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Old 10-18-2021, 09:59 PM
svsonora svsonora is offline
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Help me dial in my tuning (carbs/timing)

Current engine has:
Ignitor ignition kit
adjustable main and idle jet
aftermarket 55amp alternator

All else is stock.
Last friday my engine was running badly. I only managed 1400rpms, and only on my bank 1 (starter bank) which was close to fully charged. Whenever I switched to my house bank, which I had spent to 85% charge according to my victron moniter, it would bog down and die. Combined with the colder temps (first real fall night sail), subobtimal timing (I had that problem where I couldn't get optimal timing set due to alternator pulley clearance), I don't think the engine was making enough power to push the boat as well as drive the alternator.

Today I finally moved the distributor a tooth over and was able to get a good dynamic timing set. I pushed the throttle up to cruise settings, while in gear, tied up to my dock. I moved the distribution back and forth until highest RPMs reached, at about 1700rpms. Engine seemed to run better.

I next tuned the idle - I aimed for a 900rpm idle while I was in gear. I got it close, but its real rough. Whenever I ran the throttle up and back down, it would settle below the set idle RPMs and start to bog. I ended up going for 950-975 and the engine idled without dying. Out of gear, the engine idles at around 1400rpms.

Next I started to work on the high mixture. This is where it gets trippy - the main jet setting seemed to have very little effect on the RPMs, unless I closed it all the way (then the RPMs would drop). I managed to get it so that at max throttle, it would rev to 1900-2000rpms (seemed to not make up its mind where to be). This is more than I've ever seen and I was pretty pleased. With my prop, 1700rpms is considered decent.

All in all, engine runs fine now in either bank and the alternator is putting out 14 volts as designed.

I'm thinking about going back to a fixed jet and doing yet another full carb rebuild.

Any advice on my rough /random idle situation? And whats going on with my adjustable main?
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1975 Bristol 30 Sonora del Viento

Last edited by svsonora; 10-18-2021 at 10:10 PM.
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