67 L36 Vacuum Control Canister

[Duke W.]

Re: 67 L36 Vacuum Control Cansister

Tim,

The engine is making 16" at idle. I have not checked the timing as of yet. Will the B26 work at this level?

Specifiying idle vacuum without including idle speed is meaningless. The higher the idle speed is set, the higher the vacuum and vice versa. A L-36 with manual trans should idle satisfactorily at about 600 in Neutral.

Duke

[Lawrence S.]

Re: 67 L36 Vacuum Control Cansister

I idled it up to about 800 rpm because of the rich situation. I was trying to help the situation. I did have it idling at 600 before moving it. So at 800 it was at 16"

[Duke W.]

Re: 67 L36 Vacuum Control Cansister

A properly set up, unmodified manual trans L-36 should idle satisfactorily in neutral at 600 @ 14", so 12" B20 or B26 is the best fit VAC. If it's running "rich", go through the idle speed/mixture adjustement procedure in the CSM with a target idle speed of about 600.

I gave you guidance on how to find a B20 or B26 in any brand at your most convenient parts store in post #5. They cost about ten bucks.

Duke

[Lawrence S.]

Re: 67 L36 Vacuum Control Cansister

Duke, I bought the B26 VAC but it has not arrived yet. I had to order it.

I have adjusted the idle mixture circuit per the CSM, and had the car idling at 600 rpms but it seemed rich. So I adjusted the idle up to 800 to see if that would help the situation. While doing so I discovered that the vacuum advance was not working properly. Is it possible that the car could be running rich if the vacuum advance is not working?

Thanks

Lawrence

[Duke W.]

Re: 67 L36 Vacuum Control Cansister

The first question is why do you think it was rich, but never mind... (If it is rich you merely turn in the mixture screws a quarter turn or more in to lean it out.) Using a vacuum gage you should set the idle mixture to get the maximum speed/vacuum. It's an iterative process because sometimes the idle gets too high, so you adjust it back down, then work with the mixture screws again and keep repeating until it's optimized... sounds complicated, but it usually only take a couple of minutes.

A dead VAC will definitely affect the idle behavior, so there's no point doing anything more until the new B26 is installed. Achieving the proper range total idle timing, which is the sum of initial and full vacuum advance is important to achieving a proper idle. If the VAC is dead then vacuum at any idle speed with be less than if the VAC is working.

You should also check that initial timing is correct - in the range of 6-10 degrees. Then with the correct range initial and new B26 you should be able to achieve a fairly smooth idle at 600 @ 14".

I usually only change VACs with a disassembled distributor, but it can be swapped with the distributor in the car. Using a MityVac to pull the pin to the advance limit sometimes helps.

Duke

[Lawrence S.]

Re: 67 L36 Vacuum Control Cansister

The reason I think it is rich is because of the plugs fouling and it just smells rich at idle.

I have adjusted the idle mixture with a vacuum gauge on my other cars so I can get that done.

I have a MityVac so I will use that to help me swap out the vac. I have swapped them out without and it is a pain.

Hopefully the weather cooperates so I can get this done Saturday.

Thanks for help Duke.

Lawrence

[David K.]

Re: 67 L36 Vacuum Control Cansister

Guys,

Not to hijack the thread, but is the VC1765 also correct for a 427-435 with TI?

Thanks.

[Joe L.]

Re: 67 L36 Vacuum Control Cansister

Guys,

Not to hijack the thread, but is the VC1765 also correct for a 427-435 with TI?

Thanks.

David-----


If you're talking about 1967 L-71, the equivalent replacement is stamped "B1". It's NAPA VC-680.

[William F.]

Re: 67 L36 Vacuum Control Cansister

Duke,
Factory calls for 4*BTDC initial timing on a '67 L36; but in '66 did say from 4*-10* but noticed somewhat different specs for vac advance. Mine does have replacement vac can. Assuming(I know, I'll check to make sure)a B20 or B26 and stock centrifugal advance curve, where would you set initial?

[David K.]

Re: 67 L36 Vacuum Control Cansister

Joe,

Thanks for replying and yes I am talking about a 67 L-71. Should have mentioned that in my post. I am on my way to NAPA.

Thanks,

Dave

[Duke W.]

Re: 67 L36 Vacuum Control Cansister

Guys,

Not to hijack the thread, but is the VC1765 also correct for a 427-435 with TI?

Thanks.

Depends. The OE VAC is a 201 15 which doesn't meet the Two-Inch Rule, but then OE the L-71 had ported vacuum advance.

I recommend converting L-71s to full time advance, and then a B20 or B26 is required.

In fact, the B20 or B26 is best for all manual trans OE big blocks - either with OE full time vacuum advance or converted from ported.

I'm not sure about big blocks with automatics because I've never been able to obtain reliable engine vacuum data idling in Drive.

Can someone in TDB-land with a big block automatic take the measurement? Manifold vacuum at RPM idling in Drive. Be sure to set the parking brake firmly and chock the wheels when doing this test or have someone in the car holding holding the brake pedal.

Duke

[Duke W.]

Re: 67 L36 Vacuum Control Cansister

David-----


If you're talking about 1967 L-71, the equivalent replacement is stamped "B1". It's NAPA VC-680.

Joe - the B1 is a boat anchor. It can take as much as 18"' to pull it to the limit, which isn't even a good fit for base engines. We got victimized by GM's parts consolidation, which was not very well executed in many cases.

The B22 is essentially the same as the 201 15, which is a very good fit for base engines with manual trans, but I recommend the B20 or B26 for base engines with automatics. They are equivalent to the ...355.

The only other candidate for any vintage engine with full time or converted to full time advance from ported is the B28, which is for engines that generate less than 14" idle vacuum, which includes all mechanical lifter cam small blocks and L82/autos.

Of the dozen or more replacement VACs out there one of the above three is best suited to all full time vacuum advance applications for engines with single point or TI ignition systems.

Duke

[Duke W.]

Re: 67 L36 Vacuum Control Cansister

Duke,
Factory calls for 4*BTDC initial timing on a '67 L36; but in '66 did say from 4*-10* but noticed somewhat different specs for vac advance. Mine does have replacement vac can. Assuming(I know, I'll check to make sure)a B20 or B26 and stock centrifugal advance curve, where would you set initial?

The answers to your questions are in my 2012 San Diego National Convention presentation. A pdf of the PowerPoint charts is on the Web and the link has been listed on the TDB a number of times.

Duke

[Joe L.]

Re: 67 L36 Vacuum Control Cansister

Joe - the B1 is a boat anchor. It can take as much as 18"' to pull it to the limit, which isn't even a good fit for base engines. We got victimized by GM's parts consolidation, which was not very well executed in many cases.

The B22 is essentially the same as the 201 15, which is a very good fit for base engines with manual trans, but I recommend the B20 or B26 for base engines with automatics. They are equivalent to the ...355.

The only other candidate for any vintage engine with full time or converted to full time advance from ported is the B28, which is for engines that generate less than 14" idle vacuum, which includes all mechanical lifter cam small blocks and L82/autos.

Of the dozen or more replacement VACs out there one of the above three is best suited to all full time vacuum advance applications for engines with single point or TI ignition systems.

Duke

Duke-----


That may be so. However, according to the information I have, the "B1" control (NAPA VC-680) most closely matches the specifications of the original GM 1116201, 1116163, and 1116212 of all the currently available Standard Motor Products-manufactured vacuum controls.

The "B22" (NAPA VC-1802) most closely matches the specs of the GM #1973437.

[Duke W.]

Re: 67 L36 Vacuum Control Cansister

I use Lars Grimsrud's published specs for B-series replacement VACs as follows:

B22: 0 @ 7-9", 16 @ 14-16". The ...201 is 0 @ 8, 15 @ 15.5" - a pretty close match. The ...163 was substituted for the ...201 in the P & A catalogs decades ago, and the aftermarket keyed off the GM parts catalogs, not OE spec.

It was a poor choice by GM because the B1 can require 18-19" to achieve the full advance. It doesn't comply with the Two-Inch Rule for any Corvette engine. Base engines with manuals idle at 17-19", but automatics idling in drive are a few inches less. The B22 VAC is the least aggressive VAC that complies with the Two-Inch Rule for manual transmission base engines or optional engines with the base engine cam and manual transmissions.

VAC specs are sometimes quoted as norminal and sometimes a range. If nominal specs are quoted the variation can be up to one plus inches Hg and one to two degrees. That's why I encourage all to take a Mity Vac to the parts store and test for complience with specs before you accept the part.

IIRC the ...437 is that weirdo 24 degree VAC advance that was OE on the '64-'65 250/300 HP engines, and I recall there was a TSB that recommended replacement with a ...201 if the owner complained about driveability issues. (It was posted here not long ago.) I discussed the several changes to the '62-'67 250/300 HP VAC specs in my San Diego seminar (pdf of the charts are on the Web). My reocommendation is the 15" B22 for manuals and 12" B20 or B26 for automatics.

There are several cases where GM didn't select a proper VAC for the engine's typical idle vacuum behavior. In addition to the above the '63 L-76 and '65 L-78 are examples.

Duke