C2 electrical issues Ugh

[John P.]

My 65 roadster 327 with factory AC has the 327/350 package with a Holley carb list 2818. The carb was just professionally rebuilt.
The fast idle speed with cold engine sometimes starts at 15-1600 RPMs, other times there is no fast idle. I lubed cam, checked choke opening of flapper seems to happen as expected when key comes on.

In checking voltage to choke I read 10.5 with key on, also 10.5 at wiper motor. Battery itself reads 12 volts when engine not cranked.

Is there a "most likely" location for the voltage loss? I tried to check voltage at horn relay-Should there be none when engine not running but key on? Is alternator in play here? All gauges AC etc seem to be functioning.

I seem to understand the electrical foibles of these vehicles poorly as opposed to a reasonable chance with mechanical issues.

Thanks in advance. I always appreciate the expert input.

[Edward J.]

Re: C2 electrical issues Ugh

John, I would start at the ignition switch and test acc. wire on the back of switch(brown wire?), you should have battery voltage there with key on, if so work to the fuse block where the brown wire feeds the fuse for the wipers and check voltage there on both sides of the fuse(sometimes the metal connectors rust there, and you can get voltage loss through the fuse., it leaves the fuse and heads to through the firewall connectors which can be corroded also which can crate a voltage loss (check connectors by pulling the connections of in the engine compartment). The choke could tie in some how??

[John P.]

Re: C2 electrical issues Ugh

John, I would start at the ignition switch and test acc. wire on the back of switch(brown wire?), you should have battery voltage there with key on, if so work to the fuse block where the brown wire feeds the fuse for the wipers and check voltage there on both sides of the fuse(sometimes the metal connectors rust there, and you can get voltage loss through the fuse., it leaves the fuse and heads to through the firewall connectors which can be corroded also which can crate a voltage loss (check connectors by pulling the connections of in the engine compartment). The choke could tie in some how??

The lead to the choke and temp sender look original with woven cover. These appear to originate from the wiring harness and connect thru the lower portion of the ballast resistor. I did clean contacts of harness at firewall-but not sure which lead should be 12 volts there ,if any, with the key turned on.

[Edward J.]

Re: C2 electrical issues Ugh

John, do you have a wiring diagram, it sounds like the wire for choke is feed through the ballast to lower the voltage to electric coil, sometimes the factory will not require full voltage to the coil. the dia will tell. if you see that the wire is battery volts at the top of the ballast and the wire that feeds the coil is on the bottom then that is the way the factory must of done it.

[John P.]

Re: C2 electrical issues Ugh

John, do you have a wiring diagram, it sounds like the wire for choke is feed through the ballast to lower the voltage to electric coil, sometimes the factory will not require full voltage to the coil. the dia will tell. if you see that the wire is battery volts at the top of the ballast and the wire that feeds the coil is on the bottom then that is the way the factory must of done it.

I have read on Holley site and elsewhere that a full 12 volts is required for an electric choke to function properly. Just wondering if the reduced voltage could result in the fast idle not setting itself properly when starting the car cold. I guess a wire directly from battery to choke would tell me?

[Steve G.]

Re: C2 electrical issues Ugh

I have read on Holley site and elsewhere that a full 12 volts is required for an electric choke to function properly. Just wondering if the reduced voltage could result in the fast idle not setting itself properly when starting the car cold. I guess a wire directly from battery to choke would tell me?

No, the electric choke has nothing to do with your problem. The electrical component of the choke is just a heating element that warms up the bimetalic spring that sets the choke.

I'm going to apologize in advance to those that flame when there is a long response. To diagnose this problem you need at least a basic understanding of how your choke works.

When the choke spring is cold it's spring tension tries to close the choke plate. However, if you lift the air cleaner off your cold engine and you haven't touched the throttle since it was last hot, the choke will be standing wide open. It won't close because the fast idle adjusting screw is being held against the fast idle cam by the throttle return spring. When you open the throttle you lift the stop screw off the cam, freeing the cam to move and the choke should snap shut. The choke is now "set". At room temp it should just close fully. If it isn't closing all the way, increase the choke spring tension until it does.

Once the choke is set and the throttle released the fast idle stop screw is now sitting on the high step on the fast idle cam. As soon as the engine starts there is a vacuum diaphram (or piston in your case) that pulls the choke open a predetermined amount. The engine has to get some air. This is called the choke break. With opening the choke this amount the fast idle cam is now allowed to drop off the highest step. But it won't drop until you open the throttle and lift the stop screw off the cam, just as the choke wouldn't close when cold until you opened the throttle.

This next part is often what is mistaken for the fast idle not coming on. If you start the car now without touching the throttle , when it starts it will run at the high step speed. Kick the throttle once and it will drop down to the lower step, the choke break having pulled the choke off a small amount. However, if you have your foot on the throttle when it starts as soon as the engine starts the fast idle cam will have dropped from the choke break action and when you let off the pedal you won't see the high step fast idle speed. The choke break has already allowed it to drop off.

After this has happened the heat warms up the coil spring and it loses it's tension. As it does the choke starts to come further off and the fast idle cam drops to a lower step then finally off altogether.

So, the first thing to check is to make sure the choke is closing fully every time you go to start it cold. Then do the start without touching the throttle after setting the choke. See if it consistently starts on the high step. Hint. The choke can not fully close without the fast idle cam being on the high step.

There can still be other problems. The choke break adjustment is a very critical measurement. If it is pulling off too far the engine will want to stall when you try to accelerate when cold and the fast idle cam will drop too far.

Even when the choke break is adjusted properly, there is another adjustment that determines how far the fast idle cam drops in relation to the choke break movement.

The choke is by far the most challenging part of carb o'haul. And even tho this was professionally done, it may not have been well done. Because these adjustments mean bending levers and rods many times they are not even checked, instead assuming that they are as they were when originally built. Wrong.

Steve.

[William F.]

Re: C2 electrical issues Ugh

Did the '65 L79 come from the factory with an electric choke?

[John P.]

Re: C2 electrical issues Ugh

My habit has been to pump the accelerator on cold start. Perhaps a single pump to allow the choke flapper to close fully would take care of my problem? Not sure this vehicle will start with a single pump. And perhaps that opens another can of worms?

[Stuart F.]

Re: C2 electrical issues Ugh

I trust by the discussion that the choke on John's 65 is electric and it's on a Holley carb. Pardon my ignorance, but what year did they go to an electric choke?

I have one that uses a thermal temperature sensing unit that mounts at a hot point of either the intake manifold or one of the mounting bolts at a water port in the head. It varies the current to the choke to allow for a more gradual release of the choke in tune with the engine temperature. It works great. Other electrics I have had release way too soon causing the hesitation or bog expected with a cold engine.

Stu Fox

[John P.]

Re: C2 electrical issues Ugh

Yes it is a 4 barrel Holley with electric choke List 2818 not sure but I think when I asked about the carb numbers some time ago we decided it is a service replacement 4150 600cfm

[Larry M.]

Re: C2 electrical issues Ugh

Did the '65 L79 come from the factory with an electric choke?

No…………


One possible scenario is previous owner plugged the exhaust crossover(s) in the intake manifold, yet wanted some choke function, so an electric choke was installed on the carb. I went thru a similar thought process when I installed 4-tube headers, but opted for a manual choke instead.


Larry

[Steve G.]

Re: C2 electrical issues Ugh

My habit has been to pump the accelerator on cold start. Perhaps a single pump to allow the choke flapper to close fully would take care of my problem? Not sure this vehicle will start with a single pump. And perhaps that opens another can of worms?

John,
It doesn't matter whether it's a single pump of the throttle or two or more. The choke sets on the first throttle movement. Pumping it a second time just adds more raw fuel via the accelerater pump circuit.

The question is whether you make it a habit to remove your foot from the throttle after you have set the choke and pumped it however many times you like, all before you start cranking the starter. That's what matters. Foot on the throttle when it starts, you won't see high step of cam idle speed. Foot off the throttle when it starts, stop screw is on highest step.

Steve

[Stuart F.]

Re: C2 electrical issues Ugh

Back in the day, I Had a 57 post Bel Air that I raced. I had the old Heddman headers on it and the Corvette dual quads that were raised 1-1/4". I still used the stock choke, but I had to make a new heat tube arrangement. I used aluminum tubing coiled around one header tube with a brass junction fitting to another aluminum tube to the choke housing. I insulated the upper tube with a sleeve, but still had trouble getting enough heat to open the choke fully when it was adjusted to close it fully when cold. So, on a straight section of the lower tube before the coil, I used a vice grips set to pinch the the tube almost closed to add restriction. I pinched first one than another 90 degrees from the first, and so on for about 3 or 4pinches until I got enough heat to the choke. It worked beautifully. This, of course, was before electric aftermarket choke kits were available.

Stu Fox