Setting aside the reasons for going back to a single two barrel for a while, a few questions arise regarding the stock cast iron manifold. Viewers with a good memory will recall that my road draft tube went away and that there is a pcv setup that taps into the manifold. Now I need a place to plug in the vacuum advance on my distributor. You know, the one with the pertronix. It is the later distributor, not the Loadomatic. It's the 292 with the road draft tube in the valley pan setup. Groundwork laid, here are my questions:

1. Can I put a tee into the existing vacuum hole in the manifold to accommodate both the pcv and vacuum advance? If not, why not. Vacuum is vacuum isn't it?

2. If the answer to question one is "no, stupid", then can I drill and tap a hole in the manifold under the "x" in the photo for my vacuum advance? Is there a problem with drilling and tapping cast iron? Is there a better location for the vacuum advance tap?



Carl, are you out there? Mrs. H. needs her nice Silverado truck back....

thanking you all for your patience, himmelberg

 

You can tap into manifold vacuum, but then you have full vacuum advance, most run off the carb, either ported vacuum...where you don't get vacuum unitll the throttle blade open, or lower on the carb wher you have full vacumum.

I'd venture to guess the majority of setups run ported vacuum for advance, since full vacuum advance isn't really needed until you get the engine going, no real reason to "have it all right now"., since when you step on the go-pedal to the floor, you won't have it anyways.

 

I might add, just to answer your question, whether you tee it, or run a seperate hole into the intake, it's the same thing.

 

Mr. Himmelberg, good to hear from you again. I think you have two options here. There is no reason why you cannot drill and tap into the manifold and then "T" off from there. One concern would to make sure you have all metal shavings removed from the inside of the manifold cavity. The other option to avoid drilling into the manifold would be to either fabricate or find a carb spacer plate to fit under the carb for your application. You have to replace the carb studs with slightly longer ones which is not a difficult task. Most spacer plates have either a tapped hole or a nipple on the back which you can use for a vacuum access. That way you don't have a hole in your manifold and you keep it original. I noticed the firing order on it is very similar to the 289/ 302. 15426378. Interesting? There appears to be hole just above the X you made, isn't that a vacuum port? (Not familiar with these manifolds) Hope this helps!

 

I'm with Mike, you want venturi vacuum, not manifold.

 

Correct me if I'm wrong here, Vacuum advance can be hooked up to the venturi vacuum at the carburator, however for PVC function, I believe that needs direct manifold vacuum to work properly as does power brakes?

 

Yes, PCV is is hooked to the intake vacuum...i/e "always on". Vacuum advance can be run either ported ot full, I think some late 60's/early 70's muscle cars ran vacuum advance to the intake ports on the carb, but most before and since ran ported vacuum.

 

Fleshing out the groundwork it seems I missed noting that the carb in question is a Holley 94. The venturi port on these carbs were designed for the Loadomatic distributor, the way I understand it, the later distributor wanted manifold vacuum. At least, it wanted to be below the throttle blades, as in the carb spacer mentioned.

In any case, the hole in the manifold is a vacuum port and that is where my pcv valve goes. My quest is to make this as simple (ie. cheap) and as quick as possible. I will plug a 'tee' in the existing hole and try that.

The weather here is holding at a frigid 65 to 70+ degrees F in the afternoons. Cold, yes, but it does allow me to work on the truck in short bursts. It also offers respite from the bathroom remodel.

wishing spring was here, himmelberg

 

You really need to find a ported vacuum source off the carburetor. I don't think the advance mechanism is going to work right with full manifold vacuum. If you don't have ported vacuum, you may as well not run ANY vacuum advance. I don't think one method is any worse than the other...

Vern

 

I agree, the vacuum advance should be hooked up to a ported vacuum source and not manifold vacuum. Every vacuum advance that I have seen has been operated by ported vacuum. It should be very easy to test this. Put a vacuum hose on the distributor and give it a suck (or if you're fancy-smancy hook up vacuum pump) while watching the movement inside the dist. If its operated by ported vacuum the advance plate will move while you apply the vacuum.

The suspense is killing me....why get away from the extremely sexy 6-pack that you had???????
Bobby

 

OK, Bobby, but keep this under your hat. Some time ago I lucked into 3 Stromberg 97's. They were chrome plated and have some ultracharming patina... in other words, they are pretty rough. Parts are missing from two of them and I just now found a source. The plan is to rebuild and redo the setup with Strombergs, new linkage and pcv stuff. I want to massage the intake a little, there are some fitment issues at the back of the 553.

In the meantime, I need my truck. While I might be just a few months older than Mr4speed, I am about as slow as Mr. Niolon. Well, maybe more than a few months but not THAT slow. Mrs. H. will not wait much longer.

I did not want to reveal all of the lunacy brought on, no doubt, with the sub-70's temperatures and the attendant "cabin fever", but now you have the whole story... and like I said, keep it under your hat.

stealthily stromberg, himmelberg

 

I dont know if I should even reply Peter until you 'splain what happened with that lovely trips setup you spent so much time refining. And dont tell me you cant afford the gas on a professors salary!

As far as a vacuum source for the later dizzy, ported vacuum is a must as mentioned by several.

However nobody seems to have addressed or maybe doesnt understand the Holley 94 style of carb. There aint no dang ported port on one of them dang things. Is that how they say it in Texas?

You have to create your own port in the base of the carb. Fortunately the base is soft cast iron and the outlet can be small. I drill a hole just above the throttle plates and silver solder in a short length of 1/8" hobby shop brass tubing. You could also secure with a press fit, epoxy or whatever suits your fancy. Then just attach a length of vacuum hose.

Edit: i spent about 2 hours between starting and finishing this reply. Food and other life pleasures took priority so I missed your last reply.

 

Himmelberg,
Your secret is safe with me. I won't breathe a word of this to anyone. I also didn't realize that the 94 didn't have a ported port. The is a bummer, but it sounds as if 286merc has the solution for you.
The only other option you have is to run a long length of vacuum line into the cab and up to the drivers position so that you can gie it a good suck when you hammer on the throttle and need some advance.
note: this is not recommended unless you have serioulsy dark tinted windows lest the local law enforment pull you over for suspicion of toking on a hookah,

Good luck with it
Bobby

 

Bobby,
Great post! You had me in stitches!

 

Gee, Carl, I'm glad you showed up with that little tidbit on how to port the base. I guess I was assuming that we all knew that 94's are portless. Shame on me.

Gas prices aren't an issue here in the Permian Basin... we all have our own oil wells. My morbid and often self defeating curiosity is what leads me down the Stromberg trail. Seems I can't leave well enough alone.

On the other hand, I feel that the '97' exercise will give me three leaking carbs on the 553 that could easily sell for the price of a new project and a better intake for my hard earned 94's. I'd also like to run them for a while and add to my slender knowledge base.

If rebuilding carbs in the house instead of in that icebox of a shop (did I mention that winter is my least favorite time of the year?) gets Mrs. H's truck back to her quicker, then I'm golden.

I appreciate all of the responses to this complicated approach to carburetion. None of it was brought on by hookahs or bellbottoms. A nice MonteCristo from time to time is my last lingering bad habit.

appreciatively, himmelberg