# Yamaha outboard problem



## odielite

So I have a 70 hp Yamaha 2 stroke outboard that is running rough.  I've rebuilt the carbs replaced the sparkplugs and it seems to still run rough.  I disconnected each splug plug wire while it's running and the bottom cylinder doesn't make much difference, the middle cylinder some and the top cylinder will cause the engine to die. Is that normal for the cylinders to be unbalanced like that I haven't tested the compression yet and I'm trying to avoid taking it to the mechanic.  I used to fix helicopters so I should be able to tackle an outboard.


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## Bilge Rat LT 20

You may need to preform a link and sync on the carbs.
This gets them to supply fuel equally. It is in the service manual.

The carbs  can be hard to get clean in all the passages.
What was the reason you cleaned the carbs?

Do you run E gas, it eats the rubber parts and corrodes metal. In the future use non E gas.

Have you replaced the fuel pumps?
How do the plugs look?


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## rdnckrbby

Ethanol, fuel pump/ filters, is it running rough at idle or when you put some juice to it?


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## odielite

Rebuilt the carbs in dec ran fine. Went fishing a week ago and wouldn't get on plane. New fuel filter. Plugs are a little wet.  I do run e gas but put stabil in.  Runs some what rough at idle but not terrible


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## Raylander

Just an idea- maybe the fuel line from tank to engine. I know that the e gas can do a number on them as well. However i am no mechanic


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## whitetailaddict

sounds like it could be trash in carb. i have had this happen several times. clean carbs again. flush out lines. install a good fuel filter and stay as far away from e-gas as you possibly can!!!!!


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## odielite

Yeah. Just took it out and it ran awesome then got back to the ramp and it started sputtering so is now leading me to believe its fuel.


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## odielite

Thank you to everyone all tips are appreciate it


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## rdnckrbby

Ethanol is such a problem because it mixes with water unlike normal gas. I've had all kind of issues with my smaller outboards with it so I've switched to 90 octane no ethanol and haven't had any trouble since.


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## odielite

For awhile I was running a lot of gas so it never sat but lately haven't had time to fish as much so the gas tends to sit more.  Gotta buckle down.  Kinda hard to find e free gas in savannah


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## jams97ls

Parker's on Derenne and Enmark on Waters both have ethanol free gas.


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## odielite

I didn't know Parker's did.  I will definately be using parkers


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## seaweaver

Stabil was never made to handle etoh...if I'm not mistaken...it IS an etOH.
I doubt it's a sync problem. 
replace lines. I have a glass fule tank in my Dusky. The etoh eats the resin and ends up in the engine. I now run temp lines to temp plastic tanks until I dig up the deck and add a new 80 gallon tank.
pull it out to the sun yesterday....1year old temp. grade A fuel line is trashed.
etoh chemistry changes widely w/ the amount of water present. Plastics and rubber hoses are mad for a narrow chemistry range....thus at any point what is sitting in the tank or line can exceed the spec of the system and cause break down.
replace the lines, clean the carbs again...and Curse Iowa for being the first in presidential caucuses.
(the phosphates that precip. out of etoh can plug the micro jet porting on the SIDES of some main jets. alot of folk who have these over look them(Honda)they can be cleaned w/ a single wire bristle. They do not come clean w/ air and cleaner. AND check fuel pump for collected PO4s that migrate to the carbs/jets)

cw


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## seaweaver

Just fired my engine up...but has to clean the Check valve between the secondary filter and fuel pumps. Phosphate (Po4)had it jammed closed. here it is w/ the PO4 that no chem tool would take off. Had to be abraded (remember your jets) 
Got to thinking about your set up...If you have an obstruction allowing only partial fuel flow it will go to the lower carb first then attempt to fill the uppers.
pull the drains on the middle and upper bowls and work the hand bulb to see if gas is getting to both. It should be easy. Then spin the starter to see if fuel is getting to those carbs via the fuel pump.
if not check everything inbetween. I do not recall if the Yam 70 has the same check as I have .(ox66 150) if it does have a check valve it could be partially blocked.


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## odielite

Tomorrow I'm gonna look for water in the external fuel filter.  Is it possible to take the fuel pump apart without tearing it up.  So. Pull the drains on the carb bowls to see if fuel is getting to it. All three or just top and middle.  If there is a clog the bottom won't fill as quick?


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## fishingmaddog

Do a Compression test, if compression is low on one cylinder this could be the problem, they should all be within 10% of each other.


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## odielite

Bottom cylinder spark plug is wet


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## Bilge Rat LT 20

If compession is good and the carbs are good then wet plugs can be from a fuel pump leaking into crankcase enriching the mix.

The spark is good?
The diaphram in the LP pumps will die from the E gas.

 gas stations on montgomery Xroads have non E as well as others mentioned. The BP station has good clean non E gas, a buddy tested it 6 months ago. 

Recheck your carbs and test/replace the pumps.


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## Bream Pole

*gas*

Regular Stabil won't help with e-gas.  They do have a marine Stabil that advertises that it will.  West Marine recommended to me StarTron which can be bought at walmart usually in the sporting goods section.  I have used it and have had no problems even with e-gas stored over the winter in the rider mower tank.  I also use stabil when storing gas for a long time in addition to the star tron.   Be sure and close the air valve to your tank when you come in and its good to fill it so you keep a filled tank when the boat is idle.  e-gas takes moisture out of the air so the idea is to keep  as little air in the tank as possible when it is not running and to keep the tank sealed from air.  Unless your 70 hp is a very old motor the parts--seals, hoses etc-- should be made to withstand e gas.


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## odielite

Pulled the head after cleaning out the carbs to find water in the bottom cylinder,  everything looked fine so ordered new gaskets and hopefully that'll fix the dead cylinder.


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## wray912

odielite said:


> Pulled the head after cleaning out the carbs to find water in the bottom cylinder,  everything looked fine so ordered new gaskets and hopefully that'll fix the dead cylinder.



sounds like that was the problem...if not it sounds like a fire issue to me...try swaping plug wires between cylinders and coils to check the wire if its still the bottom one only could be a bad coil pack


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