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MG TD TF 1500 - Fuel mix

To get a mix not too lean, what CO emission should I aim for, using a SC.

Currently I get 1 % at idling and 3 % when driving. I would prefer 4 – 6 % to avoid overheating.
Anyone who know?

And another question - will a weaker spring give richer or leaner mix?
YS Strom

The purpose of the piston damper is to enrichen the mix during acceleration. With the throttle valve open and greater depression applied to the piston and needle, the damper slows piston rise whilst there is more draw on the fuel through the jet. Logic might then suggest that a stronger spring would also duplicate that effect at a constant throttle setting, therefore giving a richer mix.
Dave H
Dave Hill

YS
1% CO is very lean for a stable idle

Really you need to be around 13:1--(4%co)

3% when driving is ok (13.4:1)

And yes on full load / full throttle at least 4%(13:1) but preferably 5-6 (12.6-12.2)

I wouldn't fiddle with the springs, they are rated to give full piston travel at the speed where the engine develops it's greatest power
Any change will throw this opening point out of spec

I'd be adjusting the idle mixture up to around 3-3.5 and it will all fall into line

willy
William Revit

Dave
Thanks
Sounds possible that a stronger spring gives more fuel, except at full power, when the throttle will be at top even with a stronger spring I believe.

William
Thanks for your valuable information. It might save my engine.
YS Strom

I think tests have shown that the piston never reaches the top of its possible movement and rarely gets more than halfway.
Dave H
Dave Hill

Dave

Hmm, interesting. Why not use smaller carbs and make them open fully.

Eliminating such restrictions in the carbs sounds like an easier way to get more power, than porting and polishing.
YS Strom

The carbs are on the large size for an engine of only 1250cm3. I think it was the research at Manchester that showed the piston gets nowhere near the top (TTT2).
Dave H
Dave Hill

With a SC and a 1 1/2" SU HS installed on a renovated XPAG, I have aimed for a CO content over 4 % for better cooling. However, by doing so it produces a lot of soot and smoke. To get 4 % I also had to raise the needle ( Type C and 5.) 4 mm. and lower the jet 3 full revs. Tested the gas tester on exhaust from a modern car where it shown near zero.

So, I am afraid I will have to go back to the standard procedure for setting the mix and drop the idea of higher CO content.
YS Strom

This thread was discussed between 30/04/2018 and 10/05/2018

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