'76 Merc 500 - Unable to pass 2600 rpm

[Jetstreak]

Here's the situation:
Motor fires up and idles no problem.
Slow to increase up power range when giving it throttle.
With throttle fully advanced, it would not get above 2600 rpm.

Here's what struck me as odd:
I was going over some heavy chop with the motor fully advanced and only at 2600 rpm. A good bounce off the chop and the motor suddenly raced up in rpm. It wasn't the prop coming out of the water, just something goosing it briefly. I wasn't able to see how high the rpm's went because it only lasted for a second or two.

Carb History:
I rebuilt the carbs two years ago. The motor had all the fuel run out of it and it had not been run in a year and a half.

Thoughts?

 

[Jetstreak]

Re: '76 Merc 500 - Unable to pass 2600 rpm

One other note to add...I replaced the fuel tank and line this year and put in a fresh tank just days ago, so it is not old/bad fuel.

 

[Jetstreak]

Re: '76 Merc 500 - Unable to pass 2600 rpm

bump...sorry if this is frowned upon, but I need some help. Anyone?

 

[cell]

Re: '76 Merc 500 - Unable to pass 2600 rpm

I was going over some heavy chop with the motor fully advanced and only at 2600 rpm. A good bounce off the chop and the motor suddenly raced up in rpm.

This happens because your prop vents.Its still in the water,but the water is aerated thus it spins with no load.search the forum for "stator".To test you will need an dvm,and a manual....unless someone post the specs.Hows the hole shot?Have you checked the compression?Is it overheating?

 

[Jetstreak]

Re: '76 Merc 500 - Unable to pass 2600 rpm

Hey, Cell. The holeshot is not as strong as it should be. I haven't tested the compression this year, but I can't imagine it would run as solidly as it does at low rpm if that were the problem. Am i wrong there? I'll look into the stator.

 

[Jetstreak]

Re: '76 Merc 500 - Unable to pass 2600 rpm

Also, the temp seems fine. No overheating.

 

[cell]

Re: '76 Merc 500 - Unable to pass 2600 rpm

Also make sure the carbs are opening up all the way.What happens when you squeeze the fuel bulb when bogged downed?Is the fuel tank vent,or filter open/clogged?

If it ran good before,and then put in storage for a few I would always suspect the carbs being gummed up.Even if you ran them dry before storage.(you can't get everything out of em)