air mixture screws on 1406

[67sss]

adjusting right side with no problem, when adjusting the left side no change when I turn the screw all the way in(I don't turn it to tight to screw up the seat) or all the way out. I've tried the "old fashion" way to try to loosen anything that might be caught by opening up the 4 brls-full throttle- and giving full choke(manual) to see if it'll suck it threw. No luck so far.

Also, the engine will not stay running at ANY steady throttle position. As long as I'm accelerating its fine, but the minute I try to stay at a steady throttle it'll fall flat on it's face. Mash the throttle and it'll kick down and go like a raped ape, even on freeway speed of 60.

Any ideas? Thanks.

[geezer#99]

Vacuum leak!!!

[Eddie H.]

I had a similar problem on a 1406. It had plugged up idle circuits. With the engine shut off, I pulled the idle screws all the way out, then sprayed some carb cleaner through the holes that the screws came out of. I put them back in, adjusted the idle mixture, it ran fine.

[dznucks]

^^^^ i agree.


if you have compressed air, completely disassemble it and blow everything out.
When i would change the jets in mine, metal shavings would come off the jet or our of the threads and clog up the passages. it would run perfect, then i would change the jets and it did exactly as you describe. after blowing it out it ran fine.

[rayfinseats]

There is a fix for that on edelbrock.com. all you have to do is take the mixture screw all the way out and shoot the hole with compressed air. I did it twice recently. Prolem was solved.

[RichardJ]

>>adjusting right side with no problem, when adjusting the left side no change<<

Don't adjust one side at a time. You started with both fuel mixture screws the same number of turns out from the seated position. 2 turns out, if I remember? Turn both screws 1/4 turn at a time and wait to let the engine settle. After you get them close to where you want to end up, then you can try to fine tune them individually. You should not end up with them more than a 1/2 turn away from each other.
On their web page they use the terms "idle air flow" and "air screw". They are referring to idle speed screw on the side of the carb.
They refer to their adjustment procedure as "Lean-Best Idle Set". Many people use the term "Lean Roll" except they don't drop the 20 rpm. I usually leave it there or add a 1/4 turn richer to help off-idle transition. If you have a slight stumble off-idle and you know the accelerator pump is working well, the 1/4 or even 1/2 turn will usually tke care of it.

[storm9c1]

I set the screws to about 1.5 to 2 turns out. Then hook up a vacuum gauge to manifold vacuum. Start the engine and set each screw to get the highest possible vacuum setting. Verify that it's around 15" or more of vacuum. Much less and you have a vacuum leak and should diagnose that first (or you have an aggressive cam, and if so, you need to know what your base vacuum should be).

Always reset your idle back to 750 (or whatever you consider to be base idle) before moving to the next screw. Keep going back and forth until you get the highest vacuum at base idle. Allow the engine to settle for about 5-10 seconds before moving to the next screw. This procedure NEVER fails to get good off-idle response. I *only* use a vacuum gauge now to do this procedure. Forget their recommended "set by feel/sound" procedure. That only gets you in the ballpark. The vacuum gauge is far more accurate and less frustrating. And it will also clearly show if one circuit is clogged (ie: won't show any change in vacuum for that screw).

Note that I also recommend doing this with the engine already warmed up. Doing it cold will throw off the idle adjustment. When cold, the choke changes everything.

[67sss]

will check for vacuum leak first. then i'll try the carb cleaner/ compressed air thing. if that doesn't cure it, i'll take it apart and see what i find.

would any of the above suggestions fix my problem i'm having with the engine not running at a steady throttle position?

Thanks!

[geezer#99]

Vacuum leak causes the not running at steady throttle position. That's why I suggested it right away. Your idle adjustment screws have no effect at cruise. Carb should be in power mode by then.
Are you running vac advance and if so are you hooked to ported or manifold vacuum.

[67sss]

Vacuum advance. Hooked to right side of Carb. Found no vacuum leaks.
Posted via Mobile Device

[geezer#99]

So is the right side ported or manifold vacuum. If you hook up to manifold vacuum your motor will speed up due to increased timing. Then slow down your idle with the idle speed screw and then try adjusting your mixture screws.
What's your initial timing set at?

[67sss]

manifold vacuum. initial timing 8 btdc. haven't done the total timing thing. not sure how to do it. I took the truck to work this am and it idled good and even stayed steady speed on the freeway. I took both mixtures screws out and cleaned 'em. I still would like to do the total timing thing, just for sng's..