merc 5.7 carb dies after revving

[Ronny-]

I have just installed a factory new longblock and moved over the intake/carb from the old engine.
I have set the timing at 10degrees with the thunderbolt wire grounded to engage base mode.
Idle rev is adjusted down to 650rpm as the manual states this.

Now my problem is, with this low idle rpm the engine dies almost everytime i rev it and then pull back the throttle to zero.
Easiest example is when i flick the throttle lever on the carb and quikly rev it to 3000rpm and then release it just dies.
So it seems like the idle doesnt provide enough fuel to "catch" the falling revs of the engine..

Any ideas on how to resolve this other than increasing idle speed?

 

[Scott Danforth]

650 is when in gear at idle and in the water.

also, you may want to look at your shift interupt swtich. if you cant adjust it properly, then the lower shift cable needs replacing.

 

[Ronny-]

Thanks, lower shift cable was replaced last year, shift interupter is two years old (40hours of use).
Engine dies when in neutral (gear cable disengaged), so i don't think the interupter switch has anything to do with it though.

Wasnt aware that 650 was in gear, i guess this means it should be higher when in neutral, so ill see if adjusting this makes any difference.

 

[harleyman1975]

Wind it up to 700 and see if that makes a difference.

 

[TyeeMan]

If I'm not mistaken the manual will say something to the affect of, "at operating temperature, in the water tied to a dock, in gear." If no on is at the landing you could leave the boat on the trailer, or if you know someone with a test tank.

Point is that the boat can't move. You need the full load if you will at idle to properly set idle rpm.

 

[wahlejim]

Carb adjustments should be done in water.... back pressure on the exhaust will affect rpms. Boats are meant to run in water which is where the specs come from.

 

[wahlejim]

My 5.0 idles at 750 in neutral in the water and closer to 900 out of water on muffs