75HP Merc won't start

[chadchurchill]

I was out fishing the other day and stopped the motor a few times to take some casts and it started and ran just fine until it was time to head home. The motor would turn over just fine, but that was it. It didn't do anything but turn over. Got towed the 12 miles back to the boat launch ( didn't realize how expensive it is to be towed, but lucky to have insurance) and the tow operator said that it's probably the powerpack. The motor is a 1986 75hp Mercury outboard inline 4 cylinder and he said that in motors of that age there is only one powerpack, so if it goes the motor won't start. Where on the motor is the powerpack and is it something that an outboard mechanic should be doing? I'm pretty handy and good at fixing things, but have never worked on a boat motor.<br /><br />The next day I did take out the spark plugs and could smell fuel, so I believe it is getting fuel. Any ideas on simple tests to rule anything out?

 

[dilligafda]

Re: 75HP Merc won't start

First check for spark. If there is no spark, then you would need to check out the ignition components one at a time. Start with the stator, then the trigger and finally the coils. If all of that checks out, then it's the switchbox. I would be willing to bet that the in your case, the stator is the source of the problem. Get a good service manual and meters and good luck! <br /><br />Happy boating!!

 

[chadchurchill]

Re: 75HP Merc won't start

I got a manual and a meter and the stator tested fine, but when I tested the rectifier all of the tests came back opposite of what the manual said. When it said there should be continuity there wasn't and when it said there shouldn't be there was. I'm going to take the rectifier to a local repair shop and have them test it. What exactly does the rectifier do and would it cause there to be no spark?

 

[The Marine Doctor]

Re: 75HP Merc won't start

The Rectifier/Regulator turns AC to DC current to charge the battery and also sends the signal to the Tach. It also only lets the current go one way so the battery does not go dead.<br /><br />If the Regulator part of the rectifier is bad it may let the stator over charge...this might blow out certain ign parts...ie a power pack...thus losing spark.<br /><br />TMD

 

[chadchurchill]

Re: 75HP Merc won't start

OK, had an outboard mechanic look at it today and it does get a strong spark on all four cylinders. He checked over the fuel system and it looked good, so he sprayed starter fluid into the carbs and it still wouldn't start. He said it could be bad compression or a fuel pump diaphram. He didn't have his compression guage with him so he's coming back tomorrow. He did also say thet he could smell fuel in the cylinders. Anyone have any ideas?

 

[greasemonkeyozi]

Re: 75HP Merc won't start

Smell fuel in the cylinders, I should hope so... Anyways, are you sure your mechanic knows his stuff?<br /> At least rebuild your fuel pump yourself, it wont cost but about $4.00 for a fuel pump diaphram kit."real easy job." Also, do run a compression test. What is a boat mechanic doing without a compression tester?<br /> There could be a possability that your timing is way off.

 

[marinegrh]

Re: 75HP Merc won't start

compression, fire and fuel make the motor run, eliminate one, and your done, remember that phrase before you have it looked at

 

[chadchurchill]

Re: 75HP Merc won't start

I don't know why he whouldn't have a compression guage with him, seems like a pretty simple and important tool to forget at the shop.<br /><br />Would bad compession happen that abruptly? We were out fishing and shut down the engine a few times without any problems starting back up, then the last place we stopped all it would do is turn over.<br /><br />About the fuel pump. Wouldn,t the motor at least sputter a little or almost start from spraying starter fluid into the carbs even if the fuel pump diaphram was bad?<br /><br />Thanks for all your help!

 

[RICKRICK1]

Re: 75HP Merc won't start

TripleC-- have you checked to insure your cutoff switch is not activated. have seen this before and the safety swich was activated without the operator knowing.

 

[greasemonkeyozi]

Re: 75HP Merc won't start

I would avoid spraying starter fluid in your carbs, it takes away the lubrication.

 

[chadchurchill]

Re: 75HP Merc won't start

RICKRICK1:<br />Where is the cutoff switch? I don't have any kind of safety lanyard like on a PWC, but is there some other type off shutoff I should be looking for?

 

[chadchurchill]

Re: 75HP Merc won't start

OK, got a diaphram kit and installed it, but still no start. After trying to start I took out the spark plugs and they were wet from fuel, so I would guess that they're getting fuel. Also installed a fuel/water separator just for fun. <br /><br />Got a compression guage and it ranged from 150 to 160 on all four cylinders. Manual didn't state what it should read, but that it should be over 100 and there shouldn't be more than a 10% difference. <br /><br />Is there anything electrical that could cause a motor to not start that gets spark, has good compression and is getting fuel?

 

[chadchurchill]

Re: 75HP Merc won't start

OK, had another outboard mechanic look at the motor last night. Found a bad coil on the fourth cylinder, so replaced that (should run a lot better when I get it started again). Also cleaned off all the terminals because they had some corrosion on them. Tested the fuel for water and it had no water in it. Spark is weak, so ordered new ignition wires from Napa and they will arrive tomorrow. If that doesn't work, what else could cause a weak spark. Battery was just charged and all terminals were cleaned off.<br /><br />Thanks,<br />TripleC