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MG MGB Technical - Cold Starting -Hard

Cold starting on warm days on my 3-main MGB engine is, at often times, difficult. Warm starting is not a problem. Before this winter's storage the engine started fine. Any advice would be appreciated. The following info may assist in diagonosing the problem..

1. The starting procedure that I use is to turn the key, allow 5 seconds for the fuel pump to fill the carb fuel chambers, depress the accelerator pedal about 1/4 of the way and start. Choke closed.
2. Engine recently rebuilt and has good compression.
3. New starter motor.
4. pertronix distributor and coil(coil and voltage going to the coil was checked and meets specs.).
5. New copper core spark plug wires. (Had the same problem with the old graphite wires.)
6. Timing set to 35 deg. BTDC at 3000 RPMs.
7. Carburetor fuel/air mixture near perfect based on spark plug color.
8. NGK BP6ES spark plugs, gap: .030", less than 1000 miles on spark plugs. Would NGK BPR6S be better?

This is not a major problem, but any advice would be appreciated.

Frank Grimaldi
Frank Grimaldi

"depress the accelerator pedal about 1/4 of the way and start. Choke closed."
Wrong, but to clarify, what does "choke closed" mean? The cold start while referred to as "choke" is not a choke that closes as on other carbs. Instead, it opens the throttle for fast idle, and then lowers the jet for richer mixture.
Opening throttles via pedal will break vacuum and cause no start due to lean mixture. The fast idle (throttle opening) is built into the choke linkage.
First half inch of choke travel is fast idle only, correct for warm restart.
Further travel engages choke, ie, enriches mixture. More travel - richer mixture + faster idle. Colder the engine the more you need. Cold start on warm days takes about half or three quarter choke, released to fast idle only as soon as it fires.
The only time you depress the accelerator is on hot restarts if there are signs of flooding.
We used to tell customers to put the car in neutral, pull the choke out half way if warmish or all the way if cold, get out of the car, and hit the starter. That way they could not have a foot on the accelerator. Works every time - if yours does not, the carbs are not set up correctly.

FR Millmore


As Fletcher says, but I noticed that you have solid copper cored spark plugs wires. Check with your Pertonix manual about this, My understanding is that electronic ignitions don't like these wires.

Herb Adler

Following up on Herb's point, are any of the listed items new since winter storage?

BJ Quartermaine

Opps, meant to say choke full open, choke cable pushed in.

In any case I think that I solved the problem. It appears that the timing was off by only a few degrees, but enough to make a difference in starting. After resetting the timing I also notice a significant improvement in smoothness of a high gear, low RPM acceleration.

Sorry for crying wolf.

Frank Grimaldi
Frank Grimaldi

I would also check with Pertronix about the use of copper wires with their unit. They are known to malfunction, when picking up RFI, due to the old style ignition wires. RAY
rjm RAY

This thread was discussed between 24/05/2011 and 26/05/2011

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