Hello!

I have a question about my SU HS8 carburettors on my 1975 Jaguar XJ6. The carburettors are thoroughly cleaned and refurbished. All gaskets around are changed. But it has a problem.
When the engine tries to start it only coughs on the starter motor but never actually runs without the starter motor. If I now cover the intake on the right carburettor with my hand it starts and idles, if I let go it dies. It can be revved up and runs very well as long as your hand in covering the right carburettor. And again, it only applies to the right carburettor, the left works great when not covered up.

Fuel is all the way up at the top of the bridge in both carburettors and they are both set in the baseline setting on the adjustment screws according to Haynes. I assumed it was pulling air but if I spray brake cleaner around the carburettor it doesn't rev up at all.

What could be the problem? Is there something I'm missing?

 

This is a difficult question. The right hand carb is clearly too lean and not drawing the fuel. How far below the bridge is the jet? I suggest your initial setting should have both jets 2mm below the bridge. Is the needle secure? Are there any air leaks on the right side ( vacuum take offs below the manifold)?
The fuel should not be at the top of the bridge and Haynes says nothing about a baseline setting. - that is for HD8 carbs. The Jaguar instruction manual says never to touch the jet adjustment screws - we know that but we all do touch them!

 

Yeah, this one is pretty tough. What I have a hard time wrapping my head around is that partially blocking (like 90%) blocking the air intake does the trick. Sure, it doesn't run perfect but it does run. Sorry for that, the baseline-setting i have is from a PDF i got on the forums. I screw the "idle screw" one turn down after it reaches the lever and the mixture screw is one and a half turns down from when it sits flush with the bridge. The needle is secure from what i can tell, the tip can be moved sideways a bit and the springy part does so it can move up and down some 3-5 milimeters but it always springs down and sits flush with the bottom of the piston.

Regarding the vacuum leaks: This could be the issue. The AED is blocked off right now for testing and it is not drawing air from there. Neither is it drawing any air from around the carb nor from the sealing to the intake manifold. I have one tiny vacuum going from the left side of the intake manifold to the air filter housing. I cannot find any similar small vacuum hose connection on the right side of to manifold. There are two thicker hoses that do look like vacuum hoses connecting up to the side of the fender and continuing towards the firewall. Maybe next step should be replacing all of the hoses on the underside of the intake. What connections are there on these inlet manifolds?

Thanks for all the help!

 

I cannot speak for series 2, but series 1 have two main vacuum lines. One to the brake booster and one to the vacuum tank for the heater controls. I would check both those hoses.