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MG TD TF 1500 - wierd 'bRRRRuupppp' on liftoff...

The last time the toofer was out... on the journey home each time one's foot lifted off there was a distinct *new* abnormal sound. :(

Sounded like a gassy burp, or as if there's a hole in the exhaust. With the bonnet ajar... sound is louder from the left/rear carb - and ONLY on throttle liftoff.

Does not appear to be any loose bolts on manifold or the carbs. No obvious gas leakage felt anywhere.

I added some oil to the carb dashpots but made no difference.

Any ideas gents?

-carb adjustment?
-clean the plugs?
-clogged filter pancake?

{thanks in advance!}

Can you borrow a compression tester? This device screws into the spark plug holes and will tell you if there is a valve or ring problem. Do all the plugs look normal at the buisness end?

Matthew Magilton

Funny you should mention that Matt... actually went and bought a compression guage before I got the car. And have never gotten around to using it... :)

Plugs all oily & fouled. Probably too much pottering around in the city + SUs running too rich. Might need to call on Wilson Carbs over winter sometime.

But plugs & compression not the problem; spent some hours yesterday lying under the thing pushing & prodding.

Turned out to be 1 nut slightly loose on the manifold/downpipe junction.

At normal running there wasn't any obvious noticeable gas leakage at the gap. No oil stains, no sooty spray, nothing.

But only on throttle liftoff... that gap actually SUCKS air in, making that "blllrrrrp" sound. (The long straight-thru exhaust must set up a decent pressure wave, causing that vacuum.)

Tightened that nut (hardest one of the 3 to access, thanks Mr Murphy) and noise gone.

Damned - imagine if one had gotten pulled over by the cops for having an illegal "blowoff valve"... :P

sorry, forgot to say thanks Matt.

And if you ever need to borrow that compression guage, just ask. You know where to find me. :)

Will -- part of my standard, annual, routine is to replace that manifold/downpipe gasket before it burns out on its own.
Bud Krueger

Thanks Will, I still haven't gotten around to returning the old mans compression guage yet. One of the handiest little tools in my tool box is the old B.S.A. bike spanner. This is a double open ended spanner which has 'stepped' jaws giving a total of four Whitworth sizes. It is about as long as my fist, so I can fit it into places like the manifolds and the fuel pump. Pick one up for a dollar at any swapmeet. I like them so much that I have been collecting all the other brand names, about a dozen so far.
Matthew Magilton

New gasket sounds like good idea, thanks Bud.

Anyone have any thoughts on the best material & thickness?

Current one looks very thin, like paper. Would something thicker to allow a bit of 'give' to the exhaust system be better?

Will, the gaskets that I get are an assembly of copper around an asbestos-like material, Moss 290-500 or Abingdon Spares 19-117.
Bud Krueger

This sound is common to turbo-deisel trucks, when they are backing-off at speed or gearing down, in which case the the engine is likely burning air and starving.

It may well be that you are running too lean.

Gord Clark
Rockburn, Qué.
Gordon A. Clark

This thread was discussed between 05/05/2004 and 12/05/2004

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