engine revs running away. 89 mariner, 100hp 2stroke - fuel system?

S

simonp

Recruit
Joined
Feb 27, 2013
Messages
2
Hi, I need some urgent help please

1989 100hp 2 stroke mariner, oil injected, 4 cylinder. Great engine. has run well although didnt idle well, but once it got going was a good runner.

a couple weeks ago started losing power and just cutting out. Would restart, then would lose power again and cut out. ended up it wouldnt start at all.

I figured was a fuel block or something. I noticed the tote tank hose was loose at the tank end. decided to replace the hose. also replaced the fuel filter which is tucked under the throttle arms.

Fired it up again and was delighted to hear it purr sweetly during idle. first time it ran that well! took it out and it ran really well for 5 mins, but after I opened it up for a couple minutes, I had trouble slowing down. once I put it in neutral, the revs ran away to a very high level and I turned the engine off before something got damaged.

Things I have tried since then:
- checked fuel hoses, clamps and pipes for leaks, nothing looks wrong
- changed the fuel filter back to the original one
- changed the fuel hose back to the original one
- checked the throttle arms and mechanics for any sticking, nothing looks wrong

Nothing I do improves the runaway revs. its starts really easily (much easier than before any of this started) but quickly takes off to high revs and I have to turn it off real quick.

any thoughts or ideas? I dont really want to spend $$hundreds at the service centre if it might be something simple.

I just dont understand what has changed by me replacing the fuel filter and fuel hose...

thanks

simonp
 
quicktach

quicktach

Petty Officer 1st Class
Joined
Aug 24, 2012
Messages
394
Re: engine revs running away. 89 mariner, 100hp 2stroke - fuel system?

Sounds like a synchronizing problem relating to your carbs not throttling back when you reduce throttle and possibly your timing staying advanced at the same time.....have someone watch the carbs when you start up to see if the plates open by themselves....something is going on with linkage being bent/bound in a position where it "wants" to return to a previous position causing carb plates to open ??? Is the advancing/timing linkage sticking ???
 
quicktach

quicktach

Petty Officer 1st Class
Joined
Aug 24, 2012
Messages
394
Re: engine revs running away. 89 mariner, 100hp 2stroke - fuel system?

A lean air/fuel mix can cause an over rev too. Are the carbs bolted tightly to the manifold ? Is the fuel filter plugged ...causing less fuel ....to give a leaner mixture ?
 
Texasmark

Texasmark

Supreme Mariner
Joined
Dec 20, 2005
Messages
14,557
Re: engine revs running away. 89 mariner, 100hp 2stroke - fuel system?

You didn't disturb your timing when you were in there did you. Timing that is too far advanced can do that and you are lucky your key will turn yours off. On mine it wouldn't and I had the tach pegged past 7000 for a couple of minutes before I could get it shut down. But I have the little brother, 90 triple. My normal timing was about 4 before at idle and 20-22 at WOT depending on how it's measured.

Engine is running fine today (other things changed since for different reasons but...) so I guess I didn't hurt anything. I still get my normal WOT rpms.

Mark
 
quicktach

quicktach

Petty Officer 1st Class
Joined
Aug 24, 2012
Messages
394
Re: engine revs running away. 89 mariner, 100hp 2stroke - fuel system?

Thinking....if it runs away only in gear, is the prop spun out or on the way ?
 
S

simonp

Recruit
Joined
Feb 27, 2013
Messages
2
Re: engine revs running away. 89 mariner, 100hp 2stroke - fuel system?

thanks for the suggestions, everyone. given the remaining possible causes of the problem you have suggested, are way beyond my humble capabilities, I have reluctantly decided to take it into the service shop.

I am pretty sure the fuel system is airtight as I have checked and double checked it.

I am guessing the problem must be either a damaged linkage arm, or a broken seal on the carbs

I will give an update once it is fixed (assuming the service shop can find it and fix it!)

thanks again

Simon

simonp said:
Hi, I need some urgent help please

1989 100hp 2 stroke mariner, oil injected, 4 cylinder. Great engine. has run well although didnt idle well, but once it got going was a good runner.

a couple weeks ago started losing power and just cutting out. Would restart, then would lose power again and cut out. ended up it wouldnt start at all.

I figured was a fuel block or something. I noticed the tote tank hose was loose at the tank end. decided to replace the hose. also replaced the fuel filter which is tucked under the throttle arms.

Fired it up again and was delighted to hear it purr sweetly during idle. first time it ran that well! took it out and it ran really well for 5 mins, but after I opened it up for a couple minutes, I had trouble slowing down. once I put it in neutral, the revs ran away to a very high level and I turned the engine off before something got damaged.

Things I have tried since then:
- checked fuel hoses, clamps and pipes for leaks, nothing looks wrong
- changed the fuel filter back to the original one
- changed the fuel hose back to the original one
- checked the throttle arms and mechanics for any sticking, nothing looks wrong

Nothing I do improves the runaway revs. its starts really easily (much easier than before any of this started) but quickly takes off to high revs and I have to turn it off real quick.

any thoughts or ideas? I dont really want to spend $$hundreds at the service centre if it might be something simple.

I just dont understand what has changed by me replacing the fuel filter and fuel hose...

thanks

simonp
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