Mariner Magnum II 150hp V6 - Revving but not Accelerating under load

[T14CAM]

All,

I?m experiencing an issue with my Mariner Magnum II 150hp V6 2stroke outboard. Whilst idle or under load up to 2000rpm I?m happy with the engine performance, however, when I increase the load to 2500rpm the engine revs higher but fails to accelerate and would appear to lose momentum.

Initially I thought I was experiencing prop slippage, however, having replaced the propeller with a brand new one, I?m still getting the same problem... Any help would be appreciated?

Regards
Cameron

 

[roncoop75]

Re: Mariner Magnum II 150hp V6 - Revving but not Accelerating under load

Right off I was going to say slippage but you eliminated that possibility.

Hub exhaust? There is a seal at the front of the prop, IIRC, that seals exhaust gasses from running on the outside of the prop. If that seal is bad exhaust gas will pass over the prop and you'll have cavitation.

Not sure if this would wait till 2500 rpm to show up though. I'd think it would be immediately obvious.

 

[T14CAM]

Re: Mariner Magnum II 150hp V6 - Revving but not Accelerating under load

Right off I was going to say slippage but you eliminated that possibility.

Hub exhaust? There is a seal at the front of the prop, IIRC, that seals exhaust gasses from running on the outside of the prop. If that seal is bad exhaust gas will pass over the prop and you'll have cavitation.

Not sure if this would wait till 2500 rpm to show up though. I'd think it would be immediately obvious.

I'd think it would show immediately rather than wait until the 2500rpm range...In addition, this issue doesn't happen everytime I use the boat. For example, I ran at 2500rpm+ for a number of hours at the weekend and assumed that the new prop had resolved the issue, that was until last night when I experienced the problem again.

 

[Doernuth]

Re: Mariner Magnum II 150hp V6 - Revving but not Accelerating under load

Sounds like a lower going bad. Drain the oil and look for metal in the oil.

 

[j_martin]

Re: Mariner Magnum II 150hp V6 - Revving but not Accelerating under load

Sounds like a lower going bad. Drain the oil and look for metal in the oil.

or the "new" prop is bad also.

It's easy to check for hub slippage. Take off the prop nut, and make a mark on the hub by the splines, and next to it on the outside of the rubber part. Put the nut and keeper back on. Take it for a ride till it acts up, take the nut off and look at the marks. If they are still in line, the prop's good. Odds are they aren't.

I can't imagine your symptoms from the gearbox without nerve shattering ugly noises.

The prop hub should fit the lower within .050 or so. Most of the magII's came with a 4 inch lower. If it has a 4 1/2 in. LU and you put a 4 in. prop on it, it would spin out pretty easily because there's way too much exhaust over the prop. They do make an adapter ring for that. The sloppy fit is pretty obvious. A 4 1/2 in. prop won't go on a 4 in. LU.

hope it helps
John