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MG TD TF 1500 - float chamber

Been trying to work out why my plugs are always sooty. I looked at the float chambers. The lever arms are set for a 3/8" rod as per my manual. However the SU Carb manual I have says they should be set at 7/16". I guess setting them at 7/16" will drop the fuel level in the chamber and possibly solve the problem of flooding the carbs at idle. Has anyone else noticed this difference in the specs or am I missing something.

A
A R Jones

I think the thing Dave Braun suggests is more near the truth.
You need to re shape the forks to get the fuel level in the jet to the correct height. This may not be where the WSM describes it.
Take a look at Dave's site and read his set up procedure which worked very well for me.
It will help if you have an electronic caliper that has a depth gauge as well.

Here is his PDF instructions.

http://www.dbraun99.com/Setting_SU_Carburetors­_Rev_C.pdf
Hope this helps you.
Rod
R D Jones

Rod,
I find that very interesting since I had followed Dave's method but ended up with an over rich running engine, lots of smoke. I also noticed that others mentioned on the BBS they were running out of mixture adjustment. I finally went back to the old method. I believe it is very difficult to set the fuel height in the jet even though it is probably the most precise. Personally, I believe the SU carb to be a very simple design, uncomplicated and maybe we need to treat them them that way. Maybe, you can come by and show me how you do it and prove me wrong. And yes ROD, the TF is on the road so a Fall run now looks possible.
Bob
tables1

Mixture is a big concern on any carburettor and getting it right can be a chore, as we all know, but it is also very important to have multiple carburettors synchronized to the point where all cylinders are putting out equal power. I use an air meter which checks the flow of air entering the carbs at various RPMs. Even with that, adjustments can be a chore. Years ago I worked on Mercury outboard motors and one I had, had 6 carburettors on it, had to set them with a diagnostic machine. So 2 SUs aren't really that troublesome. I personally think they are a great carburettor, one of the best. JMHO. PJ
Paul161

A R, don't feel alone. I've made serious attempts at it, but I've not been able to do the 'height-in-the-jet' technique. I can setup the carburetors following the basics and follow them with tweaking to get smooth running and good looking spark plugs. Maybe one of these days I'll try to measure the height of the fuel in the jets, just out of curiosity. Bud
Bud Krueger

I had this problem -too rich -and discovered the problem lay in washer #33 (see Moss diagram). The replacement/rebuild kits sometimes supply a washer that is too thick which results in a rich mix. Removing the washer completely or, at least, installing the correct thickness washer (0.015 in) may help... Mine ran perfectly once I did that...
Geoffrey M Baker

Go with the 3/8" setting as shown in the WSM for the TD. If your SU manual is like mine (Haynes) it treats the H series carb generically and possibly only for MGA and later cars. In any case, the 7/16" setting agrees with the specs in my MGA manual, but not the TD manual.

FWIW, I found that starting with the jet at .070" as suggested by the venerable Mr. Braun was too low and I had to do a lot of leaning out/turning of the jet screw before I got close (non-TD). Now, this was on a car where I had put in richer needles, as well, so that probably had something to do with it. The manuals suggest starting at three full turns down, which equates to something more like .030", so that's where I'm going to start with my carbs going forward.
David Littlefield

Question on the 3/8" space under the forks: Is that with the float valve open, or depressed (closed).


...
MAndrus

Bob,
Sorry to be late with reply but I am in Florida with the wife looking for a new home.
Will be back later this month and will contact you then re "the road trip" :)

I found Dave's instructions on point but it is important to do all of them. In the order given.

My plugs on a steady run come out just fine biscuit brownish. There may be a little oil burning there as well. It has been many years since it was overhauled.

Really glad to hear you have the TF on the road. Looking forward to driving with you.

Rod

R D Jones

This thread was discussed between 05/09/2015 and 07/09/2015

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