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MG TD TF 1500 - Carb adjustment

I have the carbs off the car and dual mounted on the air intake manifold in a vise, so I can really get a good look at what's going on. I can now see how the mixture adjusts and can watch the choke arms move left and right as I adjust the mixture. Very helpful!

But the first thing I noticed when getting the carbs out was that the front carb fuel bowl was completely empty. Rear carb bowl full. Front empty. It's possible it dripped out overnight from a loose union, but I doubt it. It was empty BEFORE I took the carbs off the car this morning. I'm wondering what this may mean.

So currently, I've got them on a vise and both bowls filled with gas. Both floats float fine (good, the thread about repairing a leaky float sounded like a lot of work!); and I see no leakage.

I'm going to let this sit for a few hours and if I notice a change it may help me figure out what's going on. If not, I'll put it all back on the car and try setting the mix again.

Anybody have any thoughts?
Geoffrey M Baker

Did you check to see if turning on the fuel pump would fill the bowls?

An empty bowl is usually indicative of a stuck float needle, not a leaky float. A leaky float will allow the float bowl to OVERFILL.

If the float bowl will indeed fill and then drain overnight, the cause would be a porous bowl, a leak between the bowl itself and the connection to the carburetor (cracks can develop in what I call the transverse tube or arm) or bad seals / gaskets at the attachment, or insufficient clamping of the connection with the banjo bolt.

If the float needle is stuck, remove and clean with carburetor cleaner.

Also verify that you have adequate flow and pressure from the fuel pump.

Hope this helps,
Dave Braun

Dave, I checked the filters on both carb bowls and they were nice and clean. I pumped a few ounces of gas out of the fuel pump line into a glass to fill the front bowl to check for leaking; the pump was fine.
It does not look like the bowl is leaking at this point; there's still plenty of gas in the bowl now.
So we're left with a float needle.
However, both needles and piston things move up and down well, so I see no evidence of sticking.
I'll clean it and see what happens.
Geoffrey M Baker

Cleaned needles and reinstalled carb on car. Started it and she ran better than she ever has... instant start, nice low idle, responsive throttle.
After a few minutes however, she coughed, died, and now I'm back where I was yesterday; seems like its too rich, she doesn't want to start without plenty of air, then when she does start she revs high.

Geoffrey M Baker

Cleaned jets and pistons again, reset/centered the jet hole, its running better now but the gasket at the bottom of the front carb (the one between the base and the big nut) is shredding.
Geoffrey M Baker

Here's what the carbs sound and look like (also posted on the lean mixture thread)!9626&authkey=!ABcQlKeicq1F29A&ithint=video%2c.mp4

For some reason, it's flipped sideways, hope I don't give you all a neck crick... :)
Geoffrey M Baker

Geoffery, Not the needles associated with the jet. The float valve, sometimes referred to as the needle valve is in the float bowl cover directly below the fuel intake. One to clean in each float bowl cover.


Jim Haskins 1953 TD
J. M. Haskins

Thanks, Jim, for clarifying that.

They both seem to drop just fine as far as I can see.
Geoffrey M Baker

What I have done to these carbs:

installed new needle jets and float needles and gaskets, new float forks, misc parts.

Followed instructions on setting float levels, checking piston drop and adjusting mix & syncing carbs

Known problems: I must replace the front base gasket (between carb base and large jet centering nut) ... it is disintegrating and leaking a bit but tightens down OK

Symptoms: After cleaning and checking, when installed it immediately ran well, but quickly the idle dropped to where it would die without acceleration, and increasing throttle led to too high revs.

The mix nuts are set to almost closed on both carbs but symptoms are still rich mix in one or both carbs.

Geoffrey M Baker

Geoffrey -

New gaskets are available. Moss #298-208, $10.85. One set does both carbs. The glans for the jet are cork. Soak all cork gaskets in oil for 24-hr before installing. Polish off any burrs on the jets before installing the new glans.

Look at me ... trying to sound like I am an SU expert. Jeez, I'm struggling trying to get my carbs to work right, too !! I had never even touched an SU carb until a couple of months ago.

Good luck,

LM Cook

Sounds like you've just about covered every possibility with carbs. Go back to ignition as the possible cause of your problem.

If ignition is firing irregularly or intermittently--- Your symptoms will look just like flooding (rich) carbs, but don't be fooled---First Confirm steady ignition. a simple way to check is to put a timing light on one of the plug wires and point the light at something where you can easily see if there is a misfiring of the plug.

I've seen this symptom before with regular points/condenser as well as electronic ignitions. Normally dirty(oil)on points or bad condenser (even new). Electronic sensor gets hot and quits working or is intermittent then cools down and works for a while.
Richard Cameron

Good advise on having a perfectly functioning ignition system and accurately timed. However, even with new float arms and careful setting you are not assured of equal and accurate fuel levels in each jet. Do not ask how this can happen or how I know. The proof of the pudding is the fuel level. With the chamber and pistons remover pull the choke to full on and look straight down the brass sleeve surrounding the jet. The fuel level should be visible. The archive will tell you how far down in the jet. OPINIONS VARY. If you have a vernier caliper depth gauge raise the jet. by means of the choke until the fuel and jet are at the same level. Read the depth below the bridge for each carb, Take you pick from a multitude of advice and adjust the float arms for the same depth and equally. Do not be discouraged. New parts should help but several tries may be required.

Good luck,

Jim Haskins 1953 TD
J. M. Haskins

This thread was discussed between 24/04/2014 and 27/04/2014

MG TD TF 1500 index

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