Mercruiser MCM 170 stalling

[boater_bill]

Hi, I just bought a 1989 Sea Ray with a Mercruiser MCM 170. When I put it into gear and try to accelerate the engine struggles and stalls. It only seems to accelerate when I increase the throttle very slowly. I changed the oil and filter on the engine and changed the oil on the stern drive, it seemed to help a little bit but the problem still persists. I've only seen one other post like this and it seems to suggest that it is "overly rich at Idle and goes lean when you drop the throttle". I was hoping I could get some suggestions as to whether or not this is the problem and how to fix it. Please and thank you.

Bill

 

[Eric 3.7LX Alpha 1]

Is this happening while on the trailer or on the water?

I am going to suggest what I would do if I bought a "new to me boat":

complete tune up including: correct spark plugs, spark plug wires, points, cap, rotor, condenser, new fuel filter in the carb inlet and fuel water separater filter, set/check timing and dwell, and adjust idle speed... couple hundred bucks and you start out on the right foot right out of the gate.

I am pretty sure I would be doing this regardless of how it's running. If you've ever broken down on the water, you know it sucks.... if you haven't I'll be the first to tell you... it sucks! Most of these are on the annual to do list.

Check the shift cut off switch on the shift plate on the engine. If you can not see it from the controls have someone else look at it. Is it moving when the engine is acting up? It should only move when you shift the boat OUT of gear while IN the water. Not into gear and not while on land on the trailer. To better understand the system click on this link from the Adults Only Sticky created by DonS:

http://forums.iboats.com/forum/engi...3-how-to-how-the-shift-interrupt-system-works


If that checks out ok, it does sound like a fuel related issue. Could very possibly be crap in the carb. If the boat sat for awhile, it doesn't take long for gas to go South, and mess up the small passageways in the carb. If you don't wanna do all the things in the tune up list NOW, then at least look at the fuel related things, cause that's what it sounds like to me.

this is my .02 and I'm sticking with it

Welcome to Iboats and the 470 Club!

 

[boater_bill]

Thanks so much for the fast reply Eric This only happens when the boat is on the water. I do know that the spark plugs, starter and distributor were changed this season. But I will check the rotor, condenser and fuel filter and fuel/water separator. I do think it is something to do with the timing or idle speed (any advice on how to check/fix that?) I don't think it's the shift cut off switch but i'll check that as well. Also, it has been sitting a while so I think you might be right about the dirty carbs. However, I did buy some seafoam carb cleaner fluid and put it in with a tank of premium gas the first time I put it on the water and it seemed to help. Maybe I should do that again? What do you think?
Thanks again for the quick reply. I'll keep you posted on my progress.

Regards,

Bill