3.0 mercruiser loses power

[USAKICKBOXER]

Hello all I am hoping someone can help me out. I have an 89 Larson with a 3.0 merc. in it. I've had it for 3 months now and it ran fine all summer till 3 weeks ago. It had a pinging sound under load since I first bought it but it ran fine except rough at idle. I was getting 4600 rpm at WOT and 42 mph. 3 weeks ago is when the problem started. It ran the same as it always had for about 2-4 minutes then all of a sudden the rpm's slowly started dropping till it got down to 3200 and speed dropped to about 18. If I brought it back down to idle for a few seconds and jumped on it... it would make it to 4600 again for about 15 seconds and start dropping again. My first thought was a vent problem with the gas tank so I popped the gas cap off. That didn't change a thing so I checked the timing... supposed to be at 6 BTDC and it was at 14 BTDC at 1000 rpms. Adjusted timing, points, and checked dwell. I figured it may get rid of original ping also. It ran great with muffs and idle smoothed out so i took it back out on water. Ran great for about 10 minutes and ping was totally gone... then all of a sudden ping came back and within a few seconds the rpms dropped AGAIN. Engine wasn't overheating or anything to let you know. I was hoping someone out there can help me... I am stumped... it seems like a fuel problem but I take it out every Sunday and it started all of a sudden. Same tank of gas I had from the week prior. The fuel pressure guage i have is only for fuel injection not for the big line for carb so i can't check if it's dropping but the timing issue made a great difference even though i don't see how timing could change 8 degrees from one week to the next and make a quick problem so i still suspect fuel. Should I take the fuel pump off? Is that filter at the bottom of the pump the water seperator? I only checked the filter at the carb and it was clean. I'd appreciate any help. Thanks.

 

[TwoBallScrewBall]

Re: 3.0 mercruiser loses power

Hey,<br /><br />Check your timing again. You should get no pinging, ever. It sounds to me like somehow the distributor is slipping and throwing off your timing. <br /><br />You said it ran great for 10 minutes after you reset the timing then started to ping and slowed down again. You never said if you then rechecked the timing. I would do that first before you start looking for ghosts in your fuel system.

 

[whywhyzed]

Re: 3.0 mercruiser loses power

sounds like symptoms of vapour lock, like your fuel line is too close to something hot.but that wouldn' happen all of the sudden... edited post now that I reread thread

 

[USAKICKBOXER]

Re: 3.0 mercruiser loses power

No I haven't checked it again yet... The day of the test ride I only had time to put it in the water and see if it was fixed... I won't be going down to where i keep my boat until wednesday but I will post the results wednesday night. If the timing is good which i doubt because of the pinging... I may run a pressurized external fuel supply into the carb to rule out fuel problem. I guess the pinging could also be a lean missfire. Thanks for the replies guys.