Ok, time to admit I'm an idiot! Found out that one of the jubilee clips I had fitted was fouling the throttle mechanism, an amatuers mistake!
Now the engine will fire up without hardly having to pump the throttle, but the sucking noise is back when the throttle is touched & the engine will stall....
Am assuming there is still another air leak somewhere...
So am gonna have the plenum back off tomorrow or Thursday & put some instant gasket around the mating face with the trumpet base & see what that does.....

hey Chris, do you use the silicon gasket stuff normaly, or do you get a gasket set? I'm wondering because my Vitesse has developed a miss, so I'm thinking about cleaning everything up but not sure if that silicon gasket is all I need.

Kiwi, There are no gaskets involved, this extract is from page 8 of the PDF here

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When everything is cleaned, inspected and reassembled as desired the two units can be refitted to the inlet manifold. As mentioned, the plenum to trumpet housing joint is particularly vulnerable to poor sealing because the metal to metal face is typically only 1/4” wide over an aggregate length of 30”.

The effective way to close it is with a light smear of silicon gasket sealant applied to one face, quickly and accurately mated. Too much sealant can be squeezed to the inside of the joint where it may eventually break off and make its way into the engine. Too little sealant, and joint integrity will be compromised.


Ramon

Had the plenum off before & gave it a clean, I sprayed choke & carb cleaner into it & into most of the orifices that I could get to, & it cleaned the inside up quite well, but probably not really enough! The throttle assembly seemed ok though, spindle didn't seem to have any play in it either. I didn't put any instant gasket on the plenum to trumpet base joint last time though, as I thought by cleaning it up it would be ok, big mistake right?

Hello Chris,

There was a school of thought some years ago that factory engines were assembled without any sealant because the original machined faces were perfect.

Certainly when I removed my TP plenum for the first time, 8 years after it was built, there did not appear to be any prior sealant but there was a seepage of "Carbonned Goo" which I removed in the normal way.

Furthermore, because both the idle air gallery and the breather gallery were partially blocked it was probably the first time the plenum had ever been off.

There is no great pressure after all so I think that was a very minor passage of liquid thro the joint bringing their own natural oily sealant with it to complete the job.

The normal situation is for petrol vapors from the CSI to condense on the inside of the plenum and when that mixed with the breather gasses thereabouts one could imagine them getting everywhere and filling any minute gaps.

When it came time to replace my plenum I took the recommended "maintenance" route and lightly smeared gasket sealant on one face.

Ok, plenum has been off & refitted with some instant gasket on the mating faces, engine has been started & oh dear! The sucking noise & stalling with a slight touch of the throttle is still there!!
Although, I took her to the bottom of the street & back this afternoon & the sucking noise seemed to disappear, but it returned after a while.....
Will try next week to see if I can improve matters, but am having trouble with the alternator at the moment.
On a lighter note, the idle & mixture ajusting screws seem to be working after a fashion.
Your thoughts?

Im far too lazy to read the whole story but could the valley gasket have failed (or been reused in the past which leads to leaking) and cause the air leak? These are sometimes known to fail in range rovers... but it causes the water to go in the intake ports.

Ramon is right... a worn camshaft can make idle bad once the camshaft is worn completely round but it most of the time just causes horrible gas mileage and powerlessness.

hello chaps i think it could be cam shaft has no lubes on it i had 2 vdp efi and both of them misfired and was i cow to start and all the above problems put a new cam in and they were lovely after that could be ecu playing about to???????? plus the air sucking noise cold be the valey gasket or 1 of the injector seals are misssing or split rubbers?? good luck mate!!

Just had a thought, I'm using unleaded petrol in the Vitesse, but with a fuel additive, would I still need to retard the timing?

Is the additive an octane booster or a "leaded" one? The V8's have hardened valve seats and are suitable for unleaded petrol without any additive.

If memory serves you can use standard ignition timing on super unleaded (98 RON), but it's wise to retard it a few degrees if using standard 95 RON unleaded.

I use Castrol Valvemaster, which is a lead substitute, but also an octane booster....

With the price of basic petrol being so high I can't help but think that any additive is an uneccessary expense...

That may be so, but I used it on my 2600 VDP as an octane booster & it certainly helped performance....