[Mgs] 1973 MGB roadster

PaulHunt73 paulhunt73 at virginmedia.com
Wed Dec 1 01:35:28 MST 2021

A lot of niggling things there, you need to go through everything 
carefully - compressions, valve clearances, timing including vacuum and 
centrifugal advances and looking for slop when twisting the rotor back 
and fore.  Carbs checking damped movement of the pistons going up and 
dropping smartly when coming down, springs, needles, air flow and 
mixture balance.

Backfire in the exhaust or the intake?  In the exhaust that can follow a 
missed combustion, do you get a jump in the tach needle? Problems with 
the gulp valve can also cause backfiring.

Check all the hoses between front tappet chest cover and carbs, canister 
to carbs, rocker cover and tank including the separator in the back.  
Should be a non-vented tank filler cap.  A leak in any of those can 
disable the anti-runon system.  Check the valve, after running and 
switching off the valve should click as the oil pressure dies away.  
With the engine running apply 12v to the slate/pink terminal of the 
valve and it should stop the engine.


On 01/12/2021 01:10, dave northrup wrote:
> Haven’t had it too long.  Seemed to be running ok; had transmission 
> problems so we swapped out for a good one.
> Just had a very knowledgeable friend set the timing and the carbs and 
> the choke adjustment.
> Pull the choke all the way out and it starts ok; but seems to backfire 
> a bit, especially when cold. After it warms up you can push the choke 
> back in and it runs and idles ok except it seems to have a loss of 
> power in the 3000 + rpm range, and does occasionally still backfire.
> Has a Pertronix but other than that seems pretty stock including the 
> air pump.  Tends to run on a bit after you turn it off.
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