TW200 Forum banner

1 - 20 of 23 Posts

·
Registered
Joined
·
16 Posts
Discussion Starter #1
Has anyone ever fitted a different carb onto their TW? Seems there could be quite a bit of improvement in this area.
 

·
Registered
Joined
·
78 Posts
A fuel injector and ECU for that and spark control would be better thinks I.
 

·
Registered
Joined
·
32 Posts
I have been wondering the same thing. My TW (brain dead tonight...think its a 87) carb has gave me fits off and on since I bought it. Clean it out, works fine for one ride. Next time I go out to ride carb is junked up. Blamed rusty fuel tank so bought a Clarke , still same issue. Wondered if a new style TW carb might help solve the problem, or maybe see if I could figure out how to adapt a small pumper carb, maybe something like my DR has......
 

·
Registered
Joined
·
567 Posts
the xt225 forum solved the problem by using a TM33mm mikuni pumper....but the guy who sells them (or used to) highly modifies them, he cuts his own needles on a lathe and the cable mounts are custom cnc'd... factory TM's are way off for out little motors...

http://www.enduco.com/Bike/tm33manual.pdf



Other than that, Sebastian sells some alternative carbs in Europe at twparts dot com,...but I doubt they are dialed in specific
 

·
Registered
Joined
·
7,369 Posts
the xt225 forum solved the problem by using a TM33mm mikuni pumper....but the guy who sells them (or used to) highly modifies them, he cuts his own needles on a lathe and the cable mounts are custom cnc'd... factory TM's are way off for out little motors...

http://www.enduco.com/Bike/tm33manual.pdf



Other than that, Sebastian sells some alternative carbs in Europe at twparts dot com,...but I doubt they are dialed in specific




This will prolly start a pizzin contest, but here goes:



A TW200 displaces 196cc's. (roughly 12 cubic inches.



Let's say it operated at 100% volumetric efficiency (yeah, right). It's MAX air requirement would be 31 [email protected] 9,000 rpm. In the real world a stock TW prolly only needs about 25cfm.



A 33mm flatside flows about 100cfm, or 4 times the flow required for a stock TW, and 3 times the flow required for a theoretical "balls out" TW. The flatside also has some behavioral quirks which only make it suitable in certain situations.



Flatsides are easier to calculate because they have no venturi, but essentially a 33mm carb isn't just slightly bigger than a 28, it's 40 percent bigger.



It's way more complicated than this, and there's a case for a pumper carb, but few of us will ever be in that situation.



Just trying to save folks some heartache and cash. The little TK is capable of handling 99% of most folks' efforts to improve horsepower, which generally consist of aftermarket exhausts, airbox mods and rejetting to compensate.
 

·
Registered
Joined
·
567 Posts
This will prolly start a pizzin contest, but here goes:



A TW200 displaces 196cc's. (roughly 12 cubic inches.



Let's say it operated at 100% volumetric efficiency (yeah, right). It's MAX air requirement would be 31 [email protected] 9,000 rpm. In the real world a stock TW prolly only needs about 25cfm.



A 33mm flatside flows about 100cfm, or 4 times the flow required for a stock TW, and 3 times the flow required for a theoretical "balls out" TW. The flatside also has some behavioral quirks which only make it suitable in certain situations.



It's way more complicated than this, and there's a case for a pumper carb, but few of us will ever be in that situation.



Just trying to save folks some heartache and cash. The little TK is capable of handling 99% of most folks' efforts to improve horsepower, which generally consist of aftermarket exhausts, airbox mods and rejetting to compensate.


Yes the TK is is the best carb for a stock 200....the poster asked about DIFFERENT carbs, the 225 may have more cc's but the head, ports and valves are nearly identical to the 200. The xt225 guy was using the pumper carb for better OFF ROAD throttle response for where the xt tk "CV" carb lacked in certain off road situations....I agree about air flow efficiency problems, a 4valve 250-350 really wakes up with the 33 pumper, and many aftermarket houses use it. As I stated the carb was MODIFIED for use on the 2 valve 225. An off the shelf unit will not work.
 

·
Registered
Joined
·
7,369 Posts
I agree. Like I said, it's way more complicated. But I'm sure whoever's selling the 33 conversion is laughing all the way to the bank at the thought of how many people are buying his kit without putting in the extra work and expecting to bolt on horsepower when all they're really getting for 600 bucks is snappier throttle response. I don't want this happening to our TW brethren. Bigger ain't neccessarily better in our case.



All kinds of people read this stuff, and I'm not suggesting that you, or the original poster didn't "get it". I think it's important to explain that the advantage of the pumper carb is the pump, and that extra 5mm ain't doing a thing for ya.



Therefore bolting on a conventional carb of 36 or even 50mm won't do a thing for ya, so don't chase it. As long as it's jetted properly your motor is only gunna take as much air as it needs. For a carb to be "better" in our case it needs to bring something else to the party, like an accelerator pump, better fuel metering, overlap or altitude compensation, or jet availabity depending on what you're after.





I'm not saying playing with carbs won't have any value. If you want a flatside the smallest commonly-available item with a pump is a 33. What I'm saying is a 28 with a pump would do the same thing on our motors. Different brands and types of carbs all have their advantages and disadvantages, I'm just trying to explain why bigger alone won't neccessarily change anything. Since the 33 came up, and this is a carb discussion I'd like to dispel the myth about size because it's a common misconception. Humor me.



For the benefit of those less dweeby than I, I'm gunna risk an analogy:



Let's say that we as average humans are standing at sea level, and the earth is an infinite source of unrestricted air.



Our lungs have a given capacity (displacement}. No matter how blessed you may be, no matter how big your mouth (carb) and airway (intake tract) are, you can't take in more air per breath than your lungs (cylinder volume on the intake stroke) can handle. As long as your mouth isn't sewn partially shut (UNDERSIZED carb to begin with) most of us have an oversized "carb" from birth. Steve Tyler is prolly capable of 1,000 hp. But I digress.



Now let's train for a marathon and increase our lung capacity (boring, stroking, headwork, cams). If you're the poor guy born with his mouth partally sewn shut, you're gunna need surgery (a bigger carb). But the rest of us will still be fine because we had a sufficiently oversized "carb" to begin with.



Up to a point, that's a TW. All i'm sayin' is that I'm not sure you'll need a bigger mouth with typical mods.
 

·
Registered
Joined
·
32 Posts
Bought a couple of the brass sintered (SP) type from Rocky Mountain. Should have taken care of most of the junk one would have thought, especially after I rinsed out the new Clarke tank, put on a new filter, and did a full tear down, wash and blow (even used a small piece of electric wirein each hole)of the carb. Bikes got 5600 miles on it so I wouldn't think carb was way wore out, but could be wrong. I figured the DR carb wold be too big but wondered if there might be something out there more suitable. I will continue the battle to sort this out for a while longer, maybe watch for a carb off a fairly new bike, maybe even look at a brand new carb. At some point I may have to cut my losses and part it out, but I really hate to. Had too much fun on the couple rides when it ran good...............
 

·
Registered
Joined
·
154 Posts
[I put a TM33 on my BW350. I know it's comparing apples to oranges, but the improvement is incredible. The accelerator pump makes a tremendous difference in response and the starting and idling characteristics are worlds better. The BigWheel has a butterfly carb that is unsupported by it's manufacturer and most are worn out at this point and untuneable.



That being said, there were numerous complications that needed to be resolved.



The carb is too tall and the interferes with the gas tank and cdi. The slide is actuated from the opposite side of the carb which complicates cable routing and causes interference with the kickstart lever. It requires new fuel hose routing due to the pickup's location being different.



It needs to be tuned to the engine, which is an exhausting process.



All in all, I found it to be a worthwhile project, but it was certainly more complicated than I expected. It may not be as complicated on the TW but there will definitely be unexpected difficulties. If you enjoy the process, it can be very rewarding or it can be utterly frustrating. Or possibly, both.



Regards,



Mr. BIgWheel
 

·
Banned
Joined
·
10,664 Posts
Any 33mm carb will be bigger than necessary for a stock or nearly so 200cc TW engine. A 33 on a 350 tuned for torque seems about right.
 

·
Registered
Joined
·
567 Posts
Any 33mm carb will be bigger than necessary for a stock or nearly so 200cc TW engine. A 33 on a 350 tuned for torque seems about right.


Take it up with xt225.com, they all run them and they love it. (Your search for 'tm33' returned 142 results), more responsive and much easier starting than the stock cv carb.

The ports, cams, and valves of the TW are identical to the xt225, and the raptor250 is very similar, even sharing some parts, although the port arrangement is slightly different. And I'd certainly run one on a race raptor. A 30mm pumper would probably be even better though.
 

·
Banned
Joined
·
10,664 Posts
... A 30mm pumper would probably be even better though.


I said a 33mm carb is bigger than necessary for a TW200. I didn't say it was too big.
Lots of room behind a stock carb to modify a TW engine. A 33mm would simply allow more tweeking. I wonder what effect a 33mm would have on fuel efficiency?



General motors used 730cfm Quadrajets on engines as small as 283 cubic inches. Same carb used on 454s. Way more carb than all but the hairiest 283s could use. Worked good, though, because the design had a wider effective flow rate than virtually anything else on the market. No way you could run a Holley anywhere close to that flow rate on a 283 and have any low-speed throttle response.



Is there a 30mm pumper? That would be ideal for a moderately tweeked TW.
 

·
Registered
Joined
·
567 Posts
I said a 33mm carb is bigger than necessary for a TW200. I didn't say it was too big.
Lots of room behind a stock carb to modify a TW engine. A 33mm would simply allow more tweeking. I wonder what effect a 33mm would have on fuel efficiency?



General motors used 730cfm Quadrajets on engines as small as 283 cubic inches. Same carb used on 454s. Way more carb than all but the hairiest 283s could use. Worked good, though, because the design had a wider effective flow rate than virtually anything else on the market. No way you could run a Holley anywhere close to that flow rate on a 283 and have any low-speed throttle response.



Is there a 30mm pumper? That would be ideal for a moderately tweeked TW.


No, not a flatslide pumper that I know of, 33 is the smallest....the xt250 used a round slide pumper, I think it is a 28mm...but the body is too large to fit on an xt225 or TW frame, and the jetting would also need to be tweaked. I wouldn't recommend any carb changes to a stock TW at all personally. not unless your going to at least go with higher compression, shorty valve guides, and porting. You can also go with non pumpers...



http://japan.webike....ucts/45192.html



not sure if anyone here has gone with the YOSHIMURA Carburetor MIKUNI TMR-MJN28

If they have , please give reviews



Webike also sells a Keihin 33mm pumper for the TW200

http://japan.webike....ucts/27432.html



There may be a 28mm keihin version somewhere also
 

·
Registered
Joined
·
33 Posts
sorry for the bump on this thread...but to clarify one thing...



i also have an 87 tdub...just got it and plan on doing some minor mods. but is the TK a worthwhile swap? mine runs good but before i shim and jet, should i look around to see about getting the TK and adjusting it instead of the mikuni or whatever it's called. thanks again for the help guys. oh yeah...is the TK a direct swap? cheers fellas. just want to get this thing dialed and on the trail!!
 

·
Registered
Joined
·
33 Posts
oh yeah...if the TK is a good and worthwhile swap then will ANY TK work or just certain years? i though they were all the same but i'm not very well versed on this issue so i'm looking to you guys for clarification. thanks again.
 

·
Registered
Joined
·
614 Posts
oh yeah...if the TK is a good and worthwhile swap then will ANY TK work or just certain years? i though they were all the same but i'm not very well versed on this issue so i'm looking to you guys for clarification. thanks again.


TK carb is standard on a TW.

Early bikes are slide, later bikes CV. If you mean to change to a later CV, it's not really worth the expense.
 

·
Registered
Joined
·
6 Posts
Hi everyone,

I swapped the stock carb for a Mikuni 28 flatslide and I just can't make it work right.

whatever i do, when i read the plug, it's still too lean (withish / dry)

The needle is all the way up.

Main Jet is 160, I even tried 180.

first 1/4 of the throttle is good the 1/2 to 3/4 is pretty bad.

if I choke it, it's even worse !

I need a little help here




thx !
 

·
Registered
Joined
·
310 Posts
Check for an air leak at the carb boot.. if choke isn't helping your situation on a lean read at WOT, you probably have some sort of problem with air getting in.



I'm waiting for someone smarter than me to figure out the TM28 brass parts we need to get the bikes running better than they do with the TK carbs.



That means someone needs to figure out which slide, needle, needle jet, pilot jet, and main jet to run. I can't remember if TM carbs have change-able air jet screws or not... Regardless, there's about a million needles and needle jet combos to try. I don't have the skill *at the moment* to just start purchasing random five to ten dollar parts until I get it right
 

·
Registered
Joined
·
2,117 Posts
I must be wierd becaus i prefer the old carb over the newer carb. The low-mid range torque isnt worth giving up for a few more mph on the far top end. These bikes need all the instant power they can get, especially on the lower end. That being said the newer carb is less finicky and its smoother. I still miss the old bike when it comes to off-roading
 
1 - 20 of 23 Posts
Top