Merc motor spits/sputters at throttle down

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Eric B

Well-Known Member
Mar 1, 2001
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Hi all. 2000 Merc 40 classic (2 cyl). I changed to synthetic oil, started with
100%, did not leave any in oil tank. I put new plugs in. Ran tests fine.

When to lake a few weeks ago. Very little smoke, motor seemed to run
good. However, I did notice some sputtering when I throttled down and
some while its at idle, but never while I am throttleing up or when its in
gear. Could the oil be doing this?? should I try putting a mix of 50/50 of
standard oil and synthetic in?

Just thought I should post this update of mine for all.

I wont quote the entire post, but will now give history of what ive gone through.

1. Used Quick Silver oil, good grade gas, NGK plugs.. motor ran great.

2. Wanted to try using the Pennzoil Synthetic oil. Put that in, new plugs (motor craft)

*** Motor started to spit/sputter at idle ***

3. Changed to NGK plugs (gap was correct).. NO change in problem.

4. Put Quick Silver standard oil in, new NGK plugs, SAME gas.

Tested motor today, ran GREAT!

I guess for my motor, a 2000 Merc 40, the Synthetic oil wont work as well as the standard oil.

Was hoping to reduce the smoke but I really dont get much more with standard oil. The

Syn. may work fine in larger motors, Im not sure, but I know what works now for me.

Thanks for input I have gotten about this.