rough running

i am getting a constant slight mis-fire and plug fouling on the middle two plugs. the outer two are the right colour (somewhere between a rich tea and a gingernut!). the only thing that has changed is the base of the hif44 carb. when i was fitting a new steering rack a few weeks ago, i managed to crush the carb base plate by dropping the subframe down for clearance. it didnt cross my mind at the time that the carb would foul the bulkhead when the subframe was dropped. i replaced it with the base plate from a spare hif38, which appeared to be identical, but now it feels spluttery all the time and power seems to have got worse. its fitted with a late 1275 motor on electronic ignition. i am having to drop into third gear on hills and it used to pull fine in fourth. the only thing i can think off is maybe the float hinge in the carb got bent slightly. if it was flooding slightly would it have this effect on performance? its just had a full service to try to sort it but its made no difference. does anyone have any ideas? im stumped.

psychobob wrote:i am getting a constant slight mis-fire and plug fouling on the middle two plugs. the outer two are the right colour (somewhere between a rich tea and a gingernut!). the only thing that has changed is the base of the hif44 carb. when i was fitting a new steering rack a few weeks ago, i managed to crush the carb base plate by dropping the subframe down for clearance. it didnt cross my mind at the time that the carb would foul the bulkhead when the subframe was dropped. i replaced it with the base plate from a spare hif38, which appeared to be identical, but now it feels spluttery all the time and power seems to have got worse. its fitted with a late 1275 motor on electronic ignition. i am having to drop into third gear on hills and it used to pull fine in fourth. the only thing i can think off is maybe the float hinge in the carb got bent slightly. if it was flooding slightly would it have this effect on performance? its just had a full service to try to sort it but its made no difference. does anyone have any ideas? im stumped.

As cylinders 2 and 3 are very close to each other (1275cc engines), the head gasket may have failed between the cylinders. Check the compression on each cylinder and if 2 and 3 are low, then suspect the head gasket. I can't think the carb is at fault as the inlet manifold is split in two, with cylinders 1 and 2 on one branch and 3 and 4 on the other.

It's a bit of a stretch but the force of the carb hitting the bulkhead would have had the effect of 'lifting' the head from the block.
I'd have thought that the head bolts should be tight enough to prevent any problems, but I guess you'd only need a minor disturbance to potentially affect the gasket.

The obvious first step should indeed be a compression test on all 4 cylinders.
The fact that the plugs from 2 & 3 cylinders are showing definite signs of under ignition - compared with 1 & 4 which as described
appear to be behaving correctly - could indeed mean a head gasket failure between no.2 & no.3.

As already, advised, it does not seem logical that your problem is carburretion and as you have electronic ignition - that should rule
out electric gremlins.

I speak from a relative amount of experience having suffered 2 head gasket failures on my 998cc Morris Cooper in the past 12 months.
David 2010

your probably right. to my shame i left the front end (subframe+ engine!) held up by just the carb and manifold overnight! in my own defence, it was cold and dark by that point. i've ordered a compression tester from fleabay so can test it to be sure. it doesnt seem to be getting hot or losing water but if its blown between the cylinders i dont think it would get as far as an oil or water channel. oh well, another job for the christmas holidays! so much for relaxing!