Rick McC. wrote:If I'm understanding what I've read here correctly; why does everyone say it's best to disconnect the vacuum advance from the distributor, and run a static distributor timing when an automotive engine is used to power an airboat? I'm pretty much lost on this...
You are trying to further your understanding of how the timing works, and there are those here that are willing to help toward that end. It may well only be my interpretation, but the way your question is worded makes it somewhat ambiguous. This subject can seem complicated to anyone on the front side, so don't worry about that. It is difficult in any case to pose the best question when your not familiar with what you are asking about.
There are basically three ways to set-up/alter/adjust the timing:
First . . . You could 'lock it out'
. In other words, set your initial/base timing to a number that will NOT change, regardless of the RPMs. It is not variable, it is permanently fixed in one position. Consequently, it will only be optimal running in a SMALL rpm range, rather than across the board. This isn't generally recommended for that and other reasons.
Second . . . You could run 'mechanical advance'
where the initial timing is set at idle, and the springs and weights in the distributor will add timing as the engine RPMs increase. This is overwhelmingly the recommendation by most people for most airboat applications running an automotive engine.
Third . . . You could run 'vacume advance'
in addition to the mechanical previously mentioned. To oversimplify the purpose of vacume advance would be to say that it is to gain fuel efficiency when the engine is loafing around with only a partial load at lower RPMs. This generally doesn't happen on an airboat unless it is a very big engine on a very light hull, so generally it isn't used. It is worth noting that it can be beneficial in such a circumstance, but is generally not done due to the nearly non-existent difference it would make in most cases.
What wasn't really clear (to me anyway) about your question is exactly what you mean when you say 'run static distributor timing'. Depending on the context, "static" could be interpreted as fixed timing, or it would refer to the base/initial timing setting. Are you asking about running vacuum vs OPTION 1 or are you asking about running vacuum vs OPTION 2, or are you asking about OPTION 1 vs OPTION 2.
The first two responses figured you were asking about locked out (option 1) VS mechanical (option 2); but if that was your intended question, I'm not sure why you mentioned vacuum advance. If that was the case though, Swamphunter offers good advice and hits on the highpoints of the debate. Here is just one such recent thread: http://southernairboat.com/phpBB3/viewt ... 3&p=675097
If this and/or the previous posts answered your question, then that's great.
If not, re-wording your question will allow us to get more specifically to what is it you are wanting to know.
If this was just my confusion, then just say so, excuse me, and I will quit trying to help.