2engsout
Posts: 119
Joined: 2/8/2003
From: omaha, NE,
Status: offline
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Hi Guys, I am the ONLY person I know that even has a popoff gauge !! I use it all the time to tune the midrange mixures on my Walbro's and alot of my buddys carbs that need it ! When the carb butterfly swings past the 3rd idle transfer hole (located in the venturi) at about 35% throttle opening, no more fuel enters the venturi ( only air), UNTIL, the popoff occurs, which then allows fuel to begin flowing thru the high speed curcuit and out the high speed orifice downstream of the idle transfer holes. If your popoff is set too high for your particular engine / prop combo, you could be too lean between 35% and 60% throttle opening. After you have set the low speed needle for good response, and then the engine really smooths out and looses throttle response at 1/2 throttle, ( blipping the throttle from 1/2 to 3/4 throttle and the carb arm moves without an increase in rpms), your too lean at 1/2 throttle. Your full throttle needle setting could be just fine, but your too lean at 1/2 throttle. Since you don't have a needle for your 1/2 throttle setting, you need to lower the popoff pressure. That is done by shortning the spring under the metering arm, BUT , you 1st need to check what you have for a popoff as a baseline. , I have seen alot of carbs popoff in excess of 30lbs., and everyone of those engines were too lean at 1/2 throttle. My G-45's like about a 22lb. popoff. My G-38's like 15lbs. Every gas engine prop combo, is going to require something different to be just right. I set my mixures to achive an intermitant 4 stroke blip ( 1 blip approx every 2 seconds) at all constant power settings. This is something you have to listen for, and when you are there, you will ALWAYS know exactly where your mixure setting is. There is a narrow window of smooth engine operation. If its smooth, with your throttle held at a constant setting, you can't tell if your on the lean edge of the window, ( on the verge of a flat spot), or the rich edge of the window, ( on the verge of a 4 stroke blip). With your carb set with an intermitant 4 stroke blip, you will always have good throttle response and you will always know exactly where your mixure is because it will tell you every 2 seconds......... EC Distributing sells a 0-30lb. gauge for about $35.00 phone # is 615-446-6807....Everybody is going to have a different tuning method, but this method has never let me down....Hope this helps guys.......Rick Simmons
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All Forums >> Glow Engines, Gas Engines, Fuel & Mfg Support Forums >> Gas Engines >> Setting Up The Fulcrum Arm on a Walbro Carb 
Setting Up The Fulcrum Arm on a Walbro Carb - 
