Welcome to our resource for MG Car Information.



MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG TD TF 1500 - TD 4834. Still fighting my SU H4s

Finally have the fuel leaks dried up on my carbs. Started it yesterday and sync'd the throttle plates as best I can for the moment. I can idle down to about 900 with this roller cam but I'm still fighting with an inconsistent idle. I now have the engine running through a full exhaust system and the pipe is now clean. There's is no soot. But the engine will idle then speed up and come back down and may stall or speed up again. What gives? I don't have a pair of Pistons/chambers that will pass the 5-7 sec drop test. Only one was within spec at 5 secs I had 2 that went 3.5 secs. I put those 2 on because at least they were consistent. I went to The Burlen site thinking I could buy new dash pot assemblies but they aren't listed, neither Moss nor Jor Curto shows them either. I don't know if the dash pits are the problem or what. I need help figuring these out. There are closer but still no Cigar....


Bill Chasser jr
W. A. Chasser Jr


Look for a leak on the intake side of things. Also check to see that the center baffle in the intake manifold is in place and secure. There should be a bolt on the underside of the manifold which holds that baffle plate in place.

Loosen the central throttle link, and make sure each throttle snaps smartly shut. If not, lubricate the pivot points, and also adjust the end coil springs to make sure there is adequate tension. Check for leaks as above- spray carb cleaner on manifold-head and carb to manifold joints and listen for RPM change. Make sure you have the correct spring on the throttle pedal itself. Lastly, clip on an old fashioned timing light and look at the timing- make sure the spark isn't jumping back and forth, it should be steady at idle. Just some basics to check. Can you post a YouTube video? George
George Butz

I should say the rpm changes with the butterflies balanced and closed. Yes the return springs both shaft and peddle linkage are in place and functioning correctly. I am running a Baker header with integrated intake manifold so there are no baffles or screws to
Contend with and no plugs to fall out. The timing is changing as the rpm changes. I have yet to spray WD 40 at the flanges yet. BrakeKleen or ether is too volatile for my set up. But will try it tomorrow
W. A. Chasser Jr

"The timing is changing as the rpm changes."
Is that the effect or is that the cause?
I'm assuming you're using a timing light already, as George suggests, which I would have suggested, too. Sloppy distributor advance can raise & lower idle. While you have it out, snap it on each spark plug wire to see if there's intermittent sparks.
The other guys' suggestion on searching for vacuum is leak spot on, too. Are you running a stock intake manifold? Old school wrenching would advise a vacuum gauge but most didn't have to contend with the MG intake which is separated with an orifice in the center, not to mention, no vacuum ports to tap into. (I run a vacuum/boost gauge on the instrument cluster).
A handy modern day tool is the infrared laser thermometer. It comes in real handy scoping out the exhaust manifold/headers to see which are firing and which are fooling around. Use in conjunction with timing light on spark plug wires. A poor man's noncontact thermometer is a spray bottle.
Hate to say it, but spend a few minutes checking your compression. Sometimes, ya gotta start from the ground floor and work your way up. You might work your way up to discover some valve(s) needs lash.

Jim The engine is fresh with less than 10 minutes run time. New Mallory dual point with red cap and rotor, new Taylor SS core wires, new NGK plugs. We have the timing set at 6 degrees initial via a programmable timing light. I cant answer the hen before the egg question other than to say yes. Yes the timing advances with the increase in rpm. Valves are set at .016" per the cam spec
W. A. Chasser Jr

are you using semi downdraft carbs on a horizontal intake?

sounds silly to ask I know.

Bill, the piston drop in the chamber is not the problem.
Check for a vacuum leak use propane or carb cleaner or just hose to your ear.

Len Fanelli

Again with the setbacks. My new hi torque starter from British Specialties just broke apart.
W. A. Chasser Jr

Thanks everyone for your suggestions. I now have to replace my starter before I can proceed. I'll report results once a new starter arrives


Bill Chasser jr
W. A. Chasser Jr

This thread was discussed between 02/06/2015 and 04/06/2015

MG TD TF 1500 index

This thread is from the archive. The Live MG TD TF 1500 BBS is active now.