Evinrude 7.5 horse fleetwin fuel pump conversion

[andy7918]

I have been working on converting an old pressure tank system evinrude 7.5 horse to a single line fuel pumped system. A little background information on the motor: i was given it for free, basically a barn find i know nothing about it. I was able to get the motor to fire without having the correct pressure fuel tank so i decided it was worth some money and effort to get going as a converted single line system. So far i have replaced the following: fuel hoses, ignition coil, gapped points, lower unit oil, carburetor overhaul, and replaced spark plugs with a J6C. When i took it to a lake to test run it ran fine for a while, but then would stall out at full throttle. I checked the plugs and it appeared to be flooding, but was able to put around the lake no problem at half throttle or less. Today i took the carburetor and intake apart to check my work. Nothing appeared worng with the carburetor, which still has the original cork float. I don't see how that could be the problem as does cork really ever lose its floation properties? More importanly when checking the check valve hole that i had plugged on the intake, my plug appeared to have been too small of diameter and had gotten sucked into the crankcase? It was just as small vacum line cap made of rubber so i wouldn't think it could cause much damage, especially since i had been crusing around the lake on low speed with no plug at all for who knows how long. (surprising motor ran huh?) SO i put a larger plug in there today and fired it up expecting it to run great. The motor smokes like crazy, i couldn't get the rpms up at full throttle and when i checked the plugs they were fouled. I plan on taking it to the lake again and seeing if its just a matter of carb adjustment. Is there anything else that i have failed to check that could be causing the motor to smoke so much and foul the plugs? Could this somehow be a result of the plug getting pulled into the crankcase?

 

[nwcove]

Id be finding that missing plug! Then i would undo the mods that you did to the intake manifold and then do the conversion the easy way......remove one of the bypass covers and drill and tap it for the pump pulse. Jmo

 

[andy7918]

What do you mean by "bypass covers". On this motor the intake between the carburetor and check valves is only one piece.

 

[masterbt]

what is the model number

 

[andy7918]

The serial No. on a metal tag on the side of the transom mount says : 7516-25866

 

[nwcove]

there ^^ is how its typically done the 7.5's and larger motors, the conversion you did is not really wrong, but meant for the 5.5hp's as they dont have removable bypass covers.

 

[andy7918]

But shouldn't it still have worked? That definitely looks like a cleaner way, but with my plug style conversion the pump should still actuate right? What kind of fitting did you use for the pulse? Looks like you replaced some screws that went into the block with longer ones to hold your pump in place? Even if I did move the pulse to the bypass cover I don't see how that would fix the lack of power at full throttle, and the excessive smoke.

 

[nwcove]

where did the plug you used go? cant imagine it getting past the reeds?. where is the pump located?...is it plumbed right? the pulse line should be as short as possible. the way i did the conversion shown in the pics, the original screws worked just fine. the fitting i used was just a hardware store compression fitting, which is not the best way to do the conversion....a proper sized nipple is the better way, but i just use what works for me. your lack of power could be as simple as weak spark, improper hs needle setting, or .....where is the missing plug that you used for the conversion?

 

[andy7918]

The pump is located in the samme place as yours starboard side (behind the gearshift). The pulse line is not as short as possible as the existing fitting that orginally recirculated back to a pressure tank is what i used for my pulse. The pulse fitting & fuel supply are on the port side, and the fuel feed to the carb is comes from the pump back to the port side. I tried to upload some pictures but couldn't not get the file size small enough with microsoft paint. Anyways i ran it in the test tank again today and was able to get the motor to run better. And most importantly to get some high rpms out of it. I need to take it to the lake again to really test it out though.

 

[andy7918]

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[andy7918]

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[andy7918]

view of the pump & plumbing

 

[andy7918]

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[nwcove]

cant see your pic, but the shorter the pulse line the better.do you have access to a tubing bender? set up a photo bucket acct if you want to post pics while the forum "upgrade" is happening.

 

[andy7918]

A little update: I found a pressure tank for 45 bucks and bought it. I reversed my work back to stock, and took the motor to the lake. it runs waay better. I am having a separate issue with oil leaking past the spark plugs and an intermittent misfire at wide open throttle (started a new post), but the motor will get me out on the lake and it trolls great. Also NWCOVE I found the missing plug, when taking it all apart my new one fell into the same crevice in the transom mount as where the old one was hiding...