1987 Yamaha Pro V 150 losing power after it warms up

[Jsptkd]

I purchased a 1996 Stratos 285 XL with a 1987 Yamaha Pro V 150. This had been running good until just recently. When I first put the boat in the water and fire it up, it works well. It fires up quickly and runs smooth. The first hole shot is very good. As the engine runs and heats up it starts losing power. Any subsequent hole shot is non-existent. I usually have to get a buddy to move to the bow to get the boat to level out and then it will get up some speed. But this still does not get to full speed. The initial hole shot gets to about 5000 RPMs and running down the lake will reach about 5500 RPMs. Afterwards the hole shot will only get about 3500 RPMs and running down the lake is about 4500 - 5000 RPMs. I have replaced the coils with new ones and replaced the spark plugs. Still the same issue. I have checked the cold compression and see a level of 100-105 for all the cylinders. After it warms up I get a compression level of 95-100. I checked the spark with the plugs and see a weaker spark than I normally do with other engines. The engine seems to be running smooth without any misfires or sputtering. Has anyone experienced this or know where I may look next? Any assistance is appreciated.

[Texas Rig]

I have a 1990 Pro V 150 doing the exact same thing. I first thought it's fuel so I Power Tuned the carbs while on the muffs, took it to the lake and after 15 min of WOT (4000 rpms) it woke up and got back to 5600 rpms and I thought all was good. Well, 2 weeks later I go back to the lake and the same poor hole shot and maybe 4300 rpms. I power tune clean again and no change. I'm thinking now its electrical and I have no clue where to start... not 1 bolt has ever been turned on this motor.

[SkeeterStew]

I have a 1990 Pro V 150 doing the exact same thing. I first thought it's fuel so I Power Tuned the carbs while on the muffs, took it to the lake and after 15 min of WOT (4000 rpms) it woke up and got back to 5600 rpms and I thought all was good. Well, 2 weeks later I go back to the lake and the same poor hole shot and maybe 4300 rpms. I power tune clean again and no change. I'm thinking now its electrical and I have no clue where to start... not 1 bolt has ever been turned on this motor.

I had a similar issue and it turned out to be the red pin on the cable to the controller (10 pin cable) - busted clean through and only connected intermittently. Might be worth a look. If that's not it, you could smear some dielectric grease on there while it's open and put that problem to bed for another decade.

[Stormvet]

Mine did the same but it was my advance timing arm getting stuck half way. Cleaned it all up with electrical cleaner then a little spray lube. Works fine now. It was old grease that hardened over time making it stick.

[SkeeterStew]

Mine did the same but it was my advance timing arm getting stuck half way. Cleaned it all up with electrical cleaner then a little spray lube. Works fine now. It was old grease that hardened over time making it stick.

Ooh, good one! The hotfoot return spring can be trimmed down and tightened up too if the linkage is getting sticky as it gets older, causing the timing arm not to return to idle position. Be careful though, that spring has a taste for human flesh!

[Texas Rig]

Mine did the same but it was my advance timing arm getting stuck half way. Cleaned it all up with electrical cleaner then a little spray lube. Works fine now. It was old grease that hardened over time making it stick.

Is that advance timing arm you speak of the large bar that has the throttle cam attached to it that operates the throttle linkage?

[SkeeterStew]

Is that advance timing arm you speak of the large bar that has the throttle cam attached to it that operates the throttle linkage?

It's the large gray arm with a circular spring in the middle of it. It's in 2 parts. It's pointy by the flywheel and larger down by the bottom, with a circle in the middle kinda like a minute hand on a clock.

Here's a pic:

YamahaTiming.jpg~original.jpg