Old 70 Precision Blend Fuel Mix Problems

[jesfromasc]

Just moved to lakeside home and bought an old High Tide boat.

It has an old Yamaha 70 Precision Blend.

Serial: 481591
Model: 70TLRR

The oil injection was disabled and the oil is now oil/gas mix in the fuel tank.

I'm getting conflicting information on the right mix.

50:1 fouled the plugs in a matter of seconds

100:1 much better but I'm still getting some plug fouling after she has been sitting.

Once she has fresh or clean plugs and is up and running she runs fantastic!

Anything I can learn about these engines would be great.

I'd really like to keep it going for a few years before buying a new one.

Thanks,
John

 

[flyingscott]

How old is the gas? Is the choke/primer sticking/leaking? When was the last time the carbs were serviced? What is the compression? That motor should run perfect on 50-1 mix. IMHO People who disable that oil injection are people who shouldn't own motors.

 

[mjf55]

As flyingscott said, 50-1 should be great. After you get the plug fouling fixed, perhaps we can figure out what is wrong with the precision blend, and maybe even fix it.

Since the boat / motor is new to you, can you get the answers from the previous owner? If not, we will have to start at the beginning and assume its been a long time since the cleaning.

So I would suggest, making sure the compression is good. Beg, borrow or buy ( no stealing ;-) ) a compression tester. something like an Innova 3612 is only 18 dollars at Amazon. I have it and it works fine. Search these forums on how to do the test and record the results for each cylinder. It is a good thing to know.
Report back with the compression numbers.

If the gas is old, try a small standalone tank with a few gallons of fresh gas with the 50-1 oil mix.. See if that fouls the plugs.

After that, I think we will need to make sure the carb is clean.

And, last but not least, :welcome: to iBoats.

 

[jesfromasc]

Will do that, this is a winter long project so I'll be back.

FWIW fuel is new, (ethanol free) oil for mix new, and even the fuel line and tank.

Thanks

 

[robert graham]

Be sure Red Primestart lever(if equipped) is in normal/auto position....not off and not on.....

 

[ondarvr]

The 50:1 mix should not cause plug fouling, and if you have plug fouling with 100:1 after it sits for a while it means there are problems other than the pre-mix ratio. Sitting for a while should have zero affect on plug fouling.

 

[99yam40]

post up pictures of the plugs so we can see what kind of fouling is happening

I have heard very small amounts of water getting into cylinders can cause plugs to crud up

 

[jesfromasc]

Finally got to do compression check:

Cylinders from top to bottom w/3 checks per cylinder.

1: 95, 95, 95
2: 95, 90, 100
3: 90, 90, 90

I'm thinking good not super fantastic but... maybe a carb rebuild would do the trick?

Again, just trying to get a good 2017 out of this engine before buying an upgrade at the end of the 2017 season or early 2018.

I'll try to shoot a good picture of the plugs but need to get the boat on the water and running for a bit to do that.

And FWIW how hard is a rebuild on these engines?

Thanks

 

[boscoe99]

The precision blend system varies the oil ratio from about 200/1 at idle to about 50/1 at wide open throttle. If the motor is run at or near WOT then the plugs should not be fouling. If the motor is used at idle, or near idle, RPM a lot I can see the plugs fouling more so than they otherwise would. Maybe try some Pennzoil semi or 100% synthetic oil. Particularly if you are presently using Yamalube.

You might also want to check the idle mixture setting for each of the carbs. Whoever did not know what he was doing when the precision blend system was removed might have also incorrectly set the idle mixture screws. Or God knows what else on the motor.

 

[jesfromasc]

Interesting idea!
So maybe an idle tank with 200:1 and a run tank at 50:1.
That would be pretty easy to set up.

 

[99yam40]

there are lots of RPM speeds between those two RPMS

 

[boscoe99]

Interesting idea!
So maybe an idle tank with 200:1 and a run tank at 50:1.
That would be pretty easy to set up.

As 99Yam notes, there are many RPM's between idle and WOT. How would you adjust the oil supply for all of those?

Who has the time to be paying attention to the engine RPM (and load) and making an infinite number of adjustments to the oil supply system? Let the Yamaha system do it all automatically for you. Now in your case someone screwed the pooch when they removed the auto oiling system. More than likely it won't be cost effective for you to put the motor back in its original configuration.

If the motor were mine I would first try a different brand of oil to see if that solves the plug fouling problem. This assumes the motor is otherwise in good mechanical and electrical condition. You could then try tweaking the fuel/oil ratio a tad if needed to make it just a bit better.

 

[99yam40]

as I wrote way back at the 1st of this thread, post some pictures of the fouled plugs.

there is a good chance that you might be getting some water in the cylinders and fouling up the plugs if it happens that fast

 

[jesfromasc]

Thanks!
I'll keep you posted on progress.

It does have a water separation filter setup I could take a closer look at it.

Any thoughts on the compression numbers?

 

[99yam40]

very strange how the #2 kept changing.

is it all of the plugs that get fouled up?

water I was talking about may not be restricted to just in the fuel

 

[jesfromasc]

OK

Just stopped by the mechanic and, are you ready?

The oil injection system was NOT disabled so by using a mix gas I was basically running 2X the oil necessary.

Add to that the oil tank on the engine was almost empty, so it was partially shutting down and protecting itself from damage.

He says, "Can't really disable the system on this make and model - some others yes, but not this one."

Why the place I bought the boat thought it was is beyond me but great news as far as I'm concerned.

His compression check had all cylinders over 100 so I'm good to go!

Woo-Hoo