bad coil ?

[FISHFINK]

hello once again guys....

i have a 1988 25SG hp two stroke. rebuilt carbs, new gas tank, lines, filter, diaphragm.
was out in it 2 weeks ago and although it ran like a champ for an hour, lately it has been a little tough to start. use to start on 1-2 pulls, and idle right away without the choke..... when out 2 weeks ago it would take about 10 pulls to get it started, but once started it idled and ran like a champ.

anyhow, decided to start it today and let it run, but it took about 50 pulls to get it started. once started its running like a dog.
did a compression check in neutral with choke on and second plug out, and both cylinder are 110psi.

fired it up again, after about 50 pulls, and was giving it slight throttle, and wanted to check for spark, by pulling one plug wire at a time. pulled the top wire first, with an insulated pair of channel locks, and ***, it still shocked me through the insulated pliers, and stopped running immediately. ok, that coil/plug seems to be working correctly..

started it back up and did the same thing, pulling the bottom plug wire.. this time it did NOT change anything in how it was running, and although i didnt get shocked like when pulling the top wire, i could faintly hear spark jumping from the wire to plug end when reinstalling it, but it did NOT change how it ran. left it off and it ran the same as if it was on.

could i have a bad coil ? can i swap the coils and see if it does it in reverse, guaranteeing a bad coil ?

any help would be greatly appreciated.... this engine has been killing me since i bought it in September...

thanks guys...

[FISHFINK]

spark plugs are only 3 months old, but i am getting new ones tomorrow to try that also

[rodbolt17]

coil failure- incredibly rare.
sounds like your going to enter the fuel system, again.

[FISHFINK]

coil failure- incredibly rare.
sounds like your going to enter the fuel system, again.

no kidding ?. strange.... how could the bottom cylinder not be firing because of a fuel problem ? could there be too much fuel entering the cylinder and drowning the plug out ?

i am lost.... i did find out that both coils are the same, so hopefully sunday i will flip the coils and see if i then get the opposite plug to not fire.

thanks so much for the input

[99yam40]

Why not just test the spark with a spark tester to make sure it is putting out properly and will jump a 7/16" gap

Plug wires and the primary and secondary of the coils can be ohmed to make sure they meet spec in manual.

You can also measure the input to coil to see if it meets spec also

Too much fuel just like too little will not let cylinder fire properly
leaking fuel pump can dump excess fuel into crankcase

[FISHFINK]

Well I'm not sure how to rest the ohms of the coils....I do have a meter though.
Talking about the fuel though, I did install a new diaphragm and gaskets but did notice it leaks ever so slightly on the bottom of it. Not even a drip but enough that when I rub my finger on the bottom I can feel the fuel. So maybe its leaking more to the inside that I can't see and is dumping fuel into the cylinder......I'm thinking its going back to the mechanic.....
I will swap coils just to see........

Thanks much guys

[FISHFINK]

i will buy a spark tester tonihgt and hope to work on it tomorrow..

also, stopped by the local marina and talked to the parts counter person who was a mechanic, and he said also it sounds like its either getting too much or no fuel in the bottom cylinder that was not affected when i pulled that plug wire.

he said to first pull that carbs fuel drain plug, and if no fuel comes out, then its getting no fuel. if it does have fuel, he suggested to pull the diaphragm body off the house with the two screws that hold it to the carb, leaving the other two screws on, holding the assembly together, and to then pump the primer ball. it should not have any fuel coming from it, and if it does then i have a leaky gasket and it is pouring too much fuel into that bottom cylinder.

the mechanic that rebuilt the carbs suggested i always run out all of the fuel when i am done using it, but this guy said he does not like doing that, because sometimes he has seen where it lets the float fall down because of no fuel in the bowl, and sometimes lets the float get stuck in the down position, not letting in any fuel on the next startup. he also said that when running all the fuel out that there is still a little bit of gas in the bottom of the bowls, and it is easier for that small amount of fuel to crud up, then if the bowls were full of fuel.....

i hope to dig into it a little more tomorrow...

your thoughts on all of this ? thanks guys.

[99yam40]

I do not like to run motor until the motor dies from lack of fuel for the same reasons , but if the float sticks in down position it will flood the carb not starve it as the needle will be open when float is in low position.

Also when doing this with motors with multiple carbs some will run out before the others and those cylinders will be running lean and with no oil while the motor continues to run

A Yamaha service manual for your motor would help you test things and tells the specs and equipment needed

[FISHFINK]

ok guys, i was able to test a few things today...

bought an ignition tester and both coils are working properly, jumping 7/12 of an inch, or .583"..... very good spark, so that eliminates the coils.

did another compression test and both cylinder are still at 110ppsi.

started it up and it still runs really rough, pulling the bottom plug wire does not affect it at all. installed a new spark plug and nothing,.
its as if the bottom cylinder is dead. it is running on only the top cylinder.

pulled both drain screws on the carb bowls and both are getting fuel.

took the fuel pump diaphragm apart, and didnt see any holes in the diaphragm, but after putting it together i did notice the very slight leak i had known about is from a small crack in the plastic middle section of the diaphragm body.

is it possible that the small leak is causing the bottom cylinder to get too much fuel and not fire ?

when i pulled the new bottom plug it didnt seem to be over fueled.

i am now as far as i can go, unless i order a new diaphragm and plastic center section that has the crack.... i might just take it to the mechanic and let him do it... this thing is driving me crazy..

any input on this would be greatly appreciated...

thanks guys.

[99yam40]

You can put some fuel mix in a spray bottle and spray some into the throat of the bottom carb while running to see it that gets it to fire again, if it does you know it is running lean and need to go into carb to clear passages/jets

[FISHFINK]

You can put some fuel mix in a spray bottle and spray some into the throat of the bottom carb while running to see it that gets it to fire again, if it does you know it is running lean and need to go into carb to clear passages/jets

very cool tip.... i will give that a try, hopefully today after work.

if this works, is there any way i could clear the passage ways without opening up the bottom carb, like blowing compressed air into either the bowl drain hole, or removing the air adjusting screw and blow compressed air in there ? the carbs were rebuilt in september by a mechanic, and this motor has only been on the water 3 times since, and has new gas tank, lines, filter, diaphragm.... i cant see how something could have gotten into a passage way.....

i cant thank you enough for always chiming in here and lending a helping hand.
it is greatly appreciated.

[FISHFINK]

99YAM40

thanks so much man.... i got it going today...

i put some mixed fuel in a spray bottle as you suggested, started the motor, and it was running really rough. sprayed the fuel into the bottom carb, and viola.... it would run way better, confirming the bottom carb was not getting fuel.
so i took the mixture screws and bowl drain plugs off each carb. i flogged them with an entire can of power tune aerosol spray, let it set for 15 minutes, and also bent a piece of safety wire and inserted it into the bottom carb, through the drain hole, hoping to free up the float, if it was actually stuck.
put it all back together, and it ran like a champ.... it now fires up on a half a pull of the cord, as it did all along, before this last mishap.
and when it was idling i pulled the bottom spark plug wire, and it then ran rough, confirming that the bottom cylinder is now getting fuel and firing as its suppose to.

not sure if it was the power tune spray, dislodging something that may have been in the passage ways, of the wire inserted into the drain hole, but whichever it was i am now back in business.

i have the week of christmas off and plan to take it out a few times for some bass fishing.

thanks everyone, especially 99YAM40.... i couldnt have done it without you.
take care

[FISHFINK]

well, another update guys...
after thinking i fixed it last monday, the 17th, it was running and idling fine. my complete fuel pump diaphragm assembly came in yesterday, so i installed it and now the slight leak i had from the old body is gone.
after installing it yesterday i fired it up and it idled and took throttle perfectly on the water muffs.
was out there a little bit ago getting it ready for a fishing trip tomorrow, and decided to fire it up again. now the bottom cylinder is back to not firing due to lack of fuel....
i am really stumped.... so i took the bottom carb drain plug out, and there was fuel in there. took the air/fuel mixture screw out and flogged the bottom carb with the power tune spray, and did my little trick inserting a wire up into the bowl drain hole, like last time.
after it burned off the power tune spray, it was idling perfectly for about 4 minutes... then started running rough once again.
i am taking it out anyway tomorrow, hoping to get it running under load to maybe blow out the carbs, or something.
i really am at a loss on this thing.
if it acts up tomorrow its going back to the mechanic who rebuilt the carbs in september..
i am just about ready to sink the boat...... its very frustrating.
any more ideas guys ?
thanks

[99yam40]

If you are running lean because of jets/passages plugging the you can harm the motor trying to see if it will get better.
Pull carbs and clean properly

[rodbolt17]

typically with a two stroke you will blow a piston long before you "blow" out a carb passage.
takes an hour and a half to dissasemble,clean and reassemble those carbs.
probably less time than you have dinking with it so far .