25hp 2 cyl. not firing cyl 1

[vworley]

Hey, last weekend I was on the lake and the engine started running terrible. I figured out the cylinder 1 wasn't firing. Thought it was a bad coil. Replaced both coils, plugs and plug wires. Engine still doesn't fire cylinder 1. What should I be checking now. I believe the power pack is brand new...

 

[latin monkey]

Re: 25hp 2 cyl. not firing cyl 1

you might have a broken reed valve

 

[Dave1027]

Re: 25hp 2 cyl. not firing cyl 1

you might have a broken reed valve

Not likely.

OP, are you getting spark from the #1 plug?

 

[latin monkey]

Re: 25hp 2 cyl. not firing cyl 1

a damaged reed will cause a cylinder not to fire and yes it does happen. its good to check before buying parts you don't need

 

[will941s]

Re: 25hp 2 cyl. not firing cyl 1

Make sure you have spark on #1, either look for a visible arc with the plug removed, or remove that plug wire while it's running. If there is no change then it's not working, if you remove the #2 then it should shut off or some kind of change to how it runs. If you have spark, then run a compression test to make sure you have even compression on both of the cylinders. If thats good, and you replaced the coils, then it's either the trigger, the switch box, stator, or that plug wire. You would need a tester to see where the power is stopping, then replace that part.

 

[vworley]

Re: 25hp 2 cyl. not firing cyl 1

Before I replaced the coil/plug/wires I checked both cylinders by pulling off plug wires while the engine was running. Cylinder 2 shocked me, cylinder 1 did not. I can check both again when I get home. What's the best way to test these...sure what I last did was not the best way.

I have no idea where the reed valves are, or how to check them.

 

[latin monkey]

Re: 25hp 2 cyl. not firing cyl 1

i was under the impression you had spark but no fire on that cylinder. if you arent getting spark then reeds arent the problem. they are located behind the carbs on the reed block, on the crankshaft

 

[Dave1027]

Re: 25hp 2 cyl. not firing cyl 1

Before I replaced the coil/plug/wires I checked both cylinders by pulling off plug wires while the engine was running. Cylinder 2 shocked me, cylinder 1 did not. I can check both again when I get home. What's the best way to test these...sure what I last did was not the best way.

Use a timing light. I quit pulling plug wires when my heart almost stop doing that

You also can pull the plug from the cylinder, ground it's threads (I use a jumper cable to the engine block for that), connect the plug wire and crank the starter. You should see the arc.

 

[will941s]

Re: 25hp 2 cyl. not firing cyl 1

Merc manual says "Problem: No spark or weak spark on 1 cylinder.........ignition switch box or coil". If you replaced the coil then it could be the switchbox. You need a DVA meter to check it. Power coming in vs. power coming out.....esp to the #1 cylinder. Where your #2 coil connects to the switch box, you can disconnect the positive lead and check the power coming out of there going to the #2 coil. Then reconnect it and test the power going to the #1 coil. If there is a drop in the numbers or you have nothing then you know the switchbox isnt working correctly. Check that and see what happens before you go any further. I could go over the whole testing procedure but thats WAY too much information to type. It's easier to go step by step. Unless one of the other people on here can sum it up alot easier than I can off the manual.

 

[vworley]

Re: 25hp 2 cyl. not firing cyl 1

thanks so much for the tips. I don't have a timing light, so I'll be pulling plug 1 when I get home to check for spark as described. Will report findings.
I don't know where the switch box is. Any more detail on that?

As a note, I wondered if I had the coil wires swapped, but when I swapped them, the engine wouldn't start at all. Talking about the green/yellow and green/white wires going to coil 1 and 2 positive terminals. I'm assuming these are correct at this time.

 

[vworley]

Re: 25hp 2 cyl. not firing cyl 1

Merc manual says "Problem: No spark or weak spark on 1 cylinder.........ignition switch box or coil". If you replaced the coil then it could be the switchbox. You need a DVA meter to check it. Power coming in vs. power coming out.....esp to the #1 cylinder. Where your #2 coil connects to the switch box, you can disconnect the positive lead and check the power coming out of there going to the #2 coil. Then reconnect it and test the power going to the #1 coil. If there is a drop in the numbers or you have nothing then you know the switchbox isnt working correctly. Check that and see what happens before you go any further. I could go over the whole testing procedure but thats WAY too much information to type. It's easier to go step by step. Unless one of the other people on here can sum it up alot easier than I can off the manual.

Ok, if I pull the switchbox connection to coil 2, the engine won't start, so I can't check the voltage on that lead.
I started it briefly with #1 switch box wire pulled off coil 1 and the voltage appeared to be 1.7. Was reporting -1.7, although the meter was connected correctly.
If this is leaning towards indicating a bad switch box, I'll go ahead and throw out again that the switch box is brand new.

what do you think?

 

[will941s]

Re: 25hp 2 cyl. not firing cyl 1

It's possible to have gotten a bad part, or there is something killing the switchbox. I'm leaning toward that Manual says 160-250 volts going to the primary coil from the switchbox. The problem is there are soo many types of voltage reading devices, and so many ways of reading them. What kind are you using? are you reading ohm resistance or volts? Do you have mechanical spark advance? Give me as much info as you can and I can begin to narrow your exact motor and tools your using to read the problem.

 

[vworley]

Re: 25hp 2 cyl. not firing cyl 1

It's possible to have gotten a bad part, or there is something killing the switchbox. I'm leaning toward that Manual says 160-250 volts going to the primary coil from the switchbox. The problem is there are soo many types of voltage reading devices, and so many ways of reading them. What kind are you using? are you reading ohm resistance or volts? Do you have mechanical spark advance? Give me as much info as you can and I can begin to narrow your exact motor and tools your using to read the problem.

I am using a fluke meter, set to dc voltage. I think it's a model 77. I don't know if I have mechanical spark advance or not. The engine engine uses gas/oil mix. It's odd to me that the new switch box could have failed on the same cyl as the old one...

 

[will941s]

Re: 25hp 2 cyl. not firing cyl 1

If it were a fuel problem, or cooling, or something needed to be adjusted on the motor I could tell you what you need. But this however, isnt my strong point. Wiring, I have to be there to tell whats happening. Being that the same cylinder failed twice I would guess that maybe you have a ground problem or a wire going to it from the trigger isnt hooked up properly or frayed. Check the ground connections, and check the wires going from the trigger to the box, and from the box to the coil for damage. Manual says a positive charge from the stator opens #1 switch and a negative charge opens #2 switch. It could be possible that the voltage going to the switch when the stator sends a postive charge isnt being regulated and is blowing the #1 switch in the box. Should be pushing 300-350v coming out of the stator to the #1 coil and less when it's at WOT. I don't know what it takes to kill the switch box but I would check the voltage going in.

 

[jake3340]

Re: 25hp 2 cyl. not firing cyl 1

I had the same problem with my engine and currently my second CDI that blew. What could be the problem ? Wednesday I will be removing the flywheel to change the stator because the current one I have is slightly rusted and corroded. But my new cdi worked for at least 1hour untill it went off and started firing on the top piston. Mind me asking where can I get a manual for my engine ?

 

[vworley]

Re: 25hp 2 cyl. not firing cyl 1

I had the same problem with my engine and currently my second CDI that blew. What could be the problem ? Wednesday I will be removing the flywheel to change the stator because the current one I have is slightly rusted and corroded. But my new cdi worked for at least 1hour untill it went off and started firing on the top piston. Mind me asking where can I get a manual for my engine ?

Sounds identical to my problem. Took the boat to the shop yesterday. Will report their findings as soon as I know something. Hopefully it will be of help to you!