External pulse port for the Top 80
by Had Robinson
Nearly all paramotors have an external pulse port (PP) but not the Top 80. The PP is a passageway (internal or external) that connects the crankcase with the carburetor fuel pump. The pulse waves generated in the crankcase are used to power the pump. The Top 80 has an internal PP that goes from the crankcase, through the reed valve body, and then to a small hole on the engine-side face of the carburetor. This small hole is connected to the fuel pump inside the carburetor.
What is the need for an external PP on the Top 80? An external pulse port has a larger diameter which better transmits the pulses to the pump. This is why most paramotors have an external PP and carburetors with an external PP fitting. Also, an external PP can drive an auxiliary fuel pump or another pulse driven accessory. When an engine is operated in very cold or very hot conditions there are more problems with fuel delivery.
Modest mechanical skills are needed to drill and tap a hole in the Top 80 crankcase. There are a number of online videos which can help if you have never made threads on anything, especially in aluminum. The metric equivalent of the 1/4" barb is the 6mm barb though the latter does not come with a sealing O ring. If a metric barb is used, the appropriate metric drill and tap must be used.
Special tools and parts needed
- 1/4" barb x 10-32 UNF male adapter
- 10-32 tap
- #21 or 5/32" bit (hole size for the tap)
- 3/32" bit
- RectorSeal #5 pipe thread sealant or equivalent
- cutting oil
- Remove the air box and carburetor. You can let the carburetor safely hang by the throttle cable
- Remove the reed valve body
- Remove the redrive
- Mark a spot with a pencil on the side of the crankcase 12mm from the top and 16mm from the end of the opening for the reed valve body and the carburetor. The photo below
shows the approximate location of where the external pulse port is located. The location does not have to precise because the fitting does not enter the reed valve cavity.
- Stuff a clean paper-towel tightly into the reed valve body opening, right up against the crankshaft. You want to prevent stray aluminum chips from getting into the crankcase.
When the drill bit enters the reed valve body cavity, the paper-towel should clear it on the inside. Put a piece of duct tape or masking tape on the body of the cavity to catch
any shavings that enter the cavity.
- Use the 3/32" bit to drill a pilot hole in the crankcase. Drill the hole as perpendicular to the surface as possible. WHEN DRILLING ALUMINUM OR ANY METAL, PRESS THE BIT HARD
AGAINST THE SURFACE AND RUN THE DRILL SLOWLY, 100-200 RPM. Speed ruins bits! Note: if you have a drill press it is much easier to make the hole. I have used a hand
drill here for convenience. Most pilots do not have a drill press.
- Use the #21 or 5/32" bit to enlarge the hole to the correct size for the tap.
- Tap the hole. Push the tap into the hole, coat the cutting surfaces with cutting oil, and gently turn it to begin the threads. Cutting oil must be used, not ordinary
oil. If cutting oil is not used, the aluminum chips will quickly seize the tap and gall the aluminum threads.
- Clean the threads in the new hole by running the tap in and then out, clean the tap with air, and do it again a few times. Use brake cleaner to clean the new threaded hole.
Tilt the cavity down a bit and use brake cleaner to clean the cavity of all oil and chips. When done, pull out the paper-towel that protected the crankshaft cavity.
- Install the male adapter. Coat the threads with the RectorSeal. Do not use Teflon tape as it can get loose and clog the holes in the crankcase that bring oil to the
- Reassembly is the reverse. When installing the reed valve body, follow the directions given in step #5 on the reed valve page. Do not over-tighten the nuts holding the carburetor and air box onto the engine. See the Top 80 specs page for torque help.