Ignition timing for 5R engine is 10 degrees BTDC at 550 RPM, vacuum advance hose disconnected and plugged. Add 4 to 6 degrees to account for LP fuel.
The actual "rate of combustion" for a single charge of the combustion chamber remains constant throughout the RPM range and is dependent on the fuel type as to exactly how fast the particular fuel burns.
LPG fuel combustion is slower than that of gasoline so LPG needs to be lit earlier in order to have the combustion at the proper stage when the piston crosses TDC from compression stroke to power stroke.
I will search for any manuals that apply to 2F models at work today and post tomorrow.
I'll look for that number. And yes, total spark advance is an interesting situation. With propane, relative to gasoline, combustion is slower at low speeds/light loads and faster at higher speeds/loads. Hence, relative to gasoline, above idle speed we need more advance at the lower end and less advance at the high end. As this situation applies to total advance, the centrifugal advance increases with rpm while vacuum advance falls off at higher speeds/loads. Still, relative to gasoline,total advance needs to be higher and the low end and less at the high end of the speed/load curve. Outside of all that I'm still hoping to get the factory spec on base (static) timing.
Look on the engine for a "designation flat" that has been ground smooth and stamped with a Toyota designation ID for the engine.
In this case, the designation might be 4P.
I have access to a 3FG manual which gives the timing spec as 8 degrees BTDC. Of course, 8 BTDC is for a gasoline fuel configuration, so add about 4 to 6 degrees to that for LPG (12 to 14 BTDC).
I'm not sure you understand the reasoning behind the need to advance the spark point of an engine, but the need for advancing it becomes even more important at higher RPM than at idle, and that is why there are vacuum and centrifugal advance mechanisms in the distributor.
Propane fueled. I can appreciate the need for more initial advance at low rpm and reduced advanced at high rpm. I'm not too concerned with that as there is a factory version of the distributor on the engine. Initial, basic, timing is my concern. Thanks for looking into this. I'd be interested in a copy of that manual and would provided appropriate consideration for accessing that.
I will search our "archives" at work to see if there is a 2F manual.
Is the engine running on LPG or gasoline? That will affect the needed spec for ignition timing. LPG has to be "lit" earlier than gasoline, so the timing will be a little more advanced than if gasoline fueled.
Idle rpm erractic and I don't want to adust A/F ratio till I know the ignition timing is with tolerances.
Used to work on a number of these- don't have specific specs but is there an issue you're dealing with?