19 replies to this topic

[Stu.]

My money's on a vac leak then pal.

 

My Austin A30's recently been running rough at idle and found it was only running on 3 cylinders. It ran on 4 under throttle load.

 

I eventually found it to be the intake / exhaust manifold gasket breaking down on the 2nd cylinder intake.

 

I found it after spraying WD40 around the bottom of the gasket, but it had to be directed acurately over where it was breaking down to increase the engine RPM.

 

 

 

It only needs a very small gap. Have you sprayed around the cylinder head intake and exhaust manifold as well as the carb end ?

 

Putting your hand over the carb intake compensates for the vac leak because it increases the vacuum draw and pulls fuel to the ports allowing it to fire. When you have a vac leak on the manifold intake gasket, air is drawn in through the damaged gasket messing with the vacuum balance / fuel draw and prevents combustion or makes the engine run roughly.

Edited by Stu., 08 April 2016 - 07:37 PM.

[redboy]

I didn't spray the exhaust gaskets. I shall try that tomorrow when I've got my new oil filter housing and braided pipe on.

[redboy]

My money's on a vac leak then pal.
 
My Austin A30's recently been running rough at idle and found it was only running on 3 cylinders. It ran on 4 under throttle load.
 
I eventually found it to be the intake / exhaust manifold gasket breaking down on the 2nd cylinder intake.
 
I found it after spraying WD40 around the bottom of the gasket, but it had to be directed acurately over where it was breaking down to increase the engine RPM.
 

 

 
It only needs a very small gap. Have you sprayed around the cylinder head intake and exhaust manifold as well as the carb end ?
 
Putting your hand over the carb intake compensates for the vac leak because it increases the vacuum draw and pulls fuel to the ports allowing it to fire. When you have a vac leak on the manifold intake gasket, air is drawn in through the damaged gasket messing with the vacuum balance / fuel draw and prevents combustion or makes the engine run roughly.

How hard a job is it replacing inlet gasket? Think that's got to be the culprit.

[Stu.]

Mine took me an hour. Carb off, disconnect exhaust from manifold, unbolt manifold & remove, clean up head and manifold mating surfaces and re-fit with new gasket.

 

Not a difficult job.

[redboy]

Mine took me an hour. Carb off, disconnect exhaust from manifold, unbolt manifold & remove, clean up head and manifold mating surfaces and re-fit with new gasket.
 
Not a difficult job.

Nice one, I'll get round to it at some point. I was down minispares at the weekend as well. Could of picked a gasket up.