72 Mercury 65hp Thurnderbolt POWER LOSS

I just got a 72 Glassmaster with a 65ph Merc. The boat is a 15' trihull. The boat starts fine. I usually need to use the advance lever and choke but it start pretty quick. The throttle lever has to be pushed way forward start moving forward. The boat takes a long time to come off plane. Sometimes the boat will only go 10-15 MPH while other times it opens up and runs 35 to 40 mph. You can hear the motor speed up and level out and off if runs. Once up and going it stays going until you back off on the throttle.

Re: 72 Mercury 65hp Thurnderbolt POWER LOSS

I have a similar motor (74 merc 85) I am getting the kinks worked out of, except my kinks are in the shift linkage.

The first thing I would check would be the throttle cable, drop it in the lake, take the band off, start the engine and have someone else put it in gear and advance the throttle while you watch the throttle cable on the port side of the engine. After it goes in gear, you shouldn't have to move the control too far to see the cable start to move the throttle arm and rev the engine up. If the control goes almost all the way down before it moves the throttle, you are not hitting full throttle and you need to tighten the cable. You can undo the linkage at the motor, and spin the brass anchor point (its threaded) to tighten the cable, replace, fire it back up, and see if its better.

If the cable is already tight, I would decarb the motor, if that doesn't fix it maybe a carb rebuild?

Re: 72 Mercury 65hp Thurnderbolt POWER LOSS

Lancepearson1969 said:

I just got a 72 Glassmaster with a 65ph Merc. The boat is a 15' trihull. The boat starts fine. I usually need to use the advance lever and choke but it start pretty quick. The throttle lever has to be pushed way forward start moving forward. The boat takes a long time to come off plane. Sometimes the boat will only go 10-15 MPH while other times it opens up and runs 35 to 40 mph. You can hear the motor speed up and level out and off if runs. Once up and going it stays going until you back off on the throttle.

Click to expand...

Ayuh,... Odds are, it's starvin' for Fuel...

Probably the carbs, but dignosin' it will tell ya what needs fixin'...

Re: 72 Mercury 65hp Thurnderbolt POWER LOSS

Ok linkage then carbs. The plug wires look pretty old. Are rePlacement easily found?