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Discussion Starter #1 (Edited)
Tuning carburetor on 1992 CA tw200 (updated 7/11/19)

Hey guys, im almost happy with where this bike is at, but i do have a stumble at WOT (wide open throttle) heres the rundown-

1992 CA compliant tw200 (stock)
got in non riding condition, checked electrical seems ok for the most part, battery holds a 11.6 voltage overnight after being on a trickle charger and at idle is around 12.5v, 13.5v with revs

took off carb, cleaned all jets and slides, pulled air idle mixture plug and checked- factory setting was 1.5 turns out, adjusted to 2.5 but way too rich, now currently around 1.80-2 turns out. Removed top cap and slide assembly/ needle from carb, shimmed the needle with (2) M3 washers (approx .03mm thick total). Now starts without choke at that setting and idles without dying (it was sputtering and dying at idle before and required choke on a warm day with bike in the shade), it will bog if i whip the throttle open immediately, but if i roll the throttle on it revs perfect and multiple throttle whips after its off idle yield immediate response. When riding, throttle response is fantastic, however, if i twist throttle to WOT is bogs, sputters, looses power pretty much immediately. If i roll the throttle up through the revs smooth it seems OK, but throwing it into WOT seems to create a lean condition.

What brand is the stock carburetor on a 1992 CA model? What is the stock main jet size on this bike, as well? I tried looking when it was apart and couldnt read whatever was stamped on it. Will a 130 main jet for the newer model tw200 be too much for this bike? Thanks!
 

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Welcome. I have a 1993 and the only issues with the carb that I have had was a thumping at wide open throttle. That was caused by a lean condition/ not enough gas for that speed. My carburetor boot was bad so I was getting too much air which only really affected it at WOT full speed. I sealed up the intake and never had another issue. The next size jet bigger may not hurt but since these bikes are not ran WOT much it would probably just hurt your mileage without much increase. Your lower rpm issues I think you probably didn't need the shim. Using the choke isn't bad. If mine has been sitting even when it is hot I usually have to put the choke about 2/3 out, it cranks and push the choke off and take off. I tried another carb for experimental purposes and mainly it was too rich. I reinstalled my stock carb and it runs great. Play around with the air fuel screw as it does slightly affect some of the other speed ranges also. At least these carbs are easy to get to. Good luck.
 

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Discussion Starter #3
thank you for the feedback- after i initially cleaned the carb and before i added shims or adjusted the idle mixture screw, pulling the plug yielded white residue on the very edge of the plug filament, and white residue from the end of the arc all the way almost to the base of it. Now, since riding it (for a very short period of time) with the shims and air fuel adjustment, those areas are a mocha brown color. im also getting a much more responsive throttle while riding, primarily mid-range where one tends to cruise most often. I also have an issue with the air box boot being old, and im assuming, hardened and shrunk. it does not fit snug over the entire mouth of the intake side of the carb, but barely touches it all the way around the edge, so perhaps that it affecting the top end/ WOT. are these tubes for the older tw200 available anywhere, and is there a temporary fix or that, such as wrapping with electrical tape, or is that just going to make a mess?

also just to note- i am at about sea level.
 

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That air box boot and all sounds like your issue. That is pretty much what mine was. I rigged mine somehow with alternate rubber tubing. I need to order the stock one. Partzilla, Bike Bandit, [email protected] cycles etc. Just look around.
 

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Discussion Starter #5
well, i wrapped that area with electrical tape and took it for a spin and noticed no difference. i removed electrical tape and at idle i sprayed some carb cleaner on that area, and there was no change in idle speed (that i could tell).
 

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I am not a fan of shimming a needle, instead preferring a richer (skinnier) needle if needed.
That is not to state that it cannot be made to work, but the profile will be off.

Surprised that it does not like mixture of 2.5 turns from gentle seat, but behaved non-WOT in mid-range.
Is enrichener not seating?

How did it behave with one of the two shims removed?

Are you sure that WOT is lean...balking...hesitating
versus blubbering from being too rich?

Before pulling the spark plug, how was it run?
...and did you cut power and coast to a stop?

See the first link in post one of this thread:
https://www.tw200forum.com/forum/technical-help/63620-carb-diagnostics.html
 

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Discussion Starter #8
I believe what led me to think it was a lean condition was before i shimmed the needle, and before i pulled the brass plug and adjusted the idle mixture screw, it was a little difficult to start the bike, the bike required nursing at idle in order to not die when cold and warm, and when i pulled the plug after riding around the diode had white residue on the tip, and the arc had the white residue all the way down to the threaded shoulder.
 

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This was my 2 cents 2 1/2 years ago

Off the showroom, it required choke (enrichener actually, on the TeiKei MV28 carb) for warm starts and it had idling issues ...deceleration diaphragm seemed to affect fast idle...when it dropped to "normal" it would die on the 18 mile ride home. Drilled the plug and adjusted from factory 1 1/4 turns out to 2 3/4 allows restarts, even after 2 hours sitting in ~65 F ambient...and ended idle issues. Pilot, needle and main jets seem OK up to 5,000 feet elevation (home is 2,200)

Stock jetting was fine up to 8,500 feet
 

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Discussion Starter #11
By rip and strip, you mean remove and clean? I had removed the air filter prior to any work and checked, and it appeared that the P.O. had put in a newer, clean filter, it was slightly lubricated with what I'm assuming is filter oil and didnt appear to have any dirt in it, but I can certainly clean it with some soap and hot water and see if that makes any difference. I plan on replacing the battery and I've got a replacement coil on its way to me, so I guess I'll see how these changes affect it.
 

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Fairy 'nuff - you hadn't mentioned that previously - as the air filter is a prime component in carb issues, I thought I'd bring the matter up

The "battery thing" was more of a "by the way" sort of a thing - yeah - it's on it's way out .... ;)
 

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Check battery posts and recommendations on the site. I got a small AGM battery for about $40.00 that is half the size and weight and outlasted my other batteries.
 

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Discussion Starter #15
swapped out the old coil for new this morning. Still has that flat spot at WOT, it sounds like a kind of rapid stuttering and jerks just slightly as it happens.

on a side note, which brand/ model agm batter are you using? Thanks!
 

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Discussion Starter #16
Is there a possibility the float height is off, causing it to starve at WOT, but not through out the rest of the range? i tried attaching the old fuel drain hose to the float bowl and opening the screw to check what level the fuel would rise to, but it wasnt flowing out enough to fill the drain hose, however, if i unscrew it with no hose attached the fuel flows out of the float bowl drain no problem.
 

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swapped out the old coil for new this morning. Still has that flat spot at WOT, it sounds like a kind of rapid stuttering and jerks just slightly as it happens.

on a side note, which brand/ model agm batter are you using? Thanks!
I got the Scorpian YTZ7S, $44.95 from Batterystuff.com at this time. I have been happy with it so far, a few months. It seems way better than all of the lead acid batteries I have had. I thought something was wrong with the starting system and was getting ready to trace all starting ground leads. It would turn over slow with a new lead acid battery. It works great with the AGM battery. That was from my post of 2/2017. It was smaller so I had to make spacers around it but it works great.

That WOT issue sounds like you may be lacking fuel. You may want to put in a bigger main jet. Our bikes were designed pre-ethanol so ethanol runs a little leaner. I would only go up one size.
 

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Discussion Starter #18
I would love to order a new main jet and try it out, but I dont know what size would be a step up from stock. I couldnt read the number on the main jet when I had the bowl off of it initially and I have read that the carbs in the 92 CA version had totally different jetting than your later models.
 

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I have written this before -- jets wear out. Start with a brand new #114 high speed jet and a brand new #40 pilot jets -- if you buy them from Yamaha. The hole in the center erodes and gets bigger and the mixture gets richer. I have had this problem on my two '87 TW's and a friend who using Euclidian logic determined his mid 90's TW mixture needed to be richer but ordered a new #114 jet at my insistence (along with a variety of richer jets), had to painfully admit I was correct (and thereby he was wrong) in that it was running to rich to begin with when he installed the new #114 and it ran perfectly. Ha ha! Fun to be right sometimes.

Aliexpress sells about a dozen jets of you pick assorted sizes for about the cost of one jet from Yamaha. Ditto for pilot jets.

And lastly, it could be your CDI going bad. Hopefully not.

Where in Calif are you?
 
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