1950’s E/J pressure fuel line to fuel pump w/bypass cover

[SHELL KOTTKAMP]

Considering having two of my 1958 Johnson 7.5hp’s converted from double pressure fuel line to a single fuel line w/fuel pump.  I remember reading where there was some discussion on the factory original covers with their curved inner wall performing better than some of the aftermarket flat surface bypass covers.  Is there any thoughts on this?  Seems if there is a difference in performance I would just remain with the factory double pressure line set-up .  Thanks, Shell in Oregon.

[crosbyman]

never heard about flat bypass covers.  why not just use the air pressure nipple and just mount the pump somewhere if you are worried. You can also just drill a pulse hole on  the bypasscover  and  mount the pump on it if is  the ones with the moldings all ready for a pump.  . This is the cleanest method    just plug the air nipple behind the carb.  I would not worry to much on the “performance”  of a 60+ year old engine.

another  option is drill the bypass cover  and  install  elbow to get a pulse line. mount the pump somewhere .

I have done various options and  I found the best  one to be  pump  on a plate over the bypass cover.  Jst use longer bolts  and  off-set the pump  to fit.  drill both the  bypass cover and plate to allow pulses to reach the pump…. centered with the plate hole.

 

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1 user thanked author for this post.

Gary H.

[frankr]

The original covers with a curved inner wall directs the incoming air/fuel mix into the intake ports.
Replacing that with just a flat plate would result in two results: 1st, you would lose the flow deflector.
2nd, it would eliminate the hunk of metal that the flow deflector was made of. That would reduce crankcase compression.
But,I must admit that this is the first time that I’ve heard if anybody noticing the difference.

[SHELL KOTTKAMP]

Thank you Frank for your response, that I believe is the thread I saw years back, i.e., reduced performance.  My uneducated guess is the engineers at OMC had the inside of the bypass cover casted with that curve just for the reasons you mentioned.  I’ll see if I can find that thread.

[SHELL KOTTKAMP]

Here’s one thread on this subject.  https://www.aomci.org/forums/topic/qd-20-conversion-to-fuel-pump/

[RICHARD A. WHITE]

I, at one time, mounted a flat plate to the outside of a normal bypass cover, with a hole drilled thru to allow the movement of pressure.

 

I filled the outside cavity of the bypass cover with JB weld to make it easier for the plate to seal against the cover, the plate had the mounting holes for the fuel pump in it so we were good to go. I suppose I could have just made a gasket but what fun is there in that..lol

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[Fastwin18]

RICHARD A. WHITE wrote:

I, at one time, mounted a flat plate to the outside of a normal bypass cover, with a hole drilled thru to allow the movement of pressure.

 

I filled the outside cavity of the bypass cover with JB weld to make it easier for the plate to seal against the cover, the plate had the mounting holes for the fuel pump in it so we were good to go. I suppose I could have just made a gasket but what fun is there in that..lol

I’ve converted several by filling the outside of the original cover with jb weld. Then use a belt sander to make sure any excess jb weld is removed and the surface is flat. Finally drill 3 holes and tap the outer 2 to match the thread of the screws for the pump.
Worked just fine for me.

[Author]

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