Its really 50:1 ratio my Mercury 140HP 1979? dont looks like...

[mrangelo]

Something weird here. I been running in to a problem since got the boat (Crestliner Apollo with mercury 140hp 1970) that if i put it on neutral the RPM drop very low and goes off. To turn it on i need to disengage the transmission and push foward to give him gas and crank it for maybe 30 seconds. Today i was installing a new gas tank and I put on it exactly 10 gallons of 50:1 and 5 gallons of just gas expecting to add the oil later. I Forgot the oil and cranked the motor and like always took some time to turn on. Around 5 minutes later I started putting it on neutral and guess what, never goes off. Then i turned off and now is turning on with just a touch in the key. Apparently and looks like dont have those 5 gals of 50:1 fixed the problem. Can be possible that maybe 25:1 or something like that is better for him? Im going to the lake tomorrow and im not sure to add the oil for those 5 gallons of just running it like that.

Any help is appreciated.

 

[JoshOnt]

Have you looked up the correct ratio for your motor? That would be a good place to start. I would say it would be best to get a copy of the manual for your motor. Got one for mine and it was well worth the money.

 

[mrangelo]

Have you looked up the correct ratio for your motor? That would be a good place to start. I would say it would be best to get a copy of the manual for your motor. Got one for mine and it was well worth the money.

thank you, i found one that is general for all of those motors, uffff is thousands of pages, lets start reading haha

 

[roscoe]

You are not running 25:1, you are now at 75:1.

You need 50:1

2.6 ounces of oil per gallon of gas.

13 ounces for 5 gallons

16 ounces for 6 gallons.

 

[racerone]

Many folks are confused by the concept of mixing oil with the gas.----------The motor will " run " on straight gas but not for long.----------The motor will run on 16:1 as well.------It will smoke a lot on that mix and will take forever to wear it out.------The mix of 50: has been chosen by the manufacturers to give good running characteristics.------And an acceptable number of running hrs for the motor.

 

[Dekker500]

The idle running characteristics can be changed by adjusting the carb's idle adjustment... which can require adjusting due to different fuel octane or oil mix. Look up the manual to see how this is done for your engine, and it may be a quick fix.

 

[emckelvy]

Sounds like you're just marginally lean on the idle mixture. You may just be able to richen-up the mixture a bit and be ok. Turn each carb's idle mixture adjusting screw approx 1/8 turn CCW. If you find it runs better, you're going in the right direction.

Warm the engine up in the water, try and accelerate and if it doesn't bog, you're close enough. If it does bog, turn each screw another 1/8 turn rich (CCW) and see if that helps.

With no accelerator pump, you have to run the mixture richer than what will give the smoothest idle. So your idle might be a bit "lumpy" but as long as it doesn't die when you put it in gear, and you have good acceleration out of the hole, that's about as good as it gets.

HTH.............ed

 

[Chris1956]

50::1 is the gas/oil mixture for full throttle running. Motors require the most oil at high speed. Running at less than 50::1 will cause motor damage, if you run at full throttle. You can probably (probably) run at 100::1 if you do not exceed idle speed.

Your motor is a good one. I am not sure why you would want to ruin it.

 

[Mi duckdown]

What Chris posted.

 

[Msking]

Hello,

I know its been a while on this subject but I was having problems with my engine throttling down on full throttle. I took it in to a shop and the shop owner said this is a high dome three ring piston. He explained what was happening was blow by which might be caused by my 50:1 fuel mixture. He went on to explain how merc was one of the last to convert to 50:1. He said the mixture should be 16:1 and this should stop the blow by on the pistons causing the throttling down. Any thoughts?

 

[emckelvy]

I think you better find another mechanic. This is not a racing motor and it doesn't require 16:1 mix. He's really off on his boating history, Merc was one of the pioneers of 50:1 mix and they brought out their own branded outboard oil to back it up.

Your motor is certified at the factory to run with a mix of 50:1 outboard oil, regardless of what the ill-informed shop owner says.

Besides, the "high domes" on the pistons have absolutely nothing to do with any so-called "blowby". He may be theoretically correct that more oil might seal the piston rings a bit better, but that's besides the point and is irrelevant to the running symptoms you've described. This is something that racers do and the optimum mix for hi-performance engines is different than what your engine will run on.

Consider this, you accidentally caused your fuel-oil mix to be approx 75:1 which is Leaner than 50:1 and your motor ran better. Your experience is exactly opposite of what that shop owner was telling you! :facepalm:

Back to fixing your motor, make sure you run on 50:1 fuel-oil mix and richen-up on your idle mixture on all (3) carbs and I expect she'll purr like a big, angry, Tower of Power kitten! Cheers.........ed

 

[racerone]

There are many shop owners who will tell those " tall tales "-------Take big steps in rapid succession away from that shop !!!