1967 435 vacuum reading and timing

[Danny P.]

Re: 1967 435 vacuum reading and timing

Thanks Mark. It may have been touching, not sure. When I put it back on I will be sure to make sure their is a gap.

Mark , find yourself a old coil that you know it works just to try and go for a road test , i think the Carbs. are ok, try removing the crome shield on top of Cap see if there any arcing from the coil wire,

[Gary J.]

Re: 1967 435 vacuum reading and timing

Can you post pictures of the top side of both coils, repro and original for comparison?

[Larry E.]

Re: 1967 435 vacuum reading and timing

Are we sure we are barking up the correct tree? How about gas percolation? Type of gas used? Just a thought.
Larry

[Mark F.]

Re: 1967 435 vacuum reading and timing

Thanks Danny, Yes, carbs are fine. After taking a second look, I think my coil is a reproduction. As you mentioned, finding an original is like find hens teeth. But I'm going to try. If you know of a good source of who might have one or know where one is please let me know. I did speak with someone here in MN who has a shop that is dedicated to working on C2's. He told me that what most are doing, since the 263's are so hard to find is to use a 207 coil and change out the inside of the ignition box to solid state. While the car all the judging it could ever get, I am still going to try to find an original 263. Thanks again for all your info and help. I send you pics of my vette.

[Danny P.]

Re: 1967 435 vacuum reading and timing

Can you post pictures of the top side of both coils, repro and original for comparison?

Gary ,the coil on the left is the Delco repro

IMG_5915.jpg263 coil.jpg

[Duke W.]

Re: 1967 435 vacuum reading and timing

Good Evening,



After reading an archived thread on the NCRS site about "427 overheating" it was clear I was not the only one having this issue. The discussion in the thread circled back to the vacuum advance can on the distributor, timing advance and Hg vacuum ported or manifold. Due to how this car was campaigned and Judged all the components are 100% original including the B20 vacuum can. My questions are this: 1. The vacuum line going to my vacuum can comes directly off the bottom plate of the center carb. Is the manifold or ported? If ported I don't see a direct manifold place to hook up to. 2. Using the vacuum fitting at the bottom plate of the center carb, my engine at idle ( 800-900 rpm) pulls 5 Hg (10 cm) inches. At 3500 rpm it pulls about 17-18 Hg inches (45 cm Hg) The timing advances using the mechanical as it should. Are these vacuum readings normal?

First off the B20 VAC is no way original. It's an aftermarket replacement for the 12" 355 16. The OE L-71 VAC is the 15" 201 15.

The vacuum port at the bottom of the center carb as shown in the photo in post #4 is ported (no vacuum at idle) unless the baseplate has been modified to make it full time, which is fairly easy to do, but the carb has to come off and be partially disassembled for this job.

If it is still ported, the easiest way to convert to full time is by teeing into the choke vacuum break source, with is full time manifold vacuum. Remove the short hose from the ported vacuum source and place a vacuum cap over it. Then remove the choke vacuum break hose and make a new harness with 1/8" vacuum tubing and a plastic tee to run signal line to both the choke vacuum break diaphragm and the upstream side of the vacuum advance steel pipe.

If equipped with OE 15" 201 15 you would need to replace it with a 12" B26. The B20 has the same specs, but was discontinued over a decade ago as part of a part consolidation effort, but you should check it, start @ 6", 16 @ 12".

The OE L-71 centrifugal is start @ 900, 30 @ 3800, and you should check to see if it's been modified. If not set initial (at less than 900 VAC signal line disconnected and plugged) in the range of 6-10 to obtain the optimum total WOT advance of 36-40, as high in that range as the engine will tolerate without detonation.

Set idle at about 900 and it should pull about 14"HG and pull away smoothly from a dead stop without excess clutch slipping.

Your stated manifold vacuum readings are confusing. Manifold vacuum in the USA is traditionally quoted in inches of Mercury If you are stating that your manifold vacuum is only 5" Hg at 800-900 someone has installed a HUGE overlap cam, like maybe a L-88 cam, and I'm surprised it will idle that low. Or maybe you are not measuring idle vacuum properly. You must "tee" the vacuum gage into a source of full time manifold vacuum like the choke vacuum break source or the VAC signal line AFTER you convert it to full time vacuum advance.

Duke