1977 Mercury 85hp will not go over 5mph

[rcam97]

I have a 1977 mercury 85hp inline 4 cyl. The carbs have been cleaned and have new gaskets and needles and seats. The compression is around 140psi on all cylinders.
The problem is that it will idle fine and will run up to about 5mph and no more than that. It will rev up out the water on the muffs but not in the water.
Any ideas will be much appreciated.

(Edit)
I tried adjusting the carbs and found that when I make adjustments on the lower carb the engine does not run any differently no matter how much I adjust the set screw in or out, but the adjusting the top carb will make significant differences in how it runs. So I am guessing the lower carb needs to be removed and reinspected. Could the float height cause this problem?

 

[Barnacle_Bill]

Re: 1977 Mercury 85hp will not go over 5mph

Check for a strong spark at all plugs. Just because it revs high out off water (which you should NEVER do) doesn't mean anything.

 

[rcam97]

Re: 1977 Mercury 85hp will not go over 5mph

Thanks, will do

 

[crem1]

Re: 1977 Mercury 85hp will not go over 5mph

Throttle linkage adjustment and possibly a reed valve check wth timing tossed in for good measure

 

[arsenalpsu]

Re: 1977 Mercury 85hp will not go over 5mph

I would bet you have no spark in the cylinders you were adjusting the carb on. Could be the stator, coils, spark plugs, the dist., or just a bad connection or wiring. You'll have to trace it down.

 

[Doug57]

Re: 1977 Mercury 85hp will not go over 5mph

Float height can kill you but I'd bet spark would be more likely. If you have good spark go ahead and pull the carbs back off and check float settings and make sure the high speed jets aren't stopped up. You also need to go ahead and check the stator. Test are simple on the ignition system and the best fix on an outboard is PM PM PM so it don't break to start with.

 

[rcam97]

Re: 1977 Mercury 85hp will not go over 5mph

Thanks for all of the quick responses. I will get right on it.

 

[rcam97]

Re: 1977 Mercury 85hp will not go over 5mph

Thank you everyone for the great advice.

It turns out that I have no spark on the lower 2 cylinders. This outboard is an I-4. It has an ignition coil for each cylinder. So now I am wondering, is there is anything that could cause just the two lower coils not to spark other than if the coils are faulty or should I just buy 2 new coils?

It also already has a new stator

 

[rcam97]

Re: 1977 Mercury 85hp will not go over 5mph

Alright the coils are fine now, they just had bad ground connections. Now the problem is that the coil for the #2 cylinder is not receiving any power from the positive lead. So my question is, could the switch box be bad? Or could a bad stator cause this?

Thanks in advance