1968 Renken MerCruiser I/O fuel issues

[Prodigy29]

Hi all

I have been working on my 1968 Renken with a 4cyl Mercruiser with 2 single barrel Carter RBS carbs that were just rebuilt. The issue I am having was that about 2 weeks ago after getting everything back together, the engine would start up and run fine until warmed up. Then it dies and won't start up unless I throttle up to get some gas in the carbs before turning it over. It will not stay running at idle once it is warm. It runs great anywhere above 2000rpm though. Then yesterday I went to work on it and couldn't even get it started. I tried a bunch of things and then noticed that the throttle pump on the carbs were not shooting any fuel in when I manually pressed them down. I was going to pull the carbs again to see if the float was correct but when I disconnected the fuel lines, I noticed there was ZERO fuel in them at all. I then disconnected the line at the pump and there was no fuel in the line at all. Could a bad fuel pump work at higher RPM? I was under the impression that if your fuel pump is going bad, it would die at higher RPM or at WOT but usually run fine at idle? Any thoughts what could be causing the lack of fuel to the carbs? Any suggestions would be helpful!!

 

[kenny nunez]

Try running it with a outboard 6 gallon tank to eliminate the fuel tank and see what happens.

 

[harleyman1975]

How old is the pump? the diaphrams could be rotted or stretched out or have holes in them.

 

[Prodigy29]

The fuel tank is the same age so fairly new. I will try to run it with an outboard tank though to see how that goes.

I was told the fuel pump was replaced about 4 years ago by the prior owner. I just bought it last year so it's hard to tell what was really done. I will pull it this weekend and see what kind of condition it's in.

Thanks for the suggestions!

 

[Rick Stephens]

Do you have a canister fuel filter/water separator inline? I have seen pumps not able to prime is the filter is not filled up before installing.

 

[Prodigy29]

So I replaced the fuel lines this weekend and was able to get it running again.The problem was a clogged vent hose. I have an inline fuel filter installed that you can see the fuel in, it never gets filled up though. I'm not sure if that is normal but it only gets about half full.

I pulled the pump and it is in good condition. No tears or anything that looked like it would be causing any issues.

As for how it is running, It does great when cold. Once it warms up, it has a very hard time keeping an idle(it idles at 1000 rpm) it usually runs for about 5 min then dies. After it dies, it will not start back up without throttling up before trying to start it and then you have to throttle above 3500 rpm for a few seconds before dropping back to idle or it will just die again. Then it will run for a few minutes and die again. Once it is warm, it also dies if i throttle anywhere around 2000 rpm. it sputters up then just dies.

 

[Bondo]

I have an inline fuel filter installed that you can see the fuel in, it never gets filled up though. I'm not sure if that is normal but it only gets about half full.

Ayuh,.... Welcome Aboard,.... Those are completely Illegal on a boat, 'n an explosion hazard,... 'n no, they don't completely fill up,...

It sounds like ya got a possibly pretty boogered up fuel system,....
Insteada movin' willy nilly, why don't ya use the diagnostics talked about above,...
Fuel pumps ain't tested by takin' 'em apart,... ya measure it's pressure, 'n test it's flow,....

By the sounds of it, a full on carb rebuild oughta be step #1,....