Max RPM for Mercruiser 120

[egleas84]

I think it's 4300. Can anyone confirm? Thinking about changing prop pitch

 

[Alumarine]

Re: Max RPM for Mercruiser 120

That's right, 3900-4300.

 

[egleas84]

Re: Max RPM for Mercruiser 120

Thanks!

 

[egleas84]

Re: Max RPM for Mercruiser 120

Is it safe to run it to 4200-4600? My mechanic suggested a 15x17 prop and noted that the RPM's should be about there for optimal engine performance.

 

[jimbo_jwc]

Re: Max RPM for Mercruiser 120

Mine is 1987 3.0 liter 130hp mercruiser w/Alpha1 drive ? I thought i saw 4400-4500rpm 50mph 1 person min gas .

 

[egleas84]

Re: Max RPM for Mercruiser 120

Mine is 1987 3.0 liter 130hp mercruiser w/Alpha1 drive ? I thought i saw 4400-4500rpm 50mph 1 person min gas .

What size prop you swinging? What boat?

 

[jimbo_jwc]

Re: Max RPM for Mercruiser 120

Thompson 196 18 1/2 ' approx 2400# . I'll look at prop to get dia and pitch number off of in daylight . Most rpm I've seen 4600 rpm ,Other NADA site list weight as 1900# and the only one I have found on net was on for sale in Germany with larger engine , 100 gal fuel tank , 40 gal fresh water tank . Mine could be 500# less with 4cyl , smaller gas tank ,no fresh water tank , rated 1300# 7 person and gear.

 

[egleas84]

Re: Max RPM for Mercruiser 120

Nice rig. Look like a 17p... Cant be sure from a picture of course. Interesting that your boat is 1.5 feet longer and nearly 700 lbs heavier but you can go so much faster. Of course all boats are crafted differently. My Merc 120 is probably the 2.5 liter though. Not sure.

 

[jimbo_jwc]

Re: Max RPM for Mercruiser 120

I was suprized at speed and hole shot first time got it running right . I think it has unique hull . Two guys and fishing supplies and full tank dropped to 46mph on gps .
Pics of hull on other post.

 

[jimbo_jwc]

Re: Max RPM for Mercruiser 120

My boat would'nt run right at first , rebuilt carb but got wrong accelerator pump , fuel pump , then used air to purg fuel line to tank with cap off and could brarely hear it bubble then it started to perculate , choke setting was wrong because fuse holder was broke that choke heater is powered by . Happy now it idles 600rpm and first time I wot in tank rubber impeller scattered . Was glad it was on driveway.

 

[egleas84]

Re: Max RPM for Mercruiser 120

My boat would'nt run right at first , rebuilt carb but got wrong accelerator pump , fuel pump , then used air to purg fuel line to tank with cap off and could brarely hear it bubble then it started to perculate , choke setting was wrong because fuse holder was broke that choke heater is powered by . Happy now it idles 600rpm and first time I wot in tank rubber impeller scattered . Was glad it was on driveway.

I'm going to have to try purging my fuel line that same way... I've had most of the same work done to my boat. Not sure if the carb is working right yet; waiting for some warmer water before I take it back to the guy (I'll do anything but carbs)

 

[jimbo_jwc]

Re: Max RPM for Mercruiser 120

Mine was 23yr old boat with approx 30 hrs on and gas was freshly added to get it running to sell but he couldnt get it too . He came down from $6100 to 5000 throwed in new battery . NADA price was alot lower but it was want I wanted and looked like new . I didn't know if there is a screen in fuel pick up
But these guys on here can probly tell you . When I finaly figured that flow to pump was not enough to run anyway near WOT I gave it some air .

 

[jimbo_jwc]

Re: Max RPM for Mercruiser 120

The number on the prop looks like mercruiser part # with the last 17P . I measured from center 14.5
"dia. motor says 4200-4600 paint starting to wear . 181cid must be = 3.0 L

48-78118-a40-17p prop so IT's 14.5" X 17Pitch still don't know if its cupped or not but was told its orignal

 

[egleas84]

Re: Max RPM for Mercruiser 120

The number on the prop looks like mercruiser part # with the last 17P . I measured from center 14"dia. motor says 4200-4600 paint starting to wear . 181cid must be = 3.0 L

I'm dropping down to the 17p (15x17) my engine is the 2.5L according to the plate on the engine. It also said I'm WOT @ 3900-4300. I bought a new 14.5 x 19 and got 32MPH @ 3800-4000 (no change in speed @ 4000, but it was just me) that prop replaced some off brand (marina had no idea who made it) 14.5 x 19 that had the wrong thrust washer on it and was giving me 30 MPH @ 4400 that prop was junk the thrust washer was causing it to hang off the shaft too far and cavatating....

I'm thinking I'll be going 32MPH @ 4300 with a 15x17 but have a better hole shot and be running the engine where it should be.

 

[jimbo_jwc]

Re: Max RPM for Mercruiser 120

How much hp is this one ? 1987 thundercraft cabin cuddy ski - $2500 (canton)

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Date: 2011-04-20, 6:32PM EDT
Reply to: see below

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1987 thundercraft cabin cuddy 3.0 4cyl. mercruiser alpha drive all hydrolic has new starter battery complete tune up winterized at the moment cd player. carb has been rebuilt a solid boat all safety equipment been inspected last year and has sticker sticker on boat good thru 2013 all electrical parts have been replaced and are new goes about 40 mph electric start have two sets of skiis tube ski jackets ropes a tow eye also have tube and kneeboard all teak wood has been redone cabin is real nice hold 3-4 people in cabin outside hold 5 people comfortable everything come with it has a 30 gallon tank and depth finder bilge pump all on switches. int. has a few tears price is negotiable. please call Brian at 330-488-0650 or 330-488-2713 thank you


?Location: canton
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[jimbo_jwc]

Re: Max RPM for Mercruiser 120

Thompson 196 18 1/2 ' approx 2400# . I'll look at prop to get dia and pitch number off of in daylight . Most rpm I've seen 4600 rpm ,Other NADA site list weight as 1900# and the only one I have found on net was on for sale in Germany with larger engine , 100 gal fuel tank , 40 gal fresh water tank . Mine could be 500# less with 4cyl , 27gal gas tank ,no fresh water tank , rated 1300# 7 person and gear. Also untill I got it running right I had it ideling about 800-900 rpm and when you would put in gear made heavy clunking sound compared to 600 rpm .

48-78118-a40-17p prop so IT's 14.5" X 17Pitch still don't know if its cupped or not but was told its orignal

 

[jimbo_jwc]

Re: Max RPM for Mercruiser 120

48-78118-a40-17p prop so IT's 14.5" X 17Pitch still don't know if its cupped or not but was told its orignal