84' Yamaha 70ETLN (Please help, Im ready to go fishing)

[gerront]

Hi, my name is Richard and i have a 84' yamaha 70ETLN 2 stroke outboard that is giving me a fits. Recently i took the boat to the local boat ramp, backed her in the water, fired right up...idled just fine. Then i slowly make my way out past the no wake zone and open her up. Shoots out of the hole, planes out in just a few seconds and quickly gets up to 30 or so MPH. During this time i can be on and off the throttle and it is responsive with NO problems but then it will lose power instantly and the motor shakes and sounds muffled. After this you can let it sit for a long time, fire it up and take off again only to have it repeat the process. I could tell somehing wasnt firing right. So i took the boat out and brought her home and replaced the spark plugs and gapped to factory specs. and fixed a loose spark plug wire. I cranked her up (out of water/hooked to hose pipe) and she fired right up and idled great. Thinking i had hopefully found the problem, i tooke the boat back out the next day. opened the throttle, planed out for a few minutes then BLLAAAA...los power again.

With this being said and having read some similiar posts, Do i have a coil pack problem? (I made sure all 3 coils were working before i took it back out)
Seems as soon as the motor gets up to temp. it feels like its misfiring, but the spark plugs are new?

Any help with GREATLY appreciated.
Thank you in advance,
Richard (ALABAMA)

[jays225]

Are you shure your water pump impeller is good? Ive had motors in the past that would run good on the hose, cause of the water pressure, but wernt able to pick up water on their own? Good luck to ya!!

[99yam40]

test your alarm system. Sounds like motor is over heating and going into safe mode, limiting RPM and the alarm is not sounding.
If this is the problem then change water pump and thermostat to see if that helps

[gerront]

Are you shure your water pump impeller is good? Ive had motors in the past that would run good on the hose, cause of the water pressure, but wernt able to pick up water on their own? Good luck to ya!!

Im assuming its good. While its running (planed out), there is a steady stream of water shooting out of the back. But i did notice when its at idle and the boat is not moving there is a very small amount of water coming out if any a all if im not mistaken.

[gerront]

test your alarm system. Sounds like motor is over heating and going into safe mode, limiting RPM and the alarm is not sounding.
If this is the problem then change water pump and thermostat to see if that helps

I didnt even know that engine had these features. I do not have ANY kind of manual or literature on this motor. I bought the boat from a old lady. The boat was her husbands who was deceased. I do know the motor did not come on the boat, but it was bought used and installed, as it was in great condition compared to the other one.

Any chance you know where i could start? I dont have alot of money to invest in several parts to try and fix this problem. Your advice may have just saved me the expense of new coil packs already...lol and thank you again.....

[jays225]

The water pump impeller is like the insurance policy for the engine!!! If you have some mechanical experiance it a pretty easy job on most engines, and usually arround $20 for the part!! Your best bet would be to get a service mannual for your engine, unlike breaking down in a car you break down in a boat your STUCK!!!! The way you describe the symptoms sounds to me like your overheating? Still the water pump is supposed to be changed fairly often, would not hurt to change reguardless!!!! Good luck and happy boating!

[gerront]

The water pump impeller is like the insurance policy for the engine!!! If you have some mechanical experiance it a pretty easy job on most engines, and usually arround $20 for the part!! Your best bet would be to get a service mannual for your engine, unlike breaking down in a car you break down in a boat your STUCK!!!! The way you describe the symptoms sounds to me like your overheating? Still the water pump is supposed to be changed fairly often, would not hurt to change reguardless!!!! Good luck and happy boating!

Im convinced this is it as well. I just ordered a water pump rebuild kit and will go from there. Where do i find a service manual at?

[jays225]

Do like a google search for it! Yeah the impeller is $24.45 on these guys site! they have about the best prices on parts!!!!!!!!!!!

[gerront]

Ok so the impeller was ate up. Missing two paddles and half of another. I dropped the lower end replaced EVERYTHING in the water pump (bought rebuild kit). Then i get home and dropped the lower end in a large tupperware storage container filled with water. The water inlet just did sink below the water line, but did submerge. Cranked her up and let it idle for minute then revved it up a few times and i got NO water out of the tube up top, but after it got warmed up it looked like steam (i guess) faintly coming out. I took the tube loose and blew into it and air passes through it fairly easy, there was a very small amount of restriction and it was blowing the air out of the inlet at the bottom of the lower end. What gives? Does the lower end need to be more into the water?

[gerront]

Please HELP.....PLEASE....

Took the boat out today and it immediatly messed up again...... Cranked right up and i was in neutral idling for the most part, waiting for my wife to get to the dock, (maybe 2-3 mins) we go to leave and the boat wont even plane out due to the low rpms/power loss. There was very little water from the telltale at this time. After fishing and scratching my head for 30 or so minutes i cranked up and tried again. Full power was there on and off the throttle and after one continous high speed run....water was shooting out of the telltale. I stopped into again and let it sit and idle and water was still coming out good. So i called it fixed. Me and the wifey took off and got about a mile away from the boat ramp and continued fishing

One hour later an expected thunder head comes rolling in, so we pack it in. We crank and plane out and after running at a slow speed...guess what? The engine falls back down to low rpm. So i through it in neutral and check the telltale...theres hot steamy water coming out of the tell tale??????? What the hell is going on here? New plugs, wires, waterpump, and 3 freshly cleaned in/out carbs.... Is there still trash in the cooling? Reading another post on overheating, someone had replied the the impeller pieces that were broken off could be clogging the exhaust? What can i take off to clean this????

[99yam40]

Need to check/replace the thermostat and PRV (pressure relief valve).
While you have them out drop lower unit and try flushing passages with a water hose. If that doea not take care of the overheating then you will have to pull head and exhaust cover plate to clean out passages, but the bolts may not come out if it is a older motor

[gerront]

Need to check/replace the thermostat and PRV (pressure relief valve).
While you have them out drop lower unit and try flushing passages with a water hose. If that doea not take care of the overheating then you will have to pull head and exhaust cover plate to clean out passages, but the bolts may not come out if it is a older motor

I pulled the thermostat out and it had a tiny piece of rubber back behind it. Cleaned all of that out and inspected the thermostat. It was surprisingly clean and functional. Im going topull that plate off and see what i can find i guess? Wonder how tight i need to torque the bolts back???

[gerront]

Need to check/replace the thermostat and PRV (pressure relief valve).
While you have them out drop lower unit and try flushing passages with a water hose. If that doea not take care of the overheating then you will have to pull head and exhaust cover plate to clean out passages, but the bolts may not come out if it is a older motor

99yam40....you must REALLY know your stuff. I just very cautiously tried removing one the cover plate bolts and it twisted in half very easily. Hopefully just this one cover bolt wont effect anything.....Im going to take out the thermostat and put the hose tight up to it and flush it with the lower end off...god i hope something comes out and it fixes my problem....im going to run the water into a bucket to see if i caught anything.....thank you so much for your help.....

[99yam40]

Try putting hose onto water tube on lower end and flush that way also.

Did you test the thermostat in a pot of water to see what temp it opened and how far?

[gerront]

Whats the chances its the coil pack failing???

Try putting hose onto water tube on lower end and flush that way also.

Did you test the thermostat in a pot of water to see what temp it opened and how far?

I didnt know i could do that with the thermostat? Being it was spring loaded i just assumed it would open when the water was hot enough to produce pressure to let the water in....

Ok, I dismantled the lower end again and hooked the hose up to the hose going to the telltale (the tube fit inside my spay nosel perfect) and slowly turned the water on. Watching about 4-5 gallons of water flush out of the lower end into a large bucket and nothing came out. Then i connected the hose up to piping where it meets with the water pump and blasted water through there.....water shooting out of the telltale very strong.
Then i reassembled everything and crank the boat with a foot on the lower end a let it run for 10 mins or so.....to continue flushing out the system. Thinking ive got this flushed and figured out. I hit the lake....Runs fine for about 5 mins then i lose power/rpms again..... I asked a few other guys who have had bass boats that were around and they all said i probably had a coil pack failing??? What are your thoughts on the coil pack??