Thumping when accelerating

[AcogDoc]

Well.... I’m back!! Boat is running took it out for the first time since the switch boxes were fixed. I have a 1996 mercury 150 off shore on the boat (2 stroke) and when I’m accelerating I get like a thump... thump... thump.. it’s pretty noticeable and you can feel it. If you accelerate quickly it will go away and you can slow back down and everything IS fine. But it’s always the initial acceleration. It’s not like grinding from putting in forward or reverse too slow it’s not like that at all. It’s a more like thump than a grind. Any ideas what this could be??

[steplift20]

What year is your motor?
Is it carbs?
I have a 150 merc too , what I would check
Check plugs and plug wires, make sure they are in good
Change the water separator if you have one
It might be a carb problem if you have them could be a miss fire
Good luck

[AcogDoc]

1996 mercury 150 off shore 2 stroke carbs.

[spareparts]

trim the motor up and grab the lower unit, pull back and see if you get any unusual movement, if the motor mounts are shot, it will make noise like that. If it is jumping in and out of gear(feels like you hit a log), adjust your shift cables before any damage is done. When adjusting the cables do it with the engine running. Think about the shifter being a clock, neutral is 12, you want fwd in by 10, reverse somewhere around 2 o'clock, get fwd in as soon as you can, without it grinding before going in reverse. Try to keep it balanced, but if you have to favor one or the other, give fwd the bias

[AcogDoc]

Thanks spare! I’m gonna look into it. I did change the cables before this noise started happening and before the switch box dilemma. And I noticed it after I changed the cables. I swear I did everything right. I’ll check the trim business and the control cables. But if I remember correctly it’s in forward at about 10 and reverse about 2. Is there any reading material you can point me in the direction to try and make some adjustments the right way?? You’re the best man. As always thank you for your help.

[Blue_Runner]

Great advice, sounds like something might be going on there with the new cables.

[steplift20]

Sounds like spareparts pointed you in the right direction especially after you changed the cables and that's when the issue started.

[AcogDoc]

I’m hoping it’s just a simple cable adjustment. I thought I did everything right when I installed them. Does anyone have any literature or direction to point me in to make sure I do it just right?

[AcogDoc]

I adjusted the cables and took the boat out for a quick cruise. The thumping did not stop. But on a good note it shifts A LOT better. It wasn’t bad but it’s noticeably better now. I also lighted the trim up and didn’t noticed any noise or anything. I’m wondering if it could be the prop?? Like a hub within the prop? Any ideas?

[garbubba]

I'm running an old 200hp merc. pretty much the same motor. Can't say that sounds familiar. A spun hub could possible do that but when you go to take off you'll get nothing. Which doesn't sound like the case. I wouldn't think ignition or fuel would be the cause either. It sure sounds like the dog is slipping in the transmission. Which would take us back to the cables. You could disconnect the remote control & try shifting it by hand, that should eliminate a cable issue. Take someone with you & see if you can feel where the thump is coming from, if it's not the top of the motor, it almost has to be in the foot.

Not much help, I know.

Good luck.

[steplift20]

I don't know how to adjust the cable but I feel like that's your problem. I had a issue like that years ago only in reverse ,I brought it back and Jimmy from anglers marine who was a great mechanic adjusted it on land but said if it still happens to bring it back and thank god it didn't happen but he said the adjustment is very small so I can see you not getting it 100 percent right but I
would bet that's your problem