89 30hp missfire after 10min warm up

[wormz]

need some help, been throwing parts at it.
i have an 1989 evinrude 30hp. when starting boat cold, it will go WOT for about 10-15 minutes (can just about set your watch to it) and it will start a missfire, total lack of power like your going from wide open throttle to pressing a cuttoff switch, as fast as it cutts off, it takes back off WOT. about 1 second between cut offs. idles fine.(brrrrr-puh-brrrrr-puh-brrrrr-puh)
any help woul dbe great!
ive eliminated fuel, its not starving for fuel. it seems to be an ignition breakdown. is there a safety switch or something under the flywheel (like a coil pick-up?)that can cause this?

 

[iwombat]

Re: 89 30hp missfire after 10min warm up

It could be your kill switch shorting out, but 10 minutes sounds like enough time for the power pack to warm up and start misbehaving.

If you can idle it on the muffs, or in a barrel at home try heating the powerpack with a hair dryer and see if you can make it happen.

 

[wormz]

Re: 89 30hp missfire after 10min warm up

power pack? is that the coils? ill definatley try it!

 

[iwombat]

Re: 89 30hp missfire after 10min warm up

The power pack is what signals the coils to fire. It's one step up the chain - trace the wires from the coils.

Although the coils are as good a suspect too.

 

[wormz]

Re: 89 30hp missfire after 10min warm up

thats under the flywheel i see, how do you test that with a hair dryer? is there anything/way to test it? probability of both coils going bad is very slim(or would one cause this to?)
i think that may be the culprit...not much left. ill post back if i can get one installed to let everyone know if it fixes it.
thankx

 

[iwombat]

Re: 89 30hp missfire after 10min warm up

Power pack isn't under the flywheel, that's the stator. Your wires from the timing pickup should go directly to the powerpack. Then the wires from the powerpack go to the coils.

Hrm. Maybe I'd better look at a diagram for your engine before I go making too many assumptions. But I can't imagine an '89 having any other set-up.

 

[iwombat]

Re: 89 30hp missfire after 10min warm up

Nope, you're right the powerpack is under the flywheel on that. Heat up the coils and see if that's your problem. I'm still guessing powerpack, but that'll have to be tested in another way.

 

[wormz]

Re: 89 30hp missfire after 10min warm up

Nope, you're right the powerpack is under the flywheel on that. Heat up the coils and see if that's your problem. I'm still guessing powerpack, but that'll have to be tested in another way.

yes, i got the flywheel off and see some damage to the power pack. some of the plastic looks like it has contacted the flywheel. i see a little part of metal inside the pack that looks like it shouldnt have been visible before. its only $170 and ill have it in 4-5 days.
thankx alot iwombat!

 

[iwombat]

Re: 89 30hp missfire after 10min warm up

Would have liked to see you verify that before shelling out $170 though. Maybe all it needed was a little adjusting to set back off of making contact with the flywheel.

 

[wormz]

Re: 89 30hp missfire after 10min warm up

installed new power pack... still does it. the old one still needed replaced. the new one looks like i thought it should.
at any matter i went WOT for near 13-15 minutes and it starts to rev limit at about 1/4 speed. it idles fine and even trolls fine, if i try to build a wake, it sputters.
i can duplicate the problem in my driveway witht he cups attached. let it idle for 20 minutes and i hit the trhottle and it rev limits like flicking a light switch????
any advice?

 

[flabum]

Re: 89 30hp missfire after 10min warm up

Check all the ground wiresfor looseness and corrosion. try it with the fuel cap off. When it happens, pump the primer ball.

 

[HighTrim]

Re: 89 30hp missfire after 10min warm up

Also not a good idea to "hit the throttle" when you are running on muffs. The outboard will go into thermal runaway, that is not good.

 

[wormz]

Re: 89 30hp missfire after 10min warm up

definatley not fuel cut-out. i can spray some fuel into it(carb cleaner) and it does not help it, it doesnt change. if i take the cover off it runs for an hour without missing. with the cover on it takes a couple inutes and it cutts off again.
seems to be temperature related for sure, like its getting warm under the cover and making it do this.
ive heated the coils/no change. grounds are cleaned as of now and it still does it.

shew.....
thanks for all the advice!

 

[Harker]

Re: 89 30hp missfire after 10min warm up

Notice exaust coming out from under the hood? It may need a gasket between the exaust and powerhead..exaust could be choking it out.

 

[iwombat]

Re: 89 30hp missfire after 10min warm up

Check the proximity of your plug wires to the latches in the cowl. If the wires are close enough they can arc over to the cowl latch and cause exactly what you describe.

 

[wormz]

Re: 89 30hp missfire after 10min warm up

will do! ill check that now! no exhaust is under the cowl. it is a sudden drop out in power not choke out. (like hitting the off swith repeditly)

 

[wormz]

Re: 89 30hp missfire after 10min warm up

unplugged the temp sender and it doesnt make a difference. it will bog out with the cover off, like when it gets warm it starts to bog/ both coils seem to cut out, it has no power, until the rpm drops to near troll speed. i can remove the cover and it doesnt change.
if im at 10% throttle it doesnt seem to effect anything runs fine...any more and it will cut-out.
additionally it will do it with hitting the throtlte on the carb without the advance moving...still does it.
could it be the power pack coil undeer the flywheel shorting?

 

[iwombat]

Re: 89 30hp missfire after 10min warm up

You might want to try this at night and look for any kind of arcing going on. It sure sounds like something is shorting out or taking a quick path to ground. How do your plug wires look?

 

[wormz]

Re: 89 30hp missfire after 10min warm up

its dark now, no arcing.
i got an ohm meter and have checked the coils. they are the same resistance form post to ground. the wires are new and plugs are new.

 

[wavrider]

Re: 89 30hp missfire after 10min warm up

How did the magnets look in the flywheel?
Is there a thermal cut off switch on this model, I do not have a manual so not sure if you have one or not?