rpm's jump

[dgg190]

First a bit of history and then on to my problem. I have an old Reinell V190 with a merc 888. I?ve had it for a few years now and have been fixing up a little each year. It is my first boat and I?ve learned a lot. Previous owners had equipped it with automotive parts. It now has:
new fuel system c/w a marine electric fuel pump
new Mallory marine electronic distributor
new Holley marine carb (rebuild it every other year)
a new cam (mercury specs for the 888)
marine alternator
marine starter
new rebuilt heads and marine head gaskets (compression on all cylinders 150)
marine water pump
new engine coupler (with about 75 hours on it now)
new leg (about 20 hours) and propeller (about 5 hours) 14.5? 17? pitch 4 blade
complete new wiring, including gauges
Likely a few other things? The engine is now very reliable, just need new upholster work, but that's another story.

My problem is this, when I?m towing a skier or tube after say 5 ? 10 minutes the rpm will jump suddenly from normally 2,400-2,600rpm to 3,000 and boat will start to slow down. Sometimes if I pull back a bit on the throttle and then engage it again things will be fine but other times it will not help. If I stop raise the leg and clean the weeds off the leg (the lake has huge amounts of weeds) then things will be fine for another 5-10 minutes, then things repeat.
The other night we went for a cruise down the lake. About an hour total (with 6 people) at 3,000 rpm (30mph according to gauge) with no problems. When we got back huge amounts of weeds on leg.
Any thoughts as to what is going on.

 

[Foxstan]

Sounds like the prop could be slipping on the rubber hub. This would account for a jump in engine speed while the boat actually slows down. This will only get worse as the hub wears. A prop shop can do a torque test on it to see what the break-a-way point is. A really worn one can be spun by hand even with the engine in gear. Do you carry a spare prop? Might be a good time to slip it on as a comparison. Hubs can be replaced by a shop.

 

[dgg190]

Thanks for the quick response Foxstan. Its a new prop this season. Yes I had the old prop too. It does the same thing.

 

[Foxstan]

Aeration of the prop can do the same thing but I suspect that the weeds are the source of the problem.

 

[Bondo]

My problem is this, when I?m towing a skier or tube after say 5 ? 10 minutes the rpm will jump suddenly from normally 2,400-2,600rpm to 3,000 and boat will start to slow down. Sometimes if I pull back a bit on the throttle and then engage it again things will be fine but other times it will not help. If I stop raise the leg and clean the weeds off the leg (the lake has huge amounts of weeds) then things will be fine for another 5-10 minutes, then things repeat.
The other night we went for a cruise down the lake. About an hour total (with 6 people) at 3,000 rpm (30mph according to gauge) with no problems. When we got back huge amounts of weeds on leg.
Any thoughts as to what is going on.

Ayuh,.... Stay outa the weeds,....

To deweed the prop, go from forward to neutral, to reverse, hit the throttle abit, then continue on yer way,......

The weeds are yer problem,.....

 

[dgg190]

The only objection to this is I don't see other boats out there stopping to deweed their props and on the hour burn down the lake no issues, but had weeds on leg when we got back.

The lake is about 25 ft deep for most of it and the weeds are all chopped off a few feet below the surface due to all the boat traffic.

I will try the deweed suggestion though. Thanks Bondo. Perhaps they all know your trick, that or they have all had you help them. Thanks for all your posts Bondo.

 

[Bondo]

I don't see other boats out there stopping to deweed their props and on the hour burn down the lake no issues, but had weeds on leg when we got back.

Ayuh,.... Teach 'em the trick, 'n maybe they got another 5 mph in their boat, along with better gas mileage,....

A prop can't Push, when choked with weeds,....