76 OMC 235 - Hard Shift Issue

zag123

Cadet
Joined
May 6, 2012
Messages
16
I've managed to tune-up my 76 OMC 235, updating the distributor with a points conversion, added a high-output coil, new plugs & wires. Rather than rebuilding the Holley carb, I purchased an Edelbrock #1409 marine carb. I made a few adjustments to the linkage to the carb, though mainly on the carb itself. While in neutral I have the motor set to run at 650 RPMs. When I shift from neutral to forward or reverse all is well, though when cold, it stumbles a bit (bad fuel I suspect). When I'm attempting to slowly decrease speed from WOT I notice that the boat will shift (rather HARD) to neutral before the motor is at idle. I'm assuming that the electric shift is engaged based upon the location of the shift/throttle lever. If this cannot be adjusted, should I adjust the linkage at the carb to remain at idle for a longer duration? I'm worried about applying too much pressure to the carb linkage, forcing the carb to remain at idle while the lever is moving. Is there some other adjustment that I can make, or a change to a sensor or something?
 

Howard Sterndrive

Rear Admiral
Joined
Nov 5, 2008
Messages
4,603
Re: 76 OMC 235 - Hard Shift Issue

sounds like the issue is right in your helm shifter. There is a rotary switch in there that probably does have some adjustment via oblong holes to facilitate centering the switch into the neutral position.

Some boat builders used the OMC shifter for which adjustment should be described in the factory manual, others used an off-the-shelf shift/throttle control.
 

zag123

Cadet
Joined
May 6, 2012
Messages
16
Re: 76 OMC 235 - Hard Shift Issue

Great news. I'll take a look at it tonight. Thank you!
 

Redrig

Master Chief Petty Officer
Joined
Oct 13, 2009
Messages
849
Re: 76 OMC 235 - Hard Shift Issue

yeah , you want that thing shifting as smoothly as possible, you can tear up a shift spring in no time with hard shifts.
 

Howard Sterndrive

Rear Admiral
Joined
Nov 5, 2008
Messages
4,603
Re: 76 OMC 235 - Hard Shift Issue

I was also thinking something might be going on where the prop torque is needed to hold the spring wound, and slowing makes it lose its grip - I don't know that much about the innards of the electrics though.
 

HorizonblueDK

Petty Officer 1st Class
Joined
May 27, 2010
Messages
355
Re: 76 OMC 235 - Hard Shift Issue

I suspect that you have the same issue as we had on my fathers boat long time ago. He had a 1976 17 fot runabout with a 120 hp OMC, electric shift.

When throttleing down, the outdrive suddenly shiftede into neutral at approx 1400 rpms. It felt like we lost the propeller. There was nothing to do but take the lever down to neutral, and engage it again, and the outdrive went into gear as it should.

We never found out what was wrong, didn't investigate it either, but I would say that the fault lies in the throttle handle. There must be some way to adjust the switch.

Regarding your suggestion for letting the engine idle even though the handle is being moved, it can be done.

OMC engines for flybridge boats had oblong holes in the cables at the carb, a simple solution to make two cables work on the same carb. If you could find such a cable or just the cable end, you could probably adjust it, so the engine keeps ideling during the first movement of the lever.
 
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