Briggs 5HP low rpms ??

[Wishiniwuzfishin]

Hi New user, just joined and have a question. Briggs and Stratton 5 HP outboard 2005 model. Manual says it is rated for 4000 rpm but I can only get about 3020 while running wide open on boat in water....verified with a Tiny Tach. Question is how much of the lower rpm's can be attributed to a fairly heavy load (older heavy 12' aluminum boat and I weigh about 240 + probably 50-75 lbs of gear w/gas tank) and that the bow rides really high when underway. Doesn't come close to planing. Motor is adjusted down as far as it will go but the back seat is only about 8 inches from transom so most of the weight (ME LOL) is in the back. Just wondering if the low rpms is a load problem or motor problem. Motor runs very smooth through operating range just doesn't get to 4000. Thanks

 

[steelespike]

Re: Briggs 5HP low rpms ??

Welcome,
I would say most of your problem is weight and weight placement related.
Get or make yourself a tiller extension so you can sit in the middle seat.
You could try putting everything in the bow but probably not enough.
Under ideal conditions it should be able to plane and maybe run about 10 or 12 mph.
If there is a steering tensioner and its not congested where you boat you could sit in the middle seat and steer CAREFULLY by leaning slightly.
We had a flat bottom steel boat that popped on plane with 180 pounder in the middle seat.Your won't pop on plane but should plane.There are a number of briggs videos on youtube will give you an idea how they run.

 

[Wishiniwuzfishin]

Re: Briggs 5HP low rpms ??

Thanks for the reply. Actually my winter project was to move the rear 2 bench seats forward (Has 3 bench seats). I drilled out the rivets and have the 2 seats out. Now I need to drill new holes and re-mount them. Should be able to move each seat forward about 10-12". I'll try steering from the rear seat first and go from there. Not sure how much it will help but can't hurt. I do have everything else as far forward as I can get it right now. Forgot about the 50-60 lb battery for my elec. motor. It is between the bow and the front seat right now with 12' cables running back to the motor. The gas tank(3 gal.) is strapped to the front seat(after adding about 8' of gas line). Before I moved everything up front it almost felt like the bow was pointed straight up!!! Like I said the motor seems to run fine but I had no idea how much a heavy load would lower motor rpms. Apparently about 25% in my case. After I get the seats moved(and the ice melts) I'll try it and see what happens. I could move up to the middle seat without too much work I think. Just like to get a little more speed out ot the boat. My best estimate without any instruments was my top speed was like 5 mph.

 

[steelespike]

Re: Briggs 5HP low rpms ??

That steel boat we had was a 5hp.I was checking motors in operation on youtube
there is actually a 2hp on a light jon boat with a light operator in the middle seat
it actually appears to plane.There was also a number of videos of the briggs in operation wasn't very impressive to me but did appear to plane.Its a fun look just to see all the screwy motors in operation.

 

[QC]

Re: Briggs 5HP low rpms ??

Under ideal conditions it should be able to plane and maybe run about 10 or 12 mph.

I have a 14 ft. Sea Nymph and a Briggs and that is exactly how she behaves. Maybe 250 lbs total weight in the boat.

 

[steelespike]

Re: Briggs 5HP low rpms ??

Most transoms are set at a slight angle if yours is unusually vertical you may need to buy or make wedges to put between bracket and transom to allow the motor to tuck in a little more.
If your boat is what I call a small 12', narrow, under 5 ft., Maybe 11'9" with an pretty narrow bottom it may have more trouble planing.No doubt QCs 14 ft is wider and obviously longer.The length helps planing as well.
The height of the motor can help or hurt planing as well.The antivent plate just above the prop should be about even with the bottom of the bosat.
Simply add 1/4" sticks on the top of the transom to set the height.Just be sure the clamps have a good grip.
By the way there was a youtube video of a Briggs that broke off at the steering pivot and was lost in the water.

 

[Wishiniwuzfishin]

Re: Briggs 5HP low rpms ??

It is a SMALL 12 footer. 11'6" LOA with 48" beam at its widest. Never paid any attention to the transom angle. Just dropped the motor to its lowest mount (as far as trim angle). Did measure the shaft length the other day and I do think the prop may be sitting to far in the water. Have to try shimming it up some. But..........I am picking up my next project tomorrow. Just bought a 70's??(forgot to even ask what year it was) 16' Arrowglass tri-hull. Interior was stripped to replace floor(looks like he did a good job with the floor) and no motor. Never wanted a tri-hull before but in my advancing years I think I will really appreciate the stability while fishing. Gonna turn it into my dream fishing machine for my local lakes. My questions from here on in will be about it!!! Again, thanks for all replies.