Old yamaha stalls after 3 minutes of idle

[Slowsteps]

I've been trying to repair a 1977 3.5HP 2 stroke aircooled Yamaha outboard for the last month. It worked ok till this year. It starts fine, runs idle smoothly for around 3 minutes and then stalls. I've timed it - it's always around 3 minutes. After that i can start it again but it stalls after ten seconds, then i can't start it anymore. The next morning i can repeat this process.

I've replaced the sparkplug, have new fuel, installed a new filter / waterseparator and opened up the carb (looks clean)

I'm at a loss now. one of the fuel hoses has a plastic wrap, but it's been like that for years and it looks pretty tight.

I'm wondering if it could be an internal engine problem because it might relate to the engine heating up.

 

[Ray Neudecker]

Re: Old yamaha stalls after 3 minutes of idle

More likely to be a fuel restriction in the carb. Confirm by doing a compression and fire test.

 

[bernieb]

Re: Old yamaha stalls after 3 minutes of idle

Nothing like trying a different gas tank ,be sure it's vented at the cap and nothing like running some seafoam to an old engine,you can get it at most auto parts store. If your in salt water the cooling passages can be closing off and if the engine has a thermostat it may be stuck shut.

 

[range_time]

Re: Old yamaha stalls after 3 minutes of idle

I’m going to throw in a few thoughts.
If you can get this to happen at almost the same time, each time, I think its either fule related or temp related. A bad (read cracked fuel line) somewhere in the system may suck air and not gas and so over time it depilates the fuel in the bowl and you get a stall. Or it could be that your heating up your coil or CDI box by that time and just killing the spark. My guess (and that is all it is) is on a fuel problem.

 

[Slowsteps]

Re: Old yamaha stalls after 3 minutes of idle

Thanks for the tips. The engine is in sweet water. Before i can do a compression test i need the manual for the right values (plus the tool). I'm not sure if i'm willing to invest more money into it

I've been looking for an online directory of yamaha outboards but there is very little info on engines from before 1984.

I don't know if the engine has a thermostat. It's pretty minimal, which makes it fun to work on. Is there an easy way to spot this without taking the CDI box apart? There is one loose wire running towards the box but it looks like it's alway been loose.

 

[bossee]

Re: Old yamaha stalls after 3 minutes of idle

Hi,
If You have luck this 1973 Yamaha 3,5 hp Owner's manual may apply to Your 1977 also (I would be surprised if any major difference between a -73 and -77).

http://www.yamahaownershandbook.com.au/lib/download.php?f=624-28199-60.pdf

 

[Slowsteps]

Re: Old yamaha stalls after 3 minutes of idle

thanks for the link

looks very similar. Only big difference is the fuel ratio. On the side of my engine it says 100:1 and this manual speaks of 50:1

 

[deejaycee_2000]

Re: Old yamaha stalls after 3 minutes of idle

It sounds to me like your ventilation cap is not open by your fuel tank ....

 

[Slowsteps]

Re: Old yamaha stalls after 3 minutes of idle

It sounds to me like your ventilation cap is not open by your fuel tank ....

it think it is: i can hear it hiss when i open it.

 

[deejaycee_2000]

Re: Old yamaha stalls after 3 minutes of idle

well there you go .... remember to have it open ... happens to everyone once in a while ....

 

[bossee]

Re: Old yamaha stalls after 3 minutes of idle

Hi,

Gasil ratio are these days usually 50 parts gas and 1 part oil = 2% on 2-stroke outboards.
100:1 will only be 1% oil and you have not much margin then. Better safe then sorry...
On many 2-stroke with oil injection system the gasil ratio is also variable so you could get lest say 150:1 at idle but at full throttle 50:1.


/Bo