1992 pro50 outboard performance tuning help

[gbftats7]

i bought a boat with a 92' yamaha pro 50 outboard. Im having some trouble diagnosing the problems, because the motor has been modified a bit.

first problem is when it idles cold or warm it has what sounds like a miss that kills the engine. It will run for about 30 seconds perfectly smooth then hits a dead spot and dies. I set the CDI box to factory specs, and it didnt help.

The motor has good compression, and good spark. The head is slightly milled but I dont know if that would affect anything.

The second problem is it sounds like it is flooding out when I roll the throttle through slowly. If I go straight to full throttle it gets up and moves!

He told me the carbs are over sized which Im guessing could be part of the problem.

The last and final thing is, at top speed the engine almost sounds like it is gargling and losing a tiny bit of power.

im running 160 main jets and my plugs look bronze like they should. Ive tried tuning the fuel/air mixture screw to manuels spec, but they aren't stock so im not really sure where to go from here.

any ideas on solving some of these issues would be greatly appreciated.

[99yam40]

sound like a lean sneeze.
find out who he got oversized carbs from and see if they can give some idea how to set them.
sure will not be in Yamaha service manual

you can go back to stock maybe

[TownsendsFJR1300]

+ 1 ^^^^.

With larger carbs comes re-jetting. Sounds like on the top end, the spark plugs are showing a good sized main jet. Everywhere below the higher RPM's are off.. Often, with too large a carb, comes the loss of low end performance.

**Also, how did you "re-set" the ECU???

I agree with yam99, the engine would be best off with the stock carbs and jetted as Yamaha designed it.

I would probably look for a used set of carbs for YOUR engine. It'd be cheaper than buying numerous jets and less time consuming for unknown results...

[gbftats7]

The CDI box has an external arm that can be set to marks on the outside of the box.

I had 170's in it and plugs looked rich, the 160's have given me the best results so far, is there anyway I can work out the low end kinks without going back to stock carbs? I agree it would probably be the best option, however if possible id like to work with what I have.

+ 1 ^^^^.

With larger carbs comes re-jetting. Sounds like on the top end, the spark plugs are showing a good sized main jet. Everywhere below the higher RPM's are off.. Often, with too large a carb, comes the loss of low end performance.

**Also, how did you "re-set" the ECU???

I agree with yam99, the engine would be best off with the stock carbs and jetted as Yamaha designed it.

I would probably look for a used set of carbs for YOUR engine. It'd be cheaper than buying numerous jets and less time consuming for unknown results...

[TownsendsFJR1300]

Carb tuning can be done and likely better performance but will take patience and a bunch of testing.

As the top end seems good, try running the engine steady in the RPM range where its the worst. Kill the engine immediately (drop anchor and let it cool down), don't let it idle down (we want a picture of how their burning for that time period).

Pull the plugs and see if their rich or lean. Once back home, you'll now need either a richer or leaner jets for say the mid range if that's where your issue is. Start swapping jets and re-peat...

Of course, make sure your timing is correct, sync and link dead on, etc. Anything else out of spec will have you chasing your tail....