Lumpy engine / Vauxhall Viceroy petrol issues?

[viceboy]

When I bought my Viceroy a few weeks ago, drove it home fine no problem. Filled her up with unleaded + additive and has been running lumpy ever since.

I have changed the plugs, leads, rotor arm, distributor cap, air filter etc - no difference.

I have owned these cars before and no problems with additive added to unleaded. Having serviced it, I'm guessing it's a petrol problem. Should I find a 4-star garage, fill her up, and see how it goes? Thanks.

[Dave the Builder]

check  the timing with a strobe .
it may have not been timed up for unleaded 
also... new parts may be faulty ,so don't rule them out 

[carlton_mad]

i take it there is a carb rather than injection?

if so is it a cd 175 or similar?

stromberg carbs have a diaphragm inthe top which needs to be perfect if there is even a tiny pin hole they cause running issues you could spend a small fortune trying to sort out

try using cling film on top of the rubber diaphragm to see if that sorts it out

[encino]

Could be that filling it right up may have disturbed some muck in the tank, especially if the PO ran it with a low fuel level, and some debris may have blocked a jet in the carb.  I take it the car still has the original variajet carb.                     

[viceboy]

Yes, the car has its original variajet carb, dunno if its the cd 175 though. There was half a tank of 4 star leaded petrol in it when I bought it off the PO.

I will try adding 4 star again to see if that makes a difference. If not, I'll get the carb looked at. Thanks.

[encino]

I'm not convinced that an eighties CIH engine needs an additive to use unleaded, I ran a couple of MK 1 Carltons which had the 4 cylinder CIH for thousands of miles on regulat unleaded with no loss of compression or other problems. Just a thought.

[PeterC]

Longshot, based on non-Carlton knowledge. Maybe the air breather (usually in the fuel filler cap) is blocked. This is more obvious if you have filled the tank right up as it takes a lot less time for a vacuum to build up. Simple test is to remove the filler cap when it starts running rough - it should then behave. Usually takes a while for the engine to start gettng starved but its an easy test anyway. Thats unless there is no such thing as a little breather hole on your car.