Merc 80hp "800" ???Spark

[Bryan22]

This Model 800, 80hp 4 cyl motor runs great when running. I am not getting spark, I will check a plug for spark and here and there I at different times when the key is turned she will have a burst of good spark. 90% of the other times the key is turned there is no spark can someone point me in a solid direction? The Merc dealer in this area is not good... so I don't want to go there. I can work on it I just need to pin-point the problem.<br /><br />Thank you!

 

[Laddies]

Re: Merc 80hp "800" ???Spark

we need to know the serial number or year

 

[Bryan22]

Re: Merc 80hp "800" ???Spark

Sure, it is 3148816.

 

[Bryan22]

Re: Merc 80hp "800" ???Spark

Finding a couple past posts I did some poking around on it. The 4-post terminal block on the right side/front (in the boat facing motor, in front/to the right of the top carb) I checked the red I had 12v, then the white..... I had 12v, turned the key on and the 12v on the white went to almost nothing. From the looks of it that white goes into the dist. Am I checking the correct terminal block? There is a 3 post one on the left.

 

[Laddies]

Re: Merc 80hp "800" ???Spark

Bryan you must have 12 volts on the white termanal for the engine to run try to jumper it and see if you have spark, if you don't I have several posts on cking the system if you can't find one I will repost--Bob

 

[Bryan22]

Re: Merc 80hp "800" ???Spark

I have 12 volts on the with the ignition off, I turn the key to the "on" position, (not start) and that goes away to almost nothing. should it be doing that? It seems backwards. I should have nothing and then it should go to 12v when the key is turn to on shouldn't it?

 

[Bryan22]

Re: Merc 80hp "800" ???Spark

In the odd chance it starts ...it fires right up strong. It was doing this last fall and then it popped a fuel line so I replaced the lines and was thinking the starting issue was because of the fuel line sucking air. Now I see the spark just isn't there 90% of the time, it comes and goes????

 

[Laddies]

Re: Merc 80hp "800" ???Spark

That engine is a battery powered CD ing. system and needs to have 12 volts to the white termanal on the box to run, if it don't it has a bad switch, plug in, broken wire or oher problem in the harness, thats why I suggested jumping the red to white termanals to see if it would run then you will know if the problem is engine electrical or harness--Bob

 

[Bryan22]

Re: Merc 80hp "800" ???Spark

I did try jumping from red to white and it did not fire, I did not crank much nor did I check for spark with it like that.<br /><br />Is the white supposed to have 12v when the key is turned on? The 12v is there on red & white with the key in the off position.

 

[Bryan22]

Re: Merc 80hp "800" ???Spark

could this have anything to do with the trigger? If so, where is it, what does it look like, and is there a way of testing it?

 

[Laddies]

Re: Merc 80hp "800" ???Spark

First disconnect the mercury switch 3 post side of the box ck for spark, if none disconnect all 3 wires on that side of the box, turn the engine to TDC install a spark gap or plug in number 1 wire, with 12 volt to the white termanal 4 post side and a jumper between the brown and white 3 post side, use anouther wire a arc black post to ground, if you have fire the trigger is bad and if you don't the switch box is bad---Bob

 

[Bryan22]

Re: Merc 80hp "800" ???Spark

Ok Bob I will work on doing that in a bit here after I get a couple things taken care of and will keep you posted.<br /><br />Thanks again,<br /><br />Bryan

 

[Bryan22]

Re: Merc 80hp "800" ???Spark

Hello Bob:<br /><br />Not trying to be difficult but also don't want to mess things up here. Which is the "mercury switch 3 post side of the box? <br /><br />What I see behind the plate in front of the carbs is: a larger square box with 4 terminals (red wire, white wire, etc). Upper left a smaller box with 3 leads (2 going under the flywheel) and then another smaller "box" with a lead going to teh dist (coil wire i assume) I know a few things about engines but this set up is a different set up and I don't want to do anythng wrong so i would rather ask and clarify.<br /><br />Thanks for all your help too!

 

[Bryan22]

Re: Merc 80hp "800" ???Spark

I do understand that the larger square box is the switch box.

 

[BaysideMarine]

Re: Merc 80hp "800" ???Spark

Laddies is referring to the fact that the switch box has 4 terminal posts on the starboard side of th eengine and 3 terminal posts on the port side. The mercury switch is a block cylindrical object about 1 inch long and one lead goes to ground and the other lead goes to the bottom terminal (from memory) on the port side of the switch box.<br /><br />These mercury switches sometimes bugger up and short out the ignition all the time rather than shorting the ignition when the motor is trimmed to high up.<br /><br />Another simple check is to give the plate the switch box mounts on a knock with a hammer or similar and see if that corrects the spark problem. If so, defective switch box. Replace.<br /><br />Cheers,<br /><br />Nicholas

 

[Bryan22]

Re: Merc 80hp "800" ???Spark

I guess that is that is where some ofof my confusion comes into play. The larger box has only teh 4 terminals in it, all in a row. There is a smaller rectangular box that has 3 terminals just above the larger one. There isn't a box with 4 terminals on one side and 3 on the other. I just want to make sure I am working with the correct box in each instance. Would a pic of these parts on the motor be of interest?<br /><br />Thank you.

 

[Bryan22]

Re: Merc 80hp "800" ???Spark

Any clarification on the 2 different boxes as stated in the post right above this one?<br /><br />Thanks

 

[Laddies]

Re: Merc 80hp "800" ???Spark

Bryan, you have a system on that engine that is rare most were replaced years ago by Mercury Marine, both Merc and CDI have replacement kits at least CDIs is still avalable ) you might better find a doner engine. Here are the only tests for that system I know, engine on number 1 cyl, spark gap installed in the plug wire, key on or better the red and white termanals jumpered, remove the blue wire from the box attach a jumper wire on the termanal, each time you arc it to ground it should fire. No fire bad box--fire bad trigger---Bob

 

[Laddies]

Re: Merc 80hp "800" ???Spark

The small box with the 2 yellow wires and 1 red is the rectifier

 

[Bryan22]

Re: Merc 80hp "800" ???Spark

Hello:<br /><br />Thank you for clarifying what I have here. Based on what I was getting back here for replys I had a gut feeling what I had here was a bit different and I did not want to make troubles worse by walking into this troubleshooting chin first.<br /><br />Are upgrade kits available? Is anyone aware of that or where I may be able to get parts from a used motor like this? (1971 =or- Merc 800, Thunderbolt, 80hp) <br /><br />Our local dealer is not a good place to start here, they are pretty helpless I am sorry to say, many people dread the thought of walking into the place. I'd really like to get her going. In the morning (Sunday) I will do the testing as Bob suggests for this "unique" motor and narrow the problems. If money wasn't factor the fix would be easy... a different motor. But when this is running she is an absolute pleasure.<br /><br />Thank you again for all the help, especially you Bob, it is greatly apprecitated.