more liner power delivery.

The biggest reason for my decision of the 36 in stead of the 34 was cost.

Since I only ride on black top I have "unlimited" traction, so a bigger carb or getting more HP to the rear wheel quicker is a good thing. On my simple test drive I already did, I had to be careful in first gear going around corners because its a little "twitchy" with the throttle as in I could end up going straight when the front wheel leaves the ground.

This is another reason why I went with a wider variety of jets. I want the low end to be a little lean or just right at the most. I can run it fatter in the more open throttle positions for MORE power. This should make it less twitchy on the low end with out giving up any HP in the end.


I a shooting for fuel mileage since this bike was originally purchased as a commuter to save on my back riding a 90 hp R1100RT that weighs a little over 620 lbs or double my KLX. Since then I found out how much fun it is and well now I am addicted to the little bike. Sidewalks, parking lots, alleys, RR tracks, medians and "Old State Road" (back roads) are all fair game now. Throttle wheelies in first since the 351 kit and now second since the new carb.

 

I'm a little confused now...help me out please. I thought others here described that running rich (fat) will make it bog and not necessarily have peak power, where just right or even a tad lean generally provides the most power. So, I would expect if you want less low-end twitch, it should be a little rich there and move towards just right at WOT.

 

Well Dave, you got another 101ccs of displacement so I wouldn't think adding 2 or 3 MM to the diameter of the diameter is going to hurt any.

And talk about a gas pig. That CVK with the stage 2 Dynojet got me about 45mpg. Then I switched to the TM33 and with a 142 main and a 42.5 pilot (WAAAY too fat) I got about 50-55mpg. The smallest main jet I had was 137.5 and I ran on that last fall with no problem. Now I'm down to 132.5, Q-0, and a 40 pilot I think. I'll try it there. I also went to an 80mm cylinder and piston.

 

For the engine to bog from being too rich, its WAY too rich.

If I am driving along with the throttle twisted open pretty good and then I back the throttle off some slowly, and the bike feels like its accelerating just a little, then I know my mixture is really close or right on. This is because the air changes velocity almost instantly and the fuel takes a little longer to change because its heavier.

A little too lean will make the throttle feel "flat". OR if you have to play with the throttle to make the bike want to go faster then its a little too lean. This shows up mostly in the mid range.

I'm from the old school. What seems like its too lean to me is just right in the world of emissions and fuel economy.

For example. Setting the pilot screw here we turn it in till the engine slows, then out till it slows then split the difference. This is correct and normal. Its also what I was taught thirty or forty years ago.

On the cars from the 70s and our stock carb, you can turn that screw out a long ways and the engine will not slow down because the pilot JET is matched to the bike pretty good. This is also why the mixture screw is sealed, so we can't mess with it due to emissions and fuel economy. They know a little more fuel will make it run better, but the emissions go off the chart and the catalytic converter will glow RED HOT from burning the excess fuel.

Look at the fuel they pour through a drag car for 8 seconds. ALL they want is HP.

If the engine is under load it will burn more fuel than if not. Car carburators have a "power valve" which adds more fuel when engine (manifold) vacuum is low (open throttle and low RPM) As RPM picks up, so does vacuum and the need for more fuel goes away. The power valve closes and we are not traveling with low emissions and better fuel economy.

Our CV carbs act similar. Open the throttle all the way suddenly and the slide does not pop open all the way until the engine has caught up with the carb. AS rpm of the engine increases, the slide will open further allowing more air and fuel. This is why the pumper carb in the first place. OPEN the throttle and the engine NEEDS a shot of gas to take off like you expect it to. The air moves instantly into the manifold, the fuel takes a little longer to flow through the jets SO we give it a kick in the as s with a precise amount of fuel instantly from the accelerator pump right down the throat.

There is only one correct mixture we can be on either side of correct and the engine will still run fine But......

Its all a compromise.

David

I better get back to work

 

AMEN to that! As fun as fitting and getting the jetting right on my FCR35 has been, it has caused A LOT of frustration! Screw drivers may have been thrown in anger, and there is a good chance my cat will not take a gamble of the few lives it has remaining by being anywhere near me when I am working on the bike

This is an interesting thread though I must say. I am learning a lot.