Warm Up Question

Joined
Aug 25, 2018
Messages
3,073
Location
South Carolina
I prefer setting the initial at 8-12°, advancing to 36° at 3200 rpm, and using manifold sourced vacuum advance to kick the idle timing to 18-22°. It idles smoother, sounds deeper, and runs a lot cooler.
 
Joined
Jan 9, 2010
Messages
13,579
Location
Los Gatos, CA
It will run a lot better if you set the timing to 34-36 btdc @3000 rpm which makes the timing about 10-12 btdc @ idle
I would start with a timing tape and plot the curve. After a basic tune, set timing and idle mixture for highest vacuum. Let the number fall where it may and tune from there. Off idle is important for driveability.
Curve springs to bring in 34* at desired RPM. Limit vacuum to avoid ping. Especially if the truck will ever carry a load.
 
Joined
Dec 23, 2013
Messages
1,150
Location
Minnesota
Manual chokes had been pretty much obsolete on US cars at least 10 years by then. (Our base-model '54 Chevy had automatic choke.) Trucks and Japanese cars still had manual chokes later.
Not really. Basic cars with few or no options still had manual chokes in '64-including my '64 Falcon.
 
Joined
Mar 20, 2016
Messages
3,591
Location
Western S.C.
My '79 Mazda GLC Sport had a nice set-up - a manual choke that came off automatically as the engine warmed up.
...
I wish my '81 GLC had had that, or a simple manual choke. Instead, it had an electric choke that overcompensated for ambient temperature variations---too much choke on cold days, not enough on hot ones.
 
Joined
Jul 13, 2003
Messages
2,581
Location
Tracy, CA
Some SBC's of that vintage have an exhaust port under the carburetor that runs across each bank. This provides some pre-heat and these routinely become plugged with carbon causing cold driveability issues as described. Sometimes the carbon plug extends from the manifold into the cylinder head.

manifold.jpg
 
Joined
Jan 9, 2010
Messages
13,579
Location
Los Gatos, CA
Some SBC's of that vintage have an exhaust port under the carburetor that runs across each bank. This provides some pre-heat and these routinely become plugged with carbon causing cold driveability issues as described. Sometimes the carbon plug extends from the manifold into the cylinder head.

View attachment 127877
Plug those bad boys. I used freeze plugs in my '68 L36 "Smiley" manifold.
 
Joined
Aug 25, 2018
Messages
3,073
Location
South Carolina
I prefer to leave the exhaust crossover in if daily driving it in a cold climate. The heat helps to vaporize the fuel when the engine and air are too cold to do so, allowing more even distribution, better air/fuel homogenization, and better driveability until the engine fully warms up. You gain some power if you plug it, just due to cooler intake air temps, but that depends on whether it's worth it or not. In a daily driven vehicle, that spends 95% of its life at part throttle and <3000 rpm, I just leave it be.
 

HondOtaChOrd

Thread starter
Joined
Nov 5, 2022
Messages
80
The cable for the choke is short. This made it so I couldn't move the flap even when pulling the choke as far as the button would go.

Soon I will get a longer cable and get it set up properly. After closing manually the cold start was much better.
 
Joined
Jul 9, 2008
Messages
3,590
Location
British Columbia, Canada
The procedure is: you pull the correct knob out (check which knob is the actual choke knob as discussed above), start the engine. Once the engine catches, you need to ever so slightly push the knob back in a small amount, you will get used to exactly how much eventually. Otherwise the engine will load up with fuel. Once the engine warms up a bit you can start pushing it all the way in. If you flood the truck, open the choke fully (meaning push the knob all the way into the dash), open the throttle and crank to clear it. When I drive manual choked cars, I try and get the choke off as soon as possible but without sacrificing cold drivability.
What you say is correct. Every carbureted car I ever had required its own starting regime. Push the accelerator pedal once, three times, not at all, or whatever that engine wants. You will catch on to what works best - and then never deviate.

I agree with getting off the choke as fast as possible - but not at the expense of drivability.

For winter drivability I would be using a 5W-XX or 0W-XX oil. On an older engine I'd start off with a 5W-30 or 0W-30.

And you should not mash the throttle when an engine is cold. You might push the pedal to the floor to inject fuel before starting, but revving a cold engine is a poor practice.
 
Joined
Jul 7, 2014
Messages
3,494
Location
Winnipeg MB CA
I wish my '81 GLC had had that, or a simple manual choke. Instead, it had an electric choke that overcompensated for ambient temperature variations---too much choke on cold days, not enough on hot ones.
My wife bought an '82 GLC new. The automatic choke worked well in our cold winters.

Mazdas of that era were set up to idle high, I think so they'd get up to temperature quickly.
 
Joined
Jul 7, 2014
Messages
3,494
Location
Winnipeg MB CA
I prefer setting the initial at 8-12°, advancing to 36° at 3200 rpm, and using manifold sourced vacuum advance to kick the idle timing to 18-22°. It idles smoother, sounds deeper, and runs a lot cooler.
No pinging with that much advance? I never tried it.
 
Joined
Aug 25, 2018
Messages
3,073
Location
South Carolina
No pinging with that much advance? I never tried it.

At idle, no. The low cylinder pressure at idle wants more timing as lower pressure and poor combustion efficiency means a slower flame front. The 8-12° range set by many OEMs in the late 60s onward until EFI came around was mostly due to emissions. Late spark timing warms the engine up faster as exhaust gas temps are higher, residual cylinder temps are higher, and there's more reversion. This also made them prone to overheating in traffic. Later on, the late timing benefited catalytic converters by "cannonfire" to get them working better sooner.

Advancing the timing with manifold vacuum gives you the timing the engine wants at idle. Then when you step on the gas, throttle opens, manifold pressure drops, and thus timing retards to the mechanical curve for the higher cylinder pressure.

It has a HUGE affect on engine coolant temp. An old friend of mine came by a few years ago with his Bronco and 351W engine that was overheating. His engine builder told him it was because the block was bored .060" over and nothing he could do about it. (hogwash) He put over $1k into the cooling system between the radiator, fans, shroud, water pump, and pulleys trying to keep it cool, yet it would still creep to 210-215°F in traffic. I took a look at it, switched his vacuum advance from ported to manifold, and it stayed 180-185°F after that.
 
Joined
Jul 7, 2014
Messages
3,494
Location
Winnipeg MB CA
I've also heard of pulling out the choke and using it as a hook to hang a handbag, though I suspect that is more myth than reality.

A cruise control would definitely be a better idea.
I saw something similar done with an old (1940 or so) Fargo. The truck had a throttle control that could be pulled out to increase the idle speed. (Similar to a manual choke, but different in that it didn't enrich the mixture by closing the choke plate.)

Anyway, the owner demonstrated this low-budget open-loop "cruise control" by pulling out the shaft and inserting a dime, nickle, or quarter between the knob and the dash so as to vary the cruising speed.
 
Joined
Dec 23, 2013
Messages
1,150
Location
Minnesota
I've also heard of pulling out the choke and using it as a hook to hang a handbag, though I suspect that is more myth than reality.

A cruise control would definitely be a better idea.
Yes, that was an old 'mechanics joke' when the lady would pull into the shop with a good starting, but poor running engine. It probably did happen on occasion.
 
Top