94 88 spl.. only turning 4600 rpm

[wht07se]

Thanks for all the help that the users of this site have already given me on my boat and motor. I just recently fixed an issue i had and now i seem to have another one. Got the tach and rectifier replaced but now i find out that my motor is only taching 4500 -4600 rpm at wot. I do know that it has a 13x19 prop, 120 on 3 cylinders and 118 on the other, plugs look good but not sure how old they are. Again i am new to boating and dont really know where to start checking. I did see that in one post with similar issue is was the main jet sizes causing the probs but just dont know. Today went too out to check new gauge i did play with the trim, trimming in and out and the best i could get was 4600 rpm, there was three people in boat all weighing less then 200 lbs. Not sure of anymore info that may need.

Bryan

 

[kenmyfam]

Re: 94 88 spl.. only turning 4600 rpm

Could be for a multitude of reasons. Start by telling us what boat you are pushing with this motor.

 

[wht07se]

Re: 94 88 spl.. only turning 4600 rpm

Ya, guess i did forget that part, its s 94 key west 1720.

 

[wht07se]

Re: 94 88 spl.. only turning 4600 rpm

bump^^^^^^^

 

[kenmyfam]

Re: 94 88 spl.. only turning 4600 rpm

Now for some history. Is this outfit new to you ??
Did this issue just start ?? What RPM could you achieve before ??? and the big question.... at the RPM you see on the tach right now is the boats performance actually any different ?? it could be the tach that is the problem as you have just replaced it.
I think a 19" pitch prop may be a little much for your outfit as well, however if it performed O.K. for you previously with it then it should do the same again.

 

[wht07se]

Re: 94 88 spl.. only turning 4600 rpm

The outfit is new to me, just got about a month ago. But did test boat twice before buying and acts same as it does now. When i bought the boat that tach was not working so could not see the rpms but then again i had no idea where it should be running at either. But it does seem to run great, smooth idle, smooth trolling, and seems to make good power. Its just not turning enough rpms. Now the boat did sit for a lil while being that it was only used once last season so maybe the carbs need to be cleaned. And its not the tach, have checked with two and both read very very close. And did ask previous owner if had anyother props and answer was no and stated that one on motor was the original. Its not beat up but believe its one of the s.s. teflon coated ones and you can see where some has wore off the blades but figured that was normal.

 

[tashasdaddy]

Re: 94 88 spl.. only turning 4600 rpm

suggest doing Joe Reeves timing, it will get the Max RPMS set for the timing, the you have to play with "set up". this is engine height to the keel, proper angle of motor, distrubuting load in the boat properly. correct prop size and pitch.

you should be turning 5500 RPMS at WOT. then the motor will not lug at lower speeds.

 

[wht07se]

Re: 94 88 spl.. only turning 4600 rpm

Thanks for info, but dont have a timing light, will have to get one, and the engine height is about right, and im not sure about the right prop size. Guess i've got alot of learning and work to do.

 

[ezeke]

Re: 94 88 spl.. only turning 4600 rpm

Yor best bet is to try a propeller with a lower pitch. 90HPis not a lot of power for a heavy boat and 15 or 17 should get you closer to your target.

Unless someone has worked on the timing, you are better off to leave it alone or have it set by a shop that has the proper equipment.

 

[bob johnson]

Re: 94 88 spl.. only turning 4600 rpm

Thanks for info, but dont have a timing light, will have to get one, and the engine height is about right, and im not sure about the right prop size. Guess i've got alot of learning and work to do.

there is no short cut from where you are to where you need to go..

you will have to try some things, see what changes and which way it changed , then try some others....

you have to establish that the motor is actually running the way it should, before you react to the low rpms.

your rpms are probably within the factory specs..

but over and over i read that you want to be at the higher end of that spec..

I dont have it in front of me but most of the V4s seemed to be 4500-5500

years of low WOT rpms can have an effect on the motor!!

the motor could probably use a decarb...but you dont know the maintenance history from the previous owner do you?


id also try a 15 pitch prop and if you get good speed and are turning 5200-5500 and everything sounds right, you might not need to adjust anything!!!



good luck

bob

 

[wht07se]

Re: 94 88 spl.. only turning 4600 rpm

As far as the speed goes im getting about 35-36 mph right now with the 13x19 prop. An i dont really know the maintenance history from previous owner other then what he told, an we all know how that goes. But in general with a 17' boat and 90hp motor what type of speeds should be expected? The boat also has a 31 gal fuel tank under the center console, and all the wot runs were with the tank full, but dont think that weight should keep boat from reaching 5500+ rpms. Where would be best place to find a prop, and SS or aluminum?

Bryan

 

[bob johnson]

Re: 94 88 spl.. only turning 4600 rpm

just telling the length of the boat isnt enough information...

the hull shape, weight of the boat, both play huge roles...

weight is everything!!

250 lbs of gas is a lot!!!

it is a powerful motor though..

how much does the boat weigh??

is the foam all soaked up with water under the deck???

thus weight 500 lbs more than the factory spec sheet says???

I dont know your boat, and I dont know how old it is, but water soaked foam is nothing new... for killing boat performance..

there are 17 foot boats that NEED 21 pitch props with a 90 hp!!!!!!!

its all about the weight and hull shape...( if the engine is running good)

it is feasable that if someone got on your boat played with the trim angle and weight in the boat( move stuff around maybe) that your rig could post a 5000 rpm WOT with the prop you ahve now!!!!

I know i can gain 200 rpms with the best trim , over the trim used while getting up to planing speeds!!!

by the way taking the trailered rig to the junk yard and getting it weighed isnt a bad idea and a good reference to have...

or a gravel yard..they have drive on scales and most will do it for free...takes 5 minutes

good luck


bob

 

[wht07se]

Re: 94 88 spl.. only turning 4600 rpm

Im not sure on the weight of the boat an someone else mentioned that maybe foam is water soaked. Its a v hull but not a real deep one. Will try taking to ramp an run motor with boat on trailer to see if there is diff in rpms. My buddies dad ones local marina an got him looking for some props that I can try to see if that helps.... Why would you need such a large pitch (21) on a 17' boat?

 

[ezeke]

Re: 94 88 spl.. only turning 4600 rpm

The lighter Key West 1994 1720's were rated for 120HP so your motor is within the acceptable range, but you should set up the engine to reach a maximum of 5500 to 5800 RPM at WOT with your average load so that you don't lug the engine and shorten its life.

 

[bob johnson]

Re: 94 88 spl.. only turning 4600 rpm

Im not sure on the weight of the boat an someone else mentioned that maybe foam is water soaked. Its a v hull but not a real deep one. Will try taking to ramp an run motor with boat on trailer to see if there is diff in rpms. My buddies dad ones local marina an got him looking for some props that I can try to see if that helps.... Why would you need such a large pitch (21) on a 17' boat?

the NEED comes from making sure the rpms are in the proper range!!!

and some 17 foot boats weigh less than half of what yours does....


so the 15 and 17 pitch props would be turning way way too fast....

for each specific motor...the more weight of the boat the lower the pitch...

the less weight of the boat the higher the pitch

imagine a little hydroplane racing boat maybe 600 lbs max....

with that motor it is easily running a prop in the 20's!!

good luck

bob