68 Merc 500 thunderbolt, WOT = 6mph? <solved>

Iandayen

Seaman Apprentice
Joined
Jul 12, 2009
Messages
37
Motor sounds good, runs smooth, no coughing, no spitting.

But when I get it in the water it's like it just has no power.

When in neutral and I use the timing advancement/warmup throttle, it idles up nice and high, and when I put it back down it runs nicely at a very low idle.

When I put the throttle/gearshift all the way forward I move, but just barely, then when I put the warmup throttle forward also I get a little more power, but not much.

Squeezing the fuel bulb gives no change whatsoever, it is firm and not losing prime.

From what I understand the warmup lever actually advances the timing, could this be a timing problem? And if so, do I need a special timing light or would any timing light do? and I don't see any actual timing marks on my flywheel, just 2 notches with no identifying marks.

Edit - To clarify the work I have already done.

Rebuilt fuel pump
New Impeller/housing
New gasket on water cover over the "head" on motor



Turns out my control box was bad, and slipping inside.

Picked up another control box locally for $25 and put it on my boat.

Went out to the lake yesterday and this thing screams!
 
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