<VV> Turbo Motor Cycling

[kevin nash]

From: Brian via VirtualVairs
Sent: Wednesday, October 30, 2019 10:11 AM
To: VirtualVairs at corvair.org
Subject:  Turbo Motor Cycling

I am finishing up a project for a fellow club member to get his 1965 Turbo
convertible back on the road.  He dropped the valve seat which cause
significant damage so a total engine rebuild was necessary.  Using all stock
parts I rebuilt the engine.  I then ran it on the run stand that we have
here in our club.  I ran it with two carburetors while both the Turbo and
the carburetor were out for professional rebuilding.

While on the engine stand it ran flawlessly.  Now that is installed in the
car and the Turbo with his carburetor is installed there is a cycling
problem.  The engine fires instantly and with the choke disconnected idles
but the idle fluctuates from about 690 RPM to about 920 RPM.  The cycling is
slow in other words it will run for a couple of seconds may be as much as 30
seconds and then the idle will jump either up or down.

As mentioned all the parts are stock to include the camshaft.  Timing is set
at 24? as per the shop manual.  Not being a Turbo guru I am stumped.  Is it
possible that this cycling is caused by an improper setting of the idle
mixture or is there some other issue?  Any help would be much appreciated.
Thanks in advance.


 It sounds like a air leak- a really common one on stock Turbo's is that thick fiber gasket between the carb and throttle plate. The other cause might be a linkage/idle adjustment and or idle mixture adjustment. Idle on Turbos is supposed to be 850, and the manifold vacuum should be around 13" hg. Just for kicks and giggles, try richening the idle mixture screw 1/8th of a turn, and see if anything changes.
Kevin Nash
63 Turbo EFI daily driver, Baddest cooling fan on the planet!!