1999 250 ox66 surging

[amofgreenville]

I have a new to me 1999 Yamaha 250 ox66. Had maintenance done when I purchased in March and it ran perfectly the first three times that I had it out. The third time on the way home it ran fine until got back to the slip and was slowing down..Engine would cut out in neutral and when I put in forward or reverse (rpms dropping down below 4oo and cut out). I took it to local mechanic and was told that it needed a new CDI. I was skeptical so I ordered a used CDI on eBay and had it installed. It didn't solve the problem. Brought it home and cleaned/tested o2 sensor, cleaned VST and replaced filter, replaced all fuel filters, replaced LP fuel pumps. Started and it was still doing the same thing. I installed new plugs and it ran perfectly. I did however notice the new plugs that I removed were black on the very tips of them, they were new when I bought the boat so they only had 3 short trips on them.. What would make the plugs foul up like that, is it getting too much oil??

[jb123]

Can i also sell you a cdi ?
I would suggest you never use the person that suggested that again.
You need to clean and test fuel system
Test lp pumps also.
Ohm test plug caps

[amofgreenville]

RODBOLT....Still having problems with this engine. I've changed the VST filter and cleaned the bowl, changed all fuel filters, new LP pumps and new plugs, cleaned the o2 sensor (there was no carbon build up at all). Engine started right but hesitated to get up on plane, hardly any throttle response so I backed off and started up again..This time it took off and ran fine, just wouldn't get above 4800 rpms. Going back to slip in no wake zone and it would still surge a little bit. Checked plugs and they're starting to get fouled again...What's next