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MG TD TF 1500 - fuel to air ratio

A new question if you guy's would allow me.

I adjusted the mixture with a hot engine ( 80 centigrade) 825 RPM fuel to air ratio = 12.7 with 5% CO.

I repeated this test with 3750 rpm and it give's a ratio 11.6

WHAT are you guy's thoughts about these numbers,

Thanks in advance for your answer.

Gerard
Gerard Hengeveld

That change in ratio would seem to be a result of the needle profile - different stations on the needle control mixture - that or a slight air leak at the throttle shafts or manifold.
DLD

Sounds a little lean to me
David
D. Sander

DLD ,My carbs are overhauled by Dave B, so assume they are 100 %,

Thanks Gerard
Gerard Hengeveld

D Sander , what figures do you advice ??

Thanks,

Gerard
Gerard Hengeveld

Gerard, what are you using to obtain the values? Bud
Bud Krueger

Academically, the ideal is 14.7 to 1. I mis spoke earlier. 11.6 would be a little rich. You want to be a tad on the rich side. I am curious to see how you are reading the fuel ratio. I have had good luck with a color tune, dialing the mixture in with a bunsen blue flame. It is old school, but it works.
David.
D. Sander

Bud, I have a heath kit gas analyser whom I think works OK but who am I to say so.

Dave I agree in the old day's we never had some sophisticate apparatus as we have now but I have ,and thought give it a try using it. I also like to run a little rich with speeds above 40 Mph .Maybe it is a good idea to buy one of those with A Colour Tune.

By the way I just returned from a 50 minute drive with a speed at about 40 miles a hour and my dash gauge ( newly mounted today ) creeps up to 85 Celsius.

Measuring direct after stopping in the garage with infrared THE RADIATOR is 82 Celsius at the top bottom is about 65 C,
But the bastard is again mumbling bubbles from under the hood Can't stand it.

Many thanks for your reply's makes me a bit wiser I hope

Gerard


Gerard Hengeveld

Gerald,
Don't forget that the cooling system only accounts for 25-35% of XPAG engine cooling - the majority is done by the oil and heat transfer through the finned sump.

Make sure the oil is up to the task & there is good airflow to the sump fins.

Tony
A L SLATTERY

Tony,
Where did you get the percentage of cooling,, rad vs sump? I find it very hard to believe.
Steve
Steve Wincze

This is a good read,

http://www.e-ijaet.org/media/11I14-IJAET0514393_v6_iss2_659to667.pdf
mog

I am still looking for the reference, I am sure I kept it somewhere.

This is also interesting - it may have come from the same reference - could be on John James' Website ?.

A L SLATTERY

Found it - according to this only 11% of heat is removed by the cooling system & a similar amount by the oil.

I only have the reference as a PDF - it's an article on the XPAG Engine by Neil Cairns. I think it came from the MGCC Y-Register Website, but I could be mistaken.

Tony

A L SLATTERY

This pdf file seems to have the same diagram as was posted above, so may be the right one

http://www.mgbits.com/contents/en-uk/Heater.pdf
Geoff_MGB

Gerard,
To compensate for my lack of knowledge and experience with tuning a carburetor, I installed an oxygen sensor on my exhaust and have a digital readout hanging from my dashboard.
I also was told that ideal is 14.7:1 but I run comfortably at about 13.5 at idle. As I go through the gears under load the readout goes down to a richer mix but I believe that is normal. As the car demands more power the mixture becomes richer.
The next time I run the engine in the garage I will make note of the ratios at elevated RPM's and let you know.
Keep in mind my drive set up with the supercharger and roller lifters.

Mort 50 TD

Mort, can you let us know a bit more about the sensor? Type? Mfgr? Installation, etc.

Thanks.

.....
MAndrus

I misread those rations - an air leak would of course lean out, rather than enrich, the mixture! Oops!

An experiment with a needle change would give differing results of course.
DLD

While Stoichiometric is 14.7:1 A:F, in practice, best power and cooling comes in at about 12:1. (some of the fuel is used for cooling the intake charge, it gets evaporated, and what doesn't goes out the exhaust, and a slightly rich mixture ensures that all the air is burnt).

Smooth idle is usually around 13.2:1; and if you adjust your idle there, you will likely have suitable mixture at cruise. The SU will do its own enriching for acceleration.

Finally, when checking higher RPMs, you either need to be on the road, or have the car on jacks applying some braking load. (I'm not endorsing either, just saying). If you shut off the engine at cruise and immediately put in the clutch, coast to a stop, you can read the spark plugs. On today's fuel they will be a bit brown, not as dark as the old days, and perhaps a bit tan or light, depending on your fuel. The colortune will confuse you, it was designed for older fuels.

Hope this helps,
dave

Dave Braun

Mitch,
Will this do?
Mort

Mort 50 TD

single sensor will not tell you if one carb is lean other rich etc
mog

Gerard,
Here are the ratio's at 1000, 2000, 3000 RPM.

This is all on the lift. Not under load.

The digital number jump around a bit. I took at least a dozen shots at each RPM and these are the averages.
Mort

Mort 50 TD

to : Mort. Dave and others who helped me to get a better insight on this subject . A BIG THANK YOU !!!!

Gerard
Gerard Hengeveld

mog
Good point but with the supercharger i only have one carb.
Mort 50 TD

I put an A/F meter on my B when I put the blower on it not long ago. Fuel mix is a lot more critical with the blower. I think you will find any mix between 13.5 and 12 will be just fine.

MG LaVerne

Re cooling, reminded by that splendid diagram, I once blew a TF frost plug in the side of the block and dropped all the water out - didn't know about it. Temp gauge, of course, doesn't show it. Took half a lap to put a large hole in the top of one piston.

Lucky in a way, as the strip down revealed a cracked crank.

David
David Provan

Mort, thank you.

....
MAndrus

This thread was discussed between 09/07/2015 and 10/07/2015

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