Mariner 4hp 2 stoke

[mercuk]

I have got this mariner 4hp (same as yam 4hp) 2 stroke from the 1980's and its driving me MAD!!

It starts, stop and idles just fine. The problem is that sometimes when I put it into gear and accelerate it just bogs down BUT it only does this half the time. Thats the wierd thing...

Its does NOT stall when I shift from neutral to F/R. I have got the air/fuel screw pretty close I think.

Sometimes it will accelerate o.k and other times it just bogs down and shuts off. I'm thinking weak fuel pump but before I go and spend money on these (REALLY) expensive little diaphrams, has anyone got any decent suggestions?! Am I missing something here?! I know 100% is a fueling issue, and have cleaned carb several times over.......Revs freely in neutral...

Thanks for any replies....

 

[Maxz695]

Re: Mariner 4hp 2 stoke

I would first try to back out the air mixture screw a bit more and see if it improves. It may be the fuel pmp but try this as well as do it when its in the water. back it out throttle up. Keep doing this until you get a nice clean thrust when hitting the gas. Also from the explanation it sounds as if the float level is too low and not having enough fuel or an air leak in the lines as well as fuel filter clogged up. even a bad primer bulb, Just a few things to look at.

 

[Faztbullet]

Re: Mariner 4hp 2 stoke

Are you running it off the onboard tank in cowling or a remote tank? The onboard is gravity fed to carb/pump. Replace the diaphrams on side of carb as these will stretch with time and the new fuels and result in low fuel pressure. A remote tank would complicate the problem as pump would not have enough suction at low rpm to fill carb bowl resulting in a lean mixture symptom.

 

[mercuk]

Re: Mariner 4hp 2 stoke

Thank you very much for your time and coments Faztbuller and Max.
To to clear up the details, it is running from the internal fuel tank, not a seperate one.
The fuel pump diaphrams are stupidly expensive for the here in uk. as in ?18 each (need two of them) and about ?10 for the fuel pump gasket (need two of them as well). So into USD it works out at roughly 55$ (diaphrams) PLUS 30$ for the gaskets.

Total for 2 new diaphrams and 2 gaskets required for fuel pump over haul= $85!!! Last time I get a Yamaha based engine. Fiddly, weak, expensive Jap crap.
I'll stick to Kiekhaefer's thanks. Even if they are a bit heavier and burn a bt more fuel. At least they are strong and well built.


Gona fix it up and get rid when the spring/summer comes!

 

[oldman570]

Re: Mariner 4hp 2 stoke

I belive that if you do alittle reserch of the newer Merc motors , you will find that over the last several years, the smaller motors and some of the larger ones are made by , or on the same parts as the Jap motors. Yahama and others have been selling thier motors for less than what Merc and OMC was haveing to sell there's for because of the import tax was less than the tav for motors made in the states. The OMC and Merc companies won a court battle several years ago over it and the Johnson/Evinrude company was bought out by BRP shortly afterward. If I remmber correctly this al happened in the late 1980's or early 90's. To get a motor that was completly in the states you would need to get one of the older motors. JMO
Oldman570

 

[mercuk]

Re: Mariner 4hp 2 stoke

Oldman570, Thats quite interesting to know. I do realise that a lot of newer engines are all a mix n match of various japanesse builds and fear not, I have several old Kiekhaefer engines at my disposal. ......One of which I believe is the only one in the country.... Must post some pics up at some point....I digress....

So am I right to believe that it could be the fuel pump at fault here??!!! I have already tried backing out the mixture screw but it still seems to be somewhat tempermental......
Sometimes it will accelerate nice and sometimes it will just bog down and die......
What made me believe it was the fuel pump was that inside these fiddly jap &**$ pumps is a small spring and plate..... Now I took these two compontents out to allow more travel of the diagram and it did undoubtedly help the situation....

I'm still convienced there simply isn't enough fuel in the carb bowl to accelerate underload..... In neutral, not a problem, but i figgured there is less fuel demand when in neutral to rev up than when under load.... Am I right to think this??!!!

Is the fuel pump getting tired or is it me??!!!

 

[Faztbullet]

Re: Mariner 4hp 2 stoke

i figgured there is less fuel demand when in neutral to rev up than when under load.... Am I right to think this??!!!

Is the fuel pump getting tired or is it me??!!!

yes on both counts....

 

[tazrig]

Re: Mariner 4hp 2 stoke

yes on both counts....

^^^+1