TOPIC: Mercury 500 Thunderbolt lack of power

I have a 67 Mercury 500 Thunderbolt attached to a 67 HydroSwift (14ft). Last summer we tried to get the boat ready for the water by replacing the spark plugs, putting in a new water pump impeller and lubing the bottom end. It seemed to start fine with the warm up lever up but when moving the lever past the half way position from all the way on the engine would die. We eventually took it to the repair shop and they rebuilt and adjusted the carbs and it fires right up and we are now able to get the warm up lever off. Unfortunately I had to return home and was never able to get it in the water myself, but my brother in law took it out and it needed some tuning so the shop fine tuned the carbs. He took it out one more time and said it ran good. So basically it only hit the water twice last year.

About a month or so ago I was able to bring the boat to my place and was preparing to try it out at a local lake. I threw a battery in and put the muffs on, primed the bulb and it fired up and seemed to run fine. Out at the lake I was disappointed with the acceleration. At full throttle it moves along pretty slow (probably 10-15mph or so), almost like I'm pulling something (like it's being held back somewhat). Occasionally while cruising along it would pick up speed and start to go a little faster (like a spurt of "energy") but then it would slow down again. Also, after cruising along for a while it would just slow down like I let off the gas and then I had to back off the throttle or it would stall. After priming the bulb again it would allow more throttle and go again. It seemed to use a lot of gas and when the tank started to get low we constantly had to squeeze the bulb to keep the gas line pressurized.

One other thing I noticed was that it did not seem to squirt water out of the side hole. I was concerned about this and verified that it wasn't getting too hot or overheating. It seemed to start and run fine but just had a general lack of "get up and go." I've seen some You Tube videos of similar size boats with the same outboard and was hoping for similar results.

I'm wondering if my fuel pump needs to be rebuilt to solve the fuel pressure issue? I'm not sure what is going on with the water that is supposed to squirt out the side. How often does the water pump impeller need to be replaced? Are there other things I should check besides the impeller to ensure the water can exit?

I don't know much about outboards and was hoping to have some fun in this boat. I'm sure it just needs a little fine tuning to sort things out. It's really too small for my young family (6) but even when there was just 2 of us on board it didn't go like it should. It's a clean little boat but I may end up selling it for something slightly bigger.

Any thoughts or suggestions are appreciated.

Rick
67 HydroSwift

replace the fuel pump diaphram if it is damaged it could be flooding 2 cyls.note the lack of power and running out of fuel.cost under 10.00 you can do the job 3 screws. the diaphram and 2 gaskets go only one way.

had the same thing with mine, check the points and the timing

not sure i think they had lightning energizer by 67. if it has a 4D mag points are set at .010.

I've been reading through my seloc mercury manual and it sure sounds like the fuel pump to me.

If motor runs ok when someone operates the manual fuel pump ( primer bulb on the hose ) than the fuel pump/s need work.

Thank you everyone for the advise, I guess I need to order a new fuel pump kit and see what happens.

Rick
67 HydroSwift

ever figure your problem out? im having similar problems

Rick,
Also,...Just in case,....Make sure that the vent is open on the fuel tank.
The fuel pump diaphragm kit is Mercury Marine part number 23014A1, or at NAPA it is under Sierra Marine and part number is 18-7804.
While you have the fuel pump apart test the (2) valves.
They are identical, but one goes in one way and the other goes in just the opposite, so be sure and note which way they are positioned before removing them to test and replace their little rings of gasket that are in the kit.
You can test the valves.
One way they both will suck freely and the from that same side you should not be able to blow any air through. If either 'leak by' any air, you will need to replace them.
I'm not convinced that this is all of your problems, but it certainly sounds like it is a big part of them.
After the fuel pump is rebuilt, report the performance and we'll attack the rest of the symptoms until they are all gone.
I suspect that one carburetor might be either flooding or starving (the float the needle is not sealing properly or it is not opening) and once this issue is identified and corrected,...Perhaps you will need to open (counter-clockwise) the idle jets on both carburetors a smidge to get her to accelerate properly - but not yet.
Leave these last things alone for now & rebuilt the fuel pump.

In regards to ignition, the '67 500, serial number 2116318-2305100, could either have a magneto or it could have the solid state ingnition with the switchbox, removeable trigger asembly in the distributor housing, and round distributor cap.
A picture would be helpful to further discuss any ignition trouble-shooting.
Thom