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MG MGA - Baulking under Load

Happy Easter
I seem to have a slight problem with my MK 2 Coupe which I am delighted with and will happily do a run of 200 miles a day.
she runs fine most of the time especially at low revs and aroumd town and will accelerate easily up to 60 mph however when cruising on the motorway especially on a slight upward incline it is very slow to accelerate from 60 to 70 mph and feels as if it has reached its maximum speed - when on the flat and slight downhill it will then pull easily up to 90 mph. I have had the car for just a year and it was fully restored over a period of 6 years by a previous owner. It has the original engine rebuilt approx 7 years ago with according to the specification sheet that came with the car a slightly reprofiled cam, and with a C/R of 9.5. The compressions are steady at 160 -170 on all cylinders. It is fitted with a 25d Distributor.I had a five speed gearbox fitted last year by Peter Edney. I have checked the mixture and all seems fine all four plugs show the correct colour after a run. and she starts and runs easily and will rev happily most of the time. I have done around 4500 miles this last year with no problems.
On reading the Archives I am suspicious that the advance may not be working correctly or perhaps the advance curve is wrong ?. On my MGB I had a worn distributor and replaced that with a 123 distributor which seemed to cure any poor running problems I had.However reading through the archives there seems to be some debate regarding 123,Alden or leave with points I appreciate my distributor is not original and perhaps is not correctly profiled for the car especially as the car was restored mainly for show and was hardly used.I am not a "high Tec" person but can do most of my routine maintenance however I have found difficulty checking the timing as my old neon tester does not seem up to the job, I am getting a new timing light this week !
I am tempted with the 123 system as it has curves inbuilt for the 123 and I was pleased with it in my MGB, however I believe Alden will build one to your spec.
Am I going down the right route ? Any thoughts from you guys would be helpfull
P D Camp

PD, your problem may well be timing or equally fuel supply/carburation. Check the timing with the vacuum lead disconnected and sealed. Check all the potential areas of air leaks on the induction side, carb's, gaskets etc. There's plenty in the archives on trouble shooting for similar problems. I seem to remember a lot of issues were discussed on a recent thread under the title 'can't get my engine revs over 3000rpm'. You need to go through a logical sequence of elimination.
J H Cole

It could be the 25D. Indeed, I could never get my refurbished 25D running right. I put it down to worn or incorrect bob weight springs.

Equally, some of your symptoms remind me of my experiences with the rear carb filter box on upside down - worth a check.

Steve Gyles

Thanks Steve & JH
The Filters are on correctly -checked that after checking through the Archives yesterday-have read through JH recommended archive and will proceed logically with the tests. have achieved a better performance by retuning the carbs and will do a test run this pm. Still suspect the 25d as per Steves mail
Thanks Again
P D Camp

PD,You dont say what gear you are in at 60 mph.What rear end diff ratio do you have 4.1?
I fitted a 5 speed to my MK2 a couple of years ago and found the same thing.There is no acceleration to speak of in 5th it is strictly an overdrive.
Upgrading the distributor will improve the overall running but may not solve the problem in 5th gear.
T Cox

Paul, check the vacuum advance on your distributor with a vacuum gauge. Mine was leaking completly and showed no vacuum at all.

Andy 60 Coupe
Andy Preston

Thanks Tony
I was in 5th with a 4.1 rear end -have since balanced the carbs and tightened the vacuum tube to the distributor which was very slightly loose. Went for a 50 mile run yesterday and much improved performance. I still suspect the 25d advance curves are not quite right for my car-as per Steves mail but the performance is now acceptable.Will consider having electronic ignition with a new distributor as per 123 system as funds are available, as that worked very well for my MGB.
Really appreciate this site and the mine of information
P D Camp


You may want to consider the Chinese 45D distributor from Bob West. 50 compared to 199 for the 123. I used a 45D very succesfully on my 1500 engine before I went the 1800 route.

Steve Gyles

This thread was discussed between 13/04/2009 and 14/04/2009

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