Timing with a vacuum gauge
Because this is what happens.
Don't feel bad. I think most have thought vacuum and/or rpm was a good way.
Part of the problem with this method is the interaction with carb settings, in particular throttle position and mixture. RPM is equally related.
Increasing initial timing will lead to increased idle rpm which naturally creates more vacuum under the throttle blades.
The problem with this goes back to what spark timing is all about.
Timing is the degrees of rotation needed for complete burn.
Denser mixtures burn more quickly, and lean mixtures take more time for the flame to travel.
from MTSC 259. Ignition system analysis. 1969
The goal is to create maximum pressures with the mixture, heat, compression available while the pistons are in position to apply maximum leverage on the crankshaft.
As Chrysler reminded their techs in 1959
from MTSC-136
Running lean mixtures is great when the engine loads are low for the rpm.
At idle speeds, just slipping the engine into gear is a big load.
For maximum efficiency at idle, a relatively rich mixture is needed.
With an automatic transmission, its possible to set the timing and mixture, shift it into gear - and then note rpm, vacuum when it steadies. Can't do that with a stick shift.
For a basically stock engine with no emissions equipment, go back and see what the factory recommended for initial before CAP or CAS. Then you can experiment with increasing timing a couple degrees, resetting idle speed, then mixtures. The carburetor throttle blade positions must stay within a reasonable range of the factory setting or off-idle fuel delivery will be miscalibrated.
Best procedure for a hot rodded engine is to start with initial timing suggested in the "How To" articles. Usually 12- 16 BTC or 14-18* for typical hot rod street cams. Using a Holley type carb, keep the throttle position so transfer slots under the blade look squarish. Adjust the timing and mixture to get enough rpm the engine will idle nice. Probably a little more than a stock non-smogger, but should go into gear (automatic) at less the 900 rpm.
If you are using a smog era distributor, almost certainly will have to weld up the inside of the slots to get the advance correct. The FBO plate doesn't usually work out too well 'cause it results in the mechanical advance too early unless you fiddle withthe springs.
No & Not really.
Because this is what happens.
Don't feel bad. I think most have thought vacuum and/or rpm was a good way.
Part of the problem with this method is the interaction with carb settings, in particular throttle position and mixture. RPM is equally related.
Increasing initial timing will lead to increased idle rpm which naturally creates more vacuum under the throttle blades.
The problem with this goes back to what spark timing is all about.
Timing is the degrees of rotation needed for complete burn.
Denser mixtures burn more quickly, and lean mixtures take more time for the flame to travel.
from MTSC 259. Ignition system analysis. 1969
The goal is to create maximum pressures with the mixture, heat, compression available while the pistons are in position to apply maximum leverage on the crankshaft.
As Chrysler reminded their techs in 1959
from MTSC-136
Running lean mixtures is great when the engine loads are low for the rpm.
At idle speeds, just slipping the engine into gear is a big load.
For maximum efficiency at idle, a relatively rich mixture is needed.
With an automatic transmission, its possible to set the timing and mixture, shift it into gear - and then note rpm, vacuum when it steadies. Can't do that with a stick shift.
For a basically stock engine with no emissions equipment, go back and see what the factory recommended for initial before CAP or CAS. Then you can experiment with increasing timing a couple degrees, resetting idle speed, then mixtures. The carburetor throttle blade positions must stay within a reasonable range of the factory setting or off-idle fuel delivery will be miscalibrated.
Best procedure for a hot rodded engine is to start with initial timing suggested in the "How To" articles. Usually 12- 16 BTC or 14-18* for typical hot rod street cams. Using a Holley type carb, keep the throttle position so transfer slots under the blade look squarish. Adjust the timing and mixture to get enough rpm the engine will idle nice. Probably a little more than a stock non-smogger, but should go into gear (automatic) at less the 900 rpm.
If you are using a smog era distributor, almost certainly will have to weld up the inside of the slots to get the advance correct. The FBO plate doesn't usually work out too well 'cause it results in the mechanical advance too early unless you fiddle withthe springs.
