carburator jetting and cyclinder heads?

Tuning is the process of finding the correct jetting for any given engine.
Jetting a carb is when you change the size of the jet that controls how much fuel flows at any given speed. The ratio of fuel to air in the engine controls how much power it has and how well it runs in use. Leaner means less fuel, rich means more fuel. Leaner mixtures usually mean more power (up to a point) But if TOO lean, engine damage will result. Richer mixtures usually give less power but prolong engine life due to cooler combustion and more oil getting to the engine.
 
maniac57 said:
Tuning is the process of finding the correct jetting for any given engine.
Jetting a carb is when you change the size of the jet that controls how much fuel flows at any given speed. The ratio of fuel to air in the engine controls how much power it has and how well it runs in use. Leaner means less fuel, rich means more fuel. Leaner mixtures usually mean more power (up to a point) But if TOO lean, engine damage will result. Richer mixtures usually give less power but prolong engine life due to cooler combustion and more oil getting to the engine.
Click to expand...

so is there a point in changing the jetting size in the carburator thats calibrated to run correctly?
 
Your altitude above sea level will determine the best jet size. The higher you are above sea level the leaner you need to tune. This is because the air is thinner, less dense at a higher altitude. The closer to sea level you are the richer you can run due to air density.

There is no set rule of thumb for best performance. It is something you'll need to experiment with to find what works best for you. No one can tell you what jet size will work best for your altitude, weight, riding style, terrain, etc. Optimum tuning is a product of experimentation and experience.

Your spark plug color will tell you where you need to be/go. Dark? Go leaner. Light, to white? Go richer. Ideally you don't want any 4 stroking at WOT but a little at lower throttle settings is normal. Above all trying to get the best performance from an engine that is not well broken in is an exercise in futility. Wait until you get 2 to 300 miles on the engine before worrying too much about top performance.

Your fuel to oil ratio is also a factor. If you're trying to run with a 16:1 ratio as is suggested by many kit instructions you'll never see the best performance. It is too much oil. 32:1 is good for break in as well as thereafter. Your engine will be happy and so will you.

Good luck.

Tom
 
Last edited:
2door said:
Your altitude above sea level will determine the best jet size. The higher you are above sea level the leaner you need to tune. This is because the air is thinner, less dense at a higher altitude. The closer to sea level you are the richer you can run due to air density.

There is no set rule of thumb for best performance. It is something you'll need to experiment with to find what works best for you. No one can tell you what jet size will work best for your altitude, weight, riding style, terrain, etc. Optimum tuning is a product of experimentation and experience.

Your spark plug color will tell you where you need to be/go. Dark? Go leaner. Light, to white? Go richer. Ideally you don't want any 4 stroking at WOT but a little at lower throttle settings is normal. Above all trying to get the best performance from an engine that is not well broken in is an exercise in futility. Wait until you get 2 to 300 miles on the engine before worrying too much about top performance.

Your fuel to oil ratio is also a factor. If you're trying to run with a 16:1 ratio as is suggested by many kit instructions you'll never see the best performance. It is too much oil. 32:1 is good for break in as well as thereafter. Your engine will be happy and so will you.

Good luck.

Tom
Click to expand...

thanks for the input! since im running 16:1 should i just go ahead and drain my tank and replace with 32:1? i only have a little left in the tank, but if it will stop the oil leaking from the spark plug, exhaust/ gasket area and a bolt from the crankcase i will be happy to do it tomorrow.
 
Oil leaks from the places you mention is not a result of too much oil but bad gaskets or bad gasket mating surfaces or improper tightening of the fasteners.

The cylinder head, exhaust flange and spark plug should not leak if tightened correctly and the gaskets are good no matter the fuel to oil ratio. Address those areas and mix up a new batch of fuel in a seperate container and add it to whatever is left in your tank.

Tom
 
2door said:
Oil leaks from the places you mention is not a result of too much oil but bad gaskets or bad gasket mating surfaces or improper tightening of the fasteners.

The cylinder head, exhaust flange and spark plug should not leak if tightened correctly and the gaskets are good no matter the fuel to oil ratio. Address those areas and mix up a new batch of fuel in a seperate container and add it to whatever is left in your tank.

Tom
Click to expand...

cool, thanks! ill check the gaskets tomorrow and reseal them
 
the special cylinder heads offered come with squish bands which need to have the cylinder top milled down enough so that the clearance between head and piston is .6mm to .8mm. Without milling it down there is too much fuel mixture guarded under the squish area that doesnt burn till too late, causing loss of power. So either mill down a standard head 1mm or buy a high compression head and mill down the cylinder.
 
You must log in or register to reply here.
Back
Top