Mercruiser 140 help??

[petrey10]

I just bought an old 1971 Larson with a Gm inline 4 cylinder sterndrive engine that I thought was supposed to put out 140 horses. Well I wanted to test it out today after I bought it (it has been sitting for awhile but I dumped the gas tank, filed the points on the carb, and it would idle really)...Well we got it started and it would idle pretty well in neutral and then I could put the boat in gear and it wouldn't idle as well but still ran most of the time...Then I would try to put it in gear and BAM the engine would bog out...well then I put it in neutral and tried reving the engine up and it did pretty well...then put it in drive and it would bog down but the take off...but when I was at full throttle the engine would back fire and I would only be going 10-15mph...This was with the trim set all the way down ( the hydrolics work pretty well as I can raise and lower the prop at will)...I really wish I could get this baby running because there is only 185 hours on the engine and it came with all new leather and carpet for the interior and for 700 bucks was a steal...can anybody help me?? do I need to rebuild the carb?? is 15 mph the fastest this can go?? I was told the previous owner could go about 40 on it...the speedometer goes up to 65 so I would think I could hit 60 pretty easy... PLEASE HELP I am desperate...


I hope I stated right that the engine is a 140 model....its serial number is 2966548

 

[thumpar]

Re: Mercruiser 140 help??

If you are popping/backfiring I would check the timing and the valve lash. I have a 120 and would highly doubt 40mph unless it is a small boat, but yes you should be able to do more than 15. You should really look at the RPM's more than speed.

 

[ziggy]

Re: Mercruiser 140 help??

ya need to get yerself a mercruiser service manual. c-90-68648. mine came in 2 volumes.

ya need to do a full tune up on it. points. plugs, condeser, cap, rotor, maybe plug wires. do timeing and dwell and set it all up to the specs. in the manual. being that it's sat for a bit. it may need a carb rebuild too. but i'd start with the electric side first. then move to the fuel side if ya still got issues. if ya need some specs right away, before ya get yer service manual, i can post a few up if ya need them.

i think yer 60mph goal is a bit optomistic too. maybe 35-40.... my 165hp only does 43mph @ 4300 rpm........

 

[petrey10]

Re: Mercruiser 140 help??

could you ski going 35-40? would a different prop setup help at all? How much do you think it would cost for a shop to do all this?? I want it done right the first time and I want to get it going by the 21st of July

 

[ziggy]

Re: Mercruiser 140 help??

could you ski going 35-40

sure, no problem. that'd be to fast for me.

would a different prop setup help at all?

ya need to get yer engine runnin proper. that bein, have it reach proper wot. yers would be 4200-4600 rpm. ya do that by haveing yer engine in fine tune. then adj. the prop pitch for yer intended wot spec. then further to adj. for yer perticular appliction. ie waterskiin... if ya really are only gonna be doing the heavy load of waterskiin, ya could target yer wot for that. which would be less pitch. but i think i'd go for normal load 1st then get a second prop for skiin if the one ya end up with aint up to the job.....it's always good to have a spare prop onboard anyways, just in case.......

I want it done right the first time

if ya want that, don't take it to a shop. get the mercruiser sevice manual & do it yerself, then ya'll know it's right. everyone here on iboats is here to help ya too..... so take advatage. this is the place to be if ya want to get it right......(side note) yer mercruiser store near you will help ya out and do a good job too....ya just have to be able to reach deep in yer pockets is all............

 

[andy1canada]

Re: Mercruiser 140 help??

Howdy,

Petrey...

As the boy's said, unless you have deep pockets, do all the work you can yourself. Not only will you save $$$ but you will learn many important things about your new boat... like what to do if (make that when) you break-down out on the water.

Change that oil! (engine & drive). Change the fuel filter on the carb. Do a tune-up, compression-test. All this is back-yard stuff and there's a ton of qualified people on this forum who'll walk you through it.

Get a Merc Service Manual.

The motor you have has a great reputation and if it's not over heating and runs well, you'll get lots of fun out of it without breaking the bank on fuel costs.

I had an old 71' Fiberform runabout with the same engine and I could better 40/mph with only me in it.

I ran a 19/pitch prop for ski/tube stuff and a 21 for top-end cruising.

First get her running up to snuff, then go to the Prop Forum if you need help with that.

You've done right for yourself (and those who'll be going out with you) stumbling onto iboats.

Happy Boating!
Cheers,
Terry

 

[petrey10]

Re: Mercruiser 140 help??

you guys are being more helpful than the other forum for sure....ok well what is the first thing I should do to help it run better?? I mean the first step in the tune up?? walk me through it and I can do it...I have the time and need this boat running ASAP...I got vacation in 3 weeks and would love to get it running great by then... TEACH ME....

 

[petrey10]

Re: Mercruiser 140 help??

actually is the anyway I can make sure that my motor is the 140?? The guy that I bought it from said it was but I just want to make sure ...I have the serial number and it is ......2966548

 

[thumpar]

Re: Mercruiser 140 help??

I would start with the stuff that ziggy said or convert to electronic ignition if you don't want to mess with with points.

The drive should have a decal with the size and HP on it. Could be worn off and then I have no idea.

 

[ziggy]

Re: Mercruiser 140 help??

if it's a 4 cyl. that serial number does seem to fall within a 68-82 140hp.
http://www.marineengine.com/mfr/mercruiser_models.html

 

[petrey10]

Re: Mercruiser 140 help??

well with this serial number it could either be a 120 or 140 how can I tell the difference??

 

[ziggy]

Re: Mercruiser 140 help??

ya obviously have the seial number sticker on yer engine. there aint no other stickers?

so far the only difference i can see in a book is that the stoke and cyl. dia. is different between the two. though, w/o takin it apart to measure them, i don't know.......hopefully someone can chime in with some surefire way to tell from the outside for ya....good luck....

 

[petrey10]

Re: Mercruiser 140 help??

there is a sticker on the engine but over time has eroded away and I cant tell for sure what it is...

 

[thumpar]

Re: Mercruiser 140 help??

There should be a spot on the engine that is stamped with the serial #. It is just a bit lower and to the front of the motor from the distributor. It is a flat spot and not hard to find.

 

[whywhyzed]

Re: Mercruiser 140 help??

2966548 could be either 2.5/120HP or 3.0/140HP
How to tell:
2.5/120 has only a pulley on the front of the crank, 3.0/140 has a vibration dampner on the front of the crank

 

[petrey10]

Re: Mercruiser 140 help??

ok so the vibration dampner would not have a pulley on it correct? and the pulley/dampner would be facing the driver correct?

 

[ziggy]

Re: Mercruiser 140 help??

2.5/120 has only a pulley on the front of the crank, 3.0/140 has a vibration dampner on the front of the crank

ah, someone who knows how to tell the difference. thanks kjdkjd....

ok so the vibration dampner would not have a pulley on it correct? and the pulley/dampner would be facing the driver correct?

they'd both be a pully wheel. the dampner will be thicker and much heavier. there are two parts to a dampner. inner and outer. ya should be able to see the two different parts. yes, they'd be facing the driver. or ya could say it'd be mounted to the front of yer crank on the ft. of yer engine.....

the left pic is a pully, the right a torsional (vibration) dampner

 

[petrey10]

Re: Mercruiser 140 help??

ok its offically a 140 as it has a dampner and I can slightly tell on the sticker that it has a 40 in it.... now where do I go from here to get it tuned up?

 

[petrey10]

Re: Mercruiser 140 help??

also tried to start it today and it has sat for about 2 days since being ran....didn't touch the throttle and it turned but never fired up...went full throttle and then brought it back to neutral to try and fill the carb.....it fired for a second and then shutoff....I am starting to think I am not getting fuel to the engine (which means running too rich right??).....the prop is aluminum and I can see significant wear on the blades....looks like they are worn down....

 

[Dakota47]

Re: Mercruiser 140 help??

no fuel would mean very LEAN conditions. if your running rich that means tyo much fuel>>fyi