1968 Merc 1250 High Idle & Timing

[Hydro Mark]

Hello All -

I have a 1968 Merc 1250 125 hp inline 6. It runs great, no stumble, always starts, almost instant on plane. The only problem is high idle. Around 1600 with the spring on and 1000 with it off. 900 in the water, spring off. Didn't know the spring was off until I got home and started tinkering.

All the linkage has been adjusted per the manual with the exception of timing. The carbs are closed and the only thing now that will lower the idle is to retard the timing. So I start with the WOT timing per the manual - when I put the light on it, it's off the decal, just north of 50 deg (the 3-dot TDC mark).

I'm guessing that it couldn't be this far off and I'm doing something wrong. Any ideas?

Thanks,

Mark

 

[Hydro Mark]

Re: 1968 Merc 1250 High Idle & Timing

I figured out the problem.

The distributor drive belt had jumped a tooth. Re-aligned it and everything became adjustable as the manual said.

The next problem is I have no idea why the belt jumped. It seems tight and in good condition. Any ideas?

Thanks,
Mark

 

[Laddies]

Re: 1968 Merc 1250 High Idle & Timing

The belt jumped because the cordage in it is deteriorated and at high RPM stretches out

 

[Hydro Mark]

Re: 1968 Merc 1250 High Idle & Timing

The belt jumped because the cordage in it is deteriorated and at high RPM stretches out

Thanks Laddies. I'll have to get another.