The Chinese Motorcycle

[Mortblanc]

Well we have had a run of very warm weather and I have gotten my grubby spanners to the little motorbike.

That was not before I did some major road time on the little beast to find out its dynamics. I have clocked up a couple of hundred miles on the KY back roads and on a couple of the front roads. The bike rides well and handles great, a credit to the model it is a copy of!

My first modification was to lower the beast front and rear. I have great difficulty with a seat height of 850mm when my inside leg is 750mm. I bought the bike I did due to its adjustable rear suspension. I lowered the front 50mm and the rear 100mm. I can now touch the ground flat footed while sitting on the seat.

As expected, it is choked down to the point of barely running for the emissions passage. Who in the world ever heard of a catalytic converter on a 230cc motor! And the carburetor is sealed to the point that the air fuel mixture screw is covered with a brass plate press fitted in place. The bowl is riveted in place so that adjustment or repair is impossible.

All of this is done to choke a 230cc motor that should make 21-25 BHP to the range of 15 BHP. You folks have 125cc motors from the same Chinese factories that pump out 14hp to hit your A1 limit. Mine should do 20hp easily, attain 70mph top speed and cruise at 55-60 without strain!

Now the motor is still new and running in, but the RPM is restricted to the point that speed is unacceptably low. There is still substantial torque on call but no top end power.

I gutted the exhaust system. The catalytic converter is a piece of rolled up corrugated metal that blocks off half the exhaust pipe to slow the flow of exhaust, bring the pipe to red heat, and burn any residual hydrocarbons before they exit the muffler.

That's gone!

So are most of the internals of the silencer. I am a firm believer that if the exhaust port starts at 25mm diameter it should have an exit path 25mm in diameter all the way through no matter how many twists and turns it takes to quiet the flow.

This bike had a 25mm exhaust port and the outlet at the end of the muffler, the real outlet not the huge hole showing for the world to see, was only 20mm diameter and had a fine mesh spark arrestor screen covering it.

That's gone!

We are a bit loud at this point, but not as loud as the neighbor's Harley, or the other neighbor's Suzuki 650. Or the old lady down the road with the rusted out Toyota Camray.

At any rate, the top speed increased from somewhere south of 50mph to just above 55mph with just the exhaust work. Now that 50mph speed is the velocity I was willing to risk on a new engine that sounded like it was going to explode when I shifted into 5th gear at 45mph! I have not gone for a real top speed run since I am still in break in period. I do not want to run the TT with this thing but a 230cc motor should be able to propel an individual of normal size at 60mph cruising speed with normal gearing.

Some new carburetor jets arrived in the post and the next move is surgery on the rivets holding the carb together. It will get a jet appropriate to the altitude rather than the test machinery. It will also get mid range flow adjusted properly with access to the air fuel adjustment screw. We are speaking of going from a .90mm jet to 1.15mm jet for a 25% increase in fuel air flow and the appropriate power increase.

One of the problems the Chinese bikes have had is they are tuned so lean that they run excessively hot and wear rapidly and blow up due to the heat. They are on the ragged edge of durability to meet the legal standards and then a 16 stone westerner jumps on and winds them out for a few hours and pushes them over the edge and screams about bad Chinese bikes.

In GB that situation might become a little better with the EU4-5 standards that can only be met with fuel injection and computer control. Our laws here are almost identical. One main difference being that testing is done only in major cities. Out here in the boonies they never heard of anything like your MOT. If it rolls you can drive it. There is a healthy aftermarket world of CDI units that have assorted mapping to meet any need.

There are also new sprockets in the post. I presently have a 15 tooth front gear and a 43 tooth rear. With the transmission in its present configuration that allows me to creep at "walking pace" in 1st gear with the clutch fully engaged and not stall the motor. That is great for passing the CBT, or even creeping through mud holes, but not so much for traveling on the A roads, or in my area the green lanes, where one can be smashed if not keeping up. I have a 17 tooth front gear coming from some place near Mongolia. We will see if that 7% change allows me to roll at 55-60 and remain below red line.

Now the cost of this work has been kept in line. I do not intend to fall into that trap where one buys a cheap bike and then spends more than the cost of the vehicle on modifications that would total the price of what you wanted to start with!

The tools I have used I already owned. The carb jets were $10 U.S. for a pack of 10 assorted sizes and one will go into the 230cc and another will go into my 50cc scooter, which is another tale all its own. The gear change will cost another $10 U.S.

Hey, if anyone is headed for the States next spring they can stop by and help me build a 49cc "adventure scooter". That new 750cc Honda X scooter has lit a fire under me! I already have knobbly tires on order.