Mercruiser 120 Bogs at WOT

[sooperspeed]

ok, I got the boat running and it is running really well (thanks to the guys in the forum) other than at WOT. We took the boat out cruised around to make sure we worked out all of the kinks. It runs great, BUT when you put the throttle down it doesn't have enough power to pull me up on a wakeboard right away. It take a little bit. It seems like it lacks about 50% of what it should have. Now we did have a bit of bad gas in there, AND I have not replaced the fuel filter. Does that seem like it could be the issue? I am also thinking the I need to have someone put the throttle down while I look down the carb. Isn't there something that could potentially need to be replaced or rebuilt in the carb? <br /><br />Anyway, thanks for all the help thus far you guys rock. The boat runs great and we have had a blast this weekend. It just has a bit of trouble at WOT.

 

[Don S]

Re: Mercruiser 120 Bogs at WOT

Now we did have a bit of bad gas in there, AND I have not replaced the fuel filter. Does that seem like it could be the issue?

Well Yea, plugged filter, plugged carb, water or dead gas in everything. Do you think that should run good that way?<br />Fix the obvious stuff, then see how it runs.

 

[jeff13601]

Re: Mercruiser 120 Bogs at WOT

Didnt you have a post a while back? You did do a full tune up didnt you?

 

[sooperspeed]

Re: Mercruiser 120 Bogs at WOT

yeah, I did post a while back and thanks for the help. I'm not so smart when it comes to the boat stuff. I know I sound like a doofus, but I really had no idea that the points and condensor could be the source of the starting problems.<br /><br />We had about 1/3 of a tank of so so gas and we filled it up with premium on the way home. I am going to grab a new fuel filter tomorrow.<br /><br />I really haven't had too much experience with boats but I would think the 120 in a 16ft boat should be enough to pull a skier or a wakeboard.<br /><br />Thanks again for the help.

 

[jeff13601]

Re: Mercruiser 120 Bogs at WOT

I did the same thing because I didnt realize the imp of the points. Did you just put the points in or was the dwell set? I have a 120 in a 22 ft aluminum Sylvan. I top out about 37 and wouldnt consider it a ski boat, although I have never tried. Do you know how fast it is topping out at and what rpm is it running full? If you have 3 or 4 big adults in the boat and one skiing that is a pretty good chunk of weight

 

[sooperspeed]

Re: Mercruiser 120 Bogs at WOT

That was the first thing we did we set the point gap, then put everything together like perfectionists. The boat is a 16ft tri hull. It is actually a bit of a pig, but unfortunately I just bought the tow vehicle so our boat fund is non existent until probably next year. <br /><br />Your boat sounds like it is doing very well. From what I read this motor is really pretty tough. <br /><br />Right now ours runs right at about 37 with 4 people in the boat. I wasn't paying too much attention to the rpms but I will next time. I think that tach might be a bit off actually. This is what frustrates me. The boat runs so good in open water, but as soon as we put someone on a wakeboard or ski's behind it, the hole shot was crap. I am a dummy for not checking the fuel system, but we wanted to get the boat out just to run it on the water so bad it slipped my mind.

 

[jeff13601]

Re: Mercruiser 120 Bogs at WOT

You said you set the point gap but not with a dwellmeter. That needs to be done. If you have a tri hull you are going to need a little more to get up on plane. I had a tri hull years ago and it was heck to get it up and out of the hole. I am really pretty surprised that it tops at 37 if its a heavy fiberglass hull

 

[sooperspeed]

Re: Mercruiser 120 Bogs at WOT

when you say dwell meter to you mean an electronic meter? We have one of those. We just set the gap with a little tool my dad has. This boat does take a bit to get out of the hole for sure. Once it is one plane though we were able to cruise right at about 37. Now the tach is a bit screwy, so I wouldn't be surprised if the MPH guage was a little off also. The boat realy isn't that big, I don't know what the beam is, but it is only 16ft long. Not a whole lot of weight even though the hull is a little heavier than a V with the same lenth and width. The water we were on was glass also, no chop whatsoever.<br /><br />I am going to change the fuel filter and try to get it out on the water tonight or tomorrow night to and hopefully that will do it.

 

[jeff13601]

Re: Mercruiser 120 Bogs at WOT

Sounds like you got a good running little 120. You really do need to adjust the points with the dwellmeter. Your specs are on the starboard side of the motor. Yor going to come out of the hole hard with a trihull. Check the WOT but 37 is good top for a 120. If you want more hump out of the hole get a six. Let me know when you want to part with it. LOL

 

[DJ]

Re: Mercruiser 120 Bogs at WOT

120's were never known for their hole shot or pulling power.<br /><br />You may be overpropped, but you need an accurate tach. to tell.

 

[sooperspeed]

Re: Mercruiser 120 Bogs at WOT

The boat does need a bit of work. It isn't the most beautiful thing in the world, but she gets the job done. <br /><br />We are going to break out the dwell meter tonight and get them figured out.<br /><br />I know it won't ever be a professional towboat, but just something to play around on and enjoy the lakes and rivers in our area. I am going ot look for a goo deal this winter on a bigger boat with possibly a V8 in it. My mom doesn't like the boat because she says it is too small...

 

[3 Card]

Re: Mercruiser 120 Bogs at WOT

I have 95 Wellcraft Excel 19SX (4.3L Merc)and experienced a similar engine lag problem with skiers. Turned out to be too much prop for a good hole shot (14X23 3 Blade). I switched to a 4 blade prop (14X20) which makes a big difference in hole shot. I did give up about 8MPH in top end speed but its worth it...Much happier and pulling folks out on slalom with ease...If you can get an accurate tach reading @WOT that would help narrow it down...I believe optimum range for your engine at WOT is 4400-4800 RPMs.

 

[jeff13601]

Re: Mercruiser 120 Bogs at WOT

As long as your having fun, thats whats imp. One less person in the boat even helps a little with hole power. Like I said, I think its prob running good but everyone, including me, lol, wish they had a little more power. Try what 3 card suggests and it might be to your liking

 

[krivnalyendi]

Re: Mercruiser 120 Bogs at WOT

I've got a tri-hull 19' 1977 Ranger with a Ford V8 302 188hp - a bigger and heavier boat with a bigger engine than yours. It's older and has had a lot of problems like yours recently, but I've recently got it running smooth with a full load of 8 people and a skier behind it, and she pops out of the hole instantly. I don't know much about it but I would look into the StingRay attachment for your outdrive, available at West Marine for ($90?). I'd ask around before you make that kind of investment and modification to your outdrive, but it's supposed to make it 50%+ easier to get a smaller boat out of the hole.<br /><br />Aside from that, I'd look at the air cleaner on top of your carb and make sure that it's big enough to let the engine breathe and not old and rusted (I had a crappy 20+ y.o. rusted metal one on mine). Buy a $10 can of carb cleaner, take off the air filter and run your engine (with water!) and follow the directions to clean out your carb (this is not the best solution; consider rebuilding your carb if you think it is truly fouled) before putting the new air cleaner on. My engine was stalling like crazy and had no pickup; I had all new fuel lines and pumps and recently rebuilt carb. So I took off the air filter to let it breathe and had plenty of power; left it off too long and crap got in the carb, presumeably. <br /><br />Sprayed in some carb cleaner, ran the engine for a bit and put on the the new air cleaner - she's purring like she were new. The bigger air cleaner also lets the engine breathe better, giving you more power (might help a little with getting out of the hole).<br /><br />I've a novice but this is what I did to get my engine running smooth for cheap. Some veteran techies might want to confirm this makes any sense, though.

 

[sooperspeed]

Re: Mercruiser 120 Bogs at WOT

What size prop would help with the skiers for my engine? would the 14x20 work? I could care less about top end, I just want to be able to pull everyone around and not struggle to get everyone up.<br /><br />Also what does everyone thing about the Stingray thing? does that help?

 

[vipzach]

Re: Mercruiser 120 Bogs at WOT

Start a new thread on the stingray thing. What size prop is on it now? Did you get the gap and dwell set right? I would get those things done first, before changing a prop. Also...what about the gas? Do you have a fuel water seperator, if not I would get one.

 

[jeff13601]

Re: Mercruiser 120 Bogs at WOT

If it is a standard prop it should be a 14 x 19. Boy I hate to get into this prop debate again. lol. Spend a few hundred and get a set of those trim tabs

 

[vipzach]

Re: Mercruiser 120 Bogs at WOT

Jeff you could start a big debate just recommending those trim tabs. LOL

 

[jeff13601]

Re: Mercruiser 120 Bogs at WOT

Would get even better if I recommended a 14 x 17 stainless prop and trim tabs, lol.

 

[bobweimortz]

Re: Mercruiser 120 Bogs at WOT

What is wot rpm for merc 120