30 johnson wot

[smacka1478]

Need help with a 89 model 30 hp johnson, idles fine runs a full throttle for a short time then surges and looses power, back throttle off idles fine try full throttle again no good, wait 20 seconds or so try full throttle no worries, minute or so later same deal, took it to marine mechanic he said a few loose nuts etc he tightened them but no good, i have changed spark plugs, checked fuel line changed fuel, checked carbie bowl its clean, not a mechanics u know what, have workshop manual, any help would be much appreciated cheers

[FNQCairns]

Fuel pump or a fuel supply and/or air leak.

If I am right, be a little carefull starvation at full advance can cause problems.

cheers fnq

PS next time run it while working the bulb to keep supply up and see what happens.

[smacka1478]

thanks fnq, i have tried working the bulb but still same problem

[Spaniard_King]

carby clean.. shit floatin in carby bowl blokin main jet :P

Garry

[Blackened]

G'day
sounds to me like crud in the carby. Take it off and blow out with compressed air/flush with fresh fuel.

Dave

[Gilli]

hey smacka i had the same problem with my 25hp johnno 1989 model motor, it took ages for the dealer to fix it but ended up been salt deposits in the cooling system, what it does it causes the motor to over heat and then the overheat kill switch kicks in and drops power back down to 2000rpm. Try cutting the temperature sensor cable and then take the boat for a spin, if it doesnt do it then theres your problem.

Cheers, Gilli

[FNQCairns]

Gilli that's a good thought although I thought the engine needed to be stopped to cancel the SLOW each time. Did you need to do that?

IMO It has to be WOT RPM emptiing the fuel bowl faster than it can refill for whatever reason, hense the refilling at idle then the emptying again soon after at WOT.
Float level, needle and seat, those crappy OMC fuel connectors, fuel pump or air leak on high demand.

Will be interested to hear what turns up, I had that engine until just a few months ago and it was a picture of reliability not one problem under the cowl but I went through a few OMC style fuel connectors and always carried a spare.

cheers fnq

[Gilli]

Yeah, thats a good point FNQ, never thought of it that way. Yeah my motor was playing up and when i disconnected the temperature sensor cable(just choped it), it ran fine, bloudy omc motors for ya though. Other than that little problem of mine, she has ran fine. so try cleaning the fuel bowls and if that doesnt help then i would be disconnecting the temp. sensor.

Regards, Gilli

[smacka1478]

thanks for your responses gilli and fnq, will try them, the guy i brought the boat off said he used to run the motor dry of fuel after every use he also had'nt started the motor for about 2 years before i brought it. It was just sitting in his shed, dont know whether that makes any difference, it is a very clean motor inside and out, i have taken the carbie off and had a look at the main bowl it is spotless, i have noticed that when i put the motor up and travel home that there is a fair bit of fuel that leaks out through the carbie to the inside of the cover is that normal?
all the best, smacka

[FNQCairns]

Smacka yes pretty normal, mine did the same, replace that connector at the engine with a dealer bought original one, the aftermarket ones are not worth spit and may even blow the engine.

Sitting can cause problems although mine sat for up to 6 months at a time sometimes, very often 3 months and never had a fuel and carb related drama (doesnt mean you don't), just connector airleaks.

good luck with it,

cheers fnq

[JEWIENEWIE]

MY old jono did excactly the same thing, ended up being a bit of crap blocking the needle and seat. Fule starvation.
Jewie

[Gilli]

Yeah smacka that fuel is normal. Happens in most omc motors. Try cutting the temperature sensor cable, but make sure its rejoinable so dont cut it to short. Could be salt deposits in the cooling system but then again it could be alot of things, does the motor stay running when the loss of power occurs? and if so, can u put the throttle down a tiny bit and get the revs up a tad. If you can do that then the overheat switch is kicking in. Which drops the motors revs down and wont let them go above 2000rpm.

Regards, Gilli

[smacka1478]

thanks for your help guys, took the boat for a spin 2day put a new fuel line on it, didnt help, disconnected the temp sensor cable and problem gone, yeah gilli once the loss of power occurs the motor still runs and you can get the revs up a little b4 it happens again, so what would u recommend doing next?
thanks heaps for ya help, smacka

[Gilli]

hey smacka, Well it took a while for my motor to get fixed as there was lots of stuffing around, the dealer put a restrictor on the thermostat but that didnt help, they then took the head off the motor and there turned out to be a salt deposit about the size of a push mower spark plug and they just used a screw driver and removed it. If you know how to then take the head off your motor and look for any deposits or anything in between the cooling system. I recommend taking it to a marine mechanic or the dealer you would take the motor to get serviced at and get them to check out the block and make sure there isnt any salt deposits or foreign objects that are stuck in there that may cause it to overheat.
What is actually happening is the motor is overheating and the temp. sensor activates the power drop off, which drops the revs down to 2000rpm. You will be able to put the throttle down a bit but after bout 60 seconds of WOT RPM it will just trip again.

Hope this helps, oh by the way, you can run your motor with the temp. sensor cut and it wont hurt it but i wouldnt run it for to long like that as somehtin could block your water intake on the leg and there will be nothing to kill the motor.

Regards,
Gilli

[FNQCairns]

Great you found the problem, shame it is more complicated than simple delivery trouble.
I guess now even the waterpump may be suspect to some degree.

For future reference (mine at least) did the engine come good (cancel SLOW) by it's self each time? I don't want to complicate matters although if it did you may have a powerpack playing up forcing SLOW when not needed.

I understand SLOW can only be canceled by a lack of electrical power it doesn't do it alone but have no way to double check that understanding.

Your hand on the engine block/head when the problem occurs or would have occured will tell you a bunch, it cannot get hot without feeling hot in normal use.

good luck with it

cheers fnq

[smacka1478]

yeah fnq, the engine did come good by itself i just put the revs back to idle for 10 to 20 seconds sometimes in neutral sometimes in gear and problem solved for a minute or so. when the problem did occur i felt the water coming out the motor and it felt no hotter then any other time.
all the best smacka

[BigE]

my 92 40 rude had the same problem ended up being a dried out gasket. caby rebiuld set me back $150 best money i ever spent. carbie troubles are common on omc's that have been in storage

BigE