Power Loss / Bogging / No High RPM Range - Need Help!!!

[72Glastron75Merc]

I was cruising at WOT (for 30 - 45 min)... then suddenly the RPMs cut down to 3300... I turned off the engine and restarted, but I couldn't climb above 3300 RPM.. It felt like the boat was dragging a car under the water. The engine seemed to make a "lower" tone and after 5 minutes I noticed a little white steam-like smoke from the engine. (I believe white smoke = running lean) So, at WOT (now at 3300 RPM) I tried squeezing the priming bulb, with no change at all. However, when I tried to give it some choke (to reduce the airflow and in turn provide a more rich mixture), it almost stalled out immediately. The engine is a 1975, 65 HP, 2 cycle, 2 carb. While on the water I switched tanks (both with fresh gas, proper oil / mix, and fuel conditioner).. and no change. After reading a dozen posts, it seems like the fix for every O/B is a carb rebuild, fuel filter rebuild, or a new fuel pump... Seeing as I got the boat, engine and trailer for $400... I'd rather not have to repair all 3 only to find out it was something else... Also, does anyone know the typical cost/time to have the 3 things rebuilt at a shop vs doing it yourself? I'm handy, but never worked on a boat before... is this a DIY project? Thanks in advance!

 

[crem1]

Re: Power Loss / Bogging / No High RPM Range - Need Help!!!

Hi!

If you are slightly mechanically inclined then you can do a carburator cleaning and a new fuel pump very cheaply.

Alex

 

[kingsnakejr]

Re: Power Loss / Bogging / No High RPM Range - Need Help!!!

Much cheaper than going to a dealer. They'll charge you at least $200-$300 labor plus parts. The problem still may not be fixed. The experts here will recommend you get a repair manual, do a compression test, and spark test each cylinder.Hope this helps.
ks

 

[72Glastron75Merc]

Re: Power Loss / Bogging / No High RPM Range - Need Help!!!

Compression is excellent in all 3 cylinders... Plugs are new this season and in good shape... (less than 20 hours on the plugs)

Any other ideas? what ever caused the issue, failed... It was not a gradual loss in power / performance.

 

[j_martin]

Re: Power Loss / Bogging / No High RPM Range - Need Help!!!

My guess would be a stator high speed winding failure. To verify the thesis you need to measure voltages at the switchbox with a DVA. A factory manual would have the expected readings in it.

hope it helps
John

 

[hkeiner]

Re: Power Loss / Bogging / No High RPM Range - Need Help!!!

Using a systematic approach to troubleshooting is often cheaper and less frustrating than fixing/replacing parts at random or by guessing until the problem is solved.

An inline spark tester is an inexpensive tool and it will let you check the spark while the engine is bogging. If you see that the spark is failing during engine bog, then you have narrowed down the problem to ignition failure and your can troubleshoot that further. As previously mentioned, your shop manual will provide the needed information for performing various tests of the ignition parts using a DVA meter and a multimeter. If the spark is not failing, then you can troubleshoot the fuel side of things further.

 

[72Glastron75Merc]

Re: Power Loss / Bogging / No High RPM Range - Need Help!!!

Is there any way to test this with muffs, or do i need to take it on the water? Is a 65 HP too powerful to put into a 55 Gallon garbage can with water? Nothing hurts more than working on the engine all week, and then spending an hour to launch it... and find out the problem wasn't fixed.

 

[hkeiner]

Re: Power Loss / Bogging / No High RPM Range - Need Help!!!

Is there any way to test this with muffs, or do i need to take it on the water? Is a 65 HP too powerful to put into a 55 Gallon garbage can with water? Nothing hurts more than working on the engine all week, and then spending an hour to launch it... and find out the problem wasn't fixed.

I was cruising at WOT (for 30 - 45 min)... then suddenly the RPMs cut down to 3300... I turned off the engine and restarted, but I couldn't climb above 3300 RPM..

I think that you need to do the spark failure test during engine bog while on the water at high speed, as that is when your symptoms occur. Running a motor at high RPMs on muffs or in a tank of water is not something I would ever consider doing (it might over rev and blow the motor) and it would not replicate the engine bog conditions anyway, as there would be no load on the prop.

If testing the spark while running it on the water is too much of a pain, you can jump ahead and do some other tests on the ignition parts to see if you can find a failure. Some tests can be done with the motor turned off or idling on muffs. As previously suggested, it may likely be the high speed side of the stator and you might confirm that with some ohm tests or DVA voltage tests. Just my thoughts.