Diagnostic help needed

[G8rmac]

Sorry up front for a long post, but I need some help from Bob B or anyone that can diagnose telepathically I have a 2003 PT175 with a 40 HP Merc, ser number OT657750. The motor has been bullet proof over the years, no problems at all, always starts with one or two cranks even after a long winter. Stuck with ethanol, but I have changed out the fuel line and always use Sea Foam.

Had it out about a month ago with no problems. Took it out this week because I was going to use it to get to some hunting areas not accessible by land. The motor started right up and ran fine. Not sure if it relates, but I did get into some shallows at idle speed and churned the bottom pretty good before I could get out. Telltale stream slowed down, but after I ran some weed eater line in, it cleared up and peed like normal.

Next morning went out at Oh-dark 30 to go hunt, air temp about 35-40, water temp at 50. Motor fired right up and idled fine, not even a sputter. I let it idle 5 minutes or so and started across the lake. Didn't plan on full speed because of no moon, but when I tried to speed up, the motor got to about 3000 rpm, and would not push the boat onto plane. Felt almost like I was trying to drag another boat. I took the boat out of gear and reved the engine and it spun right up to 5000 with no problem. Put it back in gear, same problem. All through this, the motor idled fine and never missed a beat. Docked the boat and had to wait until the next day to take it to the ramp. Next day it fired right up and idled fine but still would not get over 3000 rpm in gear. Had about a half mile run back to the ramp, no change.

Any ideas?

 

[firedog978]

I know you said you changed out the fuel line but, that sounds exactly like what a 'soft bulb' causes. It will idle fine, sound fine, until you increase throttle and it starves for fuel. If it were me, I'd check all fuel line connections and put in a new bulb. I've seen brand new bulbs be bad. Cheap enough to do that.

 

[Bob Bourget2]

Im going to assume its a two stroke, since im not at work to verify your numbers. First order is to check the basics. Spark, compression, fuel quality and delivery. Check CDM connections and plugs. If it is the two stroke, drain carbs and purge fuel system and check for any contaminants. My bet is that you lost ignition to one cylinder.