1964 Out of winter hibernation - Timing - Overheating - Carb tuning

[Dino L.]

What a couple of weeks it has been tinkering with my 1964, ever since I top flighted this car, it never performed like I wanted it to.....so prior to an upcoming judging meet, I thought I would fix a couple of things.....I am sure many of you have been through the very same thing.....First I wanted to fix the lean in the rear end, which was caused by the passenger front spring not seated in the a-arm pocket, that was a job!, I then tried to start the car, and it would not go...period, oh I was just bragging about how long my 6 year battery lasted from NAPA,....well that was short lived, replaced the battery, and still won't start, no fuel.....replaced NOS fuel pump with less that 2000 miles on it...Ethanol? Got is started, and decided to chase the idling overheat problem I have had since rebuild. I started with our TDB friend Duke William teaching me about vacuum advance, centrifugal advance, advance map and its effect on engine idle tem....So with his help I tried to time the engine and continued to not be able to create enough advance, the vacuum can kept hitting the manifold, now I know and tested the 236 can worked all in at 8in HG and the 2818 Holley pulled 15in Hg at 900 rpm (definitely meets the 2" rule), this high vacuum was the first surprise, which of course I confirmed my L76 did not have the right rebuild cam it had a revised grind Comp cam....pulling the distributor before, I knew the dimple lined up with number 1 per factory specs.....so after consulting with Duke, I pulled the distributor and removed the drive gear and rotated it 180 degree to non-stock configuration....that's right the opposite of the typical fix where they are mis-installed. I believe this rotates the distributor 18 degrees... I should point out that I had the distributor rebuilt by a NCRS pro with .018" end play which was causing spark scatter, seen by the timing mark jumping around.....I shimmed the distributor to .008" end play, only had a .010" shim.....located the timing mark to 16 degrees advanced, dropped the distributor in, static timed it, started right up, and low and behold, the can and distributor orientation was now factory perfect in the center, and easily timed it.....both at idle and at 2500 rpm where full centrifugal advance came in.......and guess what.......no spark scatter and no more idle overheating....dead steady at 180......I then adjusted the Holley 2818 idle using a vacuum gage and tach....the car always had an off idle stumble.....the passenger idle screw was out 1 turn and the driver was out 2 turns......after tuning... both were set at 1.5 turns to maximize rpm, and vacuum, and a rock steady idle at 700 rpm.....I still have a bit of stumble at 30 mph and a slight acceleration, so I plan to take them both out an additional 1/4 turn.....The car drives incredibly different, in so many ways, from a stop, shifting, max revs, I can't thank Duke enough spending the hours on the phone walking me through this and troubleshooting it......and finally not having to watch the temp gage is cathardic!

[Timothy B.]

Re: 1964 Out of winter hibernation - Timing - Overheating - Carb tuning

Dino, describe the stumble more, is it like driving at low speed and when you press the gas pedal it stumbles before accelerating.

If so, check your accelerator pump linkage for correct adjustment and even look at the plastic accelerator pump cam that attaches to the throttle lever. The cam could be wore and you don't get a good pump shot when moving the throttle. One more thing to keep in mind is there is a accelerator pump check valve inside the primary float bowl that could require adjustment. The bowl needs to be removed to adjust this, it's very simple but if not adjusted correctly the first part of the accelerator pump shot gets wasted seating the check ball.

[Dino L.]

Re: 1964 Out of winter hibernation - Timing - Overheating - Carb tuning

Thanks Tim for the insight....the only stumble is around 35 mph in 2nd and steady speed, and depress the accelerator lightly.....trying to go up to 40 mph. This feels like the engine is not loaded.......when this happens, just a flat road.....doesn't happen all the time. Is the check valve adjustment in the 64 shop manual? Thanks
Dino

[Timothy B.]

Re: 1964 Out of winter hibernation - Timing - Overheating - Carb tuning

Dino,

I am not sure if the adjustment is in the shop manual.

If you want to check the accelerator check valve adjustment, remove the carburetor from the car then remove the accelerator pump. You will notice what looks like a very small bar that holds a check ball and that small bar should only allow approx .015 drop of the ball. I use a wire tie like what's in a loaf of bread as they are usually .013-.015 diameter and slide it between the check ball and bar, you will understand when you see it. If the ball drops to far the first part of the pump shot is wasted seating the check ball before fuel is pumped up to the squirter.

[Duke W.]

Re: 1964 Out of winter hibernation - Timing - Overheating - Carb tuning

I suggested to Dino that he title this thread: "Why you shouldn't buy a Comp Cams camshaft"

It turns out that this cam, part number 12-212-2 that is part of the ancient "Magnum" series does not have the distributor drive gear properly oriented, so you have to run the distributor gear "backwards" from the OE indexing.

This cam is what I call an "old school (hydraulic lifter) hot rod cam" with basic .050" specs of 230/230/106/114/110/.320/.320. The lobes are phased too early and the LSA is too narrow. It also has fairly aggressive dynamics that require a stiffer than OE spring and subsequent higher valve train loading. The design probably dates to at least the seventies.

Simulations predicted that it has more low end torque than the 30-30 and even the LT-1 cams, but is short on top end power. The L-79 cam showed significantly more low end torque with about the same top end power.

Unfortunately, if you let some "engine builder" choose your cam, something like this is often what you get.

Working with Dino via email and phone resulted in a lot of confusion early on, but once I realized the VAC was hitting the manifold with the initial timing still short of my recommended setting, I realized that the distributor gear might be on 180 out. After that we made real progress.

Dino's early '64 L-76 has the early 062 distributor, but it was apparently modified somewhere along the line to the later 069 specs, which are excellent. We followed the procedures and recommendations outlined in my 2012 San Diego presentation, and a pdf of the PowerPoint slides is on the St. Louis chapter Web site.

It now has a dialed-in spark advance map and idle speed/mixture. The reported stumble might be cured by richening the idle mixture. Next step would be to check the acclerator pump system for conformance to shop manual specs. If these actions don't do the job, one size larger main metering jet is the next step. I think the OE jet is #65, but I don't think that Dino has checked it to determine what size is actually installed.

This exercise illustrated to Dino what a huge difference dialed-in spark advance and fuel flow maps can make to how an engine performs in normal driving, even if it has a lousy camshaft design.

Of the several engines I've evaluated in the last couple of years owned by members of my SoCal chapter, I found problems in every single one - various distributor problems from sloppy end play to lousy spark advance maps, plugged vacuum advance lines, idle mixture way of of adjustment... no wonder those cars had drivability and performance issues, including overheating. In some cases the parts cost ro get everything dialed-in was zero, and the maximum was about 20 bucks

I have no doubt that there are many, many vintage Corvettes out there that need the same simple diagnostics, analysis, and simple changes to get them properly dialed-in, which will vastly improve the driving experience.

Duke

Dino - post your head gasket thickness measurement and idle vacuum at 700. (The last time we talked I recall you said 15" @ 900). I have more comments.