bc.gold 3,403 #1 Posted February 14, 2019 (edited) Credits Brian Miller you can read the full article here. http://gardentractorpullingtips.com/carbfuel.htm The Miller site offers offshore carbs with adjustable needle valves, rebuilt OEM carbs, floats, needle valve replacement throttle shafts and much more. Walbro WHG #52, #60 and #64 carburetors with a fixed/non-adjustable main jet are designed with emission controls in mind to run leaner to create less air pollution. However, the main problem with most Walbros having a fixed/non-adjustable main jet is during cooler weather operation. During cool weather, and running at 3,200 RPM, the engine will sometimes run too lean on fuel and operate erratically. To fix this, first of all, make sure the hole (orifice) in the main jet is not partially clogged. If it is, use a carburetor jet cleaner wire set or an oxy-acetylene welding torch tip cleaner to clear any debris that may be lodged in the hole. Then use 150± PSI compressed air to clear out any dirt/debris. If the engine still runs too lean on fuel, simply enlarge the hole (orifice) in the main jet a few thousandths of an inch. Then use 150± PSI compressed air to clear out any metal particles. Be careful not to enlarge the hole (orifice) in the main jet too much, or the engine will run rich on fuel! The hole (orifice) diameter in the OEM factory main jet for 100% gasoline is 3/64" (.047"). If necessary, enlarge the main jet and fuel inlet holes with a #55 (.052") drill bit. That's a .0052" difference. After doing this, for cool weather, the engine should run better, last longer and produce more power. But don't enlarge the hole (orifice) in the main jet too much! A too big of a hole (orifice) will cause an engine to run too rich on fuel, making it blow black smoke out the exhaust and possibly fouling the spark plug. If the hole (orifice) is made too large, the carburetor will be useless for gasoline, and E85 fuel must be used. But if an engine is going to be used only during warm weather and if it runs okay [during warm weather], don't enlarge the hole (orifice) in the main jet. On the newer carburetors with a fixed/non-adjustable main jet, the hole (orifice) in the main jet may need to be enlarged .002"-.003" to give the engine a little more fuel so it'll run better at higher RPM. Otherwise, the engine could "burn up" or wear out prematurely due to the lean air/fuel mixture. I have an assortment of tiny drill bits that I use on our customer's lawn & garden equipment carburetors. Edited February 14, 2019 by bcgold 1 Share this post Link to post Share on other sites
