You know what it's like..

You buy yourself a new(ish) car and everything seems really fast and powerful - then 12 months down the line, your same car has 'lost' 25mph from it's top speed !?!

You service the car regularly and have it checked over for faults but nothing seems untoward..


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If you lost 25MPH from the top then you should have bad fuel economy as well. Obviously you need a good tune up and some repairs. I would check fuel delivery, electronic ignition, mechanical timing, compression, brakes, vacuum leaks, plugged cat, etc.

 

My fuel economy is around 24mpg (overall). I'm not sure whether this is good (for a car of this cc) or bad?

The engine is a 2226, 5cyl.

 

There is also the possibility that the older Speedo is not working properly, you can verify it by using a handheld GPS unit.

My 1991 100Q gets about 22MPG during winter time and about 26.5MPG during the warmer weather. So your 24MPG sounds about right but losing 25MPH and not feeling it elsewhere would be my cause for concern. Check the CO level and compression. You might be running a bit lean, I doubt it's the compression as it would give you major starting problems if you dropped below 125PSI. Also check that the throttle opens fully and the mass air flow sensor is not sticking.