reluctant acceleration over beyond 80mph

[Deleted]

Hi

I changed the contact breaker unit and the coil on my 68 P5B Coupe recently. It has been off the road for some time because of worn top swivels. Now I took it out again on a cool sunny day and found, that the acceleration is poor. It starts, idles and runs fine on half throttle but as soon as I floor the pedal it does not accelerate over 65mph in second nor does shift up under kick-down and on the autobahn it slowly picks up speed up to 100mph but not more and again, when I put my foot in it it accelerates unsteadily, as if someone is holding it back every few seconds. It does not make any strange noises, temperature is fine. I checked timing and dwell angle which are fine.

Also I noticed a bit of vibration in idle which is new to me.

I suspect two possible sources. One is fuel supply, but should this not result in some missfire?

Second is a new earth cable on the contact breaker plate which is slightly thicker than the old one was. Might this interfere with advancing and retarding the ignition?

Any other clues?

Any help will be appreciated.

Cheers

Michael

[stantondavies]

Could be a lot of things but I would concentrate on the electrical side to start with. Double check the points are set correctly and the advance mechanism is operating. It could be a faulty condenser or the coil. Check connections. The new coil is the correct type? P5B owners should be able to advise on this.
Could also be spark plugs; check them to look for evidence of cylinder(s) misfire. Check HT leads. Distributor cap OK?
Are carburettor dashpots topped up? Fuel starvation is a possibility but I would have thought unlikely.

[Phil Nottingham]

Apart from the above did you replace the Condensor and reset the the dwell with a meter and check the timing with a strobe Also check the advance both vaccum and centrifugal

[Deleted]

I think the condenser came with the new contact breaker (?) and I checked the dwell with meter and timing with a strobe. How can I check advance centrifugal and vacuum separately?

Thanks so far
Michael

[stantondavies]

I don't know the V8 distributor but on some you can suck on the vacuum tube and watch for the base plate moving. Alternatively you can attach a thin wire to the base plate and feed it outside the distrbutor replacing the cap. With the engine running at tickover you should see the wire move when you open the throttle.
As for centrifugal advance, this depends on the bob weights and springs and I left that to the Lucas engineer who rebuilt my distributor. You can rotate the rotor arm anti-clockwise to feel the tension, but it doesn't tell you too much - you really need them checked properly; different bob weights and springs will alter the advance curve of the engine, as will weak springs. Some other member will doubtless be able to advise you further.

[harvey]

To check the vacuum advance, with the engine running. remove the pipe at the carb end and suck on it while looking at the timing marks with the strobe, for the mechanical advance, increase the rpm while looking at the timing marks with the strobe.

[lagain]

It is easier to fit, and forget, electronic ignition. My Luminition has been on since the late 70's