Motor rough and low power in gear

[jim.facey@gmail.com]

Hi all, last Sunday my motor, which was running fine, suddenly lost power, I tried shifting to neutral then reverse to clear any seaweed on the prop, no difference. It revs fine in neutral but not in gear, it’s sounds like it’s going to stall but doesn’t. I don’t have much time to troubleshoot as I am unable to spend much time in Maine where the boat lives this year. Have electronic ignition, and the hot exhaust was replaced four years ago. Could this be the advance weights in the bottom f the distributor? I just found out that they exist, and have not serviced them. Does not seem to be fuel related, unless carb clog? Would it rev in neutral? Any ideas on where to look?

[capnward]

carb clog is a common issue

If it isn't something on the prop, it sounds to me like it's fuel related, and some stuff got into the jets in the carb. I had a partially clogged idle jet once, which made the engine lose power and run rough under load. My experience is most problems are fuel related. I would remove the carburetor and check for crud in the jets, especially the main jet, the idle jet and float valve, clean the carb, put it back together with new gaskets. And check for clogs in the small holes in the side of the throttle throat above the butterfly. Also I would replace the fuel filters. It may be if you have an adjustable main jet, you can turn it in all the way and then back it off 1.5 turns. This may clear a clog in the jet without removing it. Make sure the flyweights are moving right. If you turn the rotor clockwise and feel the spring resistance, and the rotor snaps back when you release it, they are probably ok.

[Al Schober]

After 30 years with an A4, most issues seem to be fuel related. Nothing to do with the engine, but stuff like alcohol gas, old fuel lines, filters that corrode and send corrosion products downstream, etc. The A4 will run on any kind of gas - it WILL NOT run on water.
You need a clean fuel tank, primary (before fuel pump) filter (I used a Racor water separating unit), and a secondary filter right before the carb. Check the filters with a magnet - if a magnet sticks, expect trouble. Very interesting and instructive to cut open old filters and see how they look.
A pressure gauge on the carb inlet is a good thing. Tells you that your fuel system is trying to send fuel to the carb.
I like the adjustable main jet. If it gets clogged, you can often clear it just by threading it in and out a couple of times.
A spare carb is something I learned to keep aboard. Rebuild it at home, bag it, store it aboard. When you get a carb issue, swap it out (repeat as necessary). I modified my carbs to have studs - easier installation.