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MG TD TF 1500 - Mixture Settings How Many Flats

To get to the jet nuts and lifting pins on a TF you have to remove the air filters. If you set up the mixtures without the Vokes filters how many flats should you weaken the mixture by to account for the airflow restriction once the filters are replaced?

Jan T
J Targosz

Jan, due to the numerous variables between carburetors I think setting the mixture by the number of flats would be hit or miss. I think you only have two options when setting the carbs: the visual and aural observation (how it idles and the condition of the plugs) or the use of a Colortune to see the actual mixture firing in the cylinder. The Colortune would allow you to determine the efficiency of the mixture before and after adding the air cleaners.

Tim
Timothy Burchfield

Jan,
the only thing the filter on a TF does is keep out bricks.
The mix does not change when you fit them. If you use an SU spanner or cut down an open ended spanner till only couple of MM's are left of the jaws you can adjust the jets. Fiddley, but do-able.
Ray
Ray Lee

Ray, I have to add that because the tappet cover vents into only one carb the mixture will change on the front carb when the air filter is fitted. Especially if you have some blow by.

Tim
Timothy Burchfield

Rule of thumb is 12 flats to start, then tune from there.
Steve Simmons

Possibly Tim, but after 1/4 million miles it hasn't done my TF any harm, (I have only done 150000 of them).I must admit I had never thought about the vent.
Ray
Ray Lee

Interesting, never gave it a thought as to why, but there's one flat difference between the front and rear carb on the TF, both being professionally rebuilt and work beautifully. I forget which is which, but I guess the air cleaner might have something to do with it. I color tune the initial settings and that's how it came out. PJ
PJ Jennings

The setting is not critical, it can be anything from 8 to 12 flats as a starting point. Together with the float level this controls the level of fuel below the top of the jet, and the level of top of the jet from the bottom of the venturi. What you want to end up with is the fuel level 1/8 to 3/16" below the top of the jet. The top of the jet should be close to the bottom of the venturi, but this isn't always possible and is influenced by the thickness of the washers in the jet assembly, amongst other things.
Dave H
Dave Hill

Ray and PJ. My issue about the crankcase venting into one carb is based on having seen hundreds of PCV valves over the years and how cruded up they get even on well running engines. Fumes from the crankcase have to be less well burning than outside air. Based on Ray's experience and extended mileage (the engine not Ray) I'm guessing that you would need quite a bit of blow by to seriously affect the air fuel mixture on the front carb (TF). But I'll bet the difference would affect, to some degree, the colortune results.

Tim
Timothy Burchfield

Tim. I'm pretty sure the influence is insignificant.
Dave H
Dave Hill

67 years ago, I was living at an altitude of 600 feet. With the "standard" needle, I got a good tune with 6 to 8 "flats" down. In 1960, I moved to an altitude of 3500 feet and could not get a good tune with the "standard" needle. The carbs could not be leaned out enough to get a good idle or performance. I installed a lean needle and with 5 to 6 flats down, both the performance and the idle are very good. My point is, that the altitude is an important factor in tuning the carbs. I now live at 4500 feet and have had to lean out the carbs again to 3 to 4 flats down for satisfactory performance and idle. I use the spark plugs to determine the carb settings.

George
George Raham

Set the depth of the fully pushed home jets to be 0.060" down from the bore of the carb and it is the first time ever that I have been able to influence the speed of the engine using the lifting pins. A very slight adjustment of the jet stop bolts and the speed rises and falls just like the manual says. The engine purrs beautifully and the exhaust note is a delight.


Jan
J Targosz

Jan, what distance did you use when setting your floats?

Tim
Timothy Burchfield

Hi Tim,

The manual said 3/8" and Buren 7/16". I found it difficult to be precise so mine are probably somewhere in between. I tried with a 3/8" and a 7/16" drill but the there wasn't enough of shank before the flutes started so I turned a piece of wood which would stretch across the endges of the lid and bent the forks until I could just slip a .001" feeler under the jet.


Jan T

J Targosz

I believe that the measurement is now 7/16" because modern fuel is more aromatic than the fuel these cars were designed for.
Ray TF 2884
Ray Lee

Jan and Ray, I asked about the float level setting because that would alter the depth setting of the jet. So Jan, I'm thinking for your .060" setting to work for others they would need to know your float level clearance.

Regards

Tim
Timothy Burchfield

There are certainly more volatile components in there including cyclics and aromatics (like toluene and xylene). I ignore the bar thickness method, and just try to set the floats so that the fuel level is 1/8" to 3/16" (3 - 5mm) below the top of the jet, after making sure the jets are the same height.
Dave H
Dave Hill

This thread was discussed between 03/08/2018 and 10/08/2018

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