Spent a past couple days troubleshooting that elusive vacuum leak and am reaching the conclusion that this integrated head must be suffering form the same affliction that they've become notorious for, it's either cracked, has a burnt valve in cyl #3, leaking head gasket or leaking intake to exhaust gasket (that tin can looking separator visable down in the intake manifold to exhaust manifold preheat chamber).
I can get it to idle at 700 rpm with a wavering vacuum reading of around 19" but the rpm is hunting and can't be adjusted out via the mixture screw. At fast idle it'll draw a steady 21".
When I place my hand over the primary venturi it will increase in idle and smooth out (classic vacuum leak indicator).
I made up a plate to block off the EGR, disconnected & plugged every vacuum and still get no change in the idle fluctuation.
Using brake cleaner, I can spray it around the intake to head casting at cyl's 3/4 and 5/6 and get a rise in rpm. No cracks are apparent but the rpm will rise when spraying what looks like solid casting. There are head bolts in the area but it doesn't seem to be in that particular area. (very strange.....)
I adjusted the timing to get max vacuum at idle and got it around 19.5". No change. Retarded it 1" then 2" and even 4" of vacuum with no change. Verified there is no ported vacuum to the dist at 700 rpm idle.
It's possible that Varajet carb has problems but spraying around the manifold casting at the head and it increasing and smoothing out the idle is telling me theres problems with the intake in areas no where near the carb (again, very strange...)
Lastly I did a compression test and it returned the following:
#1-130
#2-145
#3-100 (wet and dry)
#4-155
#5-150
#6-130
All but #3 look good.
So, I'm looking at 2 differing plans of attack, try to find a good older non integrated 230/250/292 head and manifolds or just go ahead and do the more common swap to a SBC. Either will require reworking the exhaust which is one of the nice sub assemblies on this danged thing.....
The good news is all the new gauges, electrics and the TH350 works and will bolt up to an SBC.
Over the 250 Dave...
