Return to the home page...

Go Back   Moyer Marine Atomic 4 Community - Home of the Afourians > Discussion Topics > Fuel System

Thread Tools Display Modes
  #1   IP:
Old 10-18-2021, 09:59 PM
svsonora svsonora is offline
Senior Member
Join Date: Sep 2020
Location: Washington DC area
Posts: 22
Thanks: 1
Thanked 8 Times in 3 Posts
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?
1975 Bristol 30 Sonora del Viento

Last edited by svsonora; 10-18-2021 at 10:10 PM.
Reply With Quote
The Following User Says Thank You to svsonora For This Useful Post:
TimBSmith (10-19-2021)
  #2   IP:
Old 10-19-2021, 01:32 AM
Afourian MVP, Professor Emeritus
Join Date: Nov 2008
Posts: 3,489
Thanks: 53
Thanked 837 Times in 612 Posts
Try servicing the advance (under the distributor breaker plate).
You will probably need to reset the timing since the advance influences timing.

Reply With Quote
The Following User Says Thank You to JOHN COOKSON For This Useful Post:
Sam (10-19-2021)
  #3   IP:
Old 10-21-2021, 04:26 AM
svsonora svsonora is offline
Senior Member
Join Date: Sep 2020
Location: Washington DC area
Posts: 22
Thanks: 1
Thanked 8 Times in 3 Posts
I took the plate off when I moved the dizzy a tooth or two CCW. I also lubed up the mechanism underneath. The timing was set again after that, dynamically.
1975 Bristol 30 Sonora del Viento
Reply With Quote

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Rig Tuning Info GMcK106 Tartan 1 08-04-2013 10:41 PM

All times are GMT -4. The time now is 10:04 PM.

Powered by vBulletin® Version 3.8.9
Copyright ©2000 - 2021, vBulletin Solutions, Inc.

Universal® is a registered trademark of Westerbeke Corporation

Copyright © 2004-2021 Moyer Marine Inc.

All Rights Reserved