Engine failure at low rpm

Macdiver · Post by **Macdiver** » Thu Sep 15, 2011 10:25 am

The day started out normally with my 83 trojan with chrysler 318s. After running a short distance at about 2500 rpm and slowing down to about 800 rpm The starboard engine shut down. I could restart at about 1200 rpm and keep it running but when reduced to below 1000 rpm the engine would die. Didn't find any water in filter. Left it overnight and it was OK the next day and ran at low rpm (600). The is the second time this has happened after replacing the fuel filter the first time. Could it be just water in the gas or could it be related to the distributor cap or ignition? Has anyone experienced this senario? Any help and/or suggestions would be appreciated. The only filter I am in the process of replacing is the in-line filter, when I can get one. Thanks,

Macdiver

Molly Too · Post by **Molly Too** » Thu Sep 15, 2011 10:56 am

Amazing....I just spoke to Paul (Prowlerfish) yesterday as i had the exact same problem on Sunday, right as i was entering the Marina seawall. There i was trying to stop circling in the fairway...boy that got the adrenalin pumping.

Paul said sounds like carb issue, but to begin with, check entire fuel flow system. Besides the fuel tank line filters, there's one at the carb inlet too. Also, make sure the flame arresters are clean and free flowing.

It'll be the weekend before I can get to it...

Nancy · Post by **Nancy** » Thu Sep 15, 2011 7:50 pm

We chased that exact problem early in the season on our 228 Mercruisers. It was a bad early season - engines were stalling at high r's and low r's. First thing we did was rebuild carburetors. That fixed the high rpm problem, but they were still stalling intermittently at 800 rpm's - just like you - at the worst possible time as we were entering the fairway. Docking that boat on one engine is not fun. (The wind was blowing so hard one time that we couldn't get to our slip - had to go to a friend's dock across the way.)

We'd already gone through the fuel system. Everything OK there, so we did a full tuneup including replacing the coils. Problem solved. The general consensus is that it was the coils. Really annoying - they were only two years old and the previous ones were at least 11 years old. We had changed them for good measure two years ago and probably should have left the old ones in place.

The engines run beautifully now! They should with all those new parts!

Nancy

Big D · Post by **Big D** » Thu Sep 15, 2011 10:23 pm

Check the voltage you're getting to your coil at lower RPM. You should have battery voltage (12+) or around 10 volts if a ballast resistor is used. Check alternator output at lower RPM also. When it quits next time, pull a plug right away and check for spark. This will tell you if it's ignition related or not. Could be fuel system, could be ignition.