When tuners take some metal off the heads to get higher compression, how much is the norm when they do this?

You have to slip a washer under the cam cover bolts to get them to seal again but would they be the thickness of the amount shaved off the heads?

taa in advance :-)

you also have to shim the cam gear train in the V4

It is not as easy as you reckon...

The cover also sits on a rubber gasket which might compensate for a tenth or two. The shimming mentioned above would be needed to maintain the correct gear clearance, four circular washers per cam holder, the same thickness as is taken off should do the job. Also the thickness of the head gaskets affect the cam gear clearance & compression

i know all that , i have a skimmed down lump - the reason i ask is that i cant cure my air leak issues from my carbs not sealing on the inlet rubbers. where the heads are sitting lower in the vee the outer portion of the carbs push out the rubbers too much. Im just trying to find the amount the head has been trimmed down.

my plan is to get the carb top plate machined back the same amount ( underside ) to get them sitting back sweet. i have tried all sorts to cure this issue but to no success. Soon as i remove the carb top plate and re tighten the carb rubbers it seals ( spray wurth's equiv to wd40 on the rubbers and the revs dont pick up any more ) it runs better. Not perfect as the carbs go out of sync but its stable and its better.

That sounds like a strange issue.

The most anyone would skim the heads is 1.0 mm, I seriously doubt this amount will cause anything to foul.

Sounds strange indeed.

Why not machine the ribbers or the carbs if that is what is causing the problems?

I'd also be tempted to fit the base plate, fit the carbs and then nip that up?

Have you got the right rubbers,Something's wrong here.
The head skimming would not cause this problem,as Cammo said 1mill max.

believe me i have tried all sorts of combinations to get them to sit sweet, im waiting for g.f to reply and tell me how much the lump was trimmed down as i got it from him. thought about trying the to trim rubbers down but as its rubber i thought it would be hard to get them accurately cut down.

i use the nc35 inlet rubbers and the right ones are on the right pots too as they are different.

Surely skimming the heads can cause this problem as they drop further down the vee, this used to be the issue with the rover v8's and the triumph stag v8's - the heads could only skimmed so many times before inlet manifolds dont fit anymore.

i have tried another set of carbs to eliminate the carbs being wonky / wrong , bought another set of rvf inlet rubbers ( old ones were only a few yrs old anyway )

tried fitting the carbs on with the rubbers on the head and with the rubbers attached to the carbs - anything i tried doesnt stop the carbs pushing the rubbers towards the outside / to the head. You can physically see the carb rubbers are being strectched away from its lower part

if you machined the carbs 1mm that would not meet the rubber sealing lip on the inside of the rubbers correctly? also the lip is the part which stops on the head so trimming the outside of the rubber wouldnt help , tyring to get 1mm off the inside would be a mission surely?

Is this an NC30 or 35,Now i may be wrong but isn't there a difference beween the 30 and 35 rubbers.