Mariner 4HP 2S stalling

[TomKat]

Picked up a cheap OB to tinker with, same as this mariner 4 hp 2 stroke | eBay

Chap I bought it from had stripped the carb and it did not run thereafter, quick rebuild and it now starts but there is a little hesitation and stalls if I let it tick over for a while then try to rev it. I presume fuel starvation in the supply side. Any usual places to look?

The carb has a square port/block that the fuel feeds into which also seems to have a vac line running into it, is this some sort of fuel pump system.

I had vent open but not sure if it was working, will try with lid off.

Seems quite a powerful motor for its size, boought to see if it will push my tinker tramp at more than 4 knots!

Any tips much appreciated!

[slate1234]

have you checked the wireing,,the wire from the points to the negative on mine was coroded I replaced it and mine is all good now

[TomKat]

Think its OK, if I start it and rev it up its fine but if I let it stick ticking over for a while then try to run it harder it stalls.
Think its fuel or lack of related! Carbs been stripped and cleaned twice and seems OK but maybe I am missing something on it?

[spareribs]

very obvious but have you checked the pipe to tank and pipe to engine connections, on mine, the fuel pipe connector on the tank had the clip on metal bit sticking out slightly which was letting a bit of air in , caused fairly random stalling but that was it, no engine fiddling necessary.

[m chappelow]

Think you will find that most used or older 2 stroke engines don't like running on Tick over then will stall out when trying to increase revs unless you tickle the throttle past the slow to fast running just from general wear ,
you will find that you can get the slow running right but the top end won't be right or vice versa .
Lets face it 2 strokes thrive on revs especially single cylinder ones & any leaking oil seals or gaskets allowing air to be drawn in doesn't help neither any worn parts on the carb or linkages especially needle adjusting jets that have perhaps been nipped screwed down onto the seat which then puts a ring or a ridge on the needle point causing an all or nothing adjustment ,
Good engine though a mate of mine uses one on 3 metre zodiac flat bottom sib and he has had over 20 mph out of it in good conditions ,,and we have the vid to prove it .

[TomKat]

Originally Posted by spareribs

very obvious but have you checked the pipe to tank and pipe to engine connections, on mine, the fuel pipe connector on the tank had the clip on metal bit sticking out slightly which was letting a bit of air in , caused fairly random stalling but that was it, no engine fiddling necessary.

That was my thoughts but checked it out and all seems OK. I wonder about the fuel draw in system on the side of the carb - seems some sort of vac assisted thing. Any idea on how it works? Thinking at tick over it does not have enough vacuum to draw the fuel in enough to keep the carb bowl full. If I keep the revs up its got enough vacuum.

Any thoughts?

[yam man]

Easy way to test the diaphragm pump is to take the pipe of the crankcase were the pump gets it's compression and depression and suck and put your tongue over the pipe. if stays there pump ok if not diaphragms are shot. Make sure all fuel is drain from carb before doing this

[TomKat]

Originally Posted by yam man

Easy way to test the diaphragm pump is to take the pipe of the crankcase were the pump gets it's compression and depression and suck and put your tongue over the pipe. if stays there pump ok if not diaphragms are shot. Make sure all fuel is drain from carb before doing this

Cheers will give that a go!

[Nos4r2]

Also, if you're using a separate tank lift the fuel tank above the motor so it gravity feeds. If it's got a damaged fuel diaphragm it'll run like that, but stall after a while if you put the tank back down.