1990 OMC 4.3L Cobra Idle Question

[andrewgroup]

Last year I rebuild the 2 bbl Holley Carb. Following the IDLE adjustment procedures it seems to IDLE around 800 rpm. This amounts to about 1 - 1/2 turns out from the idle screw seats. It has a slight throb to the IDLE. Timing is 6 degrees BTC.<br /><br />Could someone explain the Interrupter switches and the overstroke switches..<br /><br />I pressed the first switch expecting it to affect the IDLE and it did not....

 

[Boatin Bob]

Re: 1990 OMC 4.3L Cobra Idle Question

Andrew...I'll take a shot at it, you have an ESA module (Enhanced Shift Asm) which pulses the ignition and drops your RPM's to about half. The module has 12v power wire and a ground and is wired to the - side of the coil. The older modules have 2 switches, the interrupt switch is a normally open and the overstroke is normally closed. When you activate the interrupt switch you complete the circuit going through the overstroke switch, if the interrupt doesn't close or if the overstroke is open then you will not activate the ESA module. You can bypass the entire switch asm by unplugging the 4 pin connector. You will have 2 wires going to it from the ESA side plus a blue jumper, just short the 2 wires together (blue and black) and see if the rpm's drop.

 

[andrewgroup]

Re: 1990 OMC 4.3L Cobra Idle Question

IS the purpose of the setup to reduce the torque / tension going into the outdrive at or near the moment of shifting. (Similar to the old double clutching the street rod)<br /><br />If this circuit is not working correctly what are the obvious symptoms?<br /><br />Noisy shifting, hard shifting, no shifting, other..<br /><br />Thanks..

 

[Boatin Bob]

Re: 1990 OMC 4.3L Cobra Idle Question

Yes...it's mostly to prevent hard shifting out of gear into neutral although it does make it easier to shift into gear and you get a reduced "clunk" when going into gear. The other factor in hard shifting is the idle speed which for most should be down around 600-650 then with a proper working ESA and lower shift cable the gears practically fall away from each other resulting in a very easy/smooth shift into neutral.