low RPM in 72 318

You could be right Ricardo, I will hve to look into that. Aside from timing it at idle, I wouldn't know how to get the correct advance at higher RPM's. If its timed correctly wouldn't the advance be correct at high RPM, supposing the distributer advance is working correctly. I did the Fastjeff advance routine and everything seems fine in there, although it is 40 yrs old, so dont know if its actually working properly. Engine revs up to 3000 no problem at idle, just not in gear and under way.

Loid58, forgive me for being such a NAZI re; Ignition timing and TAT (total advance timing).
I've been at this for while (mid 60's), and I know the importance of it.
You have my permission to call me the TAT NAZI!

loid58 said:

You could be right Ricardo, I will hve to look into that. Aside from timing it at idle, I wouldn't know how to get the correct advance at higher RPM's.
(#1) If its timed correctly wouldn't the advance be correct at high RPM, supposing the distributer advance is working correctly.I did the Fastjeff advance routine and everything seems fine in there, although it is 40 yrs old, so dont know if its actually working properly.
(#2)Engine revs up to 3000 no problem at idle, just not in gear and under way.

Click to expand...

I'm not sure what you mean by the "Fastjeff advance routine ". I'll go back and re-read and see if I can find it.

But in answer to your question and comment, I'm putting #2 ahead of #1:

(#2) Most any engine will rev up w/ no load.... regardless of correct or incorrect spark advance.
It's when we load the engine that the Advance becomes very important, and even critical in some regards.
As RPM is increased (load or no load), the ignition system is to advance the spark progressively per RPM.
it may require 8* BTDC @ 800 rpm (this is BASE.... no mechanical advance yet)
it may require 14* BTDC @ 1,800 rpm (now it's adding centrifugal advance)
it may require 18* BTDC @ 2,500 rpm
and it may require 25* BTDC @ 3,000 rpm and so on up until what's referred to as "Full In" rpm.
This is why we need to see an Ignition Advance curve graph for the Marine 318/360 as to know what this system should be doing.

There are no gasoline engines that do not benefit from a progressive spark advance.





(#1) Yes.... ideally we'd have an ignition system whereby setting BASE advance would very likely position the progressive Mechanical Advance within specs.
The mechanical mechanism provides this progressive spark advance, and does so via centrifugal force, relying on a cam/weight/return spring system.
When all is working well, setting BASE "ONLY" becomes a tad bit safer to do.... but as with any Marine Gasser, we should ALWAYS check the progressive side of this also.
BASE is BASE, and is so all day long!
Short of starting and idling on BASE Advance, it's pretty much useless for anything above idle RPM.... just not enough spark advance for any performance at the higher RPM range.

The fact that these components are 40 years old is a part of why I'm suggesting that you take a very thorough look at your ignition timing. At 40 years of service, don't be surprised if you were to find that this mechanism is no longer doing what it's suppose to be doing.

On the other hand, your 40 year old engine still wants to see a correct spark advance.... no matter how tired she is!
Sort of like an older person still requiring healthy food! LOL


What I'm basically suggesting is.... if all else is A-OK..... Compression, Fuel Delivery System, Engine Tune (of which should include what we're discussing), Final Drive Ratio, Prop Shaft, Prop Condition, Hull Clean, etc........ and if Ignition Advance is NOT doing what it's suppose to do, your "under-load" low RPM issue may be related to an incorrect Ignition Advance!
If you were to check this, and if you were to find that it's OK..... then you may have another issue.
But I certainly believe that this is a very important item to check.

As I've mentioned before, even well seasoned marine mechanics will set BASE, and walk away.
I could never do that!

Ok, so how would I set the advance at the higher Rpms? I've never done this before. I take it I would need the specs for the engine which seems hard to come by. The fastjeff test is manually snapping the advance back and forth a couple of hundred times to make sure it works. Bottom is clean, shaft is good, have no idea about the prop, could be the wrong one or out of tune, just don't know, that could be the porblem I guess.only other thing it the dist. could be bad, not advancing. I'll try to find out how to time it as you suggested, thanks
.