2.5 merccruiser with 3.0 carb???low rpms?

[keltie]

just bought a 88 renkin elite open bow with motor as above. had sparks changed and tune up as had problem getting up on step. was really sluggish with rpms of 3200-3500 and since the work now rpms of 3800. took a while to get up to speed with 3800 and 2 adults/2 kids but with 6 adults barely got to 3000 rpms and hardly moving. any simple things we could check...hoping it's not the compression!!! or timing!!! shouldn't a boat like this W)T rpms be about 4500. this is a ski boat

 

[cobra 3.0]

Re: 2.5 merccruiser with 3.0 carb???low rpms?

Drop your prop pitch. What's it now?

 

[DHPMARINE]

Re: 2.5 merccruiser with 3.0 carb???low rpms?

I am getting to hate these posts that start just got this boat.BUT maybe we can help.You are right,the RPM's are low.The boat will perform slow with more people in it,Did it run okay on the first lake test,preferrabley with the previous owner?<br />DHP

 

[keltie]

Re: 2.5 merccruiser with 3.0 carb???low rpms?

i'll have to ask about the pitch...with 2 adults/2 kids it took a while to get on step and full speed but only at 3500 rpms. full load didn;t hardly move at all. will a different pitch change the speed/torque of the boat with more load? is it beneficial having a 3 carb in a 2.5? thought inboards were supposed to be so much easier than outboards...starting to miss our little starcraft@!! changed sparks and tuned it up. any other suggestions?

 

[keltie]

Re: 2.5 merccruiser with 3.0 carb???low rpms?

i would think a 17 ft open bow ski boat is designed to hold a few adults and still get someone up on skis. there would be no way the boat could pull up a skier at that sluggish pace! a 2.5 inboard is comparable to a 120 right. our 90 outboard merc had way more power

 

[pine island fred]

Re: 2.5 merccruiser with 3.0 carb???low rpms?

welcome the the world of i/o s. check the simple stuff first. fuel tank vent line, finger filter screen in the fuel tank pick up tube, carb float bowl filter. forget the 3 carb set up, worked good on a flathead ford but not on a boat. regards fred. p.s. like a convertable everyone has to have an i/o at least once.

 

[cobra 3.0]

Re: 2.5 merccruiser with 3.0 carb???low rpms?

Keltie, your prop may be pitched too high for your application. Do you know what prop you have now? It is usually stamped on the inside or outside of the hub. Yes, downing the pitch will make a world of a difference.<br /><br />You should be turning 4200 to 4600 rpm at WOT (full out) and this can be achieved by lowering the pitch. Each inch of drop will get you an additional 200 rpm.<br /><br />I doubt the carb has anything to do with this. The 2.5 and 3.0 are very similar engines and have the same carb.<br /><br />See the following link and check out the two engines. They have the same part number for the carb. Look at the '86 year as it doesn't show a 2.5 for '88.<br /><br /> http://www.dougrussell.com/partscat...,320,439,621,739,887,1003,1140,1272,1396,1610

 

[keltie]

Re: 2.5 merccruiser with 3.0 carb???low rpms?

we have a 19 prop. so that would make a difference eh?!?! even increases the rpms. just found out too that our air filter is filthy. i just find it frustrating that a ski boat can't carry 6-7 adults and would never be able to get a skier up. any other things we should check

 

[cobra 3.0]

Re: 2.5 merccruiser with 3.0 carb???low rpms?

I have a 19" pitch prop. It is a dog compared to my 17" pitch. You could even go to a 15" pitch with all that weight, but it wouldn't be usefull if you are only two next time out as it will cause the engine to rev too high out of its range. Then again, you can swap back to your 19" for lighter loads.<br /><br />19" light loads (poor hole shot/take off)<br />17" medium loads (great hole shot/takeoff)<br />15" heavy loads (super hole shot/takeoff)

 

[Rhadley]

Re: 2.5 merccruiser with 3.0 carb???low rpms?

You never state what the actual speed is. How fast is "hardly moves?" I think you have something blocking fuel flow. Did you put the screen filter back into the carb correctly? I have this same engine and can go 30 MPH with 6 people in the boat. These things tend to bog down during fast acceleration, however. You said it was just tuned up so I assume the timing is correct.

 

[tommays]

Re: 2.5 merccruiser with 3.0 carb???low rpms?

i have a maxium 2000 sc with a 3.0 proped out perfectly the trouble is that with a motor this small perfectly is compleatly different with 2 people on board or 6 people .<br /><br />we also own and 18 ft v-8 correct craft ski boat that will pop 10 skiers out of the water with out even trying hard and would never think of going sking with 6 people on the boat thats what the beach is for<br /><br />that being said i dont think that you will every be happy pulling a skier unless you put an a very small prop that you only use for sking because thats the only way a motor this small is going to bring the boat up on plane fast enough to enjoy sking<br /><br />tommays