20hp won't start

[madmarlin]

Hi I have a 20hp mid 80's model mercury 2 stroke pull start. Which I purchaced to repair and sell I have completed putting back together and tried to start for the first time and it fired for about 10 secs before stopping and will not even look like starting after that. Have tried without fuel connected, tried new spark plugs and leads. am at a loss as to why any ideas.

 

[JB]

Re: 20hp won't start

Try the Engine FAQs, Webby.<br /><br />Good luck, and welcome to the board.

 

[Motor Boater Bill]

Re: 20hp won't start

If you have spark, check to see if the flywheel key is sheared. If you have good spark and the flywheel key is not sheared, try spraying fuel (not starting fluid) into the carb. If no spark, disconnect the wire from the terminal block to the kill switch to eliminate that as a possibility. If still no spark, then possibilities are plug wires, coils, tirgger, stator, or CDI box.<br /><br />Post your serial number and also more info after you try the above.

 

[madmarlin]

Re: 20hp won't start

Thanks will try these and will be back

 

[grandx]

Re: 20hp won't start

my moneys on a clogged jet in the carb. open it up and slide a fine wire through the jets and give her a try.

 

[madmarlin]

Re: 20hp won't start

sorry about lack of information as typing isn't my best skill.<br />serial # is 9565190 have been told mid 80's model. tryed a couple of things yesterday not getting any spark, flywheel isn't sheared and seem to be getting fuel into the cylinders as can smell it when pulling it over with spark plugs removed so would say carbie isn't blocked. as not getting any spark am looking down that road without success. I have a mid 90's model 25hp (#OG246341)on my boat so have tryed swapping plugs, leads and and ignition coils and still no spark. Am lost as to why it started the first couple of pulls and now nothing. P.S. Also tryed disconnecting kill switches still no luck. This motor also has system for charging battery which which is not connected to a battery could this effect it in some way.

 

[madmarlin]

Re: 20hp won't start

would be guessing that not a lot can go wrong with stator or trigger thus would be cdi is this right what is the most common to fail and how can i check to see which one it is.

 

[dompie99]

Re: 20hp won't start

hi,<br /><br />CDI system are quite simple ( look who's talking) to diag with a little method.<br /><br />There is a coil under the flywheel that sends a Pulse to a '' black box, telling it to activate a coil to ^produce the spark necessary to fire the spark plug, the rest is obvious.<br /><br />If you have access to an Osciloscope, look in the wiring comming from under the flywheel and probe the wires that are connected to the CDI box ( black box) you should see 2 pulses per revolutions ( 2 cyl) or more depending of the engine amount of cylinders...<br /><br />That way, you'll know if there is any trigger going to the CDI box.<br /><br />That as far i will help you here, i'm not sure if there is a battery needed for this engine or not.

 

[andy6374]

Re: 20hp won't start

Before we get to far, check for loose connections. And make sure your ignition coils are properly grounded, this is a classic 'can of worms'<br /><br />That being said...<br />My guess is with the stator or the switchbox. The switchbox and stator are the most unreliable parts in the ignition system, in that order respectively. I imagine that this is 2 cylinder, right? There should be two wires from the stator running to the top of the switchbox. There should be contiunity between these wires (as well as a particular resistance, but I don't know the numbers). If there isn't the stator is done. If there is, I would put my money on the switchbox.<br /><br />If the stator or switchbox is fried, get aftermarkets parts from CDI/Rapair. Their ignition components are far better than Merc's.<br /><br />Note if you have a DVA meter you can fully test the stator and trigger assembly. Laddies or someone else who know near everything could help here.

 

[Motor Boater Bill]

Re: 20hp won't start

If you have no spark to either plug, that suggests that the problem is upstream from the coils, so, as others suggest, stator, trigger, or cdi. The manual will give values to test the coils of the stator and I believe also the trigger. Don't overlook the possibility of bad wires shorted to ground or open. <br /><br />You mentioned that you got this to repair and sell, and that you had completed putting it back together--what repairs did you do? Is it possible something was not reassembled properly? <br /><br />Do you have the Merc manual, which includes wiring diagrams? These will be a big help.

 

[madmarlin]

Re: 20hp won't start

Thanks again, yes this model is 2 cylinders. The problem with this engine when I got it was the exhaust manifold cover plate was corroed out and the tilt was siezed, the carbie was removed and in pieces and the wiring was all disconnected plus it didn't have a fuel filter and hoses so simple repairs one would have thought. I don't have a manual at this stage but looks like I will have to get one. It is possible that the wiring is connected wrong however it is all colour coordinated and male female connectors fitted just had to plug together. Will check all wiring for good/clean connections. Have been trying to avoid removing flywheel. Don't have osciloscope so bar cleaning and redoing connections will have to take it to a mechanic. Thanks again to all for helping.