Hi guys, I've been reluctant to ask for advice on this since it has been answered over a dozen or more times on this site and also on the Yamaha Outboard site but I've tried it all and have decided that I need your help before I take it to a mechanic. Here's the problem, last year motor ran fine, would get up on a plane and run at about 4300-4500rpm wot. I knew that it wasn't the optimal operating range and that over the winter I would probably have to purchase a different prop to get the motor to work within spec, I still haven't bought one. After pulling it out of storage for the winter I took her out for it's maiden voyage to see how she was running when I found that it didn't want to run WoT. I could get her up on a plane and run at 3/4 throttle up to about 3300rpm before she would start to surge. To the forums I go to see what my problem might be. Two months of troubleshooting and testing later I still have the same problem, here is what has been done.
Round 1
Old fuel drained from tank and tank cleaned out.
Fuel/water separator installed
Fuel lines between tank and primer bulb replaced.
Fuel filter (the only 1) cleaned, didn't replace because it was screen type and easily cleaned
Disassembled fuel pump and inspected diaphragm, looked ok
Lake tested and problem persisted, bad fuel eliminated
Round 2
Removed Carbs and cleaned them, found bottom carb had significant oil residue in one of the float chambers. Soaked in carb cleaner and thoroughly cleaned with pipe cleaners, air and cotton swabs. replaced o-rings on jets in float chambers. Reassembled carbs and reinstalled on motor, did link and sync. Ran motor on muffs to test and noticed significantly less smoking and motor idled smoother. Lake tested still surging at WoT but able to reach 3600rpm before surging.
Round 3
Replaced fuel pump, also replaced gasket between pump and powerhead
Replaced spark plugs and gapped them even though old ones showed no signs of significant wear or problems.
Lake test and problem still persists, able to get to approx 3600rpm before surging.
On all of the tests I can go from idle to WoT and she will run fine until I get on a plane then start to surge. It takes approx 20-30 sec after getting on a plane before it starts but after I'm on a plane I can't go above 3600rpm without it surging.
Items I still need to check, fuel pressure, spark, compression (these I need to buy/borrow the tools to check). Are there any other tests I can do before taking this to a mechanic? Something obvious I may have overlooked?
Round 1
Old fuel drained from tank and tank cleaned out.
Fuel/water separator installed
Fuel lines between tank and primer bulb replaced.
Fuel filter (the only 1) cleaned, didn't replace because it was screen type and easily cleaned
Disassembled fuel pump and inspected diaphragm, looked ok
Lake tested and problem persisted, bad fuel eliminated
Round 2
Removed Carbs and cleaned them, found bottom carb had significant oil residue in one of the float chambers. Soaked in carb cleaner and thoroughly cleaned with pipe cleaners, air and cotton swabs. replaced o-rings on jets in float chambers. Reassembled carbs and reinstalled on motor, did link and sync. Ran motor on muffs to test and noticed significantly less smoking and motor idled smoother. Lake tested still surging at WoT but able to reach 3600rpm before surging.
Round 3
Replaced fuel pump, also replaced gasket between pump and powerhead
Replaced spark plugs and gapped them even though old ones showed no signs of significant wear or problems.
Lake test and problem still persists, able to get to approx 3600rpm before surging.
On all of the tests I can go from idle to WoT and she will run fine until I get on a plane then start to surge. It takes approx 20-30 sec after getting on a plane before it starts but after I'm on a plane I can't go above 3600rpm without it surging.
Items I still need to check, fuel pressure, spark, compression (these I need to buy/borrow the tools to check). Are there any other tests I can do before taking this to a mechanic? Something obvious I may have overlooked?
