1975 85hp mercury

[redinferno]

I have a 1975 85 hp mercury outboard and i finally got it running the other day. I bought it after it was sitting for 3 to 4 years. So first i hooked it all up and replaced the spark plugs and but in the lower gear lube. got it running went out on the lake got about 50 feet and it died. Ok so i brought it back rebuilt the carbs couldn't get it running.. pulled the fuel filter and fuel pump and cleaned up and put all new gas in and replaced a bunch of corroded wires. Now it runs pretty good! But has no power, it does not get up and go out the water and top end is not great. The only thing i can think of is something with the spark or compression? What should compression be at? and if it is bad what could be wrong like something simple as a head gasket? Any and all ideas would be appreciated!

thanks

 

[BR]

Re: 1975 85hp mercury

Red,

Sounds like you've got a good jump on the obvious trouble spots. Carbs are the culprit many times. When you say no power do you mean motor won't rev or boat won't go? The latter may indicate a prop issue. Have you checked plug wires are connected per correct firing order, timing and spark advance? Also check to see if you've got a strong spark. Should be a visible blue spark and should jump a 3/8" gap. These motors have no cylinder head. The bores are blind. What looks like a head is a water jacket cover. Check condition of your plugs after running. Clean plugs may indicate water injestion into combustion chamber. Lastly, compression should be over 100psi and within 15% from cylinder to cylinder.

Good luck!

BR

 

[redinferno]

Re: 1975 85hp mercury

I will check that tonight thanks and when i say no power ill slam the throttle down when just sitting in the water, and it doesn't jump out and go just slowly revs up and gets going..... and what do you mean by a ladder may be a prop issue?

 

[OkcOffRoader]

Re: 1975 85hp mercury

my 75 85HP was doing that, just like you it hasnt ran in 4-5 years..after replacing all the fuel line i figured i was good to go...got it in the water and it had no power and was hard to keep running...turns out the fuel line is sucking air at the tank connection, i put the tank up on one of the seats and it ran great the rest of the day...im hoping a new tank will solve my problems...this may not be your problem, but its worth looking into for sure...

 

[BR]

Re: 1975 85hp mercury

I will check that tonight thanks and when i say no power ill slam the throttle down when just sitting in the water, and it doesn't jump out and go just slowly revs up and gets going..... and what do you mean by a ladder may be a prop issue?

Red,

I wrote "latter" meaning if the motor revs up but you get no propulsion then the prop might be slipping on its hub. This does not sound like your problem though. Sounds to me like a carb adjustment issue. Did you do a link and sync after the carbs were removed and reinstalled for cleaning?

 

[redinferno]

Re: 1975 85hp mercury

link and sync? sorry not familiar with these terms i adjusted one screw on the carb to get it running with the muffs on after the carb clean. i believe it was the idle screw not sure though the one just left of the air intake.... Is there more then one screw to adjust, like is it like a car and have a highspeed adjustment or is it just the one?

 

[BR]

Re: 1975 85hp mercury

Red,

If you've removed the carbs for cleaning, then it would be appropriate to perform a "link & sync" procedure. Here's a good link to the steps required:
http://forums.iboats.com/showthread.php?t=128495

The "link" part refers to the linkage between carb throttle plates, which can be adjusted. It is importtant that both carbs open the same amount as the throttle is advanced. The "sync" part refers to synchronizing the throttle with the ignition timing spark advance and setting maximum spark advance which is important. If you're not understanding the instructions in the link above, you need to spend some time reading your manual. If you don't have a manual, it's probably time to invest in one.

The carb mixture adjustment should be tuned with the boat on the water and make sure adjustments are made to both carbs, not just one.

Good luck.