Misfiring at midrange revs

H

HUGMARS

New Member
Rover p6 2000 tc
Kiaora, currently I'm having an issue with my rover.

The problem seems to be misfiring around 2500 to 3000 rpm.
The car starts and idles fine and if you can break through the mid range it runs fine at higher rpm.

spark plugs and distributor are all in good condition.
fuel bulb is clear and pump provides sufficient fuel.
Carburettor has been cleaned, piston moves easily and jets "seem" to be clear.

My current ideas are that the timing has slipped or that there is a problem in carbs that i havent identified.

Does anyone have suggestions or wise words of wisdom?


The problem started towards the end of a long 6 hrs drive.
 
I would suspect the distributor to start with, although you say it's in good condition. Check the bearings by catching hold of the rotor arm and wiggling it about. Also, check the weights are swinging out smoothly, if they stick a bit you'll some of your advance. I'm assuming the vacuum advance is working ok?
 
Check the weights and springs of the centrifugal advance under the plate in the dizzy). but first run the car with the timing light on up through the rev range to about 3500 rpm and see if the timing is moving. Disconnect vacume advance unit and plug tube first. How old are the leads?
 
Do you have a magnetic pickup fitted for electronic ignition? I had the screw holding it down loosen recently causing poor starting an a miss at certain speeds. Once I found the screw loose (it was only about half a turn loose!) and tightened it car was back to normal.

Quick edit: if you have conventional points fitted you might want to check the small ground wire that goes to the baseplate. Those can breakdown internally and lose continuity as the plate moves with the vacuum advance etc.
 
Just in case. I chased a similar misfire for months. Checked, changed and checked all the usual potential culprits. When I removed the relatively low mileage distributer there was some slop in the shaft and the cam plate pins were worn. Got it rebuilt, problem solved (distributer doctor). All seemed fine with distributer until removed from car, and even then it didn't seem so bad, but clearly was.
 
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