My 74 F100 has electronic ignition - the distributor doesn't have points. It does have vacuum advance. When I bought the truck, the guy that owned it before me had taken off the Motorcraft carb and put on an Edelbrock 1406. I noticed that the distributor vacuum advance had no line going to it. The idiot PO said if you static time the vehicle correctly, you shouldn't need vacuum advance!

Anyway, I got around to getting a little 5/32 vacuum line and running it from the vacuum port on the front of the carb (the one to the right of the designated PCV line). The owners manual said that one, as opposed to the other one to the left of the PCV line, was the one to use. (The one on the left was a "timed vacuum" or distributor vacuum advance port for emission controlled engines; the one on the right is supposed to be just straight manifold vacuum - a vacuum advance port for non emission controlled engines).

So when I hooked up the distributor's advance to the manifold vacuum (the fitting to the right of the PCV vacuum), my idle jumped up. I've run old carb motors years ago, ones that didn't have the emission controlled vacuum advance, but I cannot remember idle jumping quite this much.

Does this sound right? Even though the motor is a '67, the distributor is obviously newer and that particular one likely came with the truck. So might that distributor have timed vacuum advance? I'm thinking perhaps yes, since the 74 model would have had some of this capability?

 

In that port you have the most vac at idle I have an edlebrock too and just recently changed it to that port but haven't taken it for a good drive yet. I had to adjust the fast idle on the carb to slow it down and may have to reset the timing before driving it ,maybe today. I just put the edlebrock on and had it to the ported vac. the faster i tried to go , the more pinging i got. I never had any pinging with the motorcraft 2/bl. i had on it and timing is the same now as it was with the 2 bl. My engine is a 302.

 

Oops double post, sorry..

 

Yeah, after thinking about the issue, I think we need to put the advance on the 'timed vacuum' rather than 'manifold vacuum'. I think.

the reason is that my distributor is an 'emissions' distributor, and its vacuum advance was never meant to run off of full vacuum, I don't think.

Did you try yours off the vacuum port to the left of the PVC?

BTW, I don't use the PVC or the power brake vacuum pulls either. My PVC comes off of a nice line off of the manifold. so my power brake fitting has the steel plug, and the PVC nipple has a rubber plug in place.

 

This is correct for all Fords of our vintage. No vac at idle.....

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I have my brake and pcv to the back too and capped off the front carb one. I had mine in the timed port , passenger side ,and had the problem with pinging . I haven't taken it for a good drive since i changed it to the one on the drivers side. My engine is a 85 302 with a dist. for a 79, no points. I was assuming you have a 360 as that's what mine had , it is a 73 , but i changed over to a 302. I have had this carb a few years and on a few other engines ,always used the vac on the drivers side with no problems. The only reason i tried the timed side was from getting advise on this forum , maybe bad advise.

 

sounds good Old Style - I'll change mine over to the one on the left. The only reason to do this is that I have my OEM distributor and advance. If my distributor was aftermarket/nonemission, would be a different and would put it on the one on the right.

JimCollins, yes, i did notice more pinging too, but that was compared to no advance at all.

so is the concensus here that you should put the vacuum on the fitting on the carb that has timed vacuum and not full manifold vacuum?

 

Like i said before , i have it on full vac now but haven't had time to get it out and see what it does. It was pinging when i had it on the timed port. The faster i got the more it pinged. It has a new dist. May have to wait a few days to check things I got to many things taking my play time away right now.

 

do you have other emission control set up on your truck Jim?

 

Your distributor doesn't know "timed" advanced, per se. It only knows centrifugal and vacuum (ported or manifold) advance. Back in the day (as I'm sure you'll recall), motors didn't have all that pollution control horse hockey. All they knew was manifold vacuum. So with manifold vacuum, at idle, the vacuum advance would be "all in". (Hence the "pull the vacuum line and plug it" deal when timing it). Now comes ported or timed vacuum on smog motors. Zero vacuum at idle - vacuum comes into play at off idle -coupla hundred RPMs off idle, thereabouts. If you had ported vacuum on your vehicle before and timed it, set the curb idle, mixture, etc, it would stay close to the same when vacuum was re-connected. With manifold vacuum connected, your vacuum advance would be "all in," causing your curb idle to be higher and needing adjustment, along with mixture, etc. But, in the the end, it's all really what works best for you and your motor. There's a bit more to it but my two finners are getting worn out....
Phew! Please excuse the long(ish) post.

 

You time your engine with the distributer vaccum disconnected and the carb vacuum plugged. Static timing has nothing to do with vacuum.

 

I do the static timing with the vac port capped off . Then connect the dist. vac line and set the carb., RPM idle and mix adjustment together , working back and forth on them. I have no emission parts accept the PCV , all other crap is gone including EGR.

 

Yeah, I just put plugs in the truck today. So the engine WOULD HAVE taken Autolite 45's with a 0.035" gap (66 or 67 390), but since the engine uses the truck's original electronic distributor, I set the gap at 0.044". So two questions:

What timing would be correct, given the '*******ization' of this setup?

Back to the vacuum advance, my factory service manual seemed to imply that ford distributors in 1974 have both centrifugal and vacuum advance, so am thinking I should use the full on manifold vacuum on the carb, since the 66/67 390 (what is in my truck) would have had that setup?

 

All factory disributors have both, centrifugal/mechanical are the same, vacuum advance is seperate, and different.

This is a topic of much debate, i'll just leave here nice and quietly saying ported/timed vacuum is what you should use....

Others will argue for full manifold vacuum, you're a smart guy, try both.....you decide which is best.

(dizzy and carb both need re-tuned to work properly, with either vacuum advance source)

 

1974 f250 360ci 2bbl distibutor problems.
I. Just changed my points,rotor and condenser and my engine runs rough when the vacum advance is engaged.Ive checked the points gap several times and they are gapped right at .017.Plugs,wires,coil,cap are also new.
Everything functioned properly before this so I don't know what I did but I can't figure it out.
Thanks for any troubleshooting ideas.