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Tuning carburetor on 1992 CA tw200

4K views 35 replies 6 participants last post by  efnick 
#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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#2 ·
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.
 
#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.
 
#4 ·
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, J@P cycles etc. Just look around.
 
#7 · (Edited)
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
 
#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.
 
#9 ·
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
 
#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.
 
#17 · (Edited)
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.
 
#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.
 
#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.
 
#19 ·
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?
 
#22 · (Edited)
One of my TW's has it and the other one doesn't and I can't tell the difference. I say if you have it use it. If not don't worry about it.

I magnified the pic of your jet and it looks corroded, much like the one I replaced.

Here is a picture of the #114 jet I replaced along with the jet I replaced it with. It solved what was wrong with my TW at the time.

Metal
 
#23 · (Edited)
elime, before i took the bike apart today i had it tuned to where it was idling reliably and had good mid range power, but stumbling top end. i took it apart and very thoroughly cleaned out the jets, and the fuel passage from where the petcock dumps into, and upon reassembling and starting the bike, it is now extremely rich at idle, to where it wont stay on without nursing the throttle, but its got immaculate top end! i think you were right, i suspect i blew out some of the corrosion in the jets today and created this new issue. i suspect its time for a carb gasket and jet kit.
 
#24 ·
Ok, update-

rebuilt the carburetor using a "moose racing" carb repair kit

replaced the main nozzle, replaced the main jet, left the pilot jet, replaced the float needle/ valve set (there was a ton of crud plugging the screen when i pulled it and a lot of brass corrosion), replaced drain plug screw, replaced air idle mixture screw, reinstalled with the original pilot jet and needle with one shim, bike started good but wasnt idling well and the air fuel fuel mixture adjustment wasnt really affecting idle at all.

Pulled carb, removed new main jet and compared to original, both marked 114 but the new jet had a smaller diameter opening than the old so i reinstalled the old jet on the new main nozzle, not too much difference in the way it ran, so pulled carb, pulled old pilot jet and compared to new pilot jet (both marked 40) and the new pilot jet has a slightly larger opening, cleaned the pilot circuit? (opening that goes from main inlet in carb to where the pilot jet is at) and reinstalled, again, issues with idle.

pulled carb, removed old needle and shim, intall new brass looking needle with no shim, now better idle with full choke, starts warming up idle goes up, put choke at halfway, idling good but ocasionally pops and then has weird idle and needs more choke, then once warm (idle raises as it warms up on choke by the way) i put choke fully off and it just doesnt want to idle. bike is slightly rich at idle and so the idle mixture postition that it likes best is at around 1 3/4 turns out from a gentle seat. with half choke it has good throttle response, though i havnt ridden it yet. ALSO, there is a leak in the intake boot (intake side of carb), confirmed by spraying with cleaning fluid and getting a raise in idle. dont know if that air leak would cause this failure to idle, though. tried increasing idle speed with the idle screw and it didnt seem to help, maybe i need to really crank that screw down or something? i dont know...
 
#25 ·
Pics in order- new rebuild kit
Float valve and filter/ screen
Float valve passage with crud in it
Old main jet next to new jet
Old needle next to new needle
 

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#26 ·
Air leak is on the intake valve side of the carb? Or on the air filter side of the carb? If its on the intake valve side of the carb. fix it before you do anything else. If its on the air filter side of the carb I don't think it would make much difference other than letting dirt and dust in.
 
#28 ·
Remember the old trick of put your hand across the carb to block air and it makes it run richer. I think with an air leak on the air filter side it will make it run a little leaner since it is bypassing the filter. On my 1993 this did make a difference. Mine at wot would chug or thump because it was lacking fuel. When I fixed the air leak on the leaking air boot on the filter side I never had another issue with it.
 
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