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Need Valve Support

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seymour064

New member
Still having issues with my merc 170 sterndrive lossing power under load. I got a chance to speak to my marina mechanic for a few minutes and he said it sounds like I may have a broken valve spring or bad lifter. Can anyone please walk me through I should do this? Thanks in advance...
 
Checked compression and the front 2 cyclinders were 130 and the back 2 140. All the plugs looked very good. I also took off the valve cover and ran the motor and appear to be working fine. Found water in the gas a few weeks ago and have been running off a portable tank and carb was rebuilt so I'm sure my gas is fine. At this point I'm stumped...
 
List of possible causes of low WOT (Wide Open Throttle) rpm.

In no particular order

Engine Won't Reach Operating RPM. Check

1. Fuel condition. Type and Octane possibly old fuel
2. Propeller pitch or diameter, damaged blades
3. Restricted fuel pickup tube or anti siphon valve Fuel System Test
4. Crankcase oil volume, high oil level can cause aerated oil and lifter collapse
5. Marine growth on hull and outdrive
6. Wrong gear ratio in outdrive
7. Restricted carburetor air intake (clogged flame arrestor)
8. Restricted exhaust system (broken exhaust shutters/flappers) in engine transom shield or drive
9. Poor cylinder compression Compression Test
10. Carburetor defective, or wrong type.
11. Fuel pump pressure and vacuum
12. Boat overloaded, improperly loaded, or improperly trimmed.
13. Engine Overheating
14. Engine timing and ignition system operation
15. Remote control cables and linkage for proper travel to open throttle plates fully.

Above copied nd pasted from another website Don s is the author.
 
I have had this problem also. Im a pretty good mechanic and it stumped me for a bit. The problem was my coil. i had 2 351ho in my formula 1976.new engines complete except for some bolt on stuff..coil,was one thing i reused. I was able to run all day with both engines running smooth. The 1 engine would only go 1/2 throttle rpm at wot.but was still running ok just would not get full power. I was tinkering/diagnosing why..I noticed that the bottom of the coil and a valley in the intake had oil in it. I pulled the coil and where it had the strap mount around it there was rust. I had already cleaned/sanded gapped points and shecked my spark was all good..Just for the hell of it i switched the coils from one engine to the other..my problem was the same but now on 2 engine. went to auto store and 40 bucks..fixed..I would start with ignition..all the things on that list that was posted are way off.or just basic problems and systems in the engine.If the boat is all the same and the only difference is the engine is not running correct..you can forget all those things like props and growth,gas,a little water in gas will give you better performance,im an aircraft mechanic and they used to have a water injection system for extra boost for takeoff..Dont over think boat problems...3 things..compression,ignition,fuel.... you have compression,fuel yes it either runs or not on fuel..unless there is a starvation problem..wich is indicated by surging,cutting in and out and popping..bad points,gap can reduce rpm,also off the wall but maybe timming..but that would be obvious,,pinging or hard to turn over when warm.. try the old sandpaper on the points gap andthen just grab a used ignition coil 10 bucks and 10 mins..process of elimination..think simple..these engines and the systems that run them are made to be simple..simple =last longer..
 
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