oldandtired

I have a 2000 model yamaha c60tlry. the engine runs fine at idle has a good
smooth run up to about 4200 rpm after a few seconds the engine loads up then runs rough at around 3100 with no change in throttle position. Putting
the throttle in neutral for a few seconds (maybe 10) the situation repeats. Good run up to around 4200 then bogs down to about 3100. I thought it might be water in the fuel so changed the fuel/water filter, checked and emptied the internal filter and same results. Have had some issues with
fouled plugs so even changed them with same results. Any ideas

[robert graham]

Motor may be running very rich from bad fuel pump causing gas to be sucked into motor. Check your plugs to see if they're wet with fuel. A new fuel pump is a relatively cheap($45) and very easy fix. Good Luck!

oldandtired

a friend and excellent mechanic took my boat today to the local lake.
he replace my water/fuel seperator filter, dumped the gas in the tank and
replaced the after market plugs I bought with oem ngk plugs.

He gave me several very important pieces of advise.

#1 Premium fuel burns slower than 87 octane fuel.

#2 if you are having plug fouling problems it's could be you are

using low octane gas. If you are using the cheap stuff (i was) it burns

too quickly and doesn't allow the oil time to burn!!! resulting in (wet)

fouled plugs.

#3 idleing causes to mixture to be on the rich side. keep warm up times

and long idles to a minimum.

Hope this helps others with the same type issues.

Robert, thanks for you time and help.

[robert graham]

Clean, fresh, stabilized 87 octane fuel will work fine if everything else on the motor is as it should be. And idling shouldn't cause fowling of plugs either, again if your motor is "right". I believe that you still may have a problem with your fuel delivery system, possibly your fuel pump. Keep us posted on your results and good luck!