Outboards (again)

[blackrose]

I have a Suzuki 5hp 4 stroke outboard which is virtually new.

 

I have to push it fairly hard against the current to get to my boat but when I throttle back the engine cuts out. I thought it might just be the idling speed so I tweaked it up a bit but it's still doing the same thing. It's a bit of a nuisance as it means I have to quickly grab the side of my boat or get carried away by the current!

 

I could increase the idle speed again but I like to have a reasonably low idling speed so that I can manouvre in still water while in gear.

 

Does anyone have any suggestions? It only does this after being pushed hard and then throttled back quickly.

Edited January 6, 2014 by blackrose

[nicknorman]

I wonder if it's momentarily seizing? Are you using the correct type and quantity of oil properly mixed? If you roll the throttle off slowly, does it still cut?

[blackrose]

It's a 4 stroke so no mixing of oil? I don't think it's seizing.

 

If I roll off the throttle slowly it doesn't cut out, but I need full revs to get to the bow of my boat and then I want to roll off the throttle quickly so I can grab the boat. If I roll off slowly I'll just get pushed back by the current before I can grab the bow.

[NMEA]

Are you using the correct type and quantity of oil properly mixed?

Hope not, its a 4 cycle

 

I'd be looking at the float height in the carb

Edited January 6, 2014 by NMEA

[Alan de Enfield]

I wonder if it's momentarily seizing? Are you using the correct type and quantity of oil properly mixed? If you roll the throttle off slowly, does it still cut?

 

Its a 4 stroke.

 

Maybe its running too hot (is there a 'tell-tale' on this model ?) and the fuel is evaporating when there is only a small amount needed (on tick over) but sufficient fuel gets thru' when the throttle is wide open.

 

Sounds unlikely but thats what a dealer told us when we had the same problem.

[Kwacker]

Has it ever been left for a long time (over winter say) with fuel in it.

The goo that settles out of old fuel plays havoc with carb. jets.

A strip-down and clean of the carb. would seem in order.

[blackrose]

Float height... Ok I've taken these sort of carbs apart before but how would I know what the correct float height should be?

 

Yes there is a tell tale and it's flowing fine. I have no idea bout the fuel evaporation theory? Where would it be evaporating to inside a carb?

Has it ever been left for a long time (over winter say) with fuel in it.

The goo that settles out of old fuel plays havoc with carb. jets.

A strip-down and clean of the carb. would seem in order.

 

I bought it last Spring and I've run it about once every 3 weeks over summer until now. It could be old fuel I suppose. I thought outboards were fairly tolerant.

 

In the short term would increasing the idle speed a bit more cure the problem? I need an easy fix as I'm using the dinghy to get on and off the boat during this flooding. No time for a carb rebuild at the moment. I'll try tweaking it up a bit more tomorrow.

Edited January 6, 2014 by blackrose

[Kwacker]

But how old is the fuel? I know from my bikes that petrol goes off very quickly nowadays.

[frangar]

I would clean the jets too....just had to do this on my landie.....there were small crystals in the carb that were causing all sorts of problems....stripped the carb...used some carb cleaner and blew everything thro with compressed air and now runs better than it has in a long while.....I agree modern fuels go off very quickly...you can get petrol stabiliser which I'm beginning to think may be a good idea.

 

The float height should be in a works manual...have you looked for one online? What make is the carb?

 

Cheers

 

Gareth

[NMEA]

Float height... Ok I've taken these sort of carbs apart before but how would I know what the correct float height should be?

 

It will be in the workshop manual, maybe even in the handbook, if you are giving the carb a clean as suggested, they do gum up if left standing for a long period as the volatiles evaporate and leave the residue so also worth doing all at the same time.

[blackrose]

But how old is the fuel? I know from my bikes that petrol goes off very quickly nowadays.

 

It's difficult to say as I've been topping it up over time. The oldest is probably about 6 months old. I've heard lots of anecdotes about old petrol but I've never had a problem before. I have petrol in my generator that's probably 2 years old and it runs fine.

It will be in the workshop manual, maybe even in the handbook, if you are giving the carb a clean as suggested, they do gum up if left standing for a long period as the volatiles evaporate and leave the residue so also worth doing all at the same time.

 

Can I just spray some carb cleaner into the air intake instead of stripping it down?

[NMEA]

 

Can I just spray some carb cleaner into the air intake instead of stripping it down?

It may help but will not address the float height if that is an issue, but so easy to do it is probably a good first step.

[frangar]

It's difficult to say as I've been topping it up over time. The oldest is probably about 6 months old. I've heard lots of anecdotes about old petrol but I've never had a problem before. I have petrol in my generator that's probably 2 years old and it runs fine.

 

Can I just spray some carb cleaner into the air intake instead of stripping it down?

In my experience nothing beats taking the jets out and cleaning the carb bowl rather than just squirting it down the air intake.

 

My chainsaw which is 2 stroke seems much more tolerant of old fuel than the weber carb on the landie which considering it's much smaller with smaller jets etc is surprising.

 

Cheers

 

Gareth

[Barry]

I have a suzuki 4hp 4 stroke that had fuel problems last year, only in my case the whole fuel system pipework was gunked up. If you're doing a carb clean it might be worth checking the whole system.

 

My symptoms were different from yours though. It ticked over fine but ran out of guts very quickly

[blackrose]

Mine has plenty of guts, just doesn't seem to like the revs being reduced too quickly.

 

Anyway, thanks for all the advice.

 

I may invest in some fuel stabiliser because I use my outboard, generator and chainsaw infrequently. Any suggestions about which brand?

Edited January 6, 2014 by blackrose

[bizzard]

Sounds like a blocked idle jet. You could try suction cleaning. Grip hold of a ball of not fluffy rag, rev engine up to high revs and hold it there and shove the rag ball up against the carbs air intake. The engine will be strangled for air and will slow down. As the revs drop to say about 800rpm or so pull the rag ball away to prevent the plug from fouling with petrol and the engine will recover to the high revs again. Shut the throttle down to see if it'll now idle.

This treatment often works.

[blackrose]

Thanks, I'll try that.

[nicknorman]

Oops, 2stroke - 4 stroke - a "wrong glasses" moment, sorry!

[Neil2]

As many have suggested it's almost certainly something gunging up the carb, outboards are notorious for it. When I had a Honda 15, every time it was serviced they found muck in the float chamber and the guys I used reckoned it was using supermarket petrol. I don't know whether there is any truth in this as I sold the boat shortly after.

[ravenspell]

I was thinking a weak mixture could be the cause of this.Remove the spark plug and see if it has a "tan " colour.This is the correct colour, a black plug means either too strong a mixture or your burning oil, A white colour means a weak mixture. You can google this to show images to give a better idea.

weak mixture can be a sign of a blocked jet or fuel line or fuel filter.

Less likely , if the mixture is ok, is it could be the spark plug.I had an old outboard that if left standing for a couple of months, the spark plug would go duff..

[cereal tiller]

Has it ever been left for a long time (over winter say) with fuel in it.

The goo that settles out of old fuel plays havoc with carb. jets.

A strip-down and clean of the carb. would seem in order.

Very much so.

 

Could be the little pilot jet partially blocked ,a small amount of gum/varnish can build up and restrict it enough to cause what the OP describes

 

The main jet is much larger.and more tolerant to negligence.

 

Remove jets,wash in acetone or a proprietary "carb"cleaner

 

A drop or two of water in the float chamber can also cause erratic idling

Edited January 6, 2014 by cereal tiller

[Burgiesburnin]

Its a 4 stroke.

 

Maybe its running too hot (is there a 'tell-tale' on this model ?) and the fuel is evaporating when there is only a small amount needed (on tick over) but sufficient fuel gets thru' when the throttle is wide open.

 

Sounds unlikely but thats what a dealer told us when we had the same problem.

 

As per Alan, the motor will naturally get hot and the fuel demand keeps the motor running at high revs.

You then back off demanding less fuel but the fuel in the carp "percolates" starving the motor.

In the current low temperatures that you have I don't know if this can be avoided but you should try to approach your boat while slowing gradually.

[bargemast]

I was thinking a weak mixture could be the cause of this.Remove the spark plug and see if it has a "tan " colour.This is the correct colour, a black plug means either too strong a mixture or your burning oil, A white colour means a weak mixture. You can google this to show images to give a better idea.

weak mixture can be a sign of a blocked jet or fuel line or fuel filter.

Less likely , if the mixture is ok, is it could be the spark plug.I had an old outboard that if left standing for a couple of months, the spark plug would go duff..

I don't think that the mixture is weak and would show up on the sparkplug, as Mike says it's running well on higher throttle settings, on which his engine is running during his short trip to his boat, and only when he arrives at his boat and reduces the revs the engine stalls.

 

It's more than likely that the carb needs a good cleaning of the jets and clearing all the tiny little fuel passages.

 

AdE's suggestion in post #5 isn't very likely but that used to happen quite a lot many years ago, and was known as "vapour lock".

 

Good luck with curing your problem Mike.

 

Peter.

[WotEver]

Jumping in on this thread, I have a Husquvarna chainsaw which won't start on idle. If a friend holds the throttle wide open when I pull the cord it starts straight away. Once hot it will idle. Until it's hot it won't.

 

Does this also sound like a gummed-up carb? The saw gets used very rarely.

 

Thanks,

Tony

[cereal tiller]

Jumping in on this thread, I have a Husquvarna chainsaw which won't start on idle. If a friend holds the throttle wide open when I pull the cord it starts straight away. Once hot it will idle. Until it's hot it won't.

 

Does this also sound like a gummed-up carb? The saw gets used very rarely.

 

Thanks,

Tony

Very likely