520R SV build has commenced

[JohnCh]

8 hours ago, Austin David said:

@JohnCh what model fuel pump did you end up with?  

 

I installed the Walbro GSS342.

[Austin David]

awesome!  The literature wasn't clear if that pump was a true positive displacement or not.  On inspection I can clearly see it has their "gerotor" internals, and looks like a check valve up top also.  Thanks!

[JohnCh]

Time for an update given it's tied to one of the modifications performed during the original build. When I redesigned the fuel system, I knew there was a risk the 3D printed lid which seals the tank and mounts the various bits, might eventually leach fuel through the layer lines. Although it worked fine for nearly 3 years and over 3500 miles, it eventually started seeping after sitting for a few days with a very full tank.

 

 

The easiest fix was to reprint the lid, then coat the underside with a plastic fuel tank sealant. The other option was to have it printed on a commercial Multi Jet Fusion printer that fuses Nylon powder rather than Nylon filament, then have it vapor smoothed. That latter process melts the outer surface, primarily to provide a glossy finish, but with the side benefit for me of closing off micropores on the surface, thus further improving the water resistance. In theory, that combination is effectively waterproof and still resistant to E10 fuel. Since I was curious about MFJ printing, and I wasn't certain how well the coating would hold up, I decided to go that route. This was also an opportunity to make a minor design change to the lid that would make future removal much easier.

 

Underside of new MJF printed lid:

 

Fuel assembly bits attached and ready for installation:

 

While it was apart, I decided to tackle the Centroid capacitance fuel level sensor which has never worked well. Although I used an earlier version of that sensor in the Westfield with great success, the newer versions feature auto rather than manual calibration. This is to compensate for the significant capacitance differences between E10 and E0 fuel for those people who switch between the two. Their auto-cal feature has a trigger point at the top of the tube that resets the 5V capacitance map point every time the fuel reaches that level and the ignition is cycled (i.e. as when filling up at the gas station) thus optimizing for the type of fuel currently in the tank.

 

With everything apart, I messed around with the sensor using a topped up gas can and a multimeter. After taking a few readings, I triggered the auto-cal function and retested everything. It is now correctly outputting 0-5V as expected. It looks like the issue was either that the trigger point was never reached when filling the tank, or the empty calibration was faulty out of the box. As a result, the sensor never had an accurate sense of remaining capacity. If my multimeter readings are to be believed — checking at full empty and half a can — this is now resolved. A few tanks should tell me if this is accurate or just wishful thinking on my part.