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MG MGB Technical - Sluggish MGB GT - Carb Problem??

Hi There -

Just wondered if anyone has ideas on what's up with my MGB GT.

It's a rubber bumper car (LE), and I've had it about 2 years. Throughout the time I've owned it, it's been by far the slowest B I have ever driven, and I've tried plenty of all types. It's always cruised OK, but it's SO slow on acceleration, way below average for these cars. I've eventually got totally fed up with it, as it now appears to be getting worse: hopeless on hills!!

The oil pressure is excellent (75psi cold, 70 psi hot with a few revs), and the engine uses absolutely no oil, and never overheats. It's a goldseal recon, but the carbs are original to the car, and have done 180k miles - I have the full history of this car, and they've never been rebuilt!!

The engine starts first time everytime, compression is excellent, but it's probably the roughest B I've tried, hates to rev even worse than normal.

I therefore suspect the carbs: I've tried richening up the mixture, but it does no good: should I just swap for a set of earlier non-emissions HS6 carbs? I like them better cos I understand them!! Will the earlier carbs/inlet manifold just bolt onto my rubber-bumper car?

Any help appreciated!
Cheers
Bruce
B. Mann

Certainly replace with HS6 carbs, you do not mention which carbs you have. With the correct manifold, heat sheild, blocks etc. these will simply bolt on.

The Haynes resto manual(Porter) also details how to de-tox a US car; some of the tips will also benefit your model.

Hope this helps.

Iwan

Iwan Jones

Also make sure the mechanical and vacuum distributor
advances are working. Check the advance at both
idle and at 4000 RPM or so.
Ronald

Is it green :)
Mike MaGee

I also own a uk BGT LE and mine ( also a gold seal MGOC fitted recon with orginal carbs) is slow too in comparison to ealier cars. I looked in an article in classic exchange and mart and it gaves the LEs top speed of 98mph and a slow 0 tp 60 some where around 13.5 secs if I rember correctly. Compare these to earlier figures of 107mph and 11.5 so they are slower out the box. Of course after all these years it possible your car has been meslessed so may not have the orginal spec. Mine has the orginal spec and is fairly slow. I like you wonder why it slower than other Bs i considered firstly it was a later car so slower secondly may be its in poor tune thirdy that its just the best engine. I have also conidered getting an older car set up. But am toying with the idea or attempting to service my current SUs just in case they are not getting optimum performance. I find my B cruises ok too and has bags of torque ( prehaps just a power balance that favours torque prehaps just little power lol) can take hills in top gear over drive with out struggling but acceleration is newer brliant. I appreate that I have not really offered any usefull advice here as I am in pritty much the same postion as you just thought I would meantion this in case there is some reason LEs are actually slower and would be interested to here any way to remedy this.
JIM

Mike all UK GT LEs were metalic pewter an austin Princess/abassator colour.
JIM

I don not think you'd want to use the HS6 carbs unless you have done lot of high performance engine work. Thats way too much carb for the stock engine. The stock carb setup should be two HIF4s.
A comprehensive tune-up is in order I'say. Like Ronald in CA suggests, check the distributor advance for proper functioning.
A thought: did the distributor come with the Gold Seal engine? Check the Lucas number to be sure it is the right one for the MGB HC engine, not some LC Morris whatever.
Andy Blackley

Obviously, what changes you do to improve performance depends upon your wallet.
Simple changes are relatively cheap - such as: 1. Lumenition instead of contcts in dizzy. 2. Twin HS4 carbs(rather than HS6's - which really need ported heads & overbores) 3. K&N Filters (not pancake ones)4. Replacing a two box exhaust with straight exhaust centre section leading to a rear box only. 5. Replacing engine fan with an electronic one.

Get a Haynes Manual.

Iwan
Iwan Jones

Hi,

I would definately check the diaphram in the vacuum portion of the distributor, they are a garbage piece of equipment, I have changed mine twice in the last 4 years on my 73 B. Ready to chuck the whole engine apparatus in the trash and go for a GM V6 with modern electronics. FWIW ALAN
Alan

Bruce - richening from the correct postion won't do anything, except possibly make it slower AND more consumptive. Have you been through the valve clearances, plug gaps, points dwell, timing, vacuum and centrifugal advance before doing anything with the carbs? This includes testing the vacuum advance diaphragm, and whilst I have done several replacements on the V8 because of fuel contamination (the port comes off the bottom of the carb throat instead of the top like the HSs or the top of ther manifold on later cars). Have you then set up the carbs air flow and mixture balanmce and strength from scratch? Are the pistons, dampers, choke and accellerator cables all working correctly?
Paul Hunt

Bruce,

Leave the engine standard with HS4's and standard distributor. All the information re ignition settings valve clearance etc is correct but are you sure that the camshaft is the correct one especially if its a gold seal engine. Whats the engine number prefix, check this out to make sure. Make sure that the valve lift is as specified because the cam may be worn and also ensure that the valve timing is correct.

Don't buy a Haynes manual, spend your money wisely or read the thread about the best thing to do that manual!!

Iain
Iain MacKIntosh

Thanks guys -

There's been a LOT of helpful info here. I mistakenly suggested that I would fit HS6 carbs - I actually meant HS4, to replace the rotten HIF carbs currently fitted.

I accept that these late rubber-bumper cars were never going to set the road alight, but mine is almost dangerous pulling out into traffic, and doesn;t want to know hills at all! It's also struggling to tick over, and I suspect that wear in the carbs is allowing air in somewhere and weakening the mixture....

Time, I think, to look for some HS4s.

Thanks again
Bruce
Bruce

Spray carb cleaner round the gaskets, throttle spindles etc, when idling and if the engine note changes you have found a vacuum leak.

That comment about Haynes is unwarrented, it implies that it is grossly incorrect. It isn't, although it doesn't go into quite the same depth as the Leyland Workshop Manual and does oversimplify some tasks. It is still a good starting point and a damn sight better than no manual at all.
Paul Hunt

This thread was discussed between 06/02/2004 and 10/02/2004

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