15hp Mariner stalls at low RPM

Tim M · 07 October 2004, 16:03

I have a 15hp 2 cyclinder 2 stroke mariner outboard. It's used regularly, however, on Tuesday it stalled when it was idling in neutral. This happen a couple of times in one outing.
Anyway, took it out again today and the problem got worse. It stalled every time I let the revs go below about 1000rpm. As it stalled more and more times it got harder and harder to start. I estimate that it must have stalled about 30 times in a 2 hour trip.

Does anyone have any good ideas as to how to sort the problem before I take it to an expensive repair person?

Thanks in advance!

Matt · 07 October 2004, 16:08

What does it do as it stalls?
Misfiring?
Running on 1 cylinder?
Excessive smoke?
Backfiring through the carb?

Tim M · 07 October 2004, 16:16

It just stops like I've hit the stop button. When it does start up again theres a lot of smoke, but thats after a lot of pulling on the cord!

Matt · 07 October 2004, 16:23

Start with electrics (IMHO of course

). Warm it up properly and wait for it to stall. Stick a plug on each HT lead and check for a healthy spark on each.

Jackwabbit · 07 October 2004, 17:01

This sounds very much like the same problems we have had with 3 cylinder Yamaha auto lube engines.
Is your engine auto lube or pre-mix?
If its auto lube my guess is blocked slow running jet in one or both of your carburettors, we have had this more times than I can remember with the auto lube system but never with the pre-mix.

Tim M · 07 October 2004, 17:02

It's a premix model.

Matt · 07 October 2004, 18:03

I still put my money on the electrical system, but if you want to test if it's blocked jets, pop into yer local model aeroplane shop and get a primer bottle. Stick some 50:1 in it. After the engine stalls and won't restart, squirt some premix down the carb throat and see if it fires again.

Jackwabbit · 07 October 2004, 18:09

Oh well keep that idea on the back burner for a while, it could still be blocked jets but a little less likely with pre-mix, they are usually have larger holes to allow the oil & petrol mix through. Unless you have got some dodgy fuel with a lot of crud in it (it can & does happen)
first move is to check the plugs as suggested by MadMat, it may also be worth checking the kill switch.

Matt · 07 October 2004, 18:12

Yeh. Basically look for a spark and fuel and then work backwards to diagnose it.

Tim M · 07 October 2004, 18:31

Will do. (This one doesn't have a kill switch on it).

As a footnote, it helps greatly starting it when I pull the choke out.....

Jackwabbit · 07 October 2004, 19:06

Quote:

Originally Posted by timofengland

Will do. (This one doesn't have a kill switch on it).

How do you manage to stop the engine without a kill switch?

Quote:

Originally Posted by timofengland

As a footnote, it helps greatly starting it when I pull the choke out.....

This is begining to sound more like a blocked slow running jet again, this is exactly the same as the problems we have had.

Tim M · 07 October 2004, 19:19

Quote:

How do you manage to stop the engine without a kill switch?

There's a red button on the front which you push to stop it......

jwalker · 07 October 2004, 21:08

Idle mixture problem, the same as Bruce Hawkins.

Do a search.

Matt · 07 October 2004, 23:42

Yep, based on the additional evidence, I'm behind jw

jwalker · 08 October 2004, 00:40

Oops, me edit button has gone. Bruce Hawkster not Hawkins. Apologies Bruce.

ADS · 08 October 2004, 08:24

Quote:

Originally Posted by timofengland

Will do. (This one doesn't have a kill switch on it).

As a footnote, it helps greatly starting it when I pull the choke out.....

I am almost certain it is a blocked slow jet. Should be quite easy to take the carb of on that.

Might be worth checking your fuel tank for bits - particularly if its a rusty metal fuel tank. Even the smallest bit of grit can ruin a good days ribbing!

Alex

jwalker · 08 October 2004, 11:13

Me edit button has gone again!

Bruce, I'm ever so sorry. Hawsker not Hawkster or Hawkins...I should stop posting after midnight.

Anyway, Tim, Tom, Tum, take out the idle mixture screw, look into the hole to check for debris, put your finger over the hole and fire up the motor. If it'll run long enough, rev it firmly once and then switch off. Replace the screw and set the idle mixture. Then report back to us for the next suggestion.

Tim M · 10 October 2004, 18:53

Thanks for the suggestions. I'll give it a go tomorrow and report back.....

Tim

mijooli · 11 October 2004, 15:51

I believe I had the same problem with a Mariner 65, when I travel very slowly, idle or go nearly full throtle the motor sort of stutters and then slumps and if I don't adjust the throttle quick enough it cuts out.

It has been suggested the holes in the carb are pretty blocked. I would like any reccommendations on any mobile outboard servicing/tuning company people may have, been trying to call TW Marine Southampton, but he seems to no longer be in business.

Cheers

Tim M · 11 October 2004, 17:42

Right, I had a go at fixing this engine this evening and heres wat happened:

Tested the plugs - they had a nice bright spark, so I can rule them out.

I tried fresh fuel (my tanks are plastic BTW) but this didn't have an affect. Took the fuel filter in the engine out and checked it. There were a few odd bits of crap in it but nothing major.

Took the carberttor off. Removed various covers and things but there was no evidence of any crap here (saying that I'm no expert in this field; I assume I was looking in the right places......where is the jet/what does it look like??). Put it back on again but still suffered from the same problem.

I'm out of ideas now. Any more suggestions before I book it into a Mariner man?

Tim