I am pleased to report again that I have added a fuel pump, and have re-purposed my return air line to the gas tank as a return gas line instead. Here is what I did…
The first decision was how I was going to get the pulse for the fuel pump. There were three options that I became aware of:
1) Convert the air return line for the gas tank into a fuel pump pulse. I didn’t really care for this option, because it was relatively involved. It meant digging into the air intake manifold and blocking a passage, removing parts, etc. This is the only option on some motors, but I had two other options, so this was my last choice. This process is also not easily reversible. You also have to find a place to mount the fuel pump as well.
2) Purchase or manufacture a plate to cover one of the bypass covers on the side of the motor. These plates are available to purchase on eBay. They don’t look that hard to make. The fuel pump mounts directly to the plate. I have plenty of aluminum plate sitting in the garage that could easily be converted. This was my second choice.
3) In this YouTube video from “Brandon’s Garage” https://www.youtube.com/watch?v=FlV8zjm4Y-A he suggests finding a later model bypass cover for your motor that has provisions for a fuel pump, but that fits your motor. I went on the hunt for such an option for my Johnson RD-15. Fortunately, I found this thread here https://www.aomci.org/forums/topic/will-this-fuel-pump-work-on-a-1955-johnson-25-hp-rde-17/ that showed exactly just that. All I had to do is find Johnson part 304646. They were quite pricey on eBay, WAY more than the aluminum conversion kit plates on eBay, but, marineengine.com had several in stock, for under $7. I was sold I bought a 304646.
The old bypass cover is shown above, and the new one is shown below, including the hole for the pulses to reach the fuel pump, and the mounting holes.
Next I needed a fuel pump.
As mentioned above in this thread, there were a few options. I was initially excited to find $12 pumps with 5 stars on Amazon, but quickly realized that they were Chinese knock-off pumps. Some people were having issues with them. They said they looked similar from the outside, but were not the same internally as the OEM pumps. I decided it was worth it to get something better.
I really wanted to get one of the smaller, less expensive OEM pumps, but after reading several threads on various forums, the smaller pumps are really only good through 20HP, and can’t handle the demand for a 25hp motor. Especially the older, gas hungry RD-15’s. I decided I should definitely get a pump specifically designed for 25hp or larger. I needed something that fit on the bypass cover, but wanted something relatively recent that would be easy and inexpensive to get replacement parts for.
For 25hp+, Sierra pumps were about $75, and OEM pumps were $90-$115. Yikes! When I found I could purchase a used OEM pump for about $5 on eBay, and a rebuild kit for $18. Perfect. I settled on Johnson pump 438556. I followed the tutorial on Dangar Marine on how to rebuild the pump. https://www.youtube.com/watch?v=bPCHbov4RuY His video was great, and I rebuilt the pump in less than a half hour.
I found that the fuel pump had much larger hose connectors than the rest of the engine. This fuel pump is good for up to 140hp. It has both 5/16 and 3/8 hose connectors on it. I went and bought a foot of 5/16 fuel line at O’reilly Auto Parts, and two hose reducer barb fittings on Amazon. The carburetor and quick-connectors both have 3/16 barbs. I was able to get the 5/16 fuel line on the 3/8 barb on the fuel pump. It was tight, but it fit. Same with fitting the 1/8 fuel line from the nipple on the cover plate to the 3/16 connector on the tank quick connect. The 1/8′” hose will fit on the 3/16″ barb, but it is tight.
A few hose clamps later, and it was all mounted and ready. Before you ask… yes I put hose clamps on the fuel pump. I just didn’t have a better picture of what I did later in the process. It was dark and I had already put the cover back on. Taking the covers off the RD-15 is a huge pain!
I then unattached the return fuel line from the gas can and started up the engine. It ran great, and gas was flowing out of the return air (now fuel) line as hoped.
I ran it in a barrel for a good 10 minutes to make sure that everything was working properly.
I then took it out to the lake yesterday, and ran it at full throttle for a few miles and it all seemed to work great. No extra gas cans, no oil slick on the water. Just a perfectly functioning motor, top speed and idle seemed unaffected.
I couldn’t be any happier. Thanks again everybody for your encouragement and help.
