Spark in plug wire but not at spark plug

[fritzalouie]

My 1988 Yamaha 50 hp is only firing on one cylinder.It starts easily but will only idle with the choke closed.
I had started it and it was idling smoothly when there was a backfire(not very loud).After that it ran as stated above.I first suspected fuel system issues but all seems right.
Can I switch over the ignition coil-plug wire combo to see if that is the problem?
If I buy a multimeter what readings should I get at the plug connector end?
What other areas should I check electrical readings from?

 

[99yam40]

Re: Spark in plug wire but not at spark plug

If you have to pull choke out to runn you need to pull and clean carbs and then follow link and sync procedure in service manual after reinstalling carbs

clean and flush fuel lines,filter, and pump so you do not put trash back into cleaned carbs
check fuel pump for tears and leaking into crankcase while you are at it.

Spark tester can be picked up at any auto part store

 

[fritzalouie]

Re: Spark in plug wire but not at spark plug

Thanks.I started it in the dark last night and there was a continuous spark from the wire itself in one wire ,a few inches from the plug cap and an intermittment spark ,plus glow in the other.Both were disconnected at the time.
I'll do the carbs but should I see if the one coil-wire works on the other cylinders?

 

[99yam40]

Re: Spark in plug wire but not at spark plug

disconnecting plug wires and not giving them the proper gap and/or place to jump spark can cause problems when it jumps places it should not be jumping. Have read it can ruin coils and cause voltage spikes back into CDI and take that out.
use a spark tester they are cheap enough or just make one yourself.

Compression, spark, and timing are all easy to test and should be done when starting to troubleshoot a motor

 

[fritzalouie]

Re: Spark in plug wire but not at spark plug

Thanks.
A different forum had said that was how to test for leakage in the wires.Hopefully I did no damage.Will pick up a spark tester?Do they give readings orjust let one know there is spark.0/

 

[robert graham]

Re: Spark in plug wire but not at spark plug

Maybe just replace all those old leaking wires?...sounds like that could be your problem.....after all, they're probably 25 years old!...

 

[99yam40]

Re: Spark in plug wire but not at spark plug

Thanks.
A different forum had said that was how to test for leakage in the wires.Hopefully I did no damage.Will pick up a spark tester?Do they give readings orjust let one know there is spark.0/

some are adjustable so you can make sure it will jump different size gaps
If you want to measure voltage they make KV testers

 

[fritzalouie]

Re: Spark in plug wire but not at spark plug

I switched over the ignition coil-plug wire combo and still only running on same cylinder.
carbs are my next chore as a squirt of Gunk carb cleaner provides a burst of power on the 2 remaining/non working cylinders but only momentarily.and even the one running one has to be choked to keep it going.
Any hints on how difficult this job is.I stick to jobs but am not really mechanical and have never attempted a rebuild.

 

[99yam40]

Re: Spark in plug wire but not at spark plug

My 1999 C40 was easy, but I have been working on all sorts of motors since before I was in high school in the 60's.
cannot say if you can or not, but would not hurt to try. A service manual would be good to have

 

[fritzalouie]

Re: Spark in plug wire but not at spark plug

Did not mention that you can't replace spark plug wir ,coil is attached.Thanks for your help.

 

[fritzalouie]

Re: Spark in plug wire but not at spark plug

On middle of three carbs; the bolt running thru front of carb that has the choke plate attached has an attachment to an electronic unit (2" long and circular),what is it?

 

[stylesabu]

Re: Spark in plug wire but not at spark plug

choke soliniod, when you push ign key in it engauges the choke.

 

[fritzalouie]

Re: Spark in plug wire but not at spark plug

Thanks.
Do you know whether the main jet on the 1988 50 hp is removable?