Timing Question

Post by **AJT** » Fri Jul 11, 2008 10:18 pm

Hi All,

I'm trying to retard the ignition (using a strobe) to stop my unleaded head pinking when hot and struggling with my Haynes manual: which way is retarding the ignition? i.e. towards the two smaller timing marks or towards TDC mark? I've currently moved it to the limit of the two smaller marks - ticks over better but pinks.

Thanks
Alan

Post by **MoggyTech** » Fri Jul 11, 2008 11:42 pm

Retard is towards TDC

Post by **mike.perry** » Fri Jul 11, 2008 11:56 pm

Buy yourself a proper BMC workshop manual.
The large marker is TDC and the small ones are 5 and 10 deg. advance, ie before TDC.
Check the plugs are clean and the points haven't slipped ie still 15 thou gap, set the vernier adjuster in the middle of its range, turn the distributor to fastest tickover then adjust the vernier screw to fine tune. Check the vacuum advance.
It works for me.

Post by **bmcecosse** » Sat Jul 12, 2008 8:47 am

Best check the mechanical advance inside the dizzy is not seized - twist the rotor arm and release - it should spring back, and suck the pipe going to the vacuum advance - you should create a vacuum (if not the diaphragm is bust) and you should see the baseplate move and release when you gasp for air.

Post by **AJT** » Sat Jul 12, 2008 9:02 am

Thanks All,

The distributor is fine: the pinking appears after about ten miles, along with a loss of power - something gets hot. I'm going to re-build the carb as this is orginal and see if this helps.

Post by **MoggyTech** » Sat Jul 12, 2008 1:35 pm

AJT wrote:Thanks All,

The distributor is fine: the pinking appears after about ten miles, along with a loss of power - something gets hot. I'm going to re-build the carb as this is orginal and see if this helps.

Condenser

Post by **AJT** » Sat Jul 12, 2008 3:26 pm

I've just remembered that my old Spitfire had the same problem: after about ten miles, pinking and loss of power; this turned out to be fuel evaporation caused by the lack of an aspestos sheet (covered with aluminium) that sat between the carbs and the manifolds. Is there something similar available for a minor?

Post by **MoggyTech** » Sat Jul 12, 2008 4:44 pm

Provided the insulator between carb and inlet manifold is there, fuel vapour lock shouldn't be a problem. Check fuel line isn't too close to the exhaust as well.

Post by **mike.perry** » Sat Jul 12, 2008 7:28 pm

Just a thought. I assume that the thermostat is OK and that it is not causing the overheating.

Post by **AJT** » Tue Jul 15, 2008 3:44 pm

Upon taking the carb to pieces I found:

Needle had 'dropped' down and was sat too high and the piston was sticking. Have totally re-built with new needle, jet, throttle spindle plus a good clean. Loads more adjustment than previously but have yet to give it a good run to see if it was the cause of the problems or purely coincidental.

Any views on what the effect would have been of these problems?

Post by **AJT** » Wed Jul 16, 2008 10:01 am

Solved! worn carb spindle was letting air in and creating a weak mixture so the engine was getting hot and pinking. Very easy fix and a vast improvement in performance.

Post by **bmcecosse** » Wed Jul 16, 2008 1:41 pm

Good result then!