Low manifold vacuum

[Meccles]

Well car has been at my friends who is professional Mechanic - and a good one. We have a good idle but advance curve was way out and car doesn’t like cold starts, misfires above 2500 and generally seemed a bit “lazy”. He found that the rotor button on new distributor was wrong one (must have been a Friday Arno build at Pertronix) and advance weights mechanism in dizzy were all loose. So that’s sorted. Carby- jetting is fine everything good there. But- we have Low manifold vacuum - 12-15 in Hg and compression while even is a bit Low 125-130 psi. There are no vacuum leaks. We suspect cam is retarded it went in straight up on marks however I didn’t degree it. It’s a crower 50230 which is just a bit more than stock. However been reading that some of these grinds can come supplied up to 4 degrees retarded[emoji51]. A rough check watching rockers at harmonic balancer indicated TDC seems ok. But looking likely I’ll have to do a tear down at least timing cover off to check cam timing. Bugger.

[DAMINK]

Could the wires from the dizzy to the amplifier be the wrong way around?
I have found if i put mine the wrong way around i can get it to idle ok if i cheat and change the timing but it does still miss at revs.
Your symptoms sounded similar to that, thats why i suggested it.

[theelms66]

Did you get a spec card with your cam 'should have all the details u need. But always dial a cam in dont rely on keyways and locating pins for accuracy.

[DAMINK]

From my limited experience (compared to others) i have found a "bigger" cam often means a duration cam and not a huge lift cam. Or both but the same symptom applies. Duration cams extend the time the valves overlap and often a side effect is low manifold vacuum at low revs. Have not checked the specs of this cam though to be honest.

I have played around with cam timing so many times and had little result. Either better high revs or better low revs depending on advancement. Never a good medium unless it was timed correctly.
Typically i used to roll the engine around until it was just even between the cam lobes on 1 or just on the intake lift side if i had no choice. That seemed to work well as a method of cam timing for me. Even with pretty hot cams.

[Meccles]

The dizzy doesn’t use an amplifier it’s a Pertronix Flamethrower 11 with Ignitor which runs to an MSD coil ( no ballast resistor). These either work, or don’t. Advance mechanism was faulty as was rotor button but these have been fixed. I do have cam card - as I did rely on marks [emoji51]most likely will have to take timing cover off as minimum. And likely inlet manifold to degree it properly [emoji30]

[Meccles]

Cam isn’t wild 266degrees duration .44 thou overall lift. Very little overlap. Will have to investigate something isn’t quite right,

[Traco]

There was a discussion about this on the Rover V8 Engine Appreciation Group on Facebook recently and it seems it's not an uncommon problem where aftermarket cams are fitted.

[Meccles]

Ok thanks