45 HP - Excessive Fuel Problem

[74 Sport Fury]

Own a "new" 16 ft 1974 Chrysler Sport Fury with a 74 Chrysler 45 HP outboard. Engine starts great (even with choke not working - wide open). Runs good at idle but bogs down when I try to give it gas (even when warmed up). 2000 rpm is the best that I can get. On our first test run went through 6 gallons of gas in 45 minutes (note, I have two new tanks so I was not stuck). Interesting note, as we were running out of gas the RPM started climbing rapidly. Hit 3000 rpm plus in a couple of seconds then engine died. I concluded that as we were running out of gas it leaned out the air/fuel mixture to the correct ratio so the engine started to take off until it ran out of gas completely. When I took the boat out of the water and lowered the engine I noticed quite a bit of fuel coming out of the exhaust port on the engine along with some water.

After doing some reading I concluded a stuck needle valve and/or gas saturated float in the carb. Purchased carb rebuild kit from iboat and overhauled the carb. Rebuild went well. I even tried blowing through the gas infeed line to the carborator while I manually moved the float up and down and it cut off the air flow as I raised the float. Tested the float in a cup of fuel and as I raised the cup of fuel the float did raise the needle valve and stop air flow (I was still blowing into the carb infeed line). Adjusted the float to factory specs (I do have a manual - Clymer) and gave it another try. Similar results to above. I then concluded that perhaps I had the float set too high. Lowered float and changed out spark plugs (just to be sure). Third try, same results as above. However, on this test I had wife drive and I pinched the gas line (restricting gas flow to the fuel pump). The engine TOOK OFF! 4000 rpm plus no problem as long as I restricted the fuel flow to the fuel pump.

Now I am stumped. I'm not sure what else to do to the carb so started looking at the fuel pump in my manual. Apparently I have a type A 2 stage pump. Fuel is pumped via crankcase pressure, a diaphragm, and reed "valves". I'm now wondering if diaphragm was leaking if this would allow gas to move into the engine (I cannot find anything in my manual covering this possibility). Guess I want some feedback before tearing into the fuel pump.

By the way, if it is the carb I suspect a replacement will be hard to find. Is it possible to install a different carb on this engine (certainly is on car engines)? If so, any suggestions on how I would go about identifying a replacement?

Thank you in advance for your help.

 

[roscoe]

Re: 45 HP - Excessive Fuel Problem

Welcome to iboats.

Reset the float to correct setting if you haven't already.

Go get the fuel pump rebuild kit. You probably will only find the diaphragms and o-rings, but not the check valves. hopefully they are ok.

Yes, a tear or pin holes in the diaphragm will allow fuel to flow into the powerhead and flood out the lower cylinder.

This is not an uncommon problem given the age of the motor, and the alcohol in today's gasoline. The new diaphragms do withstand the alcohol.

You can get the kit from many online dealers, or a Mercury dealer, or NAPA.

let us know if this solves the issue.

 

[74 Sport Fury]

Re: 45 HP - Excessive Fuel Problem

Thank you Rosco. It's really good to have confirmation that a hole in the fuel pump diaphragm could cause the problems that I am experiencing. Based on my "pinched fuel line" test I am really optimistic that once I solve the excessive fuel issue this motor may have some life left in it. I'll repost once I rebuild the fuel pump.

 

[74 Sport Fury]

Re: 45 HP - Excessive Fuel Problem

Rosco, you nailed it! Huge hole. Rebuild took about 15 minutes and engine runs GREAT! Fuel consumption seems quite reasonable now. Thank you so much for confirming my issue.

 

[roscoe]

Re: 45 HP - Excessive Fuel Problem

Made easy by the detailed account of symptoms you provided.
Happy Boating.