yamaha 40 hp problems?

[andrewpegs]

hi i have just bought my first boat and am already getting problems,engine runs for about 20 mins then cuts out,,after few more pulls she will start again ,same happens over and over,,is there suppost to be constant water squirting out of pee hole?think it is around 87 model,,any help well appreciated,thanks

 

[Tremlett 15]

hi i have just bought my first boat and am already getting problems,engine runs for about 20 mins then cuts out,,after few more pulls she will start again ,same happens over and over,,is there suppost to be constant water squirting out of pee hole?think it is around 87 model,,any help well appreciated,thanks

Has any water come out of the "tell tail" ( pee hole ) ? If not it could be the impeller, the thing that pumps the water up to cool the engine!!!

 

[Hurricane]

I assume that its a two stroke.

I had a Yamaha powered Avon JetRib which had the exact same symptoms.

I had the head taken off and it revealed scored cylinder bores which I was told had been caused by the oil mechanism failing.

The solution was to rebore it and remove the oil feed system - we then mixed the two stroke oil with the fuel ech time we filled it.

It ran fine after that.

I was told that the Yamaha oil system on the "WaveRunner" Jet was prone to this kind of failure.

 

[Cliveshep]

To be honest it sounds like fuel starvation. The cause could be a failing fuel pump but as you say it stops after 20 mins another likely candidate is your tank hose, connections and primer bulb. The two plug-in connections to engine and tank don't last for ever and can wear allowing the pump to suck in air instead of petrol. As a guide, when you run it 'till it stops do you have to prime it again with the bulb before it restarts? If so, there is your "probable cause". The other culprits are sticking float or float chamber valve in the carburettor so as it's an older engine I'd whip off the carb and thoroughly clean it, using an air-line to blow it through, your lungs are not up to this kind of blowing, and try it again having ensured that you first replace the fuel float chamber inlet valve as the rubber seating on the needle also wears leading to sticking in the closed position. The bits are cheap so you've little to lose by changing them and eliminating simple and likely causes.

Water coming out of the tell-tale is the only way to be sure the pump works. The impellor is located above the gearbox around the main drive shaft in the lower leg, the parts list exploded drawings will show you how to get at it but basically disconnect the gear rod at the front of the leg, undo the 4 bolts and the lower unit should pull off to reveal the shaft coming out of the lower unit and the pump cover housing. If you change the impellor also change the (two) oil seals below the pump. You can just dig these out with a small screwdriver.

VicS can almost certainly tell you where you can download a parts list with line drawings if you're stuck.

 

[VicS]

20 minutes is a good length of time to run. I'd be thinking that if it ran well for that length of time it would continue to do so.

I think that may rule out a number of Cliveshep's suggestions.

I dont think I've seen tank venting mentioned. It might just run for 20 minutes if the tank was not venting and then pack up. Should be apparent from a tendency for the priming bulb to be sucked down though and taking the tank cap off would solve the problem instantly.

You should get a good stream steady of water from the telltale but the first thing to check is that is not blocked. If there truly is lack of cooling water flow them your problems may be caused by overheating. Pump impeller should be changed if its not been done recently (some even recommend annually).

Exploded diagrams are HERE but strictly apply to engines imported into the USA only. They can be helpful but are no substitute for a manual.

You'll need to know the year which can be confirmed from the "year letter" on the name plate . Check it HERE

Recommended read with a motor that is new to you as many of the points covered could apply HERE