We have a 1985 Tiara 31 with dual 454 carbureted Crusaders. Most history is unknown. Starboard engine has a United GM EST Distributor kit. (Port ignition is different system.) We have been unable to get spark advance to behave properly. The United instructions prescribe base timing setting at 12 degrees with a graph showing 20 degrees distributor advance at 3000, so 32 degrees total advance.
When we bought the boat, the distributor had in it an ignition module GM # 193529288H3, which cross reference on the Rock Auto Website to AC Delco D1965A. When base timing was set at 12 degrees, change to run mode would immediately jump idle timing to apx 20 degrees, and total advance at 3000 would be about 30 degrees . Resetting timing to 30 degrees at 3000 in run mode would only drop timing to 24 degree at idle.
On advice that was probably wrong, we tried a couple of D1943A modules, which seemed to deliver only 6 degrees of advance. Resetting timing to 30 degrees at 3000 in run mode would only drop timing to 24 degree at idle. A replacement D1965A is acting similarly. We get only 6 degrees above base setting, and changing from base setting to run changes the idle advance.
Although battery isn't the best, voltage drop on initial start isn't below 10.5. After a number of starts, it drops below 10V, and engine won't run.
Several questions, I guess:
1. Is there a third module that actually should be in this system, rather than the D1965A or D1943A?
2. Assuming one or other module we have is correct, does the momentary voltage drop during engine start (usually to 10.5) somehow reset the module so the advance doesn't work or work properly?
3. If the D1943A or D1965A is correct, is there a troubleshooting process that should be followed to determine why we can't seem to set base timing at 12, switch to run mode and see idle timing still at 12 and total advance at 32, or so?
Thanks
Sleipnir (Charlie Iliff)
When we bought the boat, the distributor had in it an ignition module GM # 193529288H3, which cross reference on the Rock Auto Website to AC Delco D1965A. When base timing was set at 12 degrees, change to run mode would immediately jump idle timing to apx 20 degrees, and total advance at 3000 would be about 30 degrees . Resetting timing to 30 degrees at 3000 in run mode would only drop timing to 24 degree at idle.
On advice that was probably wrong, we tried a couple of D1943A modules, which seemed to deliver only 6 degrees of advance. Resetting timing to 30 degrees at 3000 in run mode would only drop timing to 24 degree at idle. A replacement D1965A is acting similarly. We get only 6 degrees above base setting, and changing from base setting to run changes the idle advance.
Although battery isn't the best, voltage drop on initial start isn't below 10.5. After a number of starts, it drops below 10V, and engine won't run.
Several questions, I guess:
1. Is there a third module that actually should be in this system, rather than the D1965A or D1943A?
2. Assuming one or other module we have is correct, does the momentary voltage drop during engine start (usually to 10.5) somehow reset the module so the advance doesn't work or work properly?
3. If the D1943A or D1965A is correct, is there a troubleshooting process that should be followed to determine why we can't seem to set base timing at 12, switch to run mode and see idle timing still at 12 and total advance at 32, or so?
Thanks
Sleipnir (Charlie Iliff)