Duster running rich
Lenky,
The place to start in getting good idle quality & not over rich is NOT with the carb. It is with the ign timing at idle....& many do not understand this.....
The timing controls engine efficiency. When timing is correct, more HP is produced...& less fuel [ leaner ] is used doing it.
For this particular thread, forget about total timing or a timing curve. That comes later....
This engine has a sizeable cam &, with low-ish compression, will need a lot of timing at idle, perhaps 40* or more. Yes, 40*. Getting the timing correct will get the pri throttle blades in the correct position....or at least closer to the correct position. This is important because it affects the relationship with the transfer slot, & that has a BIG impact on rich/lean.
When the timing is correct & T-slot correct, you will be able to get a consistent idle [ not smooth with this cam ] which will be on the rich side, but not smelly &/or carboning up the spark plugs.
Many smart people use a dist that has an adj vac unit that connects to manifold vacuum [ MVA ]. With MVA, the VA unit adds timing at idle. Eg, MVA adds 25* & static initial is 15*. Total timing at idle is 40*
You will see in the examples below that idle rpm INCREASED with the extra timing from MVA. The increase in rpm comes from the engine making more hp from the extra timing.
Lenky,
The place to start in getting good idle quality & not over rich is NOT with the carb. It is with the ign timing at idle....& many do not understand this.....
The timing controls engine efficiency. When timing is correct, more HP is produced...& less fuel [ leaner ] is used doing it.
For this particular thread, forget about total timing or a timing curve. That comes later....
This engine has a sizeable cam &, with low-ish compression, will need a lot of timing at idle, perhaps 40* or more. Yes, 40*. Getting the timing correct will get the pri throttle blades in the correct position....or at least closer to the correct position. This is important because it affects the relationship with the transfer slot, & that has a BIG impact on rich/lean.
When the timing is correct & T-slot correct, you will be able to get a consistent idle [ not smooth with this cam ] which will be on the rich side, but not smelly &/or carboning up the spark plugs.
Many smart people use a dist that has an adj vac unit that connects to manifold vacuum [ MVA ]. With MVA, the VA unit adds timing at idle. Eg, MVA adds 25* & static initial is 15*. Total timing at idle is 40*
You will see in the examples below that idle rpm INCREASED with the extra timing from MVA. The increase in rpm comes from the engine making more hp from the extra timing.