TW200 Forum banner
  • Hey Everyone! Enter your bike HERE to be a part of this months Bike of the Month Challenge!
1 - 5 of 5 Posts

·
Registered
Joined
·
4,781 Posts
I think you have a problem with the motor in some way and that this is not normal. I'll quote you here why I think that:
When I first got it I had to rev it pretty high just to keep it from stalling when taking off.
You then jetted and adjusted valves and said that helped with low end.
But then you said this:
I mostly ride it off-road for exploring in the desert and woods and it does ok as long as I keep the revs up.
That contradicts what you said previously that the jetting and valve adjust:
I adjusted the valves and did a dynojet kit and that helped a ton on the bottom to mid
Your gearing is going to lean towards less low end torque and need for higher rev launches, but I doubt it's enough that you have to rev the engine much to do so. Your gearing leans toward higher top end speed, which you are not getting.

So let's first confirm your sprocket gearing. You said:
It’s geared +1 up front and -1 on the rear sprocket.
Let's confirm what stock is first: 14/50 front/rear. So +1 up front is 15 teeth and -1 in rear is 49 teeth. Is that what you have?
Now let's go to the website Gear Commander and put in the TW200 years 87-13.
Leave the stock ratio as-is and modify the current ratio to yours at 15 and 49.
Rectangle Font Parallel Screenshot Number


Now scroll down to the next chart and notice that the stock gearing at 55mph is turning the motor at 7200 rpm.
Rectangle Font Parallel Pattern Screenshot


Now click on the "Current" tab and enter 6500 in the minimum rpm box. Notice the current gearing you have at 55mph is turning the motor at 6500 rpm. (Note: the ZERO rpm default has the top speed somewhere between 6300 and 7200 rpm for the speed we want of 55mph, so I adjusted the minimum rpm box to discover exactly how many rpms it takes to go 55 mph with your current gear ratio)

Rectangle Font Parallel Pattern Screenshot


As these charts show, you are turning 6500 rpm at 55mph.
So from what I can see and read from your post, you have both poor performance in the lowest rpm range and the mid to upper rpm range. Just for clarification, a TW200 should be able to run reliabliy at 2,800rpm all day long grunting through rough terrain and at 3,000 to 4,000 climb anything short of near-vertical without stalling. These things really are goats when running right. Also for clarification, they should easily reach 8,000 rpm on flat ground. Both of these clarifications will not be affected by gearing, since I'm talking rpm, not mph. Most times you want to ride off road, you gear down so you can ride at a pace you can manage the terrain. Most times you want to ride on-road, you gear up so you can ride at prevailing speed limits without screaming the motor rpm.
In YOUR case, you have neither low end rpm grunt power nor upper rpm speed.

With that established, let's discuss why your bike is so weak at lower rpms to the point you can't even launch or ride off road without revving up the engine and why your top end speed can't get you to over 55 on the flats.

Obviously the top speed on the road is the first concern to keep from getting run over or being a hazard. At 55mph, your gearing has your motor turning 6500 rpm and that's topping it out. That is a problem. A BIG problem. The causes are many, but you alluded to one that I have been recently made aware of by a memeber here that goes by oldworld124, AKA John. John and I have been discussing the TW's performance as it relates to aging engine components and something he made me aware of is how valve springs get weak over time and what the result in performance it causes. In a nut shell, the springs have a set of specs that John has measured on a couple top ends and he's discovered that they age out over time and get to the point that they no longer are at their optimal tension. This results in what is called "valve float". Valve float happens when the valve train is moving so fast, the spring can not keep up with the rpm and the valves do not fully close under the current spring tension, resulting in a couple problems; one is a loss of performance, much like you are experiencing. Another is the floating valve that isn't seating all the way before the cam lobe goes to open it again can hit the piston as it comes back up to TDC. Since the valve is floating, this should not result in catastrophic engine failure, but can put a dent in the piston crown. I've got such marks on my piston and suspect I have weak valve springs. I also notice I cannot ride flat ground above 8000 rpm even though the motor will turn 9000 rpm in neutral and revving the throttle. I have no issue with low speed performance though, so let's just hold off on that for now.
What alluded me to the possibility that your valve springs are weak is the age and milage on your bike. At 15,000 miles and being an 18 year old motor, it's quite likely your valve springs are beyond spec.

There may be other reasons for the poor performance, things like the CDI is on it's way out, a clogged air filter, low engine compression, etc. But I'll assume you've checked the air filter and the air feed from under the seat to the filter is not blocked in any way. Mice tend to use this area to store and nest, and while the filter is clean, the intake can be obstructed. Engine compression should also be tested. A compression gauge off Amazon is cheap, under $25 and a great investment as a means of testing motor performance.
I will also assume, but mention anyway, that you have changed out the spark plug for a fresh one. It's not uncommon for them to develop cracks that can only show up at higher rpm and compression but work fine at other speeds. Some other things that can affect top speed performance are:
tire pressure
chain condition
engine oil vecosity
engine timing (set by the rotor and wood drift key, the key can break and the rotor move out of position.)
valve timing (set by the cam gear through the cam chain and can either jump a tooth if the cam chain tensioner is not set properly or the chain has stretched excessively)
Carb jetting, especially the pilot jet, tends to easily get blocked or partly blocked. If your bike runs better at half choke at higher rpm, then it's a possibility. Try setting the choke at half way while at speed and see if the top speed increases. If a throttle chop at top rpm results in a popping back-fire, it's definitely too lean.

I would start with the easiest of these possibilities and work my way up. But if I were a betting man, I'd bet that either the cam chain has jumped a tooth, stretched or isn't tensioned correctly OR that the valve springs are weak and need replacing.

Keep us informed what you find as you continue troubleshooting your problem.

P.S. Some folks here might loan you a spare CDI if you get to that point. It's a way to confirm the problem by isolating without having to spend a few hundred bucks.

** EDIT **
I want to add a couple other things:
fuel flow: make sure you have full fuel flow. A clogged filter in the tank could restrict fuel flow and prevent top speed. There's also a filter screen inside the carb at the float needle. To test, open the carb bowl drain screw and the fuel petcock on the tank. You should see a steady, robust flow of fuel coming out that hose. Be careful seating the drain screw and only close it lightly. Many have damaged the screw or bowl by trying to over tighten.

Also be sure you have good quality fuel. Flush the tank by removing it and turning it over. Allow to air dry and inspect it with a flashlight. It should be spotless.

While you are at it, add an in-line fuel filter.
 

·
Registered
Joined
·
4,781 Posts
I'll point out again to my fellow riders,
the OP says gearing is such it won't rev past 6500rpm on flat ground. (15/49 gear ratio in 5th gear outputs 6500 rpm at 55mph, his top speed on flat)

THAT is a problem, not anywhere near normal. If you think it is, you also likely have a problem.
 

·
Registered
Joined
·
4,781 Posts
The Tdub has 1/4th the HP and is 50 lbs. heavier than your dirt bike, so that's not a fair comparison and that gearing is killing any real trail riding.
Arizona trails are alotsa rocks below the Mogollon rim and less rock with more dirt and forests up on top. I ran 13/55 gearing (all off road) and now run 14/55 to connect the trails. With this gearing I can ride 55-60mph and possibly faster but don't cuz I'm running around with single digit tire pressures.
With a 75mph speed limit (and everyone driving 82mph) you will never safely ride the Tdub up the I-17 .

I've taken my TW up abandoned mining trails and spurs that I would not consider on my dirt bike, look up "Smiley Rock Trail", the TW just motors thru those rock chutes.
Learn to really ride the TW, the lack of horse power, suspension and brakes will make you a better rider. I practice all my stupid stunts on the TW, low and slow hurts a lot less.
With the right gearing, a Singer sewing machine would do just fine crawling the rocks. Ha!
 

·
Registered
Joined
·
4,781 Posts
Checked the compression. 110. Seems kinda low. Maybe that’s the problem. It’s not smoking or burning oil so I’m going to guess it needs a top end. Any tips on parts? I’ve googled TW200 top end kits and haven’t found anything yet.
Yeah, I'd say that's pretty low.
When you tested compression, was the motor fully warmed up and did you hold the throttle wide open as you cranked?
Did you do a follow-up test with a little oil squirt in the cylinder? If so, what was the compression reading after?
If the compression rose, then likely rings. If not, likely valves.
 
1 - 5 of 5 Posts
Top