1978 23 sceptre inboard speed
 

I have had this boat about 12 years and the speed seems a little slow from what I have read. The engine is a 350 marine power with a velvet drive trans. At 3000 rpm 21 mph. At wot 3700 rpm 25 mph. Is this about right for an inboard or is this too slow.Thanks

Re: 1978 23 sceptre inboard speed
 

I think you are about 1000 rpm light for that engine.
Have you got a fuel line restriction someplace?

Re: 1978 23 sceptre inboard speed
 

Tach might be off a tad, reading low.
Most imboards I have been on with similar setup cruise at about 24 and top out at about 30-32. The inboards are not speed demons, but they ride GREAT.

Re: 1978 23 sceptre inboard speed
 

At 3000 RPM's I'm getting about the same cruise speed as you on a 23 inboard CC with a 350 as well. The speed has been my only gripe with this boat. Also, I would like to note that I usually run with full tanks, ice, tackle, and enough rods for 3 boats so they are real world numbers. The rough water ability and dry ride is second to none, but man is she slow! The boat is also very affected by weight, everytime you add another person it really slows you down. My outboard center consoles have not been affected by weight nearly as much. I should have gone with a diesel.

Re: 1978 23 sceptre inboard speed
 

I agree. Seems like you're not getting enough fuel.
That engine should be near 5K at full throttle.
Throttle cable adjusted properly?
Restricted fuel or vent line?
Weak pump?
Carb dirty or misadjusted?

Re: 1978 23 sceptre inboard speed
 

Ichecked the tach it's good. checked the fuel filters there good fuel press and volume are good at idle not shure about full throttle. The spark advance weights and springs look a little rough but I ran out of daylight I'll look into it moor this week end. thanks for the imput your help is appreciated.Iwill post what I find this week end.

Re: 1978 23 sceptre inboard speed
 

What size prop do u have? I have a sceptre with a fresh 350ci. prop size is 16x19. I run 2800 rpm ar 24 knots. At 3200 i'm 28 knots. good luck

Re: 1978 23 sceptre inboard speed
 

Check my previous post, I have a differnt prop then you and run 27-28 at 3200 with 315 HP.

Re: 1978 23 sceptre inboard speed
 

Is that by yourself and light on fuel? I have a tall hard-top and I'm wondering how much that makes a difference. I moved from a 15x17 to a 16x17 based on the original specs and everyone suggesions, but my cruise & fuel burn is exactly the same, but with more vibration. If I could get this boat to cruise at 22-24 knots at a reasonable RPM with 3 people and gear I would be a very...very happy camper. With 3 People, a good load of fuel & fishing equipment I am cruising anywhere between 16 & 19 knots at 3100-3300RPM's.

Re: 1978 23 sceptre inboard speed
 

I have a 23 sceptre IB with orginal 305 ( 228 hp ) cruise at 2800 18kt 9gph burn , wot is 3900 for this motor and will do 23kt. 16x15 prop. not sure of cup. This is with 3 people moderate load. So this is inline with orginal posters specs. The wheel is smaller than stock and what the 350 guys run but I dont have the hp to turn one. If the bottom was perfect light load prop true I could add 2 kt to the numbers. Best top speed was 30mph on a perfect day running with the current 4000 rpm witch is max wot rpm for the motor.