I have been reading JohnZ and Lars posts archived over at Corvette-restoration.com's page (a guy restoring a c3 has archived some great articles by these two men).

With all the old cars I've owned I admit I have always relied on others for timing and other ignition help. Shame on me I know.

So- as a reminder- the car is my stock l75 64. I drove to a show over the weekend and found that I was getting a miss under load and the car has "always" seemed to run rich. Years ago when I bought it I found a couple fouled plugs and a will put plugs/wires/cap/rotor on in the am. Simply because I've never done more than the plugs. I ohm tested the wires and they were ok so I left them be back around 2015.

With that out of the way, the car starts relatively easily after sitting long periods, new fuel pump, and I reset the float level "a bit" in the carb to help hard hit starts. I felt I had some percolation. Also, my tank is clean inside but I had some sediment in the old FLAPS filter which I swapped (thanks Doug!). Hard starts are much better.

The car idles smoothly but always smells rich. The valve guide seals have a bit of wear evidenced by a couple plugs. Perhaps a part of my rich smell. I'm aware of the "rope trick" to change them.

I note today the car idles at 18.5" vacuum around 650 rpm measured at the hose to the vacuum advance. Seems ok. Car shows 99k miles believed to be correct.

1) timing light (non adjustable, very basic on-off trigger from Sears before I was born) shows 10 degrees advance at idle with the vacuum advance disconnected and plugged. Seems good, right?

2) 6" balanced with an additional mark I made in chalk at roughly 1.35" (26 more degrees) from the original cast mark centers on zero- indicates I'm getting around appropriate 36 degrees all in with centrifugal advance (no vacuum advance). Seems good- right?

3) vacuum canister takes vacuum at 16 inches applied with mityvac and bleeds down over the course of a minute with no additional vacuum applied to about half its value- about 8". I assume this is also good, although it does nothing to tell me if I'm getting umthe proper additional advance under load. Right?

4). Somewhat unrelated- my original carb idles with the idle mixture screws fully closed. This would point to my overly rich situation as mentioned above. Any advice on this is appreciated, I'm lost.

5) afterthought- my initial timing WITH the advance hooked up is the same 10 degrees. I assume this is normal because the advance is supposed to kick in under load with manifold vacuum dropping like a stone.

Things I have not checked or replaced but will probably do so that I'm familiar with them if need to do it in a pinch- points and condenser, setting the dwell...

This is a lot of comments, and as proud as I seem about my other successes you guys can tell I'm quite uninitiated in some basic knowledge.

 

I would deal with the valve guide seals before going too much farther. Its going to be hard to keep and get a proper tune without a miss if you have oil-fouled plugs. Its not all that big of a job. Then you can figure out your carb issues - running the mixture screws in should stall the engine... If its an AFB or WCFB; its an easy rebuild. Only THEN would I start fine-tuning the timing/advance curve. Short of a SUN machine you can do a credible job with a digital 'dial back' timing light most FLAPS stores have nice Actron version for about $59 IIRC.

 

All pre-cat (1974 and earlier) cars smell of hydrocarbons. We've just gotten used to the newer cleaner cars. My advice to you would be to get the car's tailpipe emissions checked on an exhaust gas analyzer to see where you're at. You want to be under 2% CO and 250 ppm HC if possible...if you are 3% CO or higher, you are way too rich. Basically, an over-rich condition will wash the cylinders with raw fuel and wear out the engine prematurely. Black smoke out the tailpipe. One reason new fuel injected cars run 300,000 miles; no choke. If your plugs are black and dull looking, you have a problem. If they are tan or grey, you are ok. Sounds like your timing and vacuum are good as is.

 

1, 2, & 3 are all good indicators of proper tool function and engine operation. Your engine may have wear, but it runs well.

4 indicates a problem. The carb is probably due for a rebuild. It cannot hurt. You do not mention if it has the stock WCBF or an AFB (or something else).

5 indicates the vacuum advance can is piped to a ported carburetor vacuum source, rather than the correct constant manifold vacuum source. The vacuum can should see vacuum at idle, and it should add advance at idle.

The correct additional vacuum advance at idle should help to increase the idle speed, and may help to allow backing out the carb idle mixture screws (and the rich idle condition).

The things to do:
Pipe the vacuum can to a constant manifold vacuum source.
Rebuild the carburetor
Change the spark plugs.

These do not need to be done in a particular order, but all three will be needed to improve the tune.

Points, condenser, rotor and cap (old school tune up) is also good if you see or experience any timing and dwell angle variation beyond the tune up parameters.

Good luck.

 

Thank you both for the insight. FTF- yes I completely see the utility in a better timing light. I also realize the truth in your statement that I need to do the seals. I'll be rereading those threads about which type are best. Seems there are many opinions on this.

GTO- thanks for the heads up on my timing in general. I was a little thrown off at first about my advance not changing anything when I hooked it up but- duh- if it's holding vacuum it should not change anything. I suppose what's written between the lines is that you disconnect it to 1) ensure you set initial timing without a bad advance interfering and 2) to measure the action of the weights on springs to get all-in timing without interference. JohnZ really did help this young guy get a handle on a lot (despite my questions)

Edit: hold on reading 63 340's comments re: vacuum advance

 

5) afterthought- my initial timing WITH the advance hooked up is the same 10 degrees. I assume this is normal because the advance is supposed to kick in under load with manifold vacuum dropping like a stone.
Benton,
Is your vacuum canister hooked up to manifold or ported vacuum? Should be manifold vacuum and your timing should advance when you hook up the vacuum line. If advance is remaining constant when you hook up the vacuum line you're probably tied into ported vacuum or your vacuum canister is not functioning as it should.

 

You could PM 'rich5962' and see which seals he put on my '63...I think he went over and above the normal replacement parts but I'm not near my records to provide specifics... I was tied up with consulting jobs at the time so he stepped up and took care of this; normally I would have done it myself!

My seals had turned in to potato chip consistency - yours prob have too!

 

Reply this and 63 340 comments regarding the same- I'm tied into manifold vacuum -just at the carb base between the mixture screws with the steel line and short section of rubber just before the canister. This is where I read manifold vacuum at 18.5 or a little more inches. It pulls this into my mityvac gauge (with no pumping from me). So I'm not on later style ported vacuum by my reasoning.

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will do thank you Frankie.

 

Yes, I know it's grungy.

 

Just so I'm following up the help that has flooded in, I tested the initial timing again with and without the advance- I would say there is MAYBE 2 degrees difference at idle in between the scenarios. I don't know if this is material, but it's slight enough it could simply be the difference in my stance when taking the two readings.

Side note...this is fascinating. Why didn't I do it sooner?!

 

Your vacuum can is not functioning properly - time to replace it!

 

When the rubber diaphragm in the vacuum advance can becomes old, it can stiffen enough to prevent proper operation. A new one should fix the timing problem.

 

... a big source to the problem.

-Bruce

 

Yes, it sounds like the VAC is dead, plus the leak-down rate is excessive, and HEY... it only took 10 responses for someone to mention this obvious possibility.

I also sounds like you don't understand the relationship between load and vacuum advance. Load is inversely proportion to manifold vacuum, so the lighter the load, the more vacuum advance is applied.

You want a NAPA VC-1802 or equivalent in another brand that you can cross reference. Regardless of brand (as long as it's a traditional name brand) it's made by Standard Motor Products and is stamped B22.

I suggest you buy it locally, and take your Mity Vac to the store to test that the link starts to pull at about 8" and is pulled to the limit at about 15".

Don't tell the year, make, model, engine and let them look it up on the computer. It will show a different part number, which is WRONG!

Just tell them it's a custom application.

You can check that advance is correct on the car. If the initial timing is 10 the total idle advance at 500 should be about 10 + 16 = 26.

When you install the new B22 the idle speed will increase, so you will have to turn it back down to 500. Then go through the idle speed-mixture adjustment procedure in the shop manual.

In order to remove a VAC with the distributor on the engine it's best to pump down the VAC and then carefully work the pin out of the break plate. Since the link on yours is likely frozen you may have to cut it off, but since the VAC is dead it's junk in either case.

You may have noticed that Lars' paper includes an addendum by me. You should also search for a thread started by me titled..."Tuning Vintage Corvette engine..." Download and study the pdf of the Power Point presentation. It will teach you the concept of a "spark advance map" along with how to set it up for various engine configurations.

A request from me: Please post the number stamped on the dead VAC mounting bracket.

Duke

 

Duke- wow! Thank you so much! Yes, I did not yet read or missed that the 16 degrees was pulled in at idle. I do comprehend what you just said (light bulbs have been going on at least).

I will test the advance at the counter with my mityvac just as you instructed.

I asked specifically for an echlin VC 680 (B1) which was what I had read from John's write up. You are saying B22, I may need some clarity on that so I can change my order if I've made a mistake (your post suggests I have).

Setting aside for a moment my old valve guide seal issue and discussing only the tune of the engine, I am making a fuzzy connection that my rich condition is caused at least in some part by my running 10 degrees timing off idle and not your indicated 26 degrees (10 plus 16). This may also account for my car running rich even with the mixtures screws closed?

Once manifold vacuum is eliminated after (say) 3,000 rpm or a bit less I'm not longer running any vacuum advance and it has been replaced by the 26 odd degrees of centrifugal advance I note, for 36 degrees max.

I'm absolutely off to read your article and more from Lars... Many thanks again for the help (and for record the help of all the other friends here)

Benton

 

Another possibility is the advance plate is stuck.

 

It is advancing with centrifugal. I don't know enough yet to say if the two advances are fully independent.

Benton

 

Dont want to confuse you any more, but the vacuum advance should NOT see vacuum at idle. No way, absolutely not, none! Thats just how it works! My dad told me if you can not figure what is port or manifold, the vacuum advance should connect to a port that is above the throttle blades. Therefore no vacuum till off idle.
NO vacuum to vacuum advance at idle.
Lane


BTW,
Your tools are just fine,

 

That information is incorrect for Benton's car, and for any pre 1967 or so car (1966 in CA IIRC) before the smog rules were changed. Ported vacuum was introduced as a smog control measure in those years. It does not benefit performance.

The whole point of vacuum advance at and off of idle at low load is to improve performance, drivability, fuel economy, and reduce engine heat from wasted fuel.

While it may not have been OEM on later cars vacuum advance at low load also benefits post 66/67 cars.