Help! engine going mad!!!!

[spaceboy]

can someone please help me? i've got a 40 hp 2 stroke mariner, not sure of the age but not new.
the problem is that when i give her some juice she runs away with herself to the point of revving beyond control. here's what i've tried/know so far;

the butterfly valves on the carbs are working properly
out of gear she will rev happily with no run away tendencies
she's not jumping to neutral
she'll run at idle happily and in gear at low revs.

someone mentioned checking the prop bush but i'm not even sure what that is.

any advice greatfully received cos i'm at my wits end!!!!!

 

[Alumarine]

Re: Help! engine going mad!!!!

When you say "revving beyond control" do you mean even when you reduce the throttle to idle it will not stop revving high?

 

[larsst185]

Re: Help! engine going mad!!!!

This happened to me once when the crank bearing and crank seals where shot.The motor was sucking air into the crankcase via the seals.Also I would check that everything is ok with your ignition timing.

 

[spaceboy]

Re: Help! engine going mad!!!!

Hi Marc, yeh, she runs out even if i drop the throttle, i've been too afraid to stick her back into neutral incase something goes horribly wrong! i've just hit the off switch to kill the power instead.

Larsst, thanks for the crank seal advice, i'll have a look at that one, hopefully not too big a job to sort out if it is that. i'll have a friend look at the ignition timing too. many thanks again ;o)

 

[sschefer]

Re: Help! engine going mad!!!!

It's not uncommon for worn 2 stroke motors to run away on you when not under load. This is probably why the prop hub was mentioned. Is this happening in the water or just on muffs?

 

[spaceboy]

Re: Help! engine going mad!!!!

i haven't ran the engine properly in the water so its only happened so far on muffs, i can stick the prop in a barrel of water to see if that makes a difference. any suggestions on what to do if this is the case?

 

[SoFloStone]

Re: Help! engine going mad!!!!

i haven't ran the engine properly in the water so its only happened so far on muffs, i can stick the prop in a barrel of water to see if that makes a difference. any suggestions on what to do if this is the case?

Running the engine in water will not make a difference, if the engine is running away then it is running too lean which would suggest an air leak either in the crank seals, cases or between the carbs and the cases.

Regardless, the powerhead needs to be taken off and either a leak down test performed to determine where the leak is, or the engine taken apart and re-built.

Rick

 

[spaceboy]

Re: Help! engine going mad!!!!

eeek!!! sounds like an awful lot of work, and no doubt expensive! i'll speak with my local boat yard mechanic and see what he says. thanks rick

 

[steinn39]

Re: Help! engine going mad!!!!

hi

I am new to this forum and also new to outboard motors but I have been working on motorbikes for years
A good way to cheek for a bad seals is to use a start spray and spray it a round the seal. If the motor revs up the seal is bad. don't know if it works for the outboard but it works for the bikes

best regards
Steinn

 

[SoFloStone]

Re: Help! engine going mad!!!!

hi

I am new to this forum and also new to outboard motors but I have been working on motorbikes for years
A good way to cheek for a bad seals is to use a start spray and spray it a round the seal. If the motor revs up the seal is bad. don't know if it works for the outboard but it works for the bikes

best regards
Steinn

Stein,

That works great on bikes where you can get to the seals, but in outboards and PWC's you always have half the seals you cannot get to when the engine is running...

Great tip...

Rick

 

[j_martin]

Re: Help! engine going mad!!!!

Stein,

That works great on bikes where you can get to the seals, but in outboards and PWC's you always have half the seals you cannot get to when the engine is running...

Great tip...

Rick

Water works well, too, only the engine slows down when you find the leak. You also eliminate the risk of a big fireball.

my 02
John

 

[sschefer]

Re: Help! engine going mad!!!!

Water is o.k. on a 4 stroke but on a 2 stroke you'll surely blow the crank seals completely if they are already weak. Water is not a compressable liquid!

It is not ucommon for a two stroke outboard motor in a no load condition to runaway. Most all manuals warn against exceeding 2500 while on muffs for this very reason. On my mariner there is a sticker on the attenuator that tells you not to exceed 2500 rpm with the attenuator removed or a runaway condition may occur. I don't think they intended that to mean if you engine has a primary compression issue.

 

[spaceboy]

Re: Help! engine going mad!!!!

thanks, i'll give her a run in the sea to check what happens when in a load situation, always got my auxilliary to get me back in if it all goes wrong. this might just save me thousands of pounds!!!