2010-03-18 See also
Membrane Carburetor Overview
Walbro PPG Repair Kits Guide
The best thing to do if you suspect a carburetor problem is
replace the carb with new. That way you can rule out the carb as a
problem right away. Then, if you want to fix your carb, put it back on
and start troubleshooting--at least now you know it's the carb.
Two carb types are common in paramotors: membrane
(Walbro, Tillutson), and float bowl (Bing). Troubleshooting or Tuning each type is completely different. For that
matter, there are significant differences in tuning each model and
A carburetor endeavors to deliver the correct fuel/air mixture to the
motor through the entire throttle range. In a perfect world, carbs would
be made specifically for a motor but that would be cost-prohibitive so
engine makers select one that's best suited to their engine.
A few engine makers do some modifications to their carbs so be
careful and putting a stock replacement on the motor will degrade the
Problems and Solutions
(left) WG-8 carb used on the Top 80 engine. It has only one
mixture adjustment needle, the other is merely an idle stop.
1. Fuel/Air Mixture related problems. Tuning means making whatever adjustments are required to get the
mixture correct through the entire throttle range. It also includes
replacing membranes, cleaning filters when applicable and insuring the
pop-off pressure is correct. Before tuning, make sure any fuel filters
or screens are clean and the reed valves are in good shape since
problems with the reed valves can appear to be carburetor problems.
2. If there is a bubble in the fuel line right as it enters the carb,
first replace the fuel line to eliminate that as the cause. If the
bubble is still there, there's a problem in the carb. Install a rebuild
kit whose most important part is the rubber membrane. Small, nearly
invisible holes, can allow air where it's not supposed to be. If there's
still air, replace the carb.