Opinions please gents

[Adrian Southgate]

The Sierra is giving me jip. Running rich, high tickover (1200 rpm), mixture screw is fully in - 1/4 turn back, starts misfiring at 2000 - 2200 rpm, throttle stop screw is backed off and not making contact, throttle cable has slack and is free moving, as it the throttle linkage assembly. Looking for places to start.

I will be doing a compression test when I get home tomorrow and will change the condenser too. 

Anyone got anymore thoughts?

[Big Vern]

Whenever something goes wrong on the test bed you have to work through everything logically, too many times people change many things at a time and often introduce a fault that wasn't there to start with.

I guess if your taking the head off to do the head gasket then give it a good check over. Poor some of that parafin down each port with the vale closed to check the seats are good. Use all new gaskets and clean up the mating surfaces. You've sorted the carb, so should be runnin sunday!

[Adrian Southgate]

Thats my plan ...

Now I know the head gasket has a fault, probably just the return drain from the top of the engine, i'll fix that and see where we go from there. I'll be able to strip bits off the legerra over the weekend so a bit of substitution might be in order.

[Dave Adams]

Basically its ok. its a pain typing on a phone touch screen but the basics are there. nothing is essentially incorrect. air leaks cause weak running and missfires. over rich mixtures can cause hesitant running ((missfires if you like. but less noisy generally) high inlet vacuum can be caused by over advanced ignition which with a worn carb can cause rich running at tick over. where its checked most often and can give all sorts of false “faults“

[Dave Adams]

its actually an experiment i did at college when i taught the subject. we advanced the ignition and observed the results a slightly higher manifold vacuum was one result, and particularly on carburettor engines the co went up indicating a richening of the mixture (this was possible to adjust out to a degree) however advancing the ignition on fuel injection engines effected the co less (often not at all or by very little and it seemed the management systems were able to compensate.) the point of the exercise as to show that when fault finding checking the basics first can save hours of fault finding for non existing faults. the conclusion drawn (i dont know if its correct) was that the increased vacuum drew more fuel into the manifold causing the richening of the mixture, because  the still closed throttle doesn't allow the air in to compensate the extra fuel and hence the richening of the mixture. i would assume that this result would be more likely on fixed venturi carbs and would be less apparent or non existent on a variable venturi carb (or a constant vacuum carb for that matter)

[Dave Adams]

I am not disagreeing with you Vern, its just that sometimes a practical experiment wont give you the result your expecting. this experiment was devised by an older tutor and may well have been an exercise to show how different carbs react to varying engine tunes and how fault finding will have to vary with each carb type. knowing Ade would be using a Webber i was offering some advise from a remembered fault finding day at college (many moons ago) 

[32if6rv0cak3v]

Maybe a bit late on this one but I had a similar issue on a bike.

The issue was mostly down to poor feed to the ignition coils. When idling it appeared fine but when under load and revs increased the power simply wasnt sufficient to the coils.

Of course there could be other factors but maybe worth a try.

Found this out by doing a jump lead bodge which transformed the running before fixing the errant relay properly.

HTH

[allan wheatley]

could it be wrong setup eg wrong idle jet amd main jet

[1xf87h8w80hlh]

funny thing that when i overhalled the carb on the sierra some one had put the jet's in the wrong way around

[Adrian Southgate]

Re-assembly time and I have yet another problem/question.   The head gasket only has very small holes to allow the passage of coolant from the block to the head, I think they should be larger to allow better flow but don't want to compromise the integrity of the gasket by removing too much material as they are very close to the bores.

Do I run the risk and remove some gasket or fit it as it is knowing that I have restricted water flow through the engine?

[Adrian Southgate]

After looking at images on google it would appear that some of the more expensive ones have the holes open, but the cheaper ones do not. The genuine ford ones seem to have holes like the ones in my gasket, about 4-5mm round holes. I think I am going to enlarge the existing holes to 8mm and open some of the spaces where there are no holes at the moment. If the holes are in the head and the block I don't see a reason why they should be blocked by the gasket.

[1xf87h8w80hlh]

if you want to make a punsh to do the job. drill 2 holes in some flat plate us a 6mm &10mm bolt and weld them in put it in vice with the studs up then get a old hack saw blade heat it up with a plumbers blow lamp and wrap it arownd the bolts dont get it 2 hot or it will fall apart when cool grind sharp then you have a egg shape cutter you can add a handle if you like

[1xf87h8w80hlh]

mr musle or washing powder will do it 2 but you need to cleen it out good after