IIRC, K19 A.I.R was used on 1967 L71's shipped to CA. Engine suffix JA.

You may have a bad vac advance, but I would highly recommend you switch to manifold vacuum as well.

On a '67 L71 I restored a few years ago, I rerouted the vacuum advance line to a Tee going to the feed for the choke diaphragm activation on the center carburetor. This is manifold vacuum. I used the B26(VC1765) Vacuum advance and plugged the ported vacuum port. The engine ran strong, cooler at idle and idled perfectly. (see pics below)

VC1765 B26 Spec - Starts @ 5-7 "Hg, Max adv 8deg @ 11-13 "Hg

There is a way you can modify the center carburetor to utilize the ported vacuum tap for manifold vacuum, but you have to drill the base of the carb and block a portion of the port in the base. This would allow you to run manifold vacuum with the "appearance" that it's ported vacuum. Some add'l pics below showing the areas which need to be modified.

 

This there a written procedure for the carb mod? It looks like something I would be interested in doing.

 

Mike, I didn't do the modification on the one I had here but here is a quote from a NCRS member(Tim B.) who investigated the mod and wrote a description. I also attached his photo showing the area to modify. The B26 vac advance should be used with this mod as it worked fine for me using full manifold vacuum.

As you'll see, it moves the hole connected to the "ported" vac nipple into the area below the throttle plate, thus into the full manifold vac path. Note you have to plug up the original ported hole in the bore.

Keep in mind that if you have the car judged, if you don't do this mod, and instead set it up as I did with the Tee into the choke vac path, you'd probably get a small deduction for configuration.

Rich

"The drill bits show the path for ported vacuum. You can see the hole in the baseplate bore is above where the throttle blade closes and does not see vacuum until the blade is opened (ported).
Simply drill another 1/16" hole approx where the black dot is between the drill bits thus allowing manifold vacuum to the slot as this new hole is below the throttle blades. You need to put a smear of J&B weld in the ported hole so there is no vacuum leak at curb idle.
Keep this new hole well below the throttle blades like the level of the curb idle hole to the left. The black dot is hard to see, I can take a better pic if you need me too. Try to drill the new hole at the same angle as the ported hole, you will understand when installing a drill bit in the hole.
Thats all there is to it and it's easy to reverse if someone wants to have ported vacuum at idle.
I am not sure what vacuum can the factory used for the engine but make sure the specs of the new VAC allow to be pulled to the stop approx 2" less than idle vacuum. "

 

Mine has always been the way it came from the factory.

 

Strange it was running fine before. Might want to check your dwell and timing. Also I've had the points glaze and or slightly corrode over the winter lay-up-----not showing symptoms until it's been ran for a little while. And I've had condensers go sour over the winter shutdown too.

 

These are the specs I'm getting right now.

Base timing (VAC plugged) at 5* @ 800 rpm gives me 15" Hg
With manifold vacuum I get 23* @ 800 rpm with 17.5" Hg

Factory vacuum advance comes in at 15.5"@15* that seems to be the problem as this doesn't satisfy the "2 inch rule".

So I see two ways to remedy this issue.

1. Change out vacuum advance can to one the adds the timing at 12" that would let me go back to stock ported vacuum setup. It satisfies the 2" inch rule.

2. Keep the stock vacuum can and leave it hooked to manifold vacuum. Non stock configuration.

Which way would you go?

I understand per Duke Williams that additional benefits from running manifold vacuum are cooler temps and increased mpg.

Duke recommended at the 2012 NCRS National Convention in his tuning seminar the following:

Big block (SHP) 28-30 all in by 2500-3000
12" VAC
Set initial timing to achieve 36-38 degrees total timing

Factory spec states that Centrifugal advance is all in at 3800 rpm @ 30*

 

427435,

Did you buy the car new? I assumed all '67 L-71 came setup using ported vacuum advance. It was needed to sell the car in CA as k-19 wasn't option on the L-71.

 

At this point I, and probably others, wonder where you are going with this. Your car was running fine for two weeks. Then it ran fine at first the last time you drove it and suddenly wouldn't idle. Why you vectored off into timing mystifies me. If I had to shoot from the hip I'd say you had dirt in the fuel system somewhere. I had this EXACT thing happen to my BB Chevelle and it turned out to be dirt in the float bowl !

Car was running fine and then would stall at an idle...you'll hear it die at the end of this video. If I were in the cockpit I could goose the gas to keep it running. Sound familiar ?

 

Frankie,

Let me see if I can clarify. I got the car last Sept. It was fully restored to hopefully NCRS top flight condition. I drove it three or four times for maybe 30 minutes each time. During these outings the car would run fine. Then I stored the car for the winter. I did start it and warm it up to temp a couple of times over the Michigan winter which we are still in unfortunately. A month ago we had a stretch of nice 60's days so I took the car out for some longer runs. I would say 50-80 minutes each. This is when it started to stall at idle.

I thought maybe some bad gas. I checked the filters both in the tank and on carbs. I have put two tank thru it now since. I have pulled the center carb and have gone thru it looking for blockages, blown PV, correct jets, float levels, leaks and the whole deal. Everything was spot on.

After that adventure I took a look into the timing. I feel almost certain this is the problem. Initial timing is set at 5 degrees @ 750rpm per specs. With this I get 15"+- Hg. The stock VAC pulls at 15.5"@15 degrees. This fails the 2" rule. I think the VAC was getting just enough vacuum to maybe pull some but not all 15 degrees of vacuum timing at idle. But when the car became hot small vacuum leaks caused it to fail to pull the required 15.5" Hg at idle.

With the VAC switched to manifold vacuum I get 21 degrees at 800rpm with 17.5" Hg. That's the 5 degrees initial timing plus the 15+ the VAC is adding. Idle is smooth and steady.

 

Yes, I bought it new. I have never traced the source of the vacuum, but it as it came from the factory------------I've never messed with it. It also idles fine (kind of lumpy) and steady at 750 rpm-------as long as the metering plates in the end carbs aren't leaking and the plate in the center carb isn't leaking.

I'll have to look at it carefully when I get it out of it's winter cocoon.

 

The same symptoms occur if any of the 3 carbs are leaking a little fuel at idle. Opening the throttle allows enough extra air to smooth out the engine.

 

Another thing I was thinking about last night Mike----when I first got my tri-power going it was giving me fits. Sometimes it would run right, sometimes after a while it wouldn't. Biggest thing was idle problems. Tried a lot of things, even blocked off the outer carbs. Finally I went up one or two sizes on the main jets. That was it. Some say main jet size has nothing to do with idle quality---but it fixed it for me.

Anyhow you might want to keep that in the back of your mind.

 

Thanks for the clarification - been a couple decades (more like four actually) since I did the tri-power number (mostly on GTOs). A few observations. I wouldn't get overly hung up on the 2" rule - it's more like a guideline; every engine is different. Strictly my opinion and others may know more but if you can't get the car to idle properly on ported vacuum (when vacuum is basically removed from the equation at idle) then you have carb problems - it's that simple in my mind.

Full manifold vacuum will make the car idle smoother and cooler but is not a requirement to get it to idle AT ALL. I'll let others with more BB and tri-power experience weigh in at this point.

 

Actually, it was, and was mandatory in California - L-71 with K-19 used a "JA" suffix engine (photo below).

You may be thinking of the '66 L-72 427/425hp; it wasn't available with K-19, but had ported advance instead to be California-legal.

 

JohnZ,

I have an engine coded JE. Was the K-19 on the '67 L-71 connected to "ported" vacuum?

 

K19 vac requirement was tied into the choke vac signal with a Tee which is manifold vacuum. That's where I tied the vacuum advance shown in my post above.

 

Do you find it runs better on manifold vacuum vs ported vacuum? Is that why you connected it that way?

 

Yes as explained in post#21.

 

To change the VAC did you have to remove distributor or can it be done with distributor in car?

 

You can change the can with the dist installed. Reaching the screws is best accomplished by using a Mity-vac applied to the can to pull the rod away from the rear screw. This for both removal as well as installation.

You have to be careful not to drop any hardware. I use a special captive screwdriver that holds the screw.