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MG MGA - Loss of Power & Poor Acceleration

My 1957 1500 MGA has lost power and acceleration over the last year. Particularly when going up hills that previously I have taken in 3rd gear at ease, I now have to go back to 2nd and crawl up the hill.

We have tried/checked the following:
- Each cylinder compression approximately 125 PSI
- CAM Shaft timing to spec
- Value clearance in spec
- distributor timing 10 degrees before top dead centre
- Front carby running very rich
- Rear carby slightly rich

Any suggestion would be greatly appreciated.

Thanks in advance

Cheers John
J Dawson

John

A few years ago I suffered similar problems after a routine service that also included taking the filter boxes off and cleaning the filters. I then accidentally reinstalled the rear filter box upside down, blocking off the air balancing holes to the piston. Consequently the rear carb lagged horribly behind my throttle requirements with associated power loss.

see here: http://www.mgaroadster.co.uk/odds_and_sods.htm

Steve
Steve Gyles

Thanks for the quick response Steve. We had taken the top of the filter boxes off, but not the bottoms, so air balancing holes could be blocked off. Will investigate and fingers crossed it is as simple as that.
Cheers John
J Dawson

You did not mention the age of the coil....Coils usually do not just stop working, but deteriorate over time....
Most noticeable is an obvious drop in acceleration.
If the coil is old, replace it.
Edward
Edward Wesson 52TD

Another out of the box suggestion is to check your tyre pressures. I notice a distinct loss of performance and economy if the tyre pressures are low.
Neil McG

Are you firing on all 4? Try plug leads off one at a time on idle. (Similar to Ed's post)

Art Pearse

John
Plug gaps OK?
Plugs getting a bit old (>>30k miles)?
Local fuel suppliers changing their mix (less octane or more ethanol might mean a change to ignition timing)?
David
D Brown

Is the power loss constant, or only after 15-20 minutes of driving? If your power loss starts after 15-20 minutes of driving, it could be the condenser. New condensers are of notoriously low quality and a high failure rate.
M. D.

Another thing I have heard of happening is the diaphragm in the vacuum retard being holed. Test by blowing if other suggestions fail.

Paul

PS

As an aside, I was in Moss Bradford yesterday and there was another customer in who had a B series engine (actually a late MGB engine in a Marina) that was consuming 1.5 litres of oil in 20 miles. I guess that is consuming about half as much oil as petrol!

Paul Dean

Something has changed, it seems, so you can look for that, but 125 is marginal for compression. What are the valve clearances? If you have some valve recession, you may need to readjust them.

Other things that can change:

*plugged fuel filter (just happened to me)
*dirty/oily front air filter (happened to me also)
*bad condenser
*melted rubbing block on points
*points pitted/fried (if you left the key on too long)
*stuck valve on one cylinder
*distributor points plate stuck (corrosion)

Here is an odd one (happened to me):
*heater control valve dripping coolant onto distributor cap causing a misfire

Running slightly rich should not result in any huge loss of power.

When my 1500 '57 roadster was "done" I noticed it would not go up the mountains very well. I changed the "GS" needles for "no. 6" needles in the carbs at Joe Curto's suggestion, and there was a HUGE improvement. My engine has been slightly overbored, and the no. 6's are slightly richer at above 1/2 throttle I believe. If your performance was good before, but not anymore, I doubt that your needles are wrong, though they may be worn. Generally once a set of SU's is set up well, you shouldn't need to mess with them, and nothing should change suddenly, so I wouldn't go tearing into your carbs first other than to see if they are working properly - pistons come down with a thunk, jets centered, balanced, etc.

Please let us know what you find...always interesting these little cars...

JIM in NH

AJ Mail

This thread was discussed between 17/08/2013 and 21/08/2013

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