Merc 150 "bumps" while in gear. Please help!!

[fsujack21]

I have a 98 merc/mariner 150hp carb two stroke. (Sorry serial# is not on the transom bracket) I bought it off a guy who seemed reputable on eBay over the offseason. Only known problem at purchase was the tilt/trim which I rebuilt and is working fine. My problem was initially on my first test drive of the season the motor would "bump down" as I was getting into higher RPMs. I didn't notice it a lower rmps so after much research on this forum I focused on fuel starvation issues. Here is what I've done so far. Replaced primer bulb with factory merc bulb, replaced all fuel lines, rebuilt all three carbs, rebuilt fuel pump and ran on a separate on deck tank. Didnt fix the problem! So I feel like I've ruled out all fuel delivery issues. Since addressing the fuel issues im starting to notice this bump or shake even at lower rpms now.
So I've tried revving up at higher RPMs while not in gear and the motor does not shake or bump at all. This makes me think that it's not electrical? So my only other idea is lower unit. Is this something that's common for a lower unit to do when it's failing? I'm completely stumped. Please help I'm on Long Island and have a 15min canal ride just to get to the bay to test the motor and the green flies are eating me alive! Lol

 

[fsujack21]

Re: Merc 150 "bumps" while in gear. Please help!!

Maybe I'm not describing the problem well enough. The motor shakes or thumps very hard intermittently as I try to accelerate while in gear. It not like a vibration it's more like a hard thump but every few seconds and the power drops out. I hope that describes it better. I also failed to mention that all duel filters have been replaced with mercury/quicksilver parts.
Any help would be appreciated thx

 

[jimmbo]

Re: Merc 150 "bumps" while in gear. Please help!!

wire rubbing against linkages or block as thottle opened? or wires flexing and hidden break opens as throttle moved

 

[rvbrlb]

Re: Merc 150 "bumps" while in gear. Please help!!

I am by no means an expert on this, but I was out last night in our boat (first time of the year!) and had almost the exact issue. Although mine is a 200hp Evinrude, we're having the same symptoms, which makes me think that it's not really specific engine model related. I have not fixed it yet, but I think that it is in the throttle/shift linkage. I think mine is shifting in and out of gear, making the clunking noise, especially at very low speeds (just engaging into forward), it seems fine once the throttle lever is pushed past 1/2 throttle or so. Don't know if this is correct, but you're not the only one that this is happening to!

 

[Chris1956]

Re: Merc 150 "bumps" while in gear. Please help!!

Do you think the motor is coming out of gear at high RPM, and then going back into gear. Normally it sounds like a clunk-clunk. Mercs don't normally do this, but my old Johnny did it alot. It was a worn shift dog. See if the motor is all the way in forward, when your contol is in forward.

 

[rvbrlb]

Re: Merc 150 "bumps" while in gear. Please help!!

Thanks for the reply to my issue; I'll check that shift dog out, hopefully fsujack21 gets his figured out.

 

[fsujack21]

Re: Merc 150 "bumps" while in gear. Please help!!

Thanks for the replies. I went down to the boat this morning and was checking for loose wires or an interference from the linkage. While I had the motor running at idle I was pushing on the spark plug boots and I got shocked while pushing on the bottom spark plug boot on the port side.
So if there is a break in the boot could it possibly be shorting against something (was thinking the hood hatch on that side) and would that short be consistent with the motor "bumping"?

 

[Chris1956]

Re: Merc 150 "bumps" while in gear. Please help!!

Well, at least you now have something to fix. The motor would miss if the plug wire was arcing. Not sure that qualifies as a bump.

 

[fsujack21]

Re: Merc 150 "bumps" while in gear. Please help!!

Well, fixed the spark plug wires but just before I started the motor I noticed a bit of an oil slick near my motor. So I sat and waited and observed small white globules floating to the top of the water from somewhere in my lower unit. But the water was too merky to identify exactly where it came from.
So Im obviously leaking lower unit oil. Now what? I've replaced lower units before but never fixed or rebuilt one. Where should I start? Prop seal? Thx

 

[Chris1956]

Re: Merc 150 "bumps" while in gear. Please help!!

Are you sure the oil is gear oil? Residual 2 cycle oil can do that as well. Recommend you confirm gear oil before attacking gearcase.

 

[fsujack21]

Re: Merc 150 "bumps" while in gear. Please help!!

Pretty sure it's gear oil. I took it for a very brief test drive while just above idle it kept slipping out of gear and then I'd have to advance the throttle to a much higher rpm to get it to re engage gear.

 

[Chris1956]

Re: Merc 150 "bumps" while in gear. Please help!!

well, it sounds like gearcase is shot.....I mean if you need to advance throttle to get it to go into gear...that's not good.

 

[fsujack21]

Re: Merc 150 "bumps" while in gear. Please help!!

Ive done most work on outboards but never tried rebuilding a lower unit. Is it something that u can do yourself or has to be done at a shop?

 

[Chris1956]

Re: Merc 150 "bumps" while in gear. Please help!!

Rebuilding the gearcase requires some specialized knowledge and specialized tools. if you need new gears and bearings, they can be $300 each. A brand new gearcase may be had from SEI for the cost of a couple of gears. Used gearcases are avaiable for cheaper than that.

 

[rjoneslaw]

Re: Merc 150 "bumps" while in gear. Please help!!

Greetings,

Similar sounding issue. Just got my hands on a "hardly used" 2010 Suzuki 2.5 HP. Fired it up in a water barrel at the seller's house and it ran fine in neutral at various RPMs. Also runs fine in gear at very low RPMs. But as soon as I throttle up beyond about 25% when it is in gear, a clunking kicks in. It is a substantial clunk. Almost sounds as if somebody is bonking the transom with a baseball bat. The clunking is also rhythmic. The timing of it remains absolutely constant at a given RPM. When you crank up the RPMs, the clunking increases in frequency. At low RPMs, it clunks roughly every 2.5 seconds. At high RPMs, it clunks about every half second.

In addition to wanting to be able to fix this, I'm wondering if I need to have a talk with the seller about the value of his word.

Many thanks for your advice.