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?

[1xf87h8w80hlh]

if you remember the shape of gasket is Y you had to pick out the holes in the first place!!!!!

[Adrian Southgate]

I tried using a proper leather punch on another head gasket first and it was a complete fail, damaged but didn't punch through the metal sheet inside the gasket. Went with the gasket with the biggest holes in the end. 

Anyroad, she's back together and thanks to some advice and a helping hand from Mike H running better than ever, actually went for a test run about ten minutes ago. Long story cut short, the following have been contributory factors.

The head gasket had gone, allowing oil into number 1 which caused plug to foul.

The float was bent allowing the carb to overfill and the primary air correction jet was spitting into the carb on tickover and spewing fuel when you accelerated just flooding everything. That has now been corrected and it's a lot better. If the float is too low in the chamber what sort of symptoms can I expect? Would it be worth my while changing any of the jets?

Now the only other problem seems to be a lack of oomph over 2500 RPM. Now this could still be a fuel issue, either too much or not enough, or it could be the coil/condenser. It was getting too cold to work, been out there most of the weekend so plugged the legerra into the charger and will take that to work, get a set of points and condenser on the way home and steal the coil off the legerra if the condenser doesn't solve it.

[Paul Sheridan]

Did you do a compression test?  If No1 has been fouling up, the valve seats may not be sealing!

[Adrian Southgate]

First job on the list for tonight, valve seats may have sooted up while its been running like poo.

number 1 fouling was down to oil leaking in from the head gasket.

[Adrian Southgate]

Had another night of miniscule improvements.

Compression test results are not as I had hoped but very much as I had expected.

#1=9.5

#2=7.5

#3=8.5

#4=9.5

to the nearest 1/2 bar/psi whatever its measured in.

Top off the carb and fitted replacement power valve as old one had a leaky diaphragm, measured and tweaked float levels after fitting new needle valve etc. Cleaned plugs (again) and plug seats, New condenser and then checked points.Adjusted slow running throttle stop screw and mixture according to the weber carb book Dave T lent me. re-assembled the whole lot checked all the pipes were tight and fired it up

Another improvement, it is running quite smoothly considering the compression test results. There is little or no noise from the cam and I suspect it may be a little tight on two and three. Just in case there is a bit of carbom holding the valve open I have added good old redex to the tank and run a little through the carb.

I don't really want to have the head off again to de-coke it as this little problem is beginning to wind me up a bit. The other problem I now face is the rocker cover which won't come off without the choke housing being removed. One of the Sierra cross members goes across the back of the engine bay in exactly the wrong place so it has to be twisted off sideways. I have the heater matrix pipes to the left and the autochoke to the right. The auto choke seems to work perfectly but it doesn't like running with the choke on which leads me to think it may still be getting too much fuel in the mixture somewhere. 

I am going to try again tomorrow to run it into work and get some heat and redex through the engine. 

[Pete Clayton]

Compression test results are pretty low Ade, did you do it at WOT?

[Adrian Southgate]

Cold engine, errrr should it have been done at working temp?

[Pete Clayton]

From memory should be warm and with throttle wide open

[Adrian Southgate]

Sounds logical now you mention it... DOH

I'll have another go tomorrow.

[Adrian Southgate]

Daryl, check answers :-)

[Adrian Southgate]

Been fiddling again... dropped the float level by 1mm on the needle valve and decided to have a look at those aux venturi.

Now I have loads of carbs in bits all over the bench but the carb on the car has the same venturi it came with. I assumed it was as weber intended however I could have been mistaken.

In the picture below the one on the left is the one out of the carb, the one on the right is a 'spare'. Apart from the muck on the spare you may notice there is a slight difference in the actual design. I checked all the other carbs and they have the same design as the spare so I swapped the original out for a cleaned spare.

Now either the 1mm adjustment or the change of venturi has stopped the spitting, smoothed out the slow running and stopped it flooding when standing still under no load. I'm off out for a run in a bit to see if it works 'on the road' as well as it does in the drive. 

[Pete Clayton]

Weird! have you redone the compression test?