GT6 MK 3 Tuning

[Craig Simister]

Hi! 

I am trying to set my GT6 MK3 up and I was wondering what people use for CO and Timing settings.I appreciate they are listed in the workshop manual, but with todays petrol what works best generally?

Car is still running Stromberg CD150s and is on electronic ignition.

Thanks in advance, 

Craig 

Edited August 5 by Craig Simister

[Nigel Clark]

First make sure the engine is in good general health, so run a compression test, adjust valve clearances and make sure carbs and ignition system are in good condition.

For ignition timing, I would start with static at 12deg BTDC, then experiment the road. The idea is to advance the timing in small steps until the engine just pinks under load at around 2000rpm, then back off a fraction to stop pinking. 

Once the ignition timing is optimised, tune the carbs. Balance airflow and set idle speed to around 800rpm. I adjust the mixture to about 4% CO, which means it's a fraction rich, giving smooth running and good performance. 

Nigel

[Craig Simister]

Hi Nigel

Thank you for the reply, very good information I will take a look into it. The car is running rich at 8% co and the strobe indicates 6 degrees BTDC at present! Car goes well and everything but I recently had an MOT and asked them to check the emissions and I was quite alarmed by the findings!

Craig 

[Pete Lewis]

and cork up the temperature sensors onthe side of the carbs and reset the idle mixture

these stupid things get well out of control , remove the cover or remove the assy and turn the small ut to FULLY close the air bleed plunger 

you cannot set the idle mixture if these little sods are allowing idle air bypass    just close them down   easy .

reset the needles so the small delrin washer is level with the base of the air piston  and the jobs a good one 

 

Pete

Edited August 6 by Pete Lewis

[Craig Simister]

7 hours ago, Pete Lewis said:

and cork up the temperature sensors onthe side of the carbs and reset the idle mixture

these stupid things get well out of control , remove the cover or remove the assy and turn the small ut to FULLY close the air bleed plunger 

you cannot set the idle mixture if these little sods are allowing idle air bypass    just close them down   easy .

reset the needles so the small delrin washer is level with the base of the air piston  and the jobs a good one 

 

Pete

Excellent advice as well Pete. You may well be on to something with this, as my front carb is still sucking when the throttle stop screw is totally wound back! Can I just remove the temp sensors? I gather there is a Bi Metallic strip in there? How do I block off the holes?

Cheers Craig 

[Pete Lewis]

two screws  and easy to remove  

the small cast hsg. has two 0 rings to seal it to the body , if degraded any sealer will work.

the bi metal strip operates a plastic plunger that opens  bleed to by pass the  throttle plates  

its got a very dedicated testing set up which for our purposes these days is a waste of time

it is designed to allow the idle to increase in very hot under bonnet temperatures ,

but after all theses years the things are well past their best   the best answer is  give the plunger a tickle  it at room temp must be shut, so it wont be  and you screw the small nut down to just shut it down

the gaskets between carb and mani can just be turned upside down and the bleed hole is corked for good 

this was godd idea but its operation now is redundant  its far more important they stay closed when setting the idle mixture which gets richened up to compensate  , as you have found the idle screw is in fresh air

these little sods are a good cheap starting point .

Pete

[Craig Simister]

Nigel and Pete sound advice thank you both again. One of temp sensors was holding open. I have capped them off and now set the mixture and the timing. The car runs spot in now 👍🏻