Ex RNLI Yamaha 75 CETO question

[Smiffyzz]

Hi, firstly thanls for letting me join.
I have a Yamaha 75 CETO (ex rnli) /692/L/1028046/J
I was told to run it on 50:1 but it runs like a pig, plugs have the correct gap all leads in good condition etc), difficult to tickover and start. So i visited our local (port patrick) RNLI Station and spoke to the Mechanic who said to run it on 100:1 as thats what they run theres on. Not that I dont trust his expertise, i decided to try 75:1 first and it's definately better so I'm thinking of going to 100:1 on my first trip out this year (in a couple of weeks).
Any opinions on this mix please?
Also there are no gauges fitted and i'd like at least a Tacho, does anyone know where i could get one?
Thanks

 

[boscoe99]

There are a number of Yams designed to run on 100/1 premix and have no less of a life than those designed to run on 50/1, or on auto-lube which in some cases has a ratio of 200/1.

Where in the world are you? I have no idea what RNLI means.

 

[boscoe99]

 

[racerone]

Other than picking on the oil mix ratio has any real trouble shooting been done ?----How did it run last season ?----Compression test results are ?---Good spark on all cylinders ?

 

[FishMan001]

Other than picking on the oil mix ratio has any real trouble shooting been done ?----How did it run last season ?----Compression test results are ?---Good spark on all cylinders ?

Agreed ! Changing from 50:1 to 100:1 will not make it run better. Other issues are afoot !

 

[Sea Rider]

After checking cylinder compression numbers and if all plugs fires strong will add that the motor probably has the wrong prop factory delivered with for your particular boating purposes. ? What's the wot rpm revving numbers at full throttle as usually loaded ? RNLI is a Brit Rescue Service...

Happy Boating
​

 

[boscoe99]

If 75/1 works better than 50/1 one could presume that the Yamaha recommended 100/1 gas/oil ratio might be better. Cost little to nothing to give it a go.

 

[boscoe99]

It is a stretch, but what with some carburetors having miniscule orifices and passageways perhaps the slightly higher viscosity gas/oil mix might be hindering the flow of fuel to the motor.

 

[QBhoy]

Hi. The oil mix won’t have too much affect on the running of the engine. Unless your plugs are toast. I’d be running this at 50-1 for sure. Although Yamaha did used to say 100-1 on some of their engines.
I think the rnli would be using the smaller 50hp engines on their small inshore boats perhaps.
Anyway. I’d be looking at the carbs first off and doing a compression test. Not much to go wrong with these engines usually

 

[Sea Rider]

Hi, firstly thanls for letting me join.
I have a Yamaha 75 CETO (ex rnli) /692/L/1028046/J there are no gauges fitted and i'd like at least a Tacho, does anyone know where i could get one?

Would recommend this nice and cheap induction tach : https://www.hardlineproducts.com/product/hourtach-meter-up-to-8-cylinders/ Can install it on the lower motor's front pan. Check Iboats, Amazon for them. Excellent to known current wot rpm achieved with current prop as loaded, going for prop maximizations and true run hours for spot on preventive or corrective maintenances.

Happy Boating​

 

[Smiffyzz]

Hi. The oil mix won’t have too much affect on the running of the engine. Unless your plugs are toast. I’d be running this at 50-1 for sure. Although Yamaha did used to say 100-1 on some of their engines.
I think the rnli would be using the smaller 50hp engines on their small inshore boats perhaps.
Anyway. I’d be looking at the carbs first off and doing a compression test. Not much to go wrong with these engines usually

I don't know how the oil mix wouldn't have any effect on the running of the engine, surely an over oiled mix would affect the running. When I used 50:1 it ran really poor and wouldn't tick over properly with out stalling, as well as poor starting (new plugs), changing to 100:1 for a season it runs and ticks over perfectly. RNLI is Royal National Lifeboat Institution. I spoke with our local RNLI duty mechanic and he said 100:1 is what they use on their Yamaha Enduro 2 strokes.