mercury problems ?

[satman7475]

I had a 150hp Johnson faststrick,blew engine,switch to a 200hp mercury 1990 blackmax engine.Question is with my 150 johnson i was able to get up tp 55mph,but now with my 200hp merc. Im only able to get up to 50mph.My boat is a 16 ft.Stratus bass boat.I was thinking going with a biger hp I wouldbe able to get more mph.Dont get me wrong the motor runs great I was just thanking I would get more mph.Is there anything I can do to get more hp out my motor??Or is this commun for a 200hp?Thanks for your help

 

[Barnacle_Bill]

Re: mercury problems ?

Something is not set up right. Where is the cavitation plate in relation to the bottom of the hull? What is your WOT rpms? Are you sure its firing on all 6 at WOT? I run an old 83 Merc 150 on a 16ft Bonito bass boat and it will run about 65mph.

 

[DJ]

Re: mercury problems ?

Can't tell much without knowing what your wide open throttle rpm is.

 

[rabidfish]

Re: mercury problems ?

Remove that engine from the boat and install one that is under the maximum horsepower capacity for that boat!

 

[satman7475]

Re: mercury problems ?

thanks for the replies, sorry i didmt get back sooner.i do assume it is firing on all six cause the wot is right at 6000 rpm at full throddle, which from what i have read on this site is right for that engine? forgive me Ibnfshn, new to boats, what is the cavitation, hope i dont sound stupid.

 

[sprinkler]

Re: mercury problems ?

What pitch prop do you have on it? If you increase the pitch of the prop you may be able to increase your top speed. (The higher the pitch of the prop, the further it goes thru the water in one revolution.)

 

[satman7475]

Re: mercury problems ?

its a 14 1/2 by 24 pitch. i thought about chaging out to a lower pitch prop but woulndt that also increase my rpm. heard you dont want to get your rpm faster than the motor calls for and right now is 6000 at wot, so going to a lower pitch would increase it more than 6000, right? thanks for the repley

 

[sprinkler]

Re: mercury problems ?

Lowering your pitch will decrease your speed (and true, increase your RPM), not increase it. "Pitch" is analagous to gears on a car. The higher the gear, the more distance you'll travel per revolution of your crankshaft. Same with pitch - the higher the pitch, the greater distance you'll travel with one rotation of the prop.

 

[satman7475]

Re: mercury problems ?

thanks for the reply sprinkler, so what pitch would you recomend? dont know if i can get a pitch higher tha a 24 around here cola, sc. thanks for the help.

 

[sprinkler]

Re: mercury problems ?

Oh, OK, a 24. Perhaps prop pitch isn't your issue.

 

[heybaylor]

Re: mercury problems ?

sounds like the prop has blown a "hub "<br />take it to a propshop..<br />six grand on a 200 should be over 70 with a 24 pitch<br />Also there aint no law against running overpowered rigs ...........yet , but leave it to the tree huggers to change that to "whats GOOD for you " ( in thier opinion)

 

[satman7475]

Re: mercury problems ?

thats funny heybaylor, but your right, only a matter of time before that happens. but thats what in saying it sould go way more faster than only 50 mph, i mean it just seems like theres just something not right , not set right or something. i talked with a bubby and he said it was a good pulling motor not a speed motor but still sould go faster, i mean it dosend jurk or notthing runs great just slow, so please if any one else has any other info please let me know what i can do. but not complaing thats for all your inputs.

 

[256Dusky]

Re: mercury problems ?

What kind of prop is it? Make sure that it has not been repitched because it will loose bite. If it is aluminum and stmaped 24 at 6000 rpm's it is more like a 22 because of flex. As mentioned above check your cavation plate it dosent sound like it is to low but it may be to high. If the motor is mounted to the transom it should be about 1 inch above the keel that should give you a good starting point for the engine height. If it is to high and if you try to over trim it the prop will blow out and if it is to low it will pourpose badly. If is stailess and your engine is at the right height and go up to a 26 you will loose 400 rpm's and give you more top speed

 

[heybaylor]

Re: mercury problems ?

did you miss the hub slipping tip ??<br />i/e the "rubber hub " or Plastic has gone bad.<br />this results in "seems" ok at low throttle settings ..<br />when you get on it ,it slip's..results high rpm ..low speed for the prop pitch..<br />but if thats it It will soon be gone completly and you wil know ,,feels like a clutch gone in a car ..keep a tow rope handy ...good luck

 

[satman7475]

Re: mercury problems ?

sorry i dosed off, sorry ididnt mention it before when i got this motor the guy sold me a 14 1/4 by 24 pitch ss steel prop, only to find out it was really a yum prop also it was already spunn hud so i just had the hub replaced for 55 dollars. dont mean to sound dumd but i was waiting for ibnfshn to reply i dont know what a cavitation is. new to boats. so if i went to a 26 pitch prop your saying i would lose 400 rpm but gain more speed how much speed? would losing rpm be alright? mess anything up? thanks

 

[Laotzu]

Re: mercury problems ?

I have a 16 footer with a 50 Merc and get 25mph. With a 200 I should get 100mph...right?? Are you dragging an anchor Satman? Someone mentioned tree huggers telling us what size motor to use on your boat. Far as I know if you are in the ocean and the Coast Guard boards for a 10 point inspection...max motor size is one of them. Mine calls for a 90HP max. 16 feet and over requirement.

 

[satman7475]

Re: mercury problems ?

where are you guys at dont leave yet ,the only suggestion is to reprop so far? are any other

 

[rabidfish]

Re: mercury problems ?

my guess is nobody that might know what's wrong( read: Marine professional) is willing to help you fix that engine. You pose a liability to us all.<br /><br />I am far from the "tree hugger" image so prominently diplayed previously, however, insulting the knowledge base of the pro's that frequent here will do little to get your problem solved.

 

[WillyBWright]

Re: mercury problems ?

Where is your speedometer pickup? If you're using the one on the Merc gearcase and you used the one on the Johnson, there's your answer. You're comparing two fairly inaccurate (but convenient) speed sensors. Differences in your reading on the speedo may be totally meaningless. If you have a plastic pick-up on the transom, then maybe you have an issue. But if you are using the motor's pick-up ... well one's on a Johnson and one's on a Merc. I wouldn't expect a dead even match regarding the accuracy of the speedo because of that alone.

 

[satman7475]

Re: mercury problems ?

dame good response willybwright i didnt think of that i am using the same speedtack wiht two differnt motors, didnt think of that, somewheres to start any way, thats for the reply