'85 Force 50hp high speed miss

S

savdxgrace

New Member
I just aquired a '85 pontoon boat with a '85 Force 50hp. I had to replace the head gasket to get it running. It also got a new t-stat and brand new spark plugs. It seemed to run pretty good at the house with the water hose hooked up. The first time I put it in the water, it ran good for about 10 minutes or so and then seemed to develop a miss at higher RPM's. I stopped, checked the compression again after the gasket change, looked at the plugs and let it cool for awhile. When I went out again, after a few minutes the miss came back. It is not a constant dead miss, something seems to be breaking down when hot. The motor never died nor did it leave me stranded, just was not at full power. Once in awhile, it would pick up and run great for just a minute or two and then return to the underpowered condition. Where do I start???
 
Fun Times

Fun Times

Active Member
Well I looked up some basic parts for your engine and it looks like you might have a set of breaker points in the IGN system, So you might start there, They some times will make the engine run like that if the points and condenser is getting hot, Ect, Here is a link to where it talks about the breaker points, Scroll down a little to see what I found. http://www.mercruiserparts.com/Show...br=1213&bnbr=14&bdesc=SPECIAL+TOOLS+-+TUNE-UP.

Here is the main link to look up part numbers only for your engine, Sorry no photos in here, Some times they do have photos, But at least it may help give you an idea of what is going on with the parts system in your engine. Also It might help if you could find a service manual for your engine Because they normaly would have a good troubleshooting chart to follow with different engine running problems. Well I hope this helps you out a little with a starting point anyways, I wish you Good luck with it.:cheers:

http://www.mercruiserparts.com/selectSerailRange.asp?doc_nbr=50+H.P.+(1985)

OR try this one if you can't find your engine Serial number in the link above. http://www.mercruiserparts.com/selectModels3.asp?type_id=FORC
 
S

savdxgrace

New Member
When I first tried to crank the engine, it did not fire at all. I checked the compression and had 0 on the top and 110 on the bottom. I removed the head and found the blown gasket. I also found in taking the head off that there was no t-stat. I replaced the gasket, t-stat and t-stat grommet. I removed the lower unit and checked the impeller. I had purchased one but did not see any reason to comdemn the old one and put it back in. The engine fired up as soon as I applied the choke and it seemed to run well with the hose hooked up. I am getting good water flow from the engine.

As far as the fuel system goes, I did remove the carb bowl and clean it out before starting the engine. I only found what appeared to be oil in the bowl. I also used a fuel tank that has been empty and dry, stored in the garage for a couple of years. I flushed each hose and component of the fuel system with clean mixed fuel all the way to the carb before ever cranking or firing the engine. I took the cover off the fuel pump and checked the screen, it was okay. I did not secifically inspect the check valves. The vent on the tank was open.

The head did not show signs of warpage to any extent, although I did not put a straight edge on it. I did torque the head according to the manual in the proper order to the proper spec. I rechecked it after I had run the engine that afternoon and checked it one more time the next day. The plugs did not show signs of any water. I also rechecked the compression and it is still 115 on both cylinders, the same as right after the head gasket change.

How do you "spec" the coils? This engine has what I think are called "fat" coils, there are two of them.
 
Chris

Chris

Administrator
Staff member
Wowzers!

It sounds like you got it fixed up pretty good based on the compression test. :thumb:

For the coil testing, you'll probably need a good shop manual.

It'll tell you how to test the coils etc. with a multi-meter tester, Without the shop manual though, it's pretty hard to diagnose what's going on.

-Chris
 
Fun Times

Fun Times

Active Member
savdxgrace said:
I would like to know if there is a good way to test he coils, let me know. Thanks...... Walt
Click to expand...
There should be a ohm's test you could do to the coils and you should be able to find the info/speck's in the engine service manual you have, And you would be testing the ignition coils both on the primary and the secondary sides of the coils, And also checking the power and ground to see if they are with in the speck's the manaul should have for you. Here is a few links i looked up for you on the web that might be of some help to you. It's some other guy talking about how to test coils and what tools to use. I hope this helps you out a little more, Good luck with it.

http://en.allexperts.com/q/Boat-Repair-2123/checking-coil.htm

http://www.freeengineinfo.com/how-to-test-an-ignition-coil.htm

Now if you want a ton more info then just copy and past this in your web search bar at the top of your internet page and you should get some good info to look over.

How do you ohm's test 12 volt ignition coils in boats/ marine
 
dave

dave

Active Member
check the resistance between the pos/neg wires to the coil and between the pos/coil wire and compare them, if both coils are about the same they are probally alright. i would suspect the points and condensor as boat tech has mentioned. as with checking resistance on anything that you are unsure of the spec or test range start at the highest end on the scale of your meter and dial it down to a lower reading.
 
You must log in or register to reply here.
Top