a question of timing

[67-69johnman]

On the old twin cylinder j/e with the universal magnetos what is the purpose of advancing the timing when twisting the throttle. I just wonder why this is not done on four strokes or even non-outboard two strokes
I've advised fining on automotive engines by advance and retarding just curious why or why not was this used in other applications as well

 

[JB]

Re: a question of timing

Timing is advanced automatically in the distributors of many auto and other 4 stroke engines. Both rpm and vacuum are used for the auto-advance. Doing it manually in outboards saves weight and complexity. Power output would be greatly reduced without it.

 

[Faztbullet]

Re: a question of timing

I just wonder why this is not done on four strokes or even non-outboard two strokes

As posted earlier it is automatic and done thru the ECM/ECU just like late model automotive systems..

 

[nwcove]

Re: a question of timing

ob's are expected to run well from slow idle to wot. most other two strokes ( chainsaws, dirt bikes etc) are tuned/timed to run best at or near wot.

 

[Silvertip]

Re: a question of timing

On two stroke outboards, without some means of advancing and retarding timing the engine simply would not idle well or transition well from low to mid and high speed. Timing and throttle are used to control engine operation on every engine regardless whether it is a two or four stroke outboard, carbed or EFI/DFI. Sometimes timing is done mechanically and in the case of EFI/DFI it is done with an ECU (engine control unit or engine management computer). Timing an engine for WOT power with no means for retarding it at lesser RPM would likely result in severe detonation during hole shot not to mention the lack of low rpm power. Conversely, optimizing power at the low end compromises high end power. That applies to all engines. Therefore, auto advance timing (mechanical or electrical) is essential.