1980 50 hp merc - lacks power under load

[fastwin15]

Hello experts

My 1980 hp merc revs great in neutral, but in gear on the lake it doesn't get more than 30% power. Idles great, no power though. It just bogs down

Work done so far:
- compression test: 130 psi on all 4 cylinders
- replaced spark plugs
- replaced one ignition coil and one plug wire
- rebuilt starter
- re-ran some wires from the stator
- new impeller
- rebuilt carbs with new gaskets

Any thoughts? Could it still be the carbs?? This motor sat for 2 years before I bought it (and I am beginning to suspect it was at the bottom of a lake or something as it had water in the starter and sand in the carbs).

Thanks in advance.

 

[mamacyrus2]

Having similar issues. Following thread.

 

[jimmbo]

When you installed the carbs back on the motor did you verify the ignition is advancing and is synchronized to the carbs? Have you checked to verify the rest of the fuel system is up to snuff?

 

[steviethev]

Yes, do a link and sync for sure.

What do the plugs look like? Are they wet?

Did you verify strength of spark on all cylinders? When you had the carbs apart, did you verify that the float drop is correct and that the metal tab is bent correctly to allow the inlet needle to retract correctly? I had an issue once where the tab became bent on installation on one carb which didn't allow enough fuel into the bowl to run correctly. Did you verify that the main jets aren't clogged?

I have also had a switch box go bad which gave similar symptoms. It was only running on two cylinders.

 

[racerone]

Check for blockage in the exhaust tuner.

 

[fastwin15]

Thanks guys

Jimmbo - I did notice actually that the carbs aren't exactly synced with each other, though it doesn't look like it's far off. But I'm not sure how to sync them with the ignition? Another next step for me is to try running the engine on a new tank and fuel lines. The sender seems to be working fine - the ball doesn't need priming once it stars but maybe the old lines are deteriorating?

steviethev - The plugs look like the mix is a little rich but other than that they look fine. I do think perhaps the carbs need a second look and I'll be sure to note what you've suggested. As far as the swich box go, we're definitely firing on all 4.

racerone - I will do that as well. Any tips for that process?

Hopefully I'll get a chance to take a look this weekend and can make some progress

 

[steviethev]

You can find the link and sync procedure here:

http://boatinfo.no/lib/mercury/manua...-115.html#/220

I believe the procedure that is for your motor starts on page 6-11 with section 6-6. You'll need at least a test tank, and a timing light. A tachometer, and a dial indicator to verify TDC of the #1 piston, as well as a set of feeler gauges to verify clearances can all come in handy.