I'm mainly wondering about the use the piot jet, needle clip...etc
I have already figured that the fuel comes up through the main jet, and thatthe needle lets more of less fuel depending on the slide heigth (so the ratio fuel/air is correct)...but what's the use of the pilot jet? And why would you raise/lower the needle clip?
If someone can tell me what happens in the carb when you modify this...I could spend a day to get a proper jetting (not until april though...snow's gotta melt...and temp raise a bit). To do a jetting test...do I simply put in new plugs, run full throttle (avvoiding idle that would "blacken" the plug more) and see how it looks?

 

Im not sure I can answer all your questions. There is a chart on my site that explains for which throttle range each jet is used in.

The needle clip setting will affect a little over no throttle to 1/4 throttle. The clip setting will either raise or lower the needle inside the main jet allowing more or less fuel. Once the slide is high enough (1/4 throttle) the needle will have little effect on the fuel mixture.

 

 

12-22-00:Tech. Tips: Motorcycle [Carburetor Theory 101]. sorry i forgot to tell you were to go but you are smart and would of got it.

 

Pilot Jet = 0 to 1/4 throttle
Needle Jet= 1/4 to 3/4
Main Jet= 3/4 to full throttle.

The Ranges sometimes overlap. The best practice is to start with the main jet change, new plug, run it down the street full throttle, then shut it off(don't let it drop below 3/4 throttle), check the plug. Adjust/change as necessary. Then adjust the needle jet run it between 1/4 and 3/4 shut it off then check plug. Then let it idle or rev slightly check pilot. The Air/mixture screws are for fine tuning.

 

rollpsi425r:

Your link is great!!

thanks...you signature rocks!!!

 

EricsRaptor:
By needle jet, do you mean needle clip position?

Now I know what range each jet has its effects on , but why? Why does the pilot jet affects oly the first quart of the throttle opening? For the main jet, that's obvious, and the needle also...the question changes to "how does a pilot jet work? Why does he fuel go through the pilot and not the main?...etc"

Thanks

 

ROLLpsi425R,s link to carb theory 101 explains the pilot jet/air screw pretty good.

The only question I have is which is the "back of the carb and which is the "front"

I assume the back is the side closer to the air filter (back of tthe bike)and the front is the side closer to the engine (front of the bike).

...but you know what they saw about assuming.

Can someone verify this for me?

 

MacDizzy has multiple resources on carburetor theory and 'most everything else.

"Motorcycle Carburetor Manual," by Pete Shoemark, available from MotorcycleBooks.com (800) 982-4599 is a good reference with abundant diagrams and detailed explanations.

Diogenes

 

Yes- Needle Clip Pos..Don't know about pilot. Here compliments of Cal...

TESTING & PLUG READING FOR CORRECT JETTING


The three jet circuits & their ranges are:

The three jet circuits & their ranges are:
1. pilot jet..idle to 1/4 throttle
2. needle jet..1/4 to 3/4 throttle
3. main jet..3'4 to full throttle

Normally, the main jetting is done before any other changes are made.

The first thing to do is to determine whether any re- jetting is in fact necessary. One does this by a test ride & plug inspection.
To accomplish an accurate plug reading, a new plug must be used. After the quad is warmed up and the new plug installed, ride for a mile at 3/4 to full throttle in any gear you choose...your engine doesn't know what gear you're in, it only recognizes throttle position. Then, without any idling or low throttle operation shut the engine off & pull the plug to check for color on the electrode & insulator. A gray or light colored electrode/insulator indicates a lean main jet; white is a seriously lean condition & needs to be corrected immediately to prevent damage to the engine.
A dark or black colored electrode/insulator indicates a rich mixture calling for a leaner main jet. A rich condition will affect top end performance and possibly cause plug fouling but is not as critical as a lean air/fuel mix.
The ideal plug color is a tan or light brown and indicates correct jetting.

After reading the plug and making any necessary changes, another test ride/plug read should be done to verify results.
If a performance problem occurs in the needle jet circuit (1/4 -3/4), the nominal position of the needle, which is the 3rd position, can be raised to the 4th position (from the top). Usually the needle can remain in the 3rd slot.
The pilot jet, like the main jet has no adjustment & can only be replaced if necessary, usually with a larger size.

SOMETHING TO REMEMBER:

When adjusting any mechanical thing, only adjust ONE THING at a time and test. Changing more than one thing makes it difficult or impossible to determine where the problem lies