Failed emissions test

[85lebaront2]

The accelerator pump adjustment on the older Autolite 2100/4100 carbs was done by moving the accelerator pump rod up or down on the lever on the throttle shaft. Further out = faster shot, inner = slower shot, total volume is possibly larger on the outer holes, but only if the lever on the pump cover doesn't either bottom out or fail to move the diaphragm immediately.

None of this should have any effect on the idle mixture, that being said, one of the issues with these carbs and Holley 2300/4150/4160 carbs is power valve failures, the diaphragm on the power valve can leak or actually fail, resulting in a rich idle mixture. On most Holley carbs, it will be so rich as to be beyond adjustment range, the smaller passages on the Autolite/Motorcraft carbs will still allow a rich mixture but not as bad.

My experience with the 351M/400 engines has been that in stock form, the mixture can barely be gotten rich enough to even idle well, if it is rich, I would expect either a plugged air bleed, bad power valve or a minor flooding condition (float or needle and seat issue).

[delco1946]

The idle mixture screws were multiple turns out, prolly close to all the way out. I started them at 1.5 turns but the engine wouldn’t even fire up more then a couple seconds. It seems to be idling well enough now and I think I’m at 3 (maybe 3.5 turns I lost count). I do notice that it seems to respond faster /better when a gas it at least :)

I’ll take it back tomorrow to see how it tests.

[Gary Lewis]

I think you are seeing what Bill was talking about.  The internal passages are limited so it is difficult to get too much gas.  But you may have had too much if it responds better to the throttle.

Good luck!

[85lebaront2]

Ford got in trouble over the 400 engines in 1972 due to not being able to meet the emission standards and still have it run decently, if you enriched the idle mixture to where it ran well, it failed emission testing. Hopefully you can hit a "sweet spot" where it runs well and passes emissions, the 351M may respond better than the 400 since it is smaller.

[delco1946]

It passed this morning!

It is indeed set at 3 to 3.5 turns of the idle mixture screws ( twice the factory standard ) but it seems to run well with the choke adjusted to be dead center of rich/lean ( it was leaned out as for as it would turn before).

The CO was at 2.97% and the limit is 3% so close call, but the nice thing with emissions testing is that I know my gas mileage should improve now.

[grumpin]

That’s great!

[Gary Lewis]

Excellent!  

[85lebaront2]

Great! One thing I have read from people who have to deal with these tests, a fresh oil change can also help along with making sure the PCV system is in good order.