On with the brakes but while waiting for a new master cylinder some floats and valves with new seats have arrived for the float chambers so new bits fitted to carbs and new stainless exhaust fitted (needed to cut 1" off one of the front pipes to get it to fit - thanks Bell engineering!!!!)
Started the car and it was running very lumpy 5 ish cylinders
Hmmmmm
Thinking about checking out compression on 5 and 6
Anyway - Ive been on with the brakes so wanted to complete this first - new master cylinder fitted - then suspected the servo and while waiting for a replacement I removed the old servo and closed off the vacuum pipes.
When I started the car - its running on all cylinders absolutely fine. These things can send you off on a wild goose chase sometimes. So now I have to find out where the leak is. At least the engine sounds fine - a bit tappety but thats ok. New servo on its way so will fit that and then investigate the vacuum circuit - wonder whats affecting the engine running?? All good fun this head sctratching stuff eh. Has anyone come across this one before?

 

sounds like a bad spark plug or spark plug cable.

 

So, you removed the old servo and blanked-off the pipes, but where ?

There is a Reservac tank under the wing at the front, and this rots and lets air in via pin-holes. The one-way vac valve can also give trouble as it is made of Mazak, and with road salt bathing it it eventually crumbles away.

 

If you have a leak in the vacuum circuit it will suck more air into the manifold and give a lean mixture especially to the cylinder adjacent to the vac hose connection on the inlet manifold.

This would lead to misfires if the mixture were lean enough.

You could cap off the pipe just before the reservac valve, then after the valve and then by the servo to isolate which area the leak may be in.

 

Thanks for the input guys
I'm thinking the problem will probably be with the res tank.
Yes the problem did cause a very lean mixture - when I increased the fuel supply the engine ran better but when I closed off the vacuum - then the mixture was very rich. I have backed off the mixture and the engine is now running fine so investivation required in the area of the reserve tank or hoses.
I had already replaced all plugs and caps leads and dizzy cap so the problem wasnt electrical. It had to be down to fuel/air but because it was at the back of the engine it confused me.
More about this later.

 

If you closed off the vacuum pipe where you disconnected it from the servo that would lead to the leak being in the servo not the reservac tank as this would still be connected. Fraser's question re where did you close off the vac pipe ?

 

Hi Guys
The servo has been removed and the vac capped off at the servo. I have the new servo going on tomorrow so I will follow the leak when the new servo is fitted. The leak will probably be the reserve tank or pipework - it shouldnt take too long to find it. I have ordered new vacuum hoses anyway so will fit these and investigate as I go.

 

If the res tank and pipework is still connected and the vac leak went when you disconnected from the servo and capped wouldn't that indicate the vac leak is in the servo or banjo bolt connecting to the servo ?

I may be missing something mind ?