63, 327.340 idle vacuum

[Duke W.]

Re: 63, 327.340 idle vacuum

Do you have a 1963 Corvette Shop Manual?

Duke

[Peter L.]

Re: 63, 327.340 idle vacuum

Duke,
I do have a shop manual, and skimmed thru the carburator section. All I can say is "Holy crap!" There's a lot there. I can see where it's way beyond my abilities (and tools) to really set up a carb correctly. That's why I want to Custom Carbs in Middlesex, NJ in the first place. I bought it from him and had him restore/rebuild it and he couldn't get it to work properly in the first place. I do know that if I go only 1 or 2 days between starts, it works fine. Not sure why that happens.
Pete

[Richard G.]

Re: 63, 327.340 idle vacuum

Peter;
Duke knows more about the 340Hp motors than I will ever hope to.
Purchased one new and has been working on them ever since.
Basically GM did a poor job of setting the timing curves.
As I understand it the 250HP motor has the same distributor stetting as the 340hp.
That should say a lot about the poor choices GM made.
Even the factory timing marks are off as they changed the diameter of the balancer and kept the old timing spacing.
You can look up Duke's remarks, posted in this forum, on the 340hp and find out all you need to know to set a 340hp up properly.
I am using the B28 vacuum advance per Duke's recommendation. My idle is dead solid @ 850rpm.
Take care of and axial play and reduce the end play to Duke's recommendation. Be sure the little lube felt is installed on the points cam.
Takes some work but you will be happy with the results.
Rick

[Peter L.]

Re: 63, 327.340 idle vacuum

Thanks for the advise. I have ordered a B28 (sold as a 4V1053 by Rock Auto) and intend to try it. But remember, my problem is on cold start up, where it runs rough at 900 rpm and stalls unless I manually open the choke or use the gas pedal to up the rpm's to about 1500 to 2000, either for about 15 to 20 seconds. After that point it runs very smooth.
Unless your talking about my other problem, which is that when I'm in either 1st or 2nd, at 1500 to 2000 rpm, steady speed, the engine "surges" up and down . Above 2000 rpm, it's ok, and while you don't feel it as much in 3rd or 4th, it's still there (the surging -below 1500 rpm), just hardly noticeable.

[Duke W.]

Re: 63, 327.340 idle vacuum

Duke,
I do have a shop manual, and skimmed thru the carburator section. All I can say is "Holy crap!" There's a lot there. I can see where it's way beyond my abilities (and tools) to really set up a carb correctly. That's why I want to Custom Carbs in Middlesex, NJ in the first place. I bought it from him and had him restore/rebuild it and he couldn't get it to work properly in the first place. I do know that if I go only 1 or 2 days between starts, it works fine. Not sure why that happens.
Pete

The AFB is a relatively simple mechanical analog device that works pretty well if properly set up, but if you don't want to get into it yourself suggest you send it back to the rebuilder, along with photocopies of the AFB section of the manual including the spec page at the back.

If cold start is okay after only sitting a day or two, but not after sitting for a week or more the problem might be lack of fuel in the bowl due to evaporation, but if it does start the fuel pump should fill the bowls within a couple of seconds.

One thing you can do it get a plastic needle irrigation syringe from your doctor or dentist and use is to inject a few cc of fuel into the bowls if it's been sitting for a while.

The lean surge could be due to too low a fuel level, which will require a float level adjustment, or it could just be the idle mixture is too lean. The initial position for the emulsion screws is 1.5 turns out from the seat, and in my experience the final setting usually ends up within a quarter turn unless you are at high altitude.

At this point I say get the B28 VAC installed, go through the idle speed/mixture adjusting procedure in the shop manual and see if that improves things.

Duke

[Peter L.]

Re: 63, 327.340 idle vacuum

Duke,
Thanks for all your comments, suggestions, etc. I spent some time with my distributor today (about 3 hours) first checking operation with the installed VA (a B26, not a 201), and found that even with 25 " hg with my hand vacuum pump applied, the vacuum advance pin didn't move, unless I helped it manually. I noticed the groung wire was looped around the outside of the vacuum advance, and was rubbing between the advance plate and the body of the distributor housing. I re-wired it to the inside of the va, and tried it, and had the same problem. I removed the B26 va and installed the B28, and found the same thing, only at a slightly lower vacuum (it actualy moved at 20" hg). So my problem sems to be a sticky va plate mechinism in the distributor. Before I take the entire distributor out and have it cleaned, etc, I am going to try spraying some WD40 into the workings of the advance plate and see if I can flush out and lubricate what ever is holding it (sugggested by the mechanic I use for all work on the car). The centrifugal weights move freely, with no resistance (other then the springs), so I know that is not the problem. I believe it is the fact that I get no vacuum advance untill the engine either revs very high (hence a high vacuum), or warms up and what ever is stickluing gets less sticky. Either way, I'll let you know what happens after I WD40 it.
BTW, I tried moving the advance plate by hand, with the va out, and there was a ton of resistance. My understanding is that it should move by hand freely. The specs on the B26 and B28 are similar, and the B26 should have worked (same max 8 degrees of advance, but the B28 achieves it at between 6 and 8"hg, while the B26 achieves it at 11-13) if the advance plate on my distributor was not sticking. I definitely agree the B28 is better suited for this 340 HP engine, since my idle speed (900 rpm) vacillates between 12 and 13 "hg.
Thanks again,
Pete

[Duke W.]

Re: 63, 327.340 idle vacuum

Yes the breaker plate should rotate freely when the VAC is removed, and you can test the VAC before installing. A B28 should start to pull the link at about 4" and be at the limit at about 8". I bet your distributor has never been overhauled in the 55+ years it's been in the car. Forget the WD-40 business. Your distributor needs to be removed for a blueprint/overhaul, absolutely, positively, no exceptions!

As I've said many times before, the distributor is the most overlooked component on the engine, but unless it's functioning properly the engine will perform poorly in every way.

It's a relatively simple device, and the disassembly/assembly procedure along with a exploded parts photo is in your 1963 Corvette shop manual, but one thing they don't mention is that the dimple in the gear MUST be pointing in the same direction as the rotor tip, so keep this in mind upon assembly.

Back in 2012 I started a thread on a dist. blueprint/overhaul I was doing. It's here on the TDB and on the CF and contains additional tips and advice on how to set it up better than it was from the factory, including optimizing the spark advance map. Start with black springs in the Mr. Gasket 928G spring kit.

Prior to removal, set the crank at 10 degree BTC #1 compression stroke. The rotor should be pointing about 20 degrees right of engine centerline. As you pull it out the rotor tip will rotate CCW and be pointing approximately along engine centerline when the gears disengage.

Upon installation start with the rotor tip as above and it should drop in. If it doesn't fully seat you may have to tweak the oil pump drive shaft with a paint mixing stick.

Once seated, rotate until the points just begin to open and the engine should start right up with about 10 deg. initial timing. Do the final timing with a dial back timing light by revving the engine a few hundred revs above the max centrifugal point (VAC hose disconnected and plugged with a golf tee) and set at 38-39.

If it doesn't detonate you're good to go, and if the engine is in good internal condition it will run better than new.

Duke

[Peter L.]

Re: 63, 327.340 idle vacuum

Duke
Thanks for the tips. The dist was actually completely rebuilt about 6 or 7 years ago, by the engine rebuilder (a large well recommended race and street car engine rebuilder, and dyno tested after assembly). I will take it out and have it serviced, however this may seem like a dumb question. As I recall there are only about 15 or 20 degrees marked on the harmonic balancer, so how do you get to verify 36 to 38 degrees advance at higher rpms?
Pete

[Duke W.]

Re: 63, 327.340 idle vacuum

You need modern dial-back timing light. They have an adjustment that allows you to "dial in" total WOT advance. Say you want 38 degrees. That's were you set the dial or whatever type of adjustment is provided. With the VAC signal line disconnected and plugged with a golf tee, you rev the engine a few hundred above the point of max centrifugal then rotate the dist. to bring the notch on the balancer to the zero line on the tab.

A basic one (Acton) costs about 50 bucks. More expensive types also show revs and maybe dwell. This method gives you true advance, so the inaccuracy of the tab on SHP engines with the 8" torsional damper is not an issue. They are very handy for "mapping out" the spark advance map, which is EXTREMLY IMPORTANT to achieve maximum engine performance and fuel economy. Few of the OE spark advance maps are optimum and many have been modified over the years, not always for the better.

Back in the day, before dial back timing lights became common one could buy mylar timing tape that wrapped around the torsional damper. It was marked at 90 degree increments, and usually about 0-60 degrees in one or two degree increments BTC #1 compression stroke.

Duke