I have a carburetor tunning question that I hope to gain some insight from others out there who have tunned a Webber 38 DGES using an AFR gauge. Two questions really.
When I adjust the idle to the AFR numbers, the engine idles rough, clearly not the best idle according to what Webber recommends. However, this rough idle setting brings me closer to the AFR range at transition and low load cruising RPM and it seems to pull nice. When I tune to hearing smoothest idle, the engine runs rich, around 12.5 on the AFR at idle and the whole low end cruising engine circuit runs richer than I would like 13 to 13.5.
No vacuum leaks, power valve has been checked for my engine vacuum range. Carburetor jetting is currently;
Gen Info on engine: Recently rebuilt with about 7,000 miles on it. It’s a 1971, 1.9L block bored out to 2.0L, flat top pistons, larger valve size with a combination cam @0.430 lift and 268 duration (so it already has somewhat of a rougher idle than stock with a lower vacuum signal). I am running 90 octane, nonalcohol fuel. I have removed the Vacuum retard but did keep the vacuum advance on the distributer. The engine is timed with no Vac. Advanced hooked up to 36 Deg Advanced when mechanical advance is all in.
Thanks
Thadman
- Should you tune the idle circuit (at engine idle) using the stochiometric AFR number of around 14.9, rather than the Webber recommended ear/listening method? (With newer fuels and all my actual AFR idle target is around 13.9 to 14.5).
- The other question regardless of the answer, is there a method for moving between the two barrels on a 38 DGES when adjusting the idle mixtures needle valves?
When I adjust the idle to the AFR numbers, the engine idles rough, clearly not the best idle according to what Webber recommends. However, this rough idle setting brings me closer to the AFR range at transition and low load cruising RPM and it seems to pull nice. When I tune to hearing smoothest idle, the engine runs rich, around 12.5 on the AFR at idle and the whole low end cruising engine circuit runs richer than I would like 13 to 13.5.
No vacuum leaks, power valve has been checked for my engine vacuum range. Carburetor jetting is currently;
- 3.5 Aux. Venturis
- 50 idle Jets
- 155 mains
- 185 Air Correctors
Gen Info on engine: Recently rebuilt with about 7,000 miles on it. It’s a 1971, 1.9L block bored out to 2.0L, flat top pistons, larger valve size with a combination cam @0.430 lift and 268 duration (so it already has somewhat of a rougher idle than stock with a lower vacuum signal). I am running 90 octane, nonalcohol fuel. I have removed the Vacuum retard but did keep the vacuum advance on the distributer. The engine is timed with no Vac. Advanced hooked up to 36 Deg Advanced when mechanical advance is all in.
Thanks
Thadman