Re: 1956 Johnson 30 hp fuel pump conversion and electric start
Post a pic of the bypass covers on your motor. I think that they are the same ones as the '57 and '58 motors (35hp), but I'm not sure. If they are, putting a stock part on your motor is easy and I recommend it over the Mikuni.
The Mikuni pumps are normally used to convert 5.5hp OMC motors to a fuel pump system, rather than a pressure system. They are good pumps and work well in that application, because the 5.5hp motors don't have bypass covers to mount te pumps on and tap a suction/pressure source.
On the larger engines, the bypass covers are available and depending on the model/year, already have the mounting bosses and raised section to drill for the pulse air.
Here's a couple of different ways to do it. The first photo is one of my '58 Bigtwins, which has an original bypass cover on it. I mounted the pump upside down, because it is large enough to hit the throttle control rod, if mounted right side up. If you go with this option, you must remove the bypass cover from the engine in order to prevent metal shavings from getting inside of it, when drilling the suction/pulse hole. Be sure to get a new gasket for the cover, before taking it off of the motor. When drilling the mountng bosses, be sure to drill them dead center and do not go all the way through. You will need a drill bit and tap that are matched for the stock screw that is used and the tap must have a flat end on it, so that you can tap the hole as close to the bottom of the hole as possible.
The second photo is of my other Bigtwin, which has a Johnson 33hp bypass cover on it. The pump is the same as my other motor, but will fit right side up, because the mounting bosses on the 28hp and 33hp motors are very slightly lower than the older motors.
As F_R educated me on some time ago, you can mount an OMC pump on the older covers, if you get the right one. There is a pump that looks just like mine, but is not as tall. That pump works just fine, but I'm not sure of availabilty.
As a final point, be aware that part of this conversion involves removing the pressure nipple from the face of the intake manifold, under the carb. You must replace it with a flathead or panhead, stainless
of the same size, thread count and reach, as the nipple. If you try to use a screw that is too long, you will hit the reed plate, which is right behind the position of the nipple/screw. Be sure, also, to use a crush washer with the screw, to ge a good seal. Failure to complete this entire step, will result in fuel/oilmixture being sprayed all over the interior of the cowl.
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