TW200 Forum banner

1 - 11 of 11 Posts

·
Registered
Joined
·
34 Posts
Discussion Starter #1
I recently got a 1982 XT200 with about 4000 miles on it. It has the same engine as the TW200. I am wondering if the early TW200s used the same Teikei carburetors as the XT200. The last two times I started my XT200 it ran a bit rough, coughed a bit like a mild backfire before it warmed up. I think that means the mixture is lean. I think you have to take the float bowl off to adjust the mixture. Are there any pictures of the early Teikei carburetors showing what screws you need to adjust to make the mixture richer?



I wonder if the transmission is the same on the XT200 as on the TW200? It has a 5 speed transmission.



Lance
 

·
Registered
Joined
·
614 Posts
The XT200 engine is basically the same except the gearbox output shaft is longer on the TW to clear the fat tyre and the corresponding side cover has a bearing in it to support the end of the longer shaft.



I don't know about the carb but I doubt you have to remove the float bowl to adjust the idle mixture.
 

·
Registered
Joined
·
34 Posts
Discussion Starter #3
The XT200 engine is basically the same except the gearbox output shaft is longer on the TW to clear the fat tyre and the corresponding side cover has a bearing in it to support the end of the longer shaft.



I don't know about the carb but I doubt you have to remove the float bowl to adjust the idle mixture.


I looked at some diagrams to see where the fuel mixture screw is generally located. My carb does not have any screws I can access at the bottom of the carb. There is a side screw, but I think it probably adjusts idle only. From what I've seen the fuel mixture screw should be more between the main area of the carb and the cylinder. I pulled the spark plug this morning and it does have a whitish look to it. So it looks like it is running lean.
 

·
Banned
Joined
·
10,664 Posts
Usually the pilot screws are under a cap pressed in to keep you from messing with the proper setting for emissions compliance. The cap is usually just to the cylinder side of the carb of the float bowl. Look for about a 6mm round, shiny silver or brass flat spot. that is the cap. Drill a hole in the cap, thread in a screw, and pull it out with pliars.
 

·
Registered
Joined
·
34 Posts
Discussion Starter #5
Usually the pilot screws are under a cap pressed in to keep you from messing with the proper setting for emissions compliance. The cap is usually just to the cylinder side of the carb of the float bowl. Look for about a 6mm round, shiny silver or brass flat spot. that is the cap. Drill a hole in the cap, thread in a screw, and pull it out with pliars.
So is that part of the float bowl? When looking at the carb from below, there is a projection sticking straight down that looks like you should be able to stick a small screw driver up. But there is no screw to adjust, just solid metal. So you are saying to drill that out. I'm not sure you want me to thread in a screw and then pull the screw out with pliers. Sounds like that would strip the threads that you just made.
 

·
Registered
Joined
·
34 Posts
Discussion Starter #6
Usually the pilot screws are under a cap pressed in to keep you from messing with the proper setting for emissions compliance. The cap is usually just to the cylinder side of the carb of the float bowl. Look for about a 6mm round, shiny silver or brass flat spot. that is the cap. Drill a hole in the cap, thread in a screw, and pull it out with pliars.


Ok, I think I understand what you are saying now. You are saying to drill a hole in the pressed in cap. To pull the cap off you thread in a screw and pull the cap out that way. When I was looking at what I think must be hiding the pilot screw, it does not look like there is a pressed in cap. If it is, then it is not brass, but the same color as the rest of the metal in the carb. So when you remove this cap, there is no leakage from carb? The pilot screw must be sealed.
 

·
Registered
Joined
·
590 Posts
This is what the bottom of my '96 carb looks like with the float bowl off and the carb twisted 90 degrees. The idle mixture screw is the flat headed one on the right, and is accessible with the float bowl on. Often a plug is tapped into that hole the screw is sitting in. Pilot screw is sealed, yes, the plugs are just anti-tamper devices.



 

·
Registered
Joined
·
34 Posts
Discussion Starter #8
This is what the bottom of my '96 carb looks like with the float bowl off and the carb twisted 90 degrees. The idle mixture screw is the flat headed one on the right, and is accessible with the float bowl on. Often a plug is tapped into that hole the screw is sitting in. Pilot screw is sealed, yes, the plugs are just anti-tamper devices.



I did drill a small hole in the plug and got it removed. I gently screwed the pilot screw all the way in (only 1 3/4 turns). Then I turned it out 2 1/2 turns. The difference is amazing. The bike starts now with one kick. Seems like I hardly need the choke now. I'll see what it is like on a cool morning. No more popping noises when I back off the throttle. I'll check the spark plug after a while to see if the nice tan color is there. Thanks so much for the nice illustration.
 

·
Registered
Joined
·
7,369 Posts
Is there one cable, or two coming out of your throttle tube?



I'm thinkin' that back then Yamaha still used direct-pull, single-cable roundslides.



If your carb has one cable that disappears into what looks like a threaded screw cap under where the cable enters the carb it's the old type Mikuni or Keihin.



Totally different critter from any TW carb. Easy to work on, but I dunno about getting parts.
 

·
Registered
Joined
·
34 Posts
Discussion Starter #10
Is there one cable, or two coming out of your throttle tube?



I'm thinkin' that back then Yamaha still used direct-pull, single-cable roundslides.



If your carb has one cable that disappears into what looks like a threaded screw cap under where the cable enters the carb it's the old type Mikuni or Keihin.



Totally different critter from any TW carb. Easy to work on, but I dunno about getting parts.
This is a Teikei carb with a single cable entering the top of the threaded screw cap. I wonder if a TW carb could be mounted on my engine. Anyway I got the plug over the pilot screw removed. Plug came out nicely.
 

·
Banned
Joined
·
10,664 Posts
The improved starting, better throttle response, and lack of popping in the exhaust is a normal result of a better tuned carb. Take a long screwdriver bit and turn the pilot screw 1/6 turn one way or the other and see if further improvement is possible. Turn it a bit at a time in until you notice degraded performance, then count the 1/8 turns out until you go past perfection to degraded perdormance, then set the screw half way between too far in and too far out. That is a good course adjustment. There is a sticky on carb tuning at the top of this forum that lists the characteristics of a mal-adjusted carb, one list for too lean (in) and one list for too out (rich). Make small adjustments according to how the bike rides until there are no more symptoms. That is how I tune my own bikes.



Note that no two bikes, even identical models, necessarily will perform best with the exact same settings. Altitude, humidity, air temperature, engine temperature, fuel, condition of air filter, and a bazillion other variables influence the fuel mixture. As you noticed, a simple adjustment can have a major influence on engine performance. As influencing factors change, an aware rider can notice the affect on performance and make adjustments based on the butt dyno readings. With a few basic mods (allen head screws) it is easy to develop a tuning kit to carry on the bike and fevelop procedures that allow changes to be made in minutes at a gas or pee stop on a ride, with the improved performance contributing to greater riding pleasure.



Generally, I take a different approach to tuning for a ride. I really don't like wrenching on the road or trail--bad things tend to happen, like breaking the c-clip on the needle or tearing an o-ring, or dropping a screw in gravel, or something equally troublesome. With experience, a little research into environmental factors allows tuning changes to be made before a ride. I do this when I'm camped at, say, 6000 feet altitude and will be spending most of the day on mountain passes at 11,000 to 12,500 feet altitude. Sure, the bike runs a little lean early in the morning and late in the afternoon leaving and returning to camp, but it doesn't matter because the air is cool so the bike won't over-heat. However, with the bike properly tuned for high altitudes, I enjoy the maximum performance of which the engine is capable for the biggest part of the ride.



As you've discovered, tuning a carb isn't rocket science. It just takes a well-thought plan and patience.
 
1 - 11 of 11 Posts
Top