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MG TD TF 1500 - TF Carburettor Vacuum Chambers

Just realized one of my TF 1500 SU vacuum chambers is drilled to vent but the other has no drilling. Both vacuum chambers are identical otherwise and have brass dashpot piston tops (not plastic) that are sealed with a fibre gasket.
Anyone come across this before? Both vacuum chambers have a strut-like appendage cast into them for a vent hole, but one isn't drilled.
I'm about to drill a vent hole but wonder if anyone has any input on the situation.
Piston drop time is significantly longer on the unvented unit as you would expect.
Manufacturing oversight?

T W Moore

I think I remember something about this in the archives. It might be worth a look.

Kirk
Kirk Trigg

After checking the archives (why didn't I do that first?) I come to the conclusion that all SU''s must be vented, either through the cap or through the .090 hole drilled in the cast strut on the vacuum chamber. My anomaly is either a manufacturing fault or the result of parts swapping at some point.
Ref Peter Jengo June 2004 TD dash pot venting
T W Moore

The SU H-4 carbs on my TF had one damper with a hole and one without. The web in both suction champers was drilled. So I plugged the hole in the damper with JB Weld. Works OK, but the gray color looks bad against the brass cap. Wish that I had found a brass tinted filler.

Here is a Jaguar tech article that explains the venting process.

http://www.jcna.com/library/tech/tech0006.html

Lonnie
TF7211
LM Cook

I would talk to Joe Curto about your H4 carbs.

Lonnie it sounds like you have just switched caps by a DPO.
Buy the correct one from Joe.

TW I think you may have an earlier H4, Perhaps from a TD Mk II?
and an H4 from a TF. I would replace the entire undrilled bell corb. ( the one with the drilled cap and undrilled bell) since other internal drillings probably are missing, Again consult Joe Curto

Does the carb flange have two or four holes? If four then someone has just swaped the Vac chamber onto the TF carb. If two then the have swaped the entire corb for the earlier one

In any case talk to Joe Curto! They both shoud be the same with internal venting.


Don H
Don Harmer

A CORRECTED VERSION

I would talk to Joe Curto about your H4 carbs.

Lonnie it sounds like you have just switched a damper cap by a DPO.
Buy the correct one from Joe.

TW I think you may have an earlier H4, Perhaps from a TD Mk II?
and an H4 from a TF. I would replace the entire undrilled Vac chamber corb. ( the one with the drilled damper cap and undrilled bell) since other internal drillings probably are missing, Again consult Joe Curto

Does the carb flange to air cleaner have two or four holes? If four then someone has just swaped the earlier Vac chamber onto the TF carb. If two then the have swaped the entire corb for the earlier one

In any case talk to Joe Curto! They both should be the same with internal venting.

Both damper caps should be hexagonal not round and undrilled

Don H
Don Harmer

Thanks for all the input. (I tried to call Joe Curto this pm but he was out). Good article from the JCNA on SU features. Both carburetors have 4 holes on the air filter mounting face and I'm fairly certain they're a TF 1500 pair.
I've drilled a vent passage to replicate the passage in the other carburettor and the drop times for each piston/chamber assembly are now very similar. After re-assembly everything seems fine, engine started right up and runs smoothly. I'm using Tom Bryant's teflon Oring mod and finally don't seem to have any fuel weepage from the bottom of the jets.
T W Moore

This thread was discussed between 30/04/2015 and 01/05/2015

MG TD TF 1500 index

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