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MG MGB Technical - cold starting technique

my 70 b just got a tune up and runs great when warm, but is still balky when starting. It runs rough and misses til the temp comes up a bit (2 or 3 minutes), then smooths out and runs great. It is garage kept so cold is about 70 degrees. The car is all stock except for electronic ignition and foam air filters instead of the original air cleaners.

It occurs to me I may be doing something wrong when starting. I use the choke, and pump the gas twice, then turn the key, as I used to do when younger. Any advice on what could be the problem?

Hi mc.

If the roughness lasts for 2 or 3 minutes I don't think it is your starting technique that is at fault.
Pumping the gas twice may be irrelevant, depending on what carb(s) you have, it is only effective with carbs that have an accelerator jet. I assume that you begin with full choke and ease it off gradually ?.

I suspect that plug fouling may be a factor.
If your electronic ignition provides 'hotter' sparks I would try opening up the plug gaps a little (50 thou max).


Roughness/missing when cold could be due to too little or too much choke. In my experience, and especially 30 years down the road, every car is different, and you have to learn what is best for your car. Personally I'm of the 'the less the better' school as far as choke goes even though this means I have to drive it gently for the first few miles until it warms up and can dispense with the choke altogether. Which is a good thing anyway and specifically mentioned as essential for some modern cars. With the roadster I start it on full choke and push it back half-way the instant it fires, move off, then gradually back the rest of the way as it warms up. With the V8 it needs that full choke for the first five seconds or so, then gradually reduced as it warms up. As Don indicates, pumping the accelerator serves no purpose for SUs and Zenith.

Not sure about fouling, if the plugs were fouled when you tried to start it probably wouldn't start. If they are fouling up on a cold start then I'd expect any problems to develop in the early part of the warm-up, not immediately it started.

An MGB should start and run very well in a wide range of conditions. I'd be looking at ignition components condition and setup, and carb setup.
Paul Hunt 2

My cold start routine is as follows
- Pull choke all the way out
- Turn igintion key on and listen for clicking to stop. (SU carbs are full of gas and the fuel line is pressurized)
- Start car (no foot on the gas).
- Car starts right away,
- Push coke back halfway and lock.
- Let car warmup for 3-4minutes.

Car runs smooth. I hope this may help.

Randy C

MC ---

My MG Starting procedue personal page.

Check oil in engine and transmission -- WITH OUT FAIL for first time

1 - Turn the engine over for about 30 seconds -- NO CHOKE -- This I believe gets the oil pumped up into the upper engine -- valve rockers etc.

2 -- Pull a full choke -- no foot on gas -- turn the key and she fires up within 3 seconds.

3 - once it's running, I adjust the choke to keep the engine running at slowest speed possible. After about three minutes, the temp gauge will come up to 130* and I'll keep reducing choke until it's back to home position.

There is a 1/4 mile straight road out from my drive way and it's there I clean out the carbs (zoom zoom)

In all , it takes about five minutes for my car to get warmed up enough and run like it's supposed to.

That's just my story glg

One trick I have used for years for effective cold starting on my current 1973 MGB GT (and previous manual choke cars)is to pull the choke out full just before I stop the engine and lock it there. The next time I go to start the engine I turn on the ignition, wait for the fuel pump to stop clicking, put my foot on the throttle and fire her up. She nearly always starts first turn!

Paul, pulling the choke out full before shutting the engine off can cause problems in that the extra rich mixture will wash the oil film off the cylinder walls. When you start the car your rings will be short of lubrication causing excessive wear.
John H

Hi all.

For many years I have been in the habit of applying full choke immediately after the engine stops, the theory being that it slows down the evaporation of the fuel in the float chamber, which can help starting significantly in cars with a mechanical fuel pump. I guess it just saves a little fuel in cars with electric pumps.


Don, putting the choke on after the engine stops will not effect the engine and in fact may do as you suspect and reduce evaporation of fuel into the air.In the case of SU's there is no choke plate to block air flow and pulling the choke just lowers the main jet wich will than expose more fuel to the air, as jet opening is now on a thinner section of the needle.
John H

Remember, the original poster was starting in 70 degree temps here, not winter temps.

My 73 GT is a daily driver with a later model o/d tranny. You can bet I do not get under the car and check the tranny oil every time I start it! True confession: I don't even check the engine oil that often. I know the "rhythms" of my car. In hard sustained interstate driving, it will drop a pint of oil in about 1000 miles. Commuting to work, it goes more like 1500-2000 miles before it drops a pint. Weekly checking is normally sufficient. I do keep my eye on the oil pressure almost all the time. I check the transmission when I service the car every 3000 miles. Only once have I had to add any.

Cold starting: on cars with SUs - DO press the gas pedal slightly while pulling the choke out. Otherwise the adjustment screws have to drag across the fast idle cams. Pressing the gas a bit will make the choke action a lot easier and it minimizes wear. The same may apply to the ZS; I can't remember as it's been quite awhile since I've had one.

I keep my foot off the gas, or just crack it perhaps 1/4" while starting. I never pump it as that does nothing. Even in hot weather, I pull full choke on a cold start and immediately release it until I get a smooth idle. If the car balks on acceleration, I'll feather the choke back on a bit for just a moment as necessary. Generally, I find that when the temp needle starts moving off the "C", it's time to put the choke knob all the way in if I haven't already. If/when plugs get fouled, the symptom is usually long cranking time.

Allen Bachelder

With the Piper 270/2 cam, modified alloy 5 port head and deck height flat top pistons, I find that starting is much as described above. The big difference is running a .050" plug gap with an electronic ignition. The extra gap with the modifications makes a very noticeable improvement in cold running. On a cold morning (close to freezing) I can drive right off without any choke, and it will idle at the stop sign 2 miles down the road.

I recently started having ignition problems with the spark jumping inside the cap down the side of the rotor to the metal distributor shaft. I thought I might have to reduce my spark plug gap. After some investigation I found one of the "hi performance" resistor plug wires was "open". The extra plug gap and higher compression requires extra voltage to jump the gap. That big fat high voltage spark will take the easiest way to ground.


Barry Parkinson

Re Paul Eades suggestion - I agree that pulling the choke out before the engine stops is a Bad Thing, but I have found on several cars that pulling it out immediately *after* the engine is stopped also made starting easier next morning. Goodness knows how.
Paul Hunt 2

Same drill for me as Paul and Randy.

In many cases, it is how your choke system is set up that determines what "drill" will work in your case.

Remember, the choke mechanism is a two step process ~ pulled fully out, you open up the butterflies in the carbs AND also drop the jets for a rich mixture. This gets the extra gas into the engine for much the same reason that cars with an accelerator pump cold start better (usually) after a couple of pumps on the accelerator pedal. Once the engine starts, you don't need the extra gas and the cable can be let in (usually about 1/2 way in) which moves the jets up and closes the butterflies some.

The balance of throttle and jet struck by moving it in will/should give you a smooth(er) idle almost immediately. Moving the cable in as the engine warms up continues to close the butterflies and raising the jets. However, the jets rise to their normal running position BEFORE the butterfly linkage comes off of the cams that move the butterflies. About the last 1/8"~1/4" of cable movement is still on the cam (tho barely) and the choke/throttle adjust screws should be off the cams as the cable is shoved fully home.

A good discussion and instruction on how to set up the choke for HS-4s is found in the Emissions section of the Bentley Manual. I sometimes think that the Emissions section is ignored by those of us who have stripped so much of the smog gear off of our cars. There is still important info for what remains in it, however.
Bob Muenchausen

I had always started the car witrh full choke, left it until the temp moved a hair off C, then slowly pushed it in as the temp got closer to the middle.

I tried Randy and glg's idea, and what a difference. As soon as it started, i locked in the choke around the middle, and slowly moved it in from there. Much smoother warm up.

Of course, "cold start" is a relative term since it was closing in on 100 degrees today....

70 B
Ken Harris

Choke fully out, ign on and wait until fuel pump stops running. Crank for 1 second. Stop crank again and car starts (999 times out of 1000 anyway). Push choke back to fast idle cam and drive away.
Stan Best

I tried the no-pump, full choke then half choke method and it worked well. Still a little rough early but settled down pretty soon. Thanks to everyone for all the advice.

This thread was discussed between 28/05/2006 and 04/06/2006

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