Rebuilt carb/Merc 120 starts to die on acceleration then continues to run normally.

[egleas84]

I have the boat on the top in my sig line. I currently have a 14x19 (3 blade) prop on it. When increasing power the engine bogs and it takes awhile to get on plane. I have a hydro foil installed. After it gets on plane I get 32 MPH @ 4300 so the compression is probably good. Think I need a 14x21 or 14x25 to get me out of the hole better?

Thanks!

 

[Joshua Nichols]

Re: Prop pitch not big enough?

Re: Prop pitch not big enough?

NO NO NO that won't help ya.. That will just lug the engine down.. Maybe go down in pitch..http://boatpropellers.iboats.com/propeller-tutorials/rpm/?**********=026932893&*******=418620667

4 blade will give ya some holeshot

Ditch that dang hydro foil junk.. All that is is a drag wing..

 

[egleas84]

Re: Prop pitch not big enough?

Re: Prop pitch not big enough?

NO NO NO that won't help ya.. That will just lug the engine down.. Maybe go down in pitch..http://boatpropellers.iboats.com/propeller-tutorials/rpm/?**********=026932893&*******=418620667

4 blade will give ya some holeshot

Ditch that dang hydro foil junk.. All that is is a drag wing..

Don't think I can plane without it. Is a 4 blade acceptable on a Mercruiser 120? I don't want to loose any top end if I change props :-(

 

[JimS123]

Re: Prop pitch not big enough?

Re: Prop pitch not big enough?

I checked my database and just so happens I have Stingray's 1983 test data for a SVB165 running a 120 1.98 I/O.

Stingray props for top speed with a light load. The std. prop was a cupped SS 15 1/4" x 19 pitch. It gave 41.3 mph at 4530 rpm.

Stick with a 3-blade prop and go to a 17". Whatever you do, KEEP the hydrofoil, since Stingrays run well with them.

How did you determine your speed? You should be running in the low 40's, so maybe your speedometer isn't correct. Use a GPS instead. Since you are getting good rpm, I agree your engine is probably OK. If you go to a 17, you will get better performance, but undoubtedly MAY lose top speed. You decide what is your priority.

 

[Joshua Nichols]

Re: Prop pitch not big enough?

Re: Prop pitch not big enough?

The whale tail? ok have ya tried without it?

I would try a 17 pitch prop.. It will at least put you around 4600 rpm.. Sometimes a local pro shop will let ya tryout some different props to find one that works for you.. Is that GPS speed??

It's just a 120hp pushing a deep V boat.. May be all she has Capt. HMMMM does it have rot? Could have waterlogged foam.. Man that gets heavy and will slow a boat down..

 

[steelespike]

Re: Prop pitch not big enough?

Re: Prop pitch not big enough?

32 at 4300 Your about 10 mph off and 250 rpm short. on your top speed.250 rpm won't make up your speed.
You should check the compression and be sure it is in excellent tune,Be sure the throttle opens all the way.If you think it won't plane without the foil you may also be hauling around a couple of hundred pounds of water in the foam under the floor.

 

[egleas84]

Re: Prop pitch not big enough?

Re: Prop pitch not big enough?

FOAM & ROT: Not sure; the floor is very solid so when i bought it I was under the impression the cockpit sole was in decent shape; besides the dealer wasn't about to let me take a saw to the floor to check underneath. Anyway to dry that foam out? Or does it have to be removed.... It sits high in the water and feels pretty light behind my underpowered V6 Explorer. I suppose I might have to have it weighed to know for sure.

COMPRESSION: Dealer stated it was "within range". They told me the range, but I don't remember what it was.

17" PROP: How high is too high for the RPM's?


What about the 17 gallons of gas im hauling around in my inboard tank? Not exactly in the best spot behind the rear port side seat next to the engine. bad for weight distribution that cant help. Could anything else besides compression or water in the foam cause a slow down? Bad U-joint for example (no indication) or some other thing thats easy to fix.

 

[egleas84]

Re: Prop pitch not big enough?

Re: Prop pitch not big enough?

My plugs look sort of worn; and i used 89 octane and it has some left over stabil in it... either of those factors does this thing need the ignition of 87 octane?

 

[egleas84]

Re: Prop pitch not big enough?

Re: Prop pitch not big enough?

I'm not an expert... does this look like its sitting low (taken yesterday)?

 

[Joshua Nichols]

Re: Prop pitch not big enough?

Re: Prop pitch not big enough?

I guess you could weigh it.. Have a look under the floor..

Do ya a good tune up if ya haven't done one.. You will be surprized at the performance change doing a long overdue tune up will do..

 

[egleas84]

Re: Prop pitch not big enough?

Re: Prop pitch not big enough?

I guess you could weigh it.. Have a look under the floor..

Do ya a good tune up if ya haven't done one.. You will be surprized at the performance change doing a long overdue tune up will do..

I like the tuneup idea... I'll get the ole maintenance manual out. Where would be the best place to look under the floor? It will involve cutting no matter where it is...

 

[not enuf toys]

Re: Prop pitch not big enough?

Re: Prop pitch not big enough?

if its bogging down first, how clogged are the jets in the carb? how much water is in the fuel from winter storage?

 

[Joshua Nichols]

Re: Prop pitch not big enough?

Re: Prop pitch not big enough?

Yeah the bogging is a concern..

You shouldn't have to cut the floor.. I guess it matters how it is built

 

[egleas84]

Re: Prop pitch not big enough?

Re: Prop pitch not big enough?

if its bogging down first, how clogged are the jets in the carb? how much water is in the fuel from winter storage?

Not sure about jets... Or how to check or clean them either . I put marine stabil in it when I bought it then filled it up in Feb. It already had a half tank of gas; possibly from 2009... (wasn't ran last year by po). Could that gas be pretty nasty and messing up my combustion? I suppose I could syphon out the rest of the tank (ran it down to 3/4 today) and fill it with good stuff. Or should I just add more stabil marine treatment?

 

[Joshua Nichols]

Re: Prop pitch not big enough?

Re: Prop pitch not big enough?

You can add all the crap to the fuel you want... If the carb is dirty it's not going to self clean due to a fuel treatment.. What happens when you drop the throttle? Doe it go go go or does it fall on it's face?

 

[egleas84]

Re: Prop pitch not big enough?

Re: Prop pitch not big enough?

Yeah the bogging is a concern..

You shouldn't have to cut the floor.. I guess it matters how it is built

There's no where to see under there where the floor meets the engine bay is walled in fiberglass. Only opening is a couple 1/2" holes that allow water to drain into the bilge area and the engine mount is right above those. Anyone have a fiberoptic spy cam I could borrow?

 

[egleas84]

Re: Prop pitch not big enough?

Re: Prop pitch not big enough?

You can add all the crap to the fuel you want... If the carb is dirty it's not going to self clean due to a fuel treatment

So take they carb off the manifold and spray it with carb cleaner?

 

[Joshua Nichols]

Re: Prop pitch not big enough?

Re: Prop pitch not big enough?

What happens when you drop the throttle? Does it go go go or does it fall on it's face?

Spraying the outside with cleaner won't fix it, if a dirty carb is the problem... Have you ever rebuilt a carb before?

 

[egleas84]

Re: Prop pitch not big enough?

Re: Prop pitch not big enough?

What happens when you drop the throttle? Does it go go go or does it fall on it's face?

Spraying the outside with cleaner won't fix it, if a dirty carb is the problem... Have you ever rebuilt a carb before?

If I slam it down it might sputter then pick up. Sometimes shifting between in and out of forward or reverse it'll sputter once. First time I heard it I thought it might stall.

Ive never done carb work my dad has. First time for everything though. I don't think I want to take it to a marina with the shop labor these days....

 

[not enuf toys]

Re: Prop pitch not big enough?

Re: Prop pitch not big enough?

if the boat was stored since 09 with a half tank, there is water in the fuel. always store a tank full. it doesnt allow for water. and if its fuel from 09, odds are its toast.

if it is bogging when you drop the hammer and sounds like its going to stall, you need the carb looked at. and you also need to drain the fuel and start over.

does the boat have a fuel water seperater?