IDA tuning help - Lean spike

[Gaz64]

Originally Posted by markha

I should post a pic of the setup. They are on an Inglese intake that has a vacuum runner cast into the intake. So yes. And then running a PCV.
Butterflys are completely closed at idle and it runs at about 1000rpm. I actually like the idle a little lower but can not acomplish that without backing off the timing. The initial timing is already a little retarded for that cam.

I am going to try a few things this weekend and will post my findings. I am going to start by going back down to a 60 or 65 idle jet and pull the mains to make sure they are not influencing anything to start. My rpm pickup for the LM1 died, so I may not get much useful info logged until it gets repaired.

I will let you guys know. Thanks again for the help.

Mark,

Although your engine is 347 cubes, the cast vacuum runner may contribute to your idle speed.

Each cylinder can draw more easily from its respective runner AND the volume contained in the vacuum runner, each cylinder can effectively draw through 8 barrels at idle hence why the butterflies are shut and your need for "retarted" timing.

8 little tubes of 3/16 can still supply enough vacuum for brakes etc, without "overbalancing".
I'd be looking at a smaller cross sectional balance setup, which means a manifold change.

Then you can have the butterflies control the majority of air PER cylinder, and run more timing at idle with less in the distributor.

As others have said you should concentrate on the idle/progression of the motor up to 2500, before you worry about the rest.