How Do you tune A Yamaha Blaster carburetor?

Answer 1

Tune if for what? A new pipe?

Here's a long version for you and anyone else looking for power:

There are several settings on a typical 2-stroke carb; the main jet, idle jet, and needle. The jets can be removed and replaced with ones of a different size to make the engine run ideal. The needle is tapered and fits into the main jet

(a main jet is simply a small hole where the fuel enters the carb) and controls how much fuel can go thru it, picture the main and needle together as an adjustable jet. With the needle all they in it's like a cork blocking the main jet, as you pull the needle out more and more fuel can slip past until the needle is all the way out and the main jet is flowing at maximum capacity. The idle jet is just like it sounds, it supplies fuel at idle and the main jet supplies fuel at other throttle positions. The idle jest doesn't simply stop as you open the throttle and the main starts to work, but there is overlap. The engine feeds off the idle jet at idle, then as you open the throttle slowly it transitions into the main jet. So at part throttle you are feeding a little bit off of both. As the throttle opens further the idle jet stops altogether and the main does all the work except the needle is controlling the amount of fuel by blocking the main jet. The more you open the throttle the further the needle is pulled out of the main jet which allows more fuel thru. Now to tune you need to play with the jet sizes and needle position and possible the needle shape itself. The needle is adjustable in height usually via a C-clip. If you move the position of the needle then it will be pulled out or pushed into the main jet further which has a big effect on the fuel flow. If you need more fuel then you set the needle further away from the main jet or "raise the needle". Rarely ever does a needle need to pushed down deeper into the jet. The shape of the needle is equally as important but the original needle is usually just fine. For fine tuning you can buy different needles. Changing the main jet is the most common change people do, especially after adding an aftermarket exhaust. The engine will now be able to use more fuel and a bigger jet will provide that. Since the jet is bigger in diameter and needle shape and position hasn't changed, then more fuel will get past at all throttle positions. Usually but not always the idle needs to be changed up a size too because the idle controls idle and some of part throttle. If you change the ex pipe and main jet, but not the idle jet, it may run lean at idle and part throttle, then kick in hard when the idle jet fades out and the needle/main takes over. This should feel obvious especially if you know how smooth the engine runs when tuned correctly. Since many people have already done mods to this engine there is information available on what jets work best with what mods. Usually if you're just adding an ex pipe the mfg of the pipe will tell you what works best. If you also make other changes like a better air filter and open up your air box then you'll need to see what jets others have had success with, or try various jets until you get max power. Things like a dirty fuel filter can really screw up this testing because you may have the right jetting but since the filter is restrictive you think the main is too small. If this is the case you add a bigger main and now it's too rich everywhere except full throttle. So be sure everything else is working right. Use new spark plugs too, there's no better plug that a new plug, especially on a 2-stroke. Just buy the cheap plugs, don't bother with fancy platinum or multi-ground etc because they all foul out just as fast except the fancy ones cost much more to replace. So buy cheap and replace more often. I'd change my plug once or twice per trip, so every 20 miles? Depending on the oil and tune of the carb you may get much much longer life, but still, nothing is better than a fresh plug so changing too often is much better than too late. So if you try to tune a carb but the plug is partially fouled you'll never get it tuned right.

This info applies to basically all 2-stroke bikes, not just your Blaster.

Oh, and use real castor oil in your mix. It not only smells good but makes the motor run better thru better sealing. Use somewhere between 20-1 and 32-1, I prefer 20-1 for best sealing. The more oil you use will reduce your octane, so try using race gas with it. Race gas is usually better anyway, but if feel a big power increase then you really need to use it due to the oil.

If you try to get away with 50-1 or 100-1 synthetic oil then regular gas might work fine, but the engine won't seal as well so you've lost power in more ways that one. Also; never rely on the automatic oil mixers on a bike because they're inconsistent and often fail which means your engine will seize! Just mix it in a can before you pour it into the tank. Fresh mix is best so don't mix more than you plan on using right then. I'll use day old mix but some consider it ruined after it's a few hours old. Professional racers for example will only mix the gas right before the race, then afterwards they drain and dispose of any that's left.

If you're having trouble tuning the carb then try putting it back to stock jets and settings and change the main jet one size bigger at a time and only feel the full throttle power, the mid range is not important right now, you want the jet that makes the most full throttle power. Sometimes it's hard to tell, sometimes you need to go several jet sizes too far before you can tell the difference between too lean and too rich. Once the main jet for full throttle power is found, then you can play with the needle. At full throttle the needle isn't in play, so once the main is found then you can see how 1/4, 1/2, and 3/4 throttle work with different needle positions. Usually there are only two positions that work, the original setting, and one up. Any other setting is too lean or too rich for most bikes. I've never found one that worked at two up. Once the needle is set you can play with the idle thru 1/4 throttle by trying one size larger idle jet at a time. Usually one size up is all that's needed. The main jet that is the hardest to find because ideal it could be one, two or three sizes up. Plus the more oil you mix with the gas can affect jetting too, a 50-1 synthetic might work ideal at one main jet size up, but a 20-1 castrol oil mix will likely work better with two sizes larger. But the castol will make more power as long as the octane requirements are met which often require race gas as I mentioned earlier. Correct jetting, new plug, fresh castrol/race gas mix and you're golden...