MG MGB and MGB GT Tech Talk
What is the proper choking procedure? How far do I pull the choke for a cold start. When do I know when to push it back in?
If I pull it out too far, it try to kill the engine. If I read right, the first 1/2 of travel on the choke cable engages the throttle only. The second 1/2 engages the needle for fuel/air mixture.
Thanks for the tips. My first car with a manual choke! :P
A lot will depend on how your carbs are set. All cars will be slightly different.
On mine I use full choke to start then drive away gently. As the engine warms up I push it in a bit at a time until the engine will run well without it.
If the engine hunts you need to push the choke in a bit.
If it stumbles when you step on the gas you need more choke. If it kind of lopes, you have too much. The problem is, at some throttle positions a given choke setting may be too much and at others too little.
WARNING: CHOKE RANT FOLLOWS
The basic rule, as Owen and Terry described, is to use the choke as little as possible.
Actually, on SUs it isn't a choke at all. Normal carburetors do have chokes, in that there are flapper plates that obstruct incoming air and thus create an over rich mix. On SUs there are no such obstructions.
Instead, your "choke" is a way of enriching the mix by simply changing the metering of the incoming fuel charge.
Using this enrichment tool properly is one of the endearing aspects of life with an old British car. Back in the day, Englishmen were expected to be sensitive to how their machines worked and to take pride in knowing how to treat them. They just knew, or were taught early on, how to keep a clunky stone age iron motor running smoothly as it was started and warmed up without fouling spark plugs or causing their riding companions to toss lunch.
As Owen said, every car is a bit different from all of the others. Pull your choke knob fully out and fire off the engine. Patting the accelerator pedal is a complete waste of time as there are no accelerator pumps in SUs, but a certain amount of modulated throttle opening may help during the fire-off time and early running. Once running, judicious use of the choke will produce a reasonable smoothness, but you will have to change the cable position, in or out, as the warm up progresses. The idea is to balance your demands of performance with the changing power production capabilities of the engine as it warms.
Another thing to remember is that things are at their best when the engine is caused to warm up quickly. Letting an engine just sit there at idle is a really bad thing. At idle the warm up is slower and the raw gasoline that is not being burned washes the cylinder walls and piston rings, causing them to wear and fail earlier than is necessary. It also causes an increase in "coke" to be deposited on the piston crowns and combustion chamber surfaces producing less efficient burning and poor performance. The motor oil is dilutes too, fouling it with the wrong stuff and thinning it out, thus causing premature wear of the bearings and other lubricated surfaces.
The rule here is to fire the engine off, watch the oil pressure gauge and drive the car away when the the needle stops rising and stabilises. By "drive" I mean use the engine as you must, but avoid calling on it to produce any more power than is absolutely necessary. It may take five or ten miles or more of 45 MPH road work to reach a proper temperature, and much longer during the colder months.
Once warmed up, and with the choke fully home, in an ideal world you would continue to keep the engine operating for as long as possible in order to "burn off" the gasoline and water molecules that did reach the sump.
One of the best ways to improve the overall performance and increase the life of an IC engine is to do what is necessary to cause the OIL to reach full operating temp quickly. The best route for this is an oil thermostat placed in the cooler system or to simply blank off the cooler itself. I recommend at least one of these efforts, especially during Winter.
Sorry for the rant here. Yours was a simple question and it deserved a more simple answer, and Owen and Terry supplied that. I just thought that some others might benefit from knowing a bit more about "chokes" and their use, but I'll shut my trap now and go fix breakfast.:)
Jack
Jack,
I have been driving British cars for well over 25 years. Your explanation ("rant") is the absolutely the best I have ever heard. Thank you!
Dave
I don't have a choke on my Carter 500. ;)
On my dad's '63 B, we pull the choke all the way out to crank it. When it fires up, the choke is moved immediately to the halfway position never touching the gas pedal. As the engine warms up a bit & the car accelerates more smoothly the choke is pushed in fully.
Excellant post Jack. Spot on. My TD only needs a slight choke when ambiant temps are 40 or less. It is the most amazingly easy to start car I have even owned. My Crosly has to run on the choke for a few minutes. Would never start without a choke. Every car will be a bit different, due to its nature, the carb settings and termperatures.
Jacks post should be in the library for new owners. I know I benefited from that "rant".
Thanks,
Kevin
Although new to MG's I here's what I do ( and used to do when all cars had chokes...!):
Wait until the pump stops ticking,choke half out ( very dependent on choke and fast idle cam set up).As soon as she's running,light throttle to hold a fast idle and push choke home.Hold it at the fast idle until engine is warm (will warm up quicker when stationary and you can enjoy the unique MG symphony) and then drive off.Never like choke juggling while on the move and think it's kinder to the motor to be warmed up before being put under load.Can't think anyone needs to make a rapid getaway from cold and all this only takes about 5 mins.
Agree with earlier comment not to let the engine warm up at tickover and this method eliminates the perils of bore wash from rich mixture.
Pete
