83 merc 70hp WOT problems

[BassAssassin]

Howdy, <br />took out my boat on tues. and thur. On tues. it ran fine no problems. On thur. fueled up an went out. at the dock started up fine let warm up about 5 - 10 mins. went 5mph till hit buoy gave her all the gas started to get up onto plane and heard POOF or PUH(something to that accord think it was a backfire but underwater) and lost all power, down to i would say 2500 rpm(no tach) but about 10mph(goes 32 @ WOT). i didnt know what happened so i shut if off looked at prop checked the electrical and fuel lines no problems. i started it back up and same thing no power so i drove around at half throtle for about 10 mins and then all of a sudden it sputtered a few times and came back to life. gradually gave it gas and off we went. stopped after 15 min fished awhile and went to next spot no problem. after that started it up gave it the gas and no power same thing 10mph but no poof noise. so i thought it might be flooded so i cranked up the choke and let it run a couple mins. estimated rpms were 6000 w/full choke on. after a couple mins i heard it rev up a bit more and then a bit more untill it was hitting probably about 6500, shut off choke hit the throttle and ran fine. i was a little ticked by this time didnt want to take any chances so went back towards dock, got to the 5mph buoy and i cut the throttle, went a little ways and i wanted to see what wold happen if i hit the throttle SAME DAMN THING. sounds like it runs fine idleinjg and up to about 2500rpms but after that no power. what do you experts think? thanks a bunch. <br />matt

 

[Laddies]

Re: 83 merc 70hp WOT problems

Sounds like dirt in the carbs

 

[BassAssassin]

Re: 83 merc 70hp WOT problems

do you think when i fueled up i put too much oil in the gas and it is too rich? this is what i am hoping is wrong. thanks<br />matt

 

[DHPMARINE]

Re: 83 merc 70hp WOT problems

No,unless you realy went overboard on the extra oil.When new your engine ran fine on double oil.I bet triple oil would be okay.Also the higher the RPM's,the better it would run with too much oil.<br /><br />Do a fuel sample,looking for dirt and water.<br /><br />DHP

 

[BassAssassin]

Re: 83 merc 70hp WOT problems

ok ill buy some gas treatment for water. its a brand new tank though, and i looked inside when i installed it 2 weeks ago looked clean. could it be anything else? fuel pump? filter? cynlinder nort firing? what other ideas do you guys have?

 

[BassAssassin]

Re: 83 merc 70hp WOT problems

ok i bought some water treatment for the gas tank. also i bought a new filter/water separator. but i started the engine and pulled the spark plug wires one by one to chekc and make sure i was getting spark to all 3 cylinders the first to i was but the third i wasn't. in nuetral and low rpms do all the cylinders fire? i know in some i have read they dont, but i think thats the newer engines and also the 6cyl. so what doo u guys think??

 

[Valv]

Re: 83 merc 70hp WOT problems

It's always tough to pinpoint problems like this, but if you have no spark on 1 cyl it could be coil. To be sure swap coil from sparking cylinder with coil not sparking, and see.<br />This for starter, then it could be other issues.

 

[BassAssassin]

Re: 83 merc 70hp WOT problems

ya just did that and swapped plugs from different cyl, plus tried different wire from #2 cyl. still no spark. whats left? points?

 

[BassAssassin]

Re: 83 merc 70hp WOT problems

i was just told from a fishing buddy that it could be a stator. any ideas fellas? any help is appreciated

 

[BassAssassin]

Re: 83 merc 70hp WOT problems

what sends spark to the coils? is it the stator? i know my coils are good, and the wires too. plus i have brand new plugs(switched around to make sure it wasnt a bad plug). could the problem be the rectifier? am i talking to myself now?

 

[rabidfish]

Re: 83 merc 70hp WOT problems

It could be the stator. If the stator is black, some of them would fail the "hi speed" side of the circuitry. When that happened, the motor would run just about 2000 - 2500 rpms ok.<br /><br />This would be hard to detect at idle/cranking speed because the "low speed" circuit would still supply voltage. <br /><br />My guess is that you have more than one problem, making it hard to diagnose... Does the coil that has no spark have primary voltage? ( is the switchbox working? )<br /><br />All the cylinders should have spark at all times... The engines that ran on two cylinders at idle were the 100/115/125 hp models, and that was a carb issue, not spark.<br /><br />The rectifier is part of the charging system. The motor will have spark without it.<br /><br />This could get expensive. I might be tempted to see a real Mercury technician for at least the diagnostic part. Make sure he knows everything you have told us!

 

[BassAssassin]

Re: 83 merc 70hp WOT problems

ok i will check the switch box. am i just checking for current, or should it read something specific on the ohm meter? i did switch the coils around already and it is only that #3 cyl that will not spark, even with a different the other coils in its place. it sounds like the stator to me from what you described. it runs fine at low rpms(still no spark though) and some times you can feel and hear when that third cyl kicks in but it only kicks in for a sec or two then back to "normal". thanks for your help and response.<br />matt

 

[BassAssassin]

Re: 83 merc 70hp WOT problems

well i think i got the problem fixed so i am gonna go out tomarrow and try it i hope. i talked to a merc mechanic and he said it was the switchbox for sure and it wouldnt be the stator. so i took his word and bought the box hooked it up and started it. was getting a little spark now, not as much as i would like, but could only run it for a min because it is getting late here. so i will check it more tomarrow. thank you all very much this noob is very grateful. everyone has been a big help. couldnt do it without this board. TY!<br />matt