In previous stories I talked about carburetors Rich conditions and Lean Conditions, this is all fine of course if you know how to detect if your engine carburetor is set Rich or Lean.
To help with that, I will explain simple means to detect the setting of your bike. With a perfectly tuned engine you will get the power you need, it amazes me sometimes what people spent on kits to improve performance, while all they needed to do is get the settings right.
Okay that said what is a Rich Condition, while a black, scooty spark plug is a sure sign of richness, there are other indicators that are a bit subtler and better ways of dialing in the carburetor jetting.
If your engine responds crispy at low throttle when it is cold, chances are the main jet is one size larger than it needs to be. Assuming, of course, that the idle circuit is correctly tuned.
Poor fuel mileage is another sign of richness and because of the way most of us ride our motorcycles, that richness is unusually the result of a needle that is too small.
In some previous story, the tuning of a carburetor, I talked about using a Dyno, we got several reactions about this. A Dyno by motorcycle mechanics or dynamometer for English Professors, is a machine used to measure torque and rotational speed (rpm) from which power produced by an engine.
Okay this Dyno's are not something you would buy just to tune your carburetor, hence it is cheaper to visit multiple motorcycle tuning shops, until you have the right performance.
So if you don't have free access to a dynamometer, don't worry, I did years without also. With a stopwatch, tachometer, and some imagination you, too, can measure the power output of your engine accurately enough to get your carburetor dialed in correctly.
Consistency is the key to these types of performance tests. When doing any of these tests take into account air temperature and humidity.
If we look at the basics of the Yamaha Fino, it is a 115cc 4-stroke SOHC, 2 Valve, Air Cooled engine. And officially the engine is a 113.5cc engine (but guess 114cc Fino did not sounded cool enough for Yamaha marketing).
We always start our tuning / modifying with a simple study of the motorcycle, in case of the Fino, the engine is a regular visitor to our modifying shop all is this the first Yamaha Fino, the also very popular Yamaha Nouvo uses the same engine.
After we had a quick look at what the Fino is made off, we decided to not overdo ourself, as this Yamaha Fino will be mostly used by family members and collages, we surely did not wanted to forget the safety futures.
The Yamaha Fino uses a Mikumi BS25 x 1 carburetor, or Carb for the Americans, some will suggest to replace the carburetor with a more sporty one. But as we have maybe a bit more know-how, we know that the Mikumi BS25x1 carburetor can be found in much larger bikes then this 115cc Yamaha Fino scooter.
All Motorcycle engines require different oils a 4-stroke engine needs different oil then a two-stroke, The 2-stroke engine needs oil mixed with the petrol (gasoline) before combustion. In case of a 4-stroke engine the oil is just used to lubricate the engine. Make sure that you are using the right oil, the wrong type of oil can cause serious damage to your motorcycle engine.
Consider using non-synthetic oil for the break-in period according to the owners manual, the break-in period is the first 1000 kilometers. In normal situations there is no need to replace the factory oil. During the break-in period, riding at no more than 80% of top speed is highly recommended.
In addition to this, many mechanics suggest that during the break-in period owners should use non-synthetic oil, and then switch to synthetic after the break-in period is over.
With the introduction of the new Yamaha motorcycle 2008 model line, it looks that the end of the good old carburetor is in sight. The carburetor as we know it today was invented by a Hungarian engineer back in 1892.
But enough about the sentimental part, and back to our task: tuning the main jet circuit of a regular carburetor.
Tuning or adjusting the main jet circuit is where the most confusion seems to be. The main jet really doesn't come into full play until the last quarter turn of the throttle. When the needle rises in the tube far enough that gap is equal to or greater than the size of the main jet, the main jet becomes the metering device for fuel flow.
The first step in tuning the pilot circuit is, or any, carburetor is to get the idle circuit correctly adjusted. That means adjusting the idle mixture screw for the best idle. Keihin carburetors sets the idle mixture screw during assembly and seals the screw under aluminum plug to prevent an owner from changing the setting.
If the aluminum plug is removed, which can be done by carefully drilling a small hole in the plug, threading in a small screw, and then pulling out the plug, gently turn the adjusting screw all the way in until it bottoms. Then turn it two and a half turns out from the fully closed position.
Next, start the engine and bring it up to operating temperature. With the bike in the vertical position and the idle near 1000rpm, turn the idle mixture screw in slowly until the idle either slows or becomes irregular. Now turn the screw out until the engine again slows or begins an irregular idle, counting the number of turns between the too rich and too lean positions.
There is an important axiom of performance work that many novice engine modifiers or builders seem to overlook: Once you've made an engine a performance fire-breather, some of the bike's engine mechanical components may need to be beefed up to handle the extra power, with the clutch usually being the first weak link.
Make no mistake: the OEM/standard clutch pack does an excellent job handling stock power levels, as well as quite a bit more. It has an easy lever pull, smoothly controls the engine's power, and sends all of it to the transmission.
There are several ways to make something out of metal. The part can be stamped, cast, forged or machined. In fact, most motorcycle parts are a combination of more than one of these operations.
The chosen methods of metal working for a given part are usually based on economy of scale. If you are going to make a lot of a given part it is usually less expensive to have a set of dies made and cast it or forge it than it would be if you where machining it from a solid chunk of metal.
On the other hand, if you are operating in custom or small lot sizes then the CNC machines make a fully machined part not only possible but also cost effective. There is another reason to fully machine a part: if you need or want to possibly make changes to it design later on.
So what does all of this theory of metal production have to do with motorcycles? It explains why some would make billet heads and cylinders for their custom highly modified motorcycle engines.
When riding a motorcycle, we have to rely on one type of bearing or another. There are a few different styles of bearings employed in the smooth operation of any motorcycle. For instance, there are engine bearings - roller, ball and needle - that keep the internal components spinning in harmony. Wheel bearings allow the bike to roll down the road, and bearings on the front end allow the bike to turn.
The setup and maintenance of any bearing can extend or shorten its life, but especially so when it comes to the steering stem bearings of your motorcycle's front forks.
For the sake of this publication, we will limit our focus to the tapered roller bearing most commonly used since the introduction of the hydraulic front forks in 1949.