1993 150 Johnson 60* Fuel balance issue

[James R]

I have rebuilt this motor, bores, pistons, seals, gaskets etc.
The port side cylinders were badly scored and the stbd side showed signs of wear. All six have been bored. Comps 100-105.
Could not figure why the port side was so bad and not the stbd. Assumed possible lean mix due to manifold or carb seal leaks. The carb bolts on that side were not very tight.
Now we are breaking in and once again,rebuilt the same type motor last year, plugs oil up when using the extra oil. Backed off on the oil and got her running.
Not firing on all cylinders so checked the plugs. The Stbd side is getting plenty of fuel but the port side seems to be lean. Strong firing on the Stbd but feeble firing on the port.
All sparks are good. No sign of overheating on either side. No low fuel warning from the VRO and we are using about 40:1 not the VRO oiling.
Before I go tearing into the carbs etc can anyone throw some light on this.
Any input will be appreciated.

[Chris1956]

Sure, Tear down, clean and rebuild all carbs. The port side are likely clogged enough to cause damage due to lean mixture. The starboard side are likely not far behind.

Perform Link and synch and clean all filters.
BTW - double oil should not be an issue. The motor should run fine. That may be a clue to other issues.

[James R]

Thanks for the response Chris.
Not quite that simple. When I tear a motor down everything is done. Carbs go through a soak in Gunk carb and parts cleaner, rinsed and blown clean then they go in my Ultra Sonic tank for thirty minutes and again rinsed and blown clean and new kits fitted. If there is anything left its only my blood sweat and tears.
The First motor of this type that I rebuilt also hated extra oil at 32:1. Thinned the mix and she ran fine. Now she is on 50:1 and purrs on my 16FT Cobia.
This second one has, I think,the same issue with extra oil.
The plugs tell me that the port side is getting a leaner mix than the STBD.
No doubt about it. All three carbs for each side would not do the same for their individual side.
I see no leaks.
I will wait to see if anyone else has a thought.
Thanks again, your response is appreciated.

[Dhadley]

What spark plugs are you using? When the carbs were cleaned were new needle & seats installed?

[James R]

The needles and seats were replaced but I will take the carbs down again to check for any faults in that area. The plugs are new QL77JC4 the same as the previous motor.
Will let you know what I find.
Thanks guys.

[seahorse5]

Try using the factory recommended QL78YC plugs gapped to 0.030"

[James R]

Thanks for the response Seahorses5.
The manual I have calls for the QL77JC4 plugs.
The first motor has no problem with them.
Can't see how the plugs would run differently on the port side to the STBD side.
All indications are that it is a fuel supply issue but i still can't think why one side would run differently to the other. Will be taking the carbs down again.

[jonesg]

The one thing all 3 port carbs have is the fuel feed line that goes to the distribution tube that feeds all carbs on that side.
A peice of junk in that hose will starve all 3 carbs on that side.

Seems more of a common denominator than you rebuilt all 3 on that side wrong.

[seahorse5]

The manual I have calls for the QL77JC4 plugs.
.

A manual, even a factory service manual, is usually out of date shortly after they are published. That is why there are service bulletins printed if needed for upgrades, product changes, and new procedures.

Always refer to a recent factory sparkplug chart. I'm sure you are reading out of a 17 year old book for the plug chart. The plug suggestion was changed in 1996.

How would you feel if your doctor practiced medicine the same way and only prescribed medicines that were only available in 1993?

By the way, does your engine have the black colored intake manifold gaskets? If so, change them out ASAP

[James R]

Jonesq and Seahorse5 your points are well taken and thank you both for taking so much interest in this project. I will take take the carbs and fuel rails down tomorrow and order the latest plugs as recommended. The manifold seals are not the old black ones.
Great info guys.
Thanks.

[James R]

In the original rebuild the carbs were cleaned using my two methods, soaking, flushing and blowing out followed by 30 minutes in my ultrasonic tank, rinsing and blowing out. This technique has never failed me. However I was not certain that all the needles and valves had been replaced. Removed the carbs again and replaced all the needles and valves and the seals including the carb mount seals. The motor idles perfectly but coming up on RPM she cuts out.
I have started a new thread on this.
Thanks a bunch for the advice on replacing the needles.