Things you may not know.
 
1 - An engine will run richer in taller gears. This is due to the acceleration rate being slower & allowing more time for the carburetor to deliver fuel. Fuel flow always lags behind air flow as fuel is heavier.
 
2 - The longer you hold the throttle open the richer the jetting. Same reason as above.
 
3 - If you snap the throttle open & the engine doesn't respond - 90% time  it's lean. Same reason as above.

4 - CV Carbs deliver fuel in response primarily to rpm, a piston slide carburetor responds to throttle percentage opening.

5 - When your jetting is correct a carburetor will work good in a surprising large range of air temperatures and humidity. If it doesn't then your jetting is on the fringe of the optimum setting.

6 - Slightly lean and your engine response and performance will be poor, slightly rich and you will likely not notice a problem. This is why most jet kits are setup on the rich side of optimum to avoid customer complaints.

7 - Airbox modifications or removal will have the biggest impact on jetting.

8 - On a CV Carb, you do not control the rate of acceleration....that is set by the size, number of vacuum slide lift holes and stiffness (rate) of the slide lift spring.

This is looking down into the intake tract of a 2006 Suzuki GSXR750 with 66,000 km. As you can see there is considerable carbon deposits built up on the back of the intake valve. This is a fuel injected engine and the injector sprays on the back on the hot intake valve to help vaporize the fuel. Higher than normal intake valve temperatures and poor quality gas can aggravate this condition. Another issue is Ethanol in fuel. This can cause a variety of issues especially in vintage bikes and 2 strokes. Most gas has up to 10% ethanol in it and is best to use gas with the lowest amount or none at all. Some stations sell ethanol free Shell 91. I personally do not believe fuel additives can remove these deposits once they have formed but there maybe a case for using them from new to help prevent the buildup in the first place. There is a product we carry that has many good customer reviews and also acts as a fuel stabilizer (see picture below). Keep in mind that carbon deposits act like a sponge and when built up severly enough on the back of an intake valve like this can actually have a profound effect on how much fuel is being delivered. This can cause your engine run leaner then intended, reducing both performance, mileage and drive ability.

So you installed an aftermarket exhaust and now you have popping out the exhaust when letting off the throttle. First the Bad News. A small amount of this may be inevitable and its due to that new fancy muffler does not do nearly as good of job as the original did in reducing noise. You see, many bikes pop when chopping the throttle thru the exhaust even with the stock muffler, the fact is you just don't hear it due to the sheer size of the muffler and its sound deadening qualities. Given that, here are three things that can cause or aggravate this problem. 1 - an exhaust leak at the manifold or any joints in the exhaust. 2 - If you're model is equipped with air injection. 3 - Lean carburetor jetting of the low speed circuit.  Fix any leaks first, then plug the air injection if equipped. Lastly try turning out the fuel screw. Good luck!

There is a lot of confusion when it comes spark plug heat ranges. Many customers ask me for a "Hotter" plug assuming that this has something to do with the spark output. It does not. Spark plugs are made in different heat ranges & can be identified by the number stamped on the plug. The lower the number the hotter the plug generally but not always ie: Champion plugs are the opposite. The plug heat range determines thet temperature that the plug is designed to run at & has to be matched to the application. As you can see in the picture below the difference in heat range or the temperature that the plug body runs at is determined by the length of the heat path taken from the plug firing end to the cylinder head. If used outside of it's designed heat range the plug may foul or overheat. It doesn't effect the spark quality or engine temp in any way. Generally, there is never a need to alter the stock heat range unless the engine has been heavily modified.

You can easily check for drive chain wear by seeing how far you can pull the chain off the rear sprocket (see picture). If you can pull the chain off more than one third of the height of the sprocket teeth than the chain is in need of replacement sooner rather than later. Keep in mind you need to replace the front and rear sprockets at the same time or you will significantly reduce the life of the new chain.

I am sure most of you have noticed a loss in engine performance on very hot, humid days. Why is that? Both higher heat and humidity will reduce the amount of oxygen in the air that the engine ingests. Hotter air temperatures thru reduced air density and higher humidity thru the water vapor displacing oxygen. As an engine uses oxygen combined with vaporized fuel in the combustion process there will be less heat is produced in the combustion chamber there creating less cylinder pressure. Less pressure equals less push on the pistons which equated to less power at the wheels.

Why is it that if you over bore some 4 stroke engines the performance gained is more than what you would expect with the minor increase in actual displacement. As an example a YZ250F with a 2mm larger piston gains only 13cc in displacement yet will likely gain a few horsepower throughout the rev range with no other modifications. The gain actually comes from the larger bore"unshrouding" the valves in the cylinder head allowing for increased air flow. The 5 valve head is especially bad due to the crowding. All the power from a 4 stroke is in the head.

Wet Vapor Blasting was originally developed by Rolls Royce to clean delicate turbine blades. With wet vapor blasting you can  clean years of oxidation, corrosion, rust, grime and tarnish out of the tightest places while leaving a beautiful long lasting smooth oem satin finish. No other process compares when it comes to not only cleaning but surface finishing parts for a rebuild. You can also clean and restore most plastic and rubber parts. See below for examples !

Had a customer with a 500cc street bike who wanted to put a 2 tooth smaller rear sprocket to increase his top speed by approx 10km per hour. I explained to him that it may do nothing as with everything else being equal top speed is simply a function of how much horsepower your engine produces. As that isn't changing, chances are that gearing is not going to help assuming his top speed now is at approx where his bike is producing max hp. 

Pistons always have directional arrows on them showing you which way to install them. Most times the arrow point to the exhaust but there are some weird exceptions (towards PTO, etc) and you need to check before assembly. One obvious reason is locating pin location for 2 strokes and valve size pocket on 4 strokes. There is another reason. The wrist pin is often offset to lessen piston side thrust to reduce wear.