360 Questions.. pardon my ignorance.

[CoolDave]

Gotchya. Just my personal advice, but I would disable and remove the OSAC valve.

Its gone, vacuum hooked direct from carb to distributor.

Came here because I have pretty much the same truck, same setup. '74 D200 truck, 360, Holley 2210. My setup runs PERFECT, so I wanted to let you in on where I ended up with it, starting with square transfer slots:

10 degrees initial, limited to 33 all in
Ported vacuum advance
mix screws 2.25 turns out.

This equals a 700rpm idle.

For what it's worth.

Ok that sounds like I’m not far off. How did you limit the all in timing? What port on your 2210 is your advance hooked to? I feel if I bump up my base timing from 5 up to 10 I’d probably be in the vicinity of 650-700rpm for idle.

 

[RustyRatRod]

Its gone, vacuum hooked direct from carb to distributor.

Probably a good idea. Even if it was in working order, it's just less to go wrong.

 

[volaredon]

The "osac" port on the carb IS the (ported) vac advance port.

 

[TT5.9mag]

Forget about the vacuum advance for now. Plug the damn port and get a base tune up in the poor thing. Then worry about vacuum advance.

 

[CoolDave]

Forget about the vacuum advance for now. Plug the damn port and get a base tune up in the poor thing. Then worry about vacuum advance.

So what’s your basic method then? It seems everyone has an opinion on what’s “correct”.

Carb is set to a baseline 2.5 turns on the idle mix screws, idle speed screw is set to achieve a square transfer slot. Initial timing is 5 degrees at 650rpm (on the last step of fast idle cam, shop manual calls for TDC). Once it comes off that cam to regular curb idle it wants to stall unless I give it a little throttle.

So where would YOU go from there?

 

[TT5.9mag]

So what’s your basic method then? It seems everyone has an opinion on what’s “correct”.

Carb is set to a baseline 2.5 turns on the idle mix screws, idle speed screw is set to achieve a square transfer slot. Initial timing is 5 degrees at 650rpm (on the last step of fast idle cam, shop manual calls for TDC). Once it comes off that cam to regular curb idle it wants to stall unless I give it a little throttle.

So where would YOU go from there?

Give the engine what it wants, stop worrying about trying to hit a specific number or target for timing, turns of idle mixture screws ect. Don’t be afraid to adjust the idle speed screw a little from a square transfer slot either way, give it the idle timing it needs to maintain a smooth idle and not slam in to gear, and make sure to limit the total timing once you establish what it wants for initial if it’s above what the distributor was originally curved for. And the best piece of advice I’ll give is this, once you set one thing, don’t be afraid to re do it once you change something else. All of these adjustments can affect each other.

 

[RustyRatRod]

You need a vacuum gauge. You can use that to zoom right in on the air screw adjustment and to see where the engine wants the timing to be.

 

[CoolDave]

Give the engine what it wants, stop worrying about trying to hit a specific number or target for timing, turns of idle mixture screws ect. Don’t be afraid to adjust the idle speed screw a little from a square transfer slot either way, give it the idle timing it needs to maintain a smooth idle and not slam in to gear, and make sure to limit the total timing once you establish what it wants for initial if it’s above what the distributor was originally curved for. And the best piece of advice I’ll give is this, once you set one thing, don’t be afraid to re do it once you change something else. All of these adjustments can affect each other.

I’m expecting to set things a few times and tinker a lot. So questions about the process..

With it stumbling at hot idle should I first adjust the speed screw or the base timing?

Once base idle is established do I adjust the mixture screws for best idle/vacuum before bringing the vacuum can back in?

After all that, I confirm my total timing and limit the distributor weights if necessary?

You need a vacuum gauge. You can use that to zoom right in on the air screw adjustment and to see where the engine wants the timing to be.

I have a gauge, I used it in an initial setup where I got the truck running OK from a non-starter when it came home. Now I’m to the point with the truck I’m really digging in and doing the proper process to actually start driving and using it.

 

[RustyRatRod]

I’m expecting to set things a few times and tinker a lot. So questions about the process..

With it stumbling at hot idle should I first adjust the speed screw or the base timing?

Once base idle is established do I adjust the mixture screws for best idle/vacuum before bringing the vacuum can back in?

After all that, I confirm my total timing and limit the distributor weights if necessary?


I have a gauge, I used it in an initial setup where I got the truck running OK from a non-starter when it came home. Now I’m to the point with the truck I’m really digging in and doing the proper process to actually start driving and using it.

You should continue using the vacuum gauge.

 

[TT5.9mag]

With it stumbling at hot idle should I first adjust the speed screw or the base timing?

That’s fuel related.

Once base idle is established do I adjust the mixture screws for best idle/vacuum before bringing the vacuum can back in?

The vacuum advance will have zero effect on idle if on ported vacuum (where it should be for a relatively stock engine) so you’d want the idle fuel and timing sorted out prior to adding it back in to the equation.

After all that, I confirm my total timing and limit the distributor weights if necessary?

Yes and adjust the curve with springs. And I’ll add that once vacuum advance is added back in, you might have to delay it with the screw in the can to avoid detonation on early tip in at cruise.

 

[CoolDave]

So with the vacuum can disconnected I settled at 10 degrees initial, it’s a bit back from rough running and a bit higher than sounding lazy. Idle is stuck around 500-550rpm, mix screws are 2 turns out and I had to put a turn and a half into the idle speed screw. Vacuum on the gauge has a little bounce to it but not dramatic, shows to be in a good range. RPM only drops 100-125rpm when put into gear.

Here’s the issue I’m on now.. when I bring the vacuum can back in I’m at almost 50 degrees of advance at about 750rpm. It is firm going into gear but I wouldn’t say it’s slamming gears.

I measured the spark port on the carb, it show vacuum all the time, increasing with engine speed. The only other ports are on the firewall side, one for PCV and one that I believe is the heated air hookup for the air filter. Which leads me to, I’m sure, a wildly incorrect train of thought..

With those variables could I not set the motor back to TDC timing like the shop manual states and rely on the vacuum can to apply the timing? That appears to be how it would have been originally setup?

 

[TT5.9mag]

Sounds to me like you’re either using the wrong port on the carb or the carb base plate is cracked allowing vacuum where it shouldn’t be. A true ported vacuum gets its source from above the throttle blades and has zero vacuum until the throttles are opened.

 

[CoolDave]

Sounds to me like you’re either using the wrong port on the carb or the carb base plate is cracked allowing vacuum where it shouldn’t be. A true ported vacuum gets its source from above the throttle blades and has zero vacuum until the throttles are opened.

I’m starting to wonder on the carb too.. I sprayed around the base of the carb and where the intake meets the heads and didn’t find any noticeable leaks. I’ll check the back port when I have more daylight and confirm it’s not a ported source. On the curb idle should I just put another turn into the speed screw to raise the idle to 750? I can imagine that will be exposing quite a bit of that transfer slot..

 

[Bewy]

Sounds like, for whatever reason, the t/blades are open too far at idle which is causing the vac adv port to be operating at idle, adding timing.
For 'whatever reason' could be a myriad of things such as a vac leak, very low compression etc.....