rx1jim
New member
I continue to learn a tremendous amount of excellent information from this site. Regarding the set up of carb jetting, the preferred method to tell if the jets are correct is to examine the piston "wash". I had been setting up the carb jetting by looking only at the color of the spark plugs. Could someone explain the what the optimum "wash" pattern should look like on the top of the pistons?
Am I correct that I should check the piston wash after running for many miles at constant throttle positions to check the setup of the low, midrange and top end jetting?
Thanks!!
Am I correct that I should check the piston wash after running for many miles at constant throttle positions to check the setup of the low, midrange and top end jetting?
Thanks!!
YAMMIEGOD3:16
Active member
VERY SIMPLE, THERE ARE BASISLY THREE READING YOU GET OF THE TOP OF YOUR PISTON. WHICH IS THE ONLY CORRECT WAY TO CHECK JETTING.
1. TOP LOOKS NEW - YOUR RICH
2. IF TOP IS COLORED TO NICE BROWN EDGES - YOUR CORRECT
3. WHITE/ GREY/ ASH LOOKING - TO LEAN.
3:16 (yammie tony)
1. TOP LOOKS NEW - YOUR RICH
2. IF TOP IS COLORED TO NICE BROWN EDGES - YOUR CORRECT
3. WHITE/ GREY/ ASH LOOKING - TO LEAN.
3:16 (yammie tony)
mopar1rules
Active member
mopar1rules said:
That site has some great info.
2ooosrx
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- Oct 2, 2004
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This is a great read for carb jetting aswell.
http://www.snowtechmagazine.com/articles/2001/baseline/baseline.php
http://www.snowtechmagazine.com/articles/2001/baseline/baseline.php
rx1jim
New member
Thank you all very much!!!
RJH
New member
Most of the information above is correct..however..it varies with engine level of tune..
Piston wash is exactly that..un-burned fuel..cleaning the top of the piston. In older designed motors…you will see a lot of wash per the first link..which I think is in-correct…not an issue at this time.
You usually see more piston wash after you get it back from being modified...
E.G. we would tune a YZ125 with the two white marks on the intake side…of the piston...not bad…
Our latest –heavy involvement - was with a 125 cc. 13,500 rpm 42 HP shifter kart engine. It had basically no wash…you had to look very close at the piston rim for slight discoloration… you had to look really hard.
Anothor complicated way is to check the inside of the piston…dark deposit there (bottom of the crown) shows a lean condition.
My favourite check..is the side electrode on the plug. You can watch it change…you want the last half of it dark…and the half closest to the centre electrode lighter. Once you get jetting close…you can watch it move back and forth with jet changes.
You can only get accurate test results by running WOT and pulling the engine kill.
Piston wash is exactly that..un-burned fuel..cleaning the top of the piston. In older designed motors…you will see a lot of wash per the first link..which I think is in-correct…not an issue at this time.
You usually see more piston wash after you get it back from being modified...
E.G. we would tune a YZ125 with the two white marks on the intake side…of the piston...not bad…
Our latest –heavy involvement - was with a 125 cc. 13,500 rpm 42 HP shifter kart engine. It had basically no wash…you had to look very close at the piston rim for slight discoloration… you had to look really hard.
Anothor complicated way is to check the inside of the piston…dark deposit there (bottom of the crown) shows a lean condition.
My favourite check..is the side electrode on the plug. You can watch it change…you want the last half of it dark…and the half closest to the centre electrode lighter. Once you get jetting close…you can watch it move back and forth with jet changes.
You can only get accurate test results by running WOT and pulling the engine kill.