Wanting to switch my 1967 L71 to manifold vacuum

[Stuart F.]

Re: Wanting to switch my 1967 L71 to manifold vacuum

Terry;

Thanks for the heads up about the TI in 69 L-89's. That will save me some time doing a final tune on it. My son will be flying thru this coming Wednesday, so I'll have to wait.

Stu Fox

[Richard M.]

Re: Wanting to switch my 1967 L71 to manifold vacuum

Thank you Richard Mozzetta for you pictures as they are very helpful! Thanks to all of you who contribute your knowledge to this website to help keep these works of art on the road! Once I complete the conversion to manifold vacuum, I will report back with my results. Thanks again, Chris Covinsky

You're welcome Chris, glad the pics helped.

So, before you report back.........which method did you choose to convert to full time?

Rich

[Chris C.]

Re: Wanting to switch my 1967 L71 to manifold vacuum

Rich,

The car was already judged at St. Louis chapter with a score of 98.5 and I don't plan on continue with more judging. I just plan on driving and enjoying the car. I will probably install a tee on the existing vacuum line like is show on your last photo on post #14. I need to purchase the parts along with a mighty vac to install the new vacuum canister. Thanks again for all your help!

Chris Covinsky

[Chris C.]

Re: Wanting to switch my 1967 L71 to manifold vacuum

I am bringing up this old post because it will force me to finally complete the "Duke Williams vacuum conversion". I must admit I was enjoying driving the car so much that I was a little bit afraid of making a mistake and the car not driving as well as it does! That being said, I do not want to stare at my temperature gauge all weekend at Bloomington Gold if I get stuck in traffic!!! I purchased a Minivac and the full time manifold vacuum with a tee on the choke vacuum line seems to fluctuate a little between 13 and 14. Should I be concerned that the Minivac gauge seem to bounce and is not constant. I want to go to the next step and install the B26 vacuum advance canister (VC1765), is this correct? I was told the car was restored with a stock 435hp camshaft, but I don't want to make a mistake with this conversion. I want to make sure I purchase the correct vacuum advance canister, where should I purchase and what part number should I get? I also remember reading that there needs to be an adjustment to the carburetor which, not being a mechanic, I am somewhat apprehensive about! I do own a 1967 GM service manual, are there instructions shown there? I know after owning six previous midyears that I should know these things, but I am determined to learn on this one!!! Thanks in advance for any help!

Chris Covinsky

[Duke W.]

Re: Wanting to switch my 1967 L71 to manifold vacuum

VC1765 is a NAPA part number. You can cross this to any other brand on the Web or at a parts store. Just make sure what you get is stamped B26.

Some fluctuation in manifold vacuum/idle speed is normal for SHP engines due to valve overlap, but it should be less when the B26 is connected to full time manifold vacuum.

The idle speed-mixture procedure is in the CSM and is akin to changing a light bulb. Target idle speed is 900, and vacuum should be about 14".

You should be able to work the old VAC off the dist. without removing it from the engine. Use the MityVac to pull the rod to the limit and carefully work the pin out of the hole after removing the attaching screws.

You will need a couple of feet of 1/8" vacuum tubing and a tee to make a new harness that connects the carburetor full time vacuum source to both the VAC and choke vacuum break.

Duke

[Chris C.]

Re: Wanting to switch my 1967 L71 to manifold vacuum

Thank you so much for all your advice. I plan to finish this soon and will report back with results! Thanks again, Chris Covinsky

[Chris C.]

Re: Wanting to switch my 1967 L71 to manifold vacuum

Duke,

I could not find a ECH VC1765 in stock, but found a BWD V375 which shows B26 on the part. Shall I assume this is the correct part I need?

[Duke W.]

Re: Wanting to switch my 1967 L71 to manifold vacuum

The are both the exact same part made by Standard Motor Products - just a different "brand"/brand part number/marketing channel. VACs are available in at least half a dozen brands, but all are made by SMP, including Delco brand. All that counts is getting the correct B-number stamped on the mounting bracket.

Duke

[Chris C.]

Re: Wanting to switch my 1967 L71 to manifold vacuum

Sorry to bother you again Duke, but I am installing the B26 vacuum canister and the one in my TI distributor has some sort of black rubber sleeve over the rod that attaches to the advance mechanism. Should I transfer that to the new B26 canister or is it not needed??? Thanks again for all your help!!! Chris

[Chris C.]

Re: Wanting to switch my 1967 L71 to manifold vacuum

I had to make a judgment call about this rubber sleeve that was on the original vacuum advance canister on my L71. Of course now that it is all put back together, I think I made a mistake. My after the fact guess is that the rubber sleeve I removed and installed on the new B26 canister is going to limit the advance. If this is true, please let me know so I can have the pleasure of removing the big block ignition shielding once again to remove that rubber sleeve. Looking forward to finishing this conversion!!!

[Leif A.]

Re: Wanting to switch my 1967 L71 to manifold vacuum

I had to make a judgment call about this rubber sleeve that was on the original vacuum advance canister on my L71. Of course now that it is all put back together, I think I made a mistake. My after the fact guess is that the rubber sleeve I removed and installed on the new B26 canister is going to limit the advance. If this is true, please let me know so I can have the pleasure of removing the big block ignition shielding once again to remove that rubber sleeve. Looking forward to finishing this conversion!!!

Chris,
I have never seen a rubber sleeve on the arm of a Vacuum canister as it would most definitely not allow the canister to do it's job. IMHO, remove it.

[Stuart F.]

Re: Wanting to switch my 1967 L71 to manifold vacuum

I've seen the sleeve on certain OE applications, and yes it is a restrictor. It certainly isn't to prevent metal to metal contact of the rod in the slot. However, of late, I've found it necessary to inspect new replacement VAC's to ensure the rod is not bent and dragging on the side of the slot. It pays to check it with a Mityvac before installing. I have had to bend the rod on several to keep it straight through it's travel so it wouldn't bind in the slot.

Stu Fox

p.s. This is a long thread over some time. If I'm repeating myself I apologize.

[Chris C.]

Re: Wanting to switch my 1967 L71 to manifold vacuum

My main concern is that this rubber sleeve is going to limit the amount of advance, should I remove it or can it stay???

[Duke W.]

Re: Wanting to switch my 1967 L71 to manifold vacuum

You should have installed the new VAC as is without the rubber sleeve. For now, use the MityVac to test where the VAC starts and stops. It should be about 6" and 12".

Also, use a timing light to see how much advance it adds at idle, and you should run this test at a speed below where the centrigugal starts.
(See you CSM.)

Also, what is the number stamped on the VAC you removed?

Duke

[Chris C.]

Re: Wanting to switch my 1967 L71 to manifold vacuum

I did verify the start of the vacuum at six and fully open at 12. I will enjoy removing the ignition shielding one more time to remove that rubber sleeve. Is 900 rpm at Idle already engaging this centrifugal advance? I will report back what the original VAC number show. Thanks again Duke I just want to do this correctly!