1977 Merc 1500 - Throttle Issues

[MaxHill]

I am having issues with my throttle.

​When the throttle is fully engaged (wide open) the max speed is approximately 5mph.

​Sometimes the throttle will work perfectly and I can get it going full speed and sometimes it wont go.

It seems like I have this issue once I refill the boat with fuel.

​For example, yesterday I was on the water (refueled before yesterday's outing). Once I launched the boat would only run at 5mph for a half hour, then all of a sudden the throttle started working and I could go full speed. Then after about an hour of it working properly, I couldn't get up to full speed again.

​When I was out last weekend the boat work perfectly all day.

​Anyone have any idea what this issue might be? Seems like it is starving for fuel.

Any help would be appreciated.

 

[Chris1956]

Max, Several things come to mind, and without knowing the history.....

What boat and what prop pitch are you running? It is possible you are a bit overpropped, and the added weight of fuel will not allow her to rev up.

You can pump the primer bulb as well when trying to accelerate. This will eliminate the starving for fuel issue.

Also, remove the wrap cowl and push the throttle forward (engine off). Watch the distributor turn and the carbs open. As long as they move consistently, the throttle linkage is good.

When was the last time the carbs had work done on them?

 

[MaxHill]

The boat I am running is a 1977 Glastron Bowrider (I am assuming the engine is the same year as the boat, don't know if that's correct).

​The marking on my prop is QA2036X 17P. I believe this would be the information you are looking for. At one point though the boat did run fine with the full tank

​I tried pumping the primer bulb when trying to accelerate, no significant changes really.

​The distributor and the carbs open consistently.

​When the carbs have had work done last, I do not know. I haven't owned the boat very long and I haven't done any servicing to them.

Could there be water getting into my gas tank somehow? Should I try and put some gas line antifreeze?

Someone suggested I try a fuel pump repair kit.

​Thank you for taking the time to help me.

​Max

 

[MaxHill]

I don't know if this helps, but the serial number of my engine is 7067702.

Max

 

[MaxHill]

Anyone have any suggestions!?

Max

 

[Chris1956]

Max, If the primer bulb is hard, and cannot be hand-pumped, I don't think you have a fuel pump issue. A 1977 Merc inline 6 motor would have a screen under the fuel pump cover. Make sure it is clean. I would also remove one of the brass hex bolts on one of the carbs and pump the primer bulb. Fuel should flow out fo the carb drain freely. Catch the fuel in a rag and see if she has water droplets. They will bead up. Obviously, water in the fuel will put out your fire... Gas line antifreeze is not a good idea for outboards. It would be better to drain the botton of the fuel tank and get the water out.

Your 17"Pitch prop should be fine. You might check your spark plugs for color. If any of them are real clean, you likely have water leaking into the block. If any of them are real dirty, they may be fouling.


Post back

 

[MaxHill]

I couldn't find the screen.

I opened 2 of the carbs and fuel came out of both of them freely. I checked out the fuel and it looked normal. No water beaded to the top.

I looked at the spark plugs (3/6). The 2 at the top were a bit dirty with oil and the 1 at the bottom was clean. The plugs were changed at the beginning of the year.

Someone that I know mentioned that it could be the CDI. Would this make sence?

Thank you for all the help so far.

Max

 

[MaxHill]

Could it be a bad or faulty connection at some point on the switch box? Should I try taking those wire off and cleaning them up for a better connection?

​On a side note, when I did regain power on the weekend, it was when I turned the boat around 180 degrees. Maybe the movement during that turn made a connection better. I could be completely wrong but I thought I'd ask.

Max

 

[Chris1956]

Your motor should have battery powered CDI ignition. Sometimes the quick disconnect plug will have dirt or a partially broken wire interrupting spark. However, you will have spark or not have spark on the entire motor. There is no way to have spark on just some cylinders, unless some of your spark plug wires are bad. Check them for arcing to ground. Spark plug wires screw into the distributor cap, and are stranded stainless steel. They should have zero resistance.

Your clean spark plug makes me suspect water infiltration. A faulty lower crankcase seal will cause #6 and sometimes #5 cylinders to have water in them. Their compression will be normal. I am not sure what else to suggest at this time.