Mercury V-1500 bog and surge at WOT

[Slacker411]

Hi all! I have a 1978 Mercury V-1500 outboard. The issue I am having is that while running WOT the the motor bogs down then power surges back intermittently. This makes for not so fun ride going fast/slow/fast/slow. I have had this problem over the last few months. For the most part I figured it was dirty carbs, as I would pull them off, clean, and rebuild and the problem seemed to go away..for a while. The boat runs fine at lower speeds without any hesitation, bogging, or surging.

What I have done so far this time:
Cleaned and rebuilt carbs
Replaced fuel pump diaphragm and gaskets.
Replaced fuel lines
Pulled fuel tank off and cleaned it. Vent seems to be open.
Replaced water separator

I am not sure at this point if its a fuel delivery issue or a spark issue. I plan to buy a spark tester in the morning and rent a compression tester. Will post results. I am hoping it is not my coils or stator. Spark plugs are less than a year old with maybe 20-30 outings since installing them, but I will pull them in the morning to see what they are looking like. Any advice on what I might do next would be appreciated.

Thanks.

 

[Slacker411]

I figured i should mention the primer bulb was also replaced within 6 months ago. It stays filled with fuel and slightly firm while underway. Squeezing it while its bogging doesnt seem to do anything

 

[Bill kubiak]

Once the engine is running fuel is just sucked thru the primer bulb by the fuel pump and it is no longer firm, squeezing it while the motor is running does not do much if the fuel pump is good

 

[Slacker411]

I suppose i should mention that while trailered at the dock, under a load and in gear at WOT i was not able to replicate the problem. There was no power loss or surge. The rpms remained constant but seemed lower while on the trailer vs. when the boat is on plane at WOT. Another thing i noticed when i got home was that when i had my lower unit replaced they never put a lock nut on it and my prop was starting to come loose and it had about a half inch more play than it should. Also the rear thrust washers teeth do not meet the propeller shaft teeth. I imagine thats supposed to lock in place? Anyhow i tightened the prop nut as tight as i could get and it seems to be like it was before. I will have to see if that makes a difference in the water asap..and get a locknut

 

[Chris1956]

OK, you should have a spider washer to help hold the prop on. The parts are hard to describe, so just google them to see what you need. In order from the gearcase back you should have: Thrust washer, prop, splined washer (fitting with 6 "shoulders" on it), Tab washer (AKA spider washer), nylon lock nut. Sometimes the splined washer with the shoulders is part of the prop, sometimes it is separate. The spider part of the washer locks into the shoulders, when bent over.

From your description, maybe you have a loose wire in the ignition. The ign killer wire is either orange or black/yellow. If that grounds, the ign dies. Maybe yours is flapping around when out on the water, but not moving when strapped to the trailer?

 

[Slacker411]

Looks like i will be buying a voltmeter. I am ashamed to admit i am very inexperienced with a volt meter and testing electrical circuitry. As i mentioned before my splined washer does not quite go far enough down the prop shaft to meet the splines on the shaft. This seems abnormal to me . I will try to get some pics up shortly

 

[Slacker411]

 

[Slacker411]

Here is a picture of the prop shaft with the forward thrust washer pulled out some to expose more of the shaft.

 

[Slacker411]

Here is a picture with the forward thrust washer in place with the prop on. Notice how the splines on the shaft barely protrude so the rear thrust washer (splined washer) will not seat on the shaft splines. That splined washer and nut were the only things I have on there after the propeller. The spider washer (or lock nut as I described) is missing.

 

[Chris1956]

The thrust washer is not supposed to be splined. In your first picture it looks like it has splines. It should be look like this one:

http://www.crowleymarine.com/p/376846/Thrust-Washer

You need spider washer:

http://www.crowleymarine.com/p/375758/Tab-Washer

Make sure you get the right one for your motor, as they look alike. I picked the best picture of the thrust washer, it may not be the right one for you.

 

[Slacker411]

I tried to blow up this pic as much as I could. I am missing number 83(the spider washer), but 82 looks pretty similar to my rear thrust washer which has splines. I can't find any better diagrams on this old motor.

 

[Slacker411]

Here is an expanded view

 

[Chris1956]

Number 81 is the thrust washer. From your picture, the one you are using is splined, like number 82. Number 81 is not splined, but is ground to match the taper of the prop shaft. That is the one you should be using.

 

[Slacker411]

I have 81 and 82. This may be a little confusing at this point, but I've referred number 81 as the forward thrust washer as it sits in front of the prop. It can be seen in my first picture really well. The first pic has the prop pulled off and #81 (the forward thrust washer) is pulled out some sitting on the splines for better visual. The next picture shows the propeller back on the shaft and #82(rear thrust washer) and #84 as they both go on after the propeller. I haven't had a chance to take the boat out yet to see if tightening up the prop makes any difference toward my original problem with the bogging and surging. Also still confused why my splined washer doesn't contact the splines on the propeller shaft.

 

[Chris1956]

well, there are different thrust washers for different props. The diaghram you posted is likely for Merc props only.

FWIW, the thrust washer in the first picture is unlike any I have seen before, and I have had Mercs going back to 1973. I think you should get a new one.

 

[Slacker411]

Sounds like good advice =)