Outboard Engine Cuts Out at Slow Speed.

Mariner1 · 20 May 2023, 10:56

Hi, could anyone offer advice please?
Mariner 20hp (Four Stroke), Pull Start, Year of Manufacture: 2013.

I bought the engine new, condition is still like new with no more than 25 hours use since new. Engine starts & runs perfect from cold & allows very slow speed when leaving a slipway/jetty/pontoon etc. However, when the engine has reached normal running temperature, should I need to return to either tick-over (idle) in neutral or especially if I engage forward gear for slow manoeuvring, the engine stalls (cuts out) on me each & everytime. This problem hasn't started recently, it's been there since day one.
Any advice would be most appreciated,
Thanks in anticipation.
Regards
Jon.

Fenlander · 20 May 2023, 11:18

Hi and welcome to the forum. Assume it's a carb model.

I can’t bear an engine not idling or trolling without stalling.

The initial thoughts would be a too slow idle speed and/or possibly the idle mixture screw needs to come out a bit.

Beyond that a carb strip and clean may be in order. Are the plugs in good condition and correctly gapped?

Do you self service or is it dealer maintained?

Mariner1 · 20 May 2023, 13:00

Hi Fenlander,

Thanks for a prompt reply, as previously said in my thread, the engine appears to have had this issue since it came out of its box brand new. I bought it from a reputable UK Dealer & it had the usual PDI checks etc. I keep it meticulously clean, it's always flushed out out with fresh water after use. I always use clean (new) fuel in a clinically clean plastic tank & run the engine dry of fuel before storage.
Being mechanically minded I do my own basic servicing i.e., oil & filter change & yes I have changed the spark plugs on the off chance that one could have been breaking down under load. I can't remember what brand of plugs it had in from new but I changed them to NGK as per the manufactures spec in the hope that that would resolve the issue - unfortunately not! The colour of the electrodes etc., appear to be a healthy light brown, certainly not dark, wet or oily.
I have thought about a blocked idle jet within the carb, but surely the idle speed would be affected shortly after the engine has been started from cold, when the choke is pushed closed.
I don't have the facility to put a tachometer/Rev counter on it to see what the engine is currently idling at.
I suppose it wouldn't hurt to have the timing & idle speed checked at a dealers, but I was hoping to a least be able have some idea as to what the problem could be?

Many thanks & I look forward to reading any more thoughts that you may have.
regards
Jon.

Fenlander · 20 May 2023, 15:46

Well worth buying a cheap Ebay Tach which just needs winding around the plug lead so you can see what the idle speed is set to or you have no starting point to judge what to do next. Most outboards have a spec for a given idle speed in gear with the outboard leg in water which makes sure you have offset the load. I will often set 100rpm above this just to be sure.

I bet yours should be around 700rpm in water/gear and if from new it had been set at 700rpm in neutral that alone could explain your issue.

I agree you would normally expect any misbehaving due to a weak idle state to show up immediately the choke was pushed in but any small engine can be less predictable than a car size one.

The other service item I'd consider is valve clearance settings. And if all in the above posts was checked through I'd perhaps look for an inlet air leak.

Hopefully someone else might have ideas to throw in the mix.

Tach like this or similar...

https://www.ebay.co.uk/itm/394629815...Bk9SR86o8pmHYg

neil.mccrirrick · 20 May 2023, 18:37

Based on information so far I’d be looking for an air leak somewhere. Make sure the carb is tight to the manifold.

Once it’s warm spray the carb with carb cleaner over all joints. You are listening for a change in revs. If it increases you have an air leak there.

If not. Get it running when warm and pull a plug lead off, (be careful re getting a shock). If there is no change in revs it’s an electrical problem

Mariner1 · 22 May 2023, 13:39

Quote:

Originally Posted by Fenlander

Well worth buying a cheap Ebay Tach which just needs winding around the plug lead so you can see what the idle speed is set to or you have no starting point to judge what to do next. Most outboards have a spec for a given idle speed in gear with the outboard leg in water which makes sure you have offset the load. I will often set 100rpm above this just to be sure.

I bet yours should be around 700rpm in water/gear and if from new it had been set at 700rpm in neutral that alone could explain your issue.

I agree you would normally expect any misbehaving due to a weak idle state to show up immediately the choke was pushed in but any small engine can be less predictable than a car size one.

The other service item I'd consider is valve clearance settings. And if all in the above posts was checked through I'd perhaps look for an inlet air leak.

Hopefully someone else might have ideas to throw in the mix.

Tach like this or similar...

https://www.ebay.co.uk/itm/394629815...Bk9SR86o8pmHYg

Hi Fenlander,
Thanks again for your much valued advice, I shall endeavour to explore a little further. Considereing that I bought the engine new & thats its been extremely well looked after by myself & with such a low total of running hours, surely there can't be that much wrong. We shall see!
Thanks again, your advice is much appreciated.
Kind regards,
Jon.

Mariner1 · 22 May 2023, 13:44

Quote:

Originally Posted by neil.mccrirrick

Based on information so far I’d be looking for an air leak somewhere. Make sure the carb is tight to the manifold.

Once it’s warm spray the carb with carb cleaner over all joints. You are listening for a change in revs. If it increases you have an air leak there.

If not. Get it running when warm and pull a plug lead off, (be careful re getting a shock). If there is no change in revs it’s an electrical problem

Hi Neil,
Thanks for advice, I'll certainly keep an open mind & an electrical fault has crossed my mind, but I don't have the equipment or a comprehensive electrical knowledge to really know what I'm doing with that particular route!
Thanks again & much appreciated.
Kind regards
Jon.

neil.mccrirrick · 22 May 2023, 20:39

It’s more than likely something loose with that low hours. Check the carb is bolted up tightly. It’s letting air in on low revs be the sound of it. You will have right coloured plugs as with revs it will overcome a small leak