What causes no bottom end power?

[imthemedic]

Ok I thought it was the prop that was the problem since i bought the boat this year, but after trying 4 different props all that run boats the same as mine I have concluded it must be the motor. When I launch the boat engine revs to 2500rpm and then slowly climbs up in rpm. Takes about 15 seconds to get to 4500rpm then it noses over on plane. It seems fine after that I think it should have a little more however but you know lol. I also noticed when I load it on the trailer that I cant bump the throttle to power up on it if needed. The motor just stalls when it gets on a load at low rpms.

91 Johnson 200GT
all new fuel lines, filters, bulb, Lync&Sync, and checked the idle timing.

 

[ezeke]

Re: What causes no bottom end power?

What boat are you running and what is the pitch of your propeller?

What is your top RPM at WOT?

 

[imthemedic]

Re: What causes no bottom end power?

91 Stratos 201 pro, 200GT 10" jackplate prop 3" below pad, 650lbs of fisherman and gear, 1/2 tank of fuel.

Raker 24" blows out can't get it on plane.
Renegade 25" 5200rpm @ 56mph
Shooter 24" 5700rpm @ 55mph
Shooter 23" 6000rpm+ @ 51mph
Michigan Wheel 24" 4 blade 5500rpm @ 52mph

 

[ezeke]

Re: What causes no bottom end power?

Except for the Renegade which is 15%, the slip is too high. Why haven't you tried a lower pitch?

 

[imthemedic]

Re: What causes no bottom end power?

I ran a 23" and almost blew it up lol. It would turn 6000rpm on initial hit of throttle but the boat was barely moving. It was the fastest on plane of all of them but not good. I had to run 3/4 throttle to keep from over reving.
What are you suggesting?

 

[ezeke]

Re: What causes no bottom end power?

You are over 20% slip on three of your four propellers; that's too much.

The rev limit is 6700; you won't blow up the engine. If the setup is correct you might get better thrust if the engine were set lower with the lower pitch propeller.

If I raise my engine one step I can take it to the limit, but my top end does not increase and I lose bite when the water is rough.

 

[imthemedic]

Re: What causes no bottom end power?

Wow 6700 rpm. I thought 5700-5800 was the sweet spot. I haven't seen anyone turn that kind of rpm. With the smaller shooter I never really gained and additional speed when I pushed it over 6000 rpm. Odd thing it that most guys running my boat run the raker or renegade both are the recommend prop. The bigger shooter came off a friends boat that's the exact same boat minus the jackplate. It launches his boat and has a little more top end. That's why I was thinking engine issues. Also unable to apply power while loading it bogs and kills engine.

 

[ezeke]

Re: What causes no bottom end power?

I'm not recommending that you increase your top end RPM, but that you look for more thrust getting out of the hole. I think that you can get that with a lower pitch prop.

The full throttle operating range on your engine is 5,000 to 6,000 RPM so you should prop to be able to reach the top of the range or slightly higher at WOT with your average load.

The 5800 RPM recommendation is used for crossflow engines with full throttle operating range of 4500 to 5500 RPM.

 

[imthemedic]

Re: What causes no bottom end power?

Ok I understand that part. What do you think is causing the no power while loading. Seems like it just boggs the motor and kills it.