Note: Please post questions in the Rubberside or PM me...FWIW...
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Lesson 1... What and why of jetting....
First off,...
jetting is never perfect... it's a matter of getting a good average... Because perfect jetting is only perfect for the precise conditions that you are jetted for,.. and this changes hour by hour, day by day, and mile by mile...
What you are looking for, is a good average...
Bigger jets won't make your bike faster... the correct size jets will...
Exhaust pipes will go gold first, then blue, then blue black. It means hot, hotter, hotter. Running lean, or rich, can cause it,... so can excessive idling, heavy traffic, or just plain hot weather... Our big air-cooled thumper makes blue pipes easy...
Once a pipe is blued,.. it won't go away by changing jetting... until the blue is removed with Blue Job or other product, it's there to stay,... so jetting by pipe color is not practical...
If this condition is new to your bike it may be environmental, or may indicate a blockage in a jet...
If you modify your bike in a way that increases or decreases breathing... intake and/or exhaust,... jetting needs will change, and should be adjusted...
It's just common sense,... if you let more air in, more fuel is needed to keep the balance...
How much,.. depends on the how, and muchness,.. of the changes you made...
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In general...Increased breathing needs bigger jetting, decreased breathing needs smaller jetting...
Then,... it's up to where you live and ride...
thinner air = less oxygen = go leaner
hotter air = go leaner
more humidity = go leaner
higher altitude = go leaner
thicker air = more oxygen = go richer
cooler air = go richer
less humid = go richer
lower altitude = go richer
Barometric pressure effects jetting in a big way, humidity, air temp, and elevation. Some places have extreme variations,... and if you live there, your pipe will blue. I live in the high desert and temps can change 40 degrees f in a couple hours, humidity can vary wildly too. No way to jet for that.
Gold and blue are pretty!
A good indicator of overall jetting is the weather...if popping/backfiring increases on humid days, or at higher elevation, that indicates rich....less popping at those times indicates lean.
Drill out the brass plug on the idle mix screw... adjust for smooth and steady idle... if it needs more than 3 turns out, go one step larger on the pilot jet. The pilot jet will have an effect on MPG's... If you want good gas mileage, don't get carried away there...
CW, in, is going leaner,... CCW, out, is going richer...
The needle jet is adjusted by varying the spacer thickness under the plate that mounts the needle to the slide... this has the biggest effect on acceleration and in the midrange area... Say 60+ mph cruising, and half throttle acceleration...
Quote:General, seat of pants tuning...
Idle speed...
Set your idle speed with knurled screw on the left side, near the enrichment knob... Set it to be smooth and steady,... not loping or stumbling, (this ain't a Harley, don't try to make it sound like one).. (a slow loping idle is very bad for your engine)...
Idle mix... and pilot jet...
If you can get the smoothest/ highest idle speed, by setting the idle mix screw between 1 and 3 turns out from closed,... you have set your idle mix, and your pilot jet is the right size... (if you have to go more than 3 turns out,.. go up one step on pilot jet)..(if it seems to make very little difference turning the screw, you are probably rich on the pilot, and can go down a step)...
Main jet...
To test the main, accelerate from 30 or 40 mph, in 4th or 5th gear at full throttle for several seconds, then reduce throttle by about 1/8,...if power increases for a second, you are lean on the main jet. Go up one jet size and test again.
Needle jet...
If your main is good, and your pilot is good,... but you have surging at steady low speed... try pulling out the enrichment knob, one notch (do this with a fully warmed up engine)... if you get some acceleration, set your needle up a notch, or reduce the spacer...
... if it bogs instead of accelerating,.. you are either rich, or good... increase the spacer, or set the needle down a notch, until surging goes away, but you still get some bogging with the enrichment valve pulled out a notch...
There are other ways to test jetting, but this way is pretty simple and seems to get me close... for seat of pants tuning...
Huh...
(keep in mind,.. that changing the pilot, affects the needle and the main,.. and changing the needle setting, affects the main,...
Jets are additive... (the pilot doesn't stop when the needle starts, and when you are up to the main, the needle and pilot are still serving up fuel)... getting them all balanced takes some experimentation...
Jets are incrementally additive.... starting with the idle mix, then pilot, then needle, then main... Each jet adds it's volume to the next in line... Wide open throttle is accessing all of them, so changes in one, adds to next and the next..
Quote:Noobie tip... keep your idle speed up,... even though you may think it sounds really cool, the oil pump will not operate well at lower rpm's than 800 to 1000 rpm... you can cook your cam bearings with too low of an idle...
The idle speed is adjusted with a knurled knob on the left side near the choke knob...
Quote:A little explanation of how a carburetor works...
A carb is a vacuum operated fuel delivery device... Unlike fuel injection, a carb only works when when your engine sucks on it...
That is engine vacuum...
When the piston in your engine goes down, it sucks fuel from the carb,... the piston goes up, and it blows out of the muffler. Between the sucks and blows, a spark happens that ignites the fuel in your engine, and that explosion makes the piston go up and down.
The engine sucking on the carb, pulls fuel from the jets...
By turning the throttle, you open a valve in the carb that lets more suck from the engine into the carb... as the valve opens more and more, it accesses more jets. Idle, pilot, needle, and main... Increasingly more fuel,... for a bigger explosion in the engine,... and the piston moves faster, making your bike go faster.
Close the throttle, and the engine pulls less gas from the carb, and you slow down.
By changing jet sizes,.. you are adjusting the amount of fuel that can go into the engine at different speeds... Bigger jet numbers, have a bigger hole in them for the fuel to pass through...
Quote:Thinking has evolved on this topic... there used to be a lot of advice on eliminating popping and afterfires with jetting,... but that is jetting for a closed throttle...
Under what conditions popping and afterfire occurs, can be used as an indicator of which way your jetting is off,... but you should jet for performance and economy, not quiet deceleration...
Unless, popping is so annoying to you that you will tolerate a bad running bike...
Decel noise is inherent to big single engines... so is a poof at shut-off (it's just unspent fuel from the last engine cycle igniting in the pipe)...
With practice you can learn to control these noises with your riding technique,... it can even be useful in traffic for alerting drivers of your position...
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Jet your bike to run good... not to stop good...
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Ride safe...
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more specific tips follow below...
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