You needed to still switch the can after going to manifold vacuum? I just have mine with original "163" can currently. When NCRS judging I am hoping to just take a point deduction for non original configuration of vacuum line. If I need to switch VAC out as well I will have to take deduction for non OE part. I have yet to fully test car with just switching the vacuum source. I am hoping that is enough to correct my idle issue.

Thanks for the opinions and advice. I will let y'all know after I take the car on a good run.

MikeC

 

Yes.

You need to measure your manifold vacuum using a gauge to see what you need. Manifold vac at idle on this L71 was 14"Hg. The MS163-16 needs 18"Hg to fully deploy. The B26 needs 12"Hg to fully deploy, thus the 2" rule satisfied. If you just switch to manifold vacuum using the 163 it will likely have unstable/no effects at idle.

MS 163-16: 0* @ 9", 16* @ 18"Hg

B20/B26 (VC-1765) 0* @ 6", 16* @12"Hg

The purpose of switching to manifold vac is to allow timing to be fully advanced at idle so you need to use the correct adv can. You will also need to ensure your static timing is set to spec, and likely have to adjust fuel mixture and idle.

Personally, I would take a few points hit on 2 configuration issues, but have a better performing engine especially through Operations testing. Bigger hits in Ops.

Rich

 

"JE" was the non-K19 engine; both the K-19 and non-K19 engines used "ported" vacuum to the distributor.

 

You might also want to read this so you understand the theory involved:

http://www.camaros.org/pdf/timing101.pdf

 

At the risk of slightly taking this thread off on a tangent, where should a hook up my vacuum advance and which can should I use on my L71 if I was only interested in good driveability and less trouble with overheating when driving in traffic??

 

John, I believe he was asking where the K19 valve vacuum signal was sourced from.

UPC K19 A7 View A shows it going to the choke signal tap with a Tee which is manifold vacuum. That's where I sourced the vacuum for the vacuum advance on the L71 I restored a few years ago.

Rich

 

Manifold vacuum. Tap must be below the throttle plates. Tee into the choke pulloff tap mentioned above

Measure the manifold vacuum at idle and use a vacuum can that is fully deployed when vac drops to 2 in-hg below idle vacuum.

It's all been said before earlier in this thread.

Non-HEI Distributors:
P/N ID# Application Starts @ “Hg Max Adv
(Distr. Degrees @ “Hg.)
VC1802 B22 1971-72 350 4-bbl 7-9 8 @ 14-16
VC1765 B26 1965 396 Impala High Perf 5-7 8 @ 11-13
or 1966-67 Corvette Exc. High Perf.
B20 1966-67 Impala 427 Exc. High Perf.
1966-68 327 Powerglide Exc. High Perf.
1969 307 All
1969-70 396, 427 Camaro, Chevelle High Perf.
1970 400 2-bbl
1970 307 MT
1973 Camaro 350 High Perf.
VC1810 B28 1965 409 High Perf. 3-5 8 @ 5.75-8
1965 327 High Perf.
1966 327 High Perf.
1964-67 Corvette High Perf. FI
-------------------------------------------------------------------------------------------------------------------------------------------
-
VC680 B1 1959 – 63 All Chevrolet 8-11 8 @ 16-18
1964 Corvette exc. FI
1964 Impala, Chevy II
1965 396 High Perf.
1965-67 283, 409
1966-68 327 exc. Powerglide
1967-68 All 396
1969 Corvette 427 High Perf.
1969 396 Exc. High Perf.
1969 Corvette 350 TI
1969-70 302 Camaro
1970 400 4-bbl
1970 396 High Perf.
1970 Corvette 350 High Perf.
1973-74 454 Exc. HEI
VC1605 B9 1965 impala 396 Exc. High Perf. 7-9 10.3 @ 16-18
1965 327 All Exc. FI
1969 327 Camaro, Chevelle, Impala
1969-70 Corvette 350 Exc. High Perf.
1969-70 350 4-bbl Premium Fuel
1970 350 Camaro, Chevelle, Impala High Perf.
1971-72 350 2-bbl AT
1971-72 307 All
VC1675 B13 1968 327 Camaro Powerglide 9-11 8 @ 16-18
1968 327 Impala AT
1968 307 AT
1968 302, 307, 327, 350 Camaro, Chevy II
1970 350 Camaro, Chevelle Exc. High Perf.
VC1760 B19 1969 350 Camaro, Chevelle, Impala 4-bbl 5.5-8 12 @ 14-18
1969-70 350 2-bbl
VC1801 B21 1971 350 2-bbl 7-9 10 @ 16-18
1971-72 400, 402
1971-72 307 AT
Other Part Numbers & Specs:
VC700 B3 8-10 11.5 @ 19-21
VC1415 M1 6-8 10 @ 13-15
VC1420 M2 5-7 11 @ 16-17
VC1650 B12 8-10 10 @ 15-17
VC1725 B18 8-10 12 @ 13-16
VC1740 A5 6-8 12 @ 15-17.5
VC1755 A7 8-10 12.5 @ 18-20.5
VC1804 B24 6.5-8.5 10 @ 12-14
VC1805 M13 6-8 12 @ 14.5-15.5
VC1807 B25 5-7 8 @ 13-15
VC1808 B26 5-7 8 @ 11-13
(The 1808 part number has been discontinued by Echlin. It is the same as part number VC1765)
VC1809 B27 5-7 9 @ 10-12
VC1812 B30 5-7 12 @ 11.75-14

 

Same as I described in post#21. Tee off of the hose for the choke diaphragm. Note not to be confused with the hoses for the secondaries, i.e. front/rear carburetors.

I went through a exercise to do exactly that a few years ago and with help from many others it proved to be the best solution. It was a noticeable difference and the car could sit at idle for long periods of time and ran consistently under 190 degrees. The B26 was a perfect match with 14"Hg vacuum on the L71 I worked on.

The document below by Lars and Duke is very helpful information.

 

Maybe I need to test my VAC for accuracy. As I'm getting timing advance at 17.5" i should look to make sure its not cent. advance. Stock states 30 degrees at 3800rpm. The springs feel stiff to me. I wonder why they choose the "163" VAC at 18"? Even with full manifold vacuum that is too high to achieve.

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

 

Thanks for the info.

 

I pulled the stock MS 163-16 can today. Replaced with B26. Set initial timing at 8 degrees connected to Full Manifold Vacuum.
Idle speed set to 850rpm. Total idle timing 24 degrees (8 initial, 16 vacuum)manifold vacuum at idle speed = 17"

With this setup the car runs great. The idle is smooth and steady even after running hard for 75 minutes. I have fixed my issue. Thank you to all that helped and provided solutions along the way.

MikeC.

 

Glad your problem is solved. The B26 is the right can based on your tests. It should run much cooler at idle now too.

 

Hmmm. I wonder what's different. My engine will diesel when you try to shut it off if the idle is at 800 rpm. I have always had to have it right at 750 (by the tach) to get it to shut off-----at least without using the brakes and clutch as it dies.

 

What fuel are you running. I have been using 50/50 mix of 110 and 93. When I first tried just 93 I was experiencing some dieseling when I would shut off.

 

That's because your throttle plates are too far open at idle, due to having no vacuum advance at idle with "ported vacuum"; When you convert it to manifold vacuum (with a B20 or B26 can), the added 15* of timing will let you close down the throttle plates at idle, and the dieseling will stop.

 

I set my throttle plates so it looked like a square hole at the idle transfer slot. I did this when I had the carb off and upside down.

MikeC