phughes69

I have twin 470's with 2bbl Rochester carbs and still the points distributors. Just recently I had a problem with no fuel going to the port carb. Traced it down to a plugged fuel water seperator. I replaced both of them. Now the other day after a short cruise the starboard engine stalls out at idle speeds. The engine ran fine the weekend before, then I changed the fuel water seperators (10 micron filters). I took the boat out for a short cruise. Engines started up just fine and idled good (about 20 minutes), then ran good up on plane with no hesitation for about 10 minutes. Slowed down to idle speed and once the starboard engine dipped below 2000 rpm it just stalled out. I pumped the gas about 10 times and cranked it over, it kicked and then eventually started when I had the throttle wide open. It did sputter back thru the carb though. I was able to get it to run if I kept the rpm above 2000. I got the boat up on plane with no problem or hesitation or sputtering. but the same thing once I got into the no wake zone, engine dies below 2000 rpm and wont restart unless I pump the throttle about 10 times and hold it wide open, then it sputters and kicks but no start. I tried the engine again the following day and it starts up just fine when cold, but after about 5 minutes it dies again. I have verified that the choke plate is opening and wide open when it was dieing out. The engine has a new set of points, condenser, cap, rotor, and plugs, check the dwell and timing. from this year. Both engines have the same dwell and timing. Both engines draw fuel from the same tank and the fuel is about a week old from a local marina gas dock that does a good volume. I just got this boat this summer and have put about 20 hours on it so far. The carbs look new. Any suggestions on what to check? I am going to try to verify that the timing has not moved. The new fuel water seperator has 30 minutes of run time on it.

Mr Maine

Sounds like the idle circuit is clogged. Have you tried backing out the idle mixture screws? Probably runs ok at idle initially because the choke is close which makes it richer at idle.

BUP

iTrader: (9)

Just to make sure You have the 3.7 Mercruisers - the 4 banger all aluminum block with the Ford 460 cast iron head ? Correct

Is that motor still charging by the Stator or does it have the conversion Alternator kit installed ? Voltage output is especially at your problem rpm ranges ?

Next is the heads and or block mounting area would warp over time and or corrosion issues from disimulor metals that would cause leaks into the cylinders. Seen many back in the days that would not idle because of small leaks into cylinder(s).

Your fuel pressure testing psi is idle thru out rpms ???

Have you ran this engine on a portable new fuel supply ? To rule out boat side fueling issues ?? Fuel samples from the gas tank are ?

If I remember correctly these carbs very easily forming aluminum oxide because of the new fuel blends in the past years. I would really check to make sure your carb is good with no porosity and all good internal parts plus the correct ones. Possible rebuild and adjustments corrected. IMO carb rebuild and very well needing cleaning

2005 was the last year we totally quit working on these motors.