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 The Walbro W3B carb 
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Joined: Sat Feb 28, 2009 11:19 pm
Posts: 539
Location: Columbus, Ohio
Class: Jr. Clone
Chassis: Bandit
Engine: 4 cycle Clone
Post The Walbro W3B carb
I posted in another post about the pro's and con's of low pop off vs. high pop off, but for those who don't know how to set the pop off, I'll run thru it for you.

1. Remove the carb from the engine.
2. Remove the 4 screws holding on the metering side cover plate.
(distinguishable from the inlet side cover by the small hole in the center)
3. Remove the high speed needle.
4. Hook up a pressure tester to the fuel inlet on the carb.
5. Inside the carb, you'll see a small hinged arm that rotates around a small rod. Beneath this arm(called the fulcrum arm) on the end closest to the center of the carb is a very small spring. On the other end of the arm is a small inlet needle. All this is held down by a small flat-head screw.
6. Pour a small amount of fluid around the inlet needle(Some people use WD-40, some use the fuel that they run. All you need to do in reality is just get the needle seat wet.)
7. Lay the carb down on a table with the inlet stuff pointed away from your eyes ( or cover it with a cloth to catch the spray)
8. Squeeze the bulb to build up pressure in the carb, while watching the dial face. The carb should hold pressure as you work your way up the scale. You're listening for the inlet needle to un-seat, or "pop". When it does pop, it'll spray out what ever liquid you had in the carb. So be careful not to get it on your clothes or in your eyes, etc.
9. The pressure that the needle un-seats is the pop off pressure. It should be in the vicinity of 7-12 lbs. (a new spring, uncompressed, will usually be in the 10-12 lb. range. An old needle is less due to fatigue).


a. Remove the small screw holding the inlet needle fulcrum arm spring stuff.(getting the spring out can be a little tricky, so be patient.)
b. To lower pop off pressure, squeeze the spring between your fingers several times. Re-insert the spring, tighten everything up and repeat steps 6-8. Adjust as necessary. Some people cut the spring, but I don't like to do that, squeezing the spring is more desirable.
c. To raise the pop off pressure, stretch the spring slightly, or even better...use a new spring.

I'll come back later and tell you how to set the fulcrum height on the carb.
Hope this helps.

"It's not in my nature to spend money sparingly when I'm having a good time"

Thu Aug 08, 2013 12:32 pm
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