40 hp Rough Idle

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Barry Loos

Well-Known Member
Jul 2, 2001
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My PT 175 came with a 2001 Merc, 40hp, 2 Cycle. It has a very rough idle at the specified 850 RPM in gear. My dealer said that this is typical because Merc went from 4 cylinders (old engine) to 2 cylinders in the new engine. The dealer said the two larger pistons in the new 40hp seem to compete with each other during idle instead of complimenting or balancing with each other as with the old 4 cylinder models. He also said the new style Japanese carburetor does not allow him to set the idle as accurately as with the old engines. When I have to idle through a long
Barry - I'm no mechanic, but have the same engine (2000 model 40 Merc on my PC 175) and have not had the problem you describe. I do quite a bit of trolling with my 4 year old where i've got the motor engaged in gear and in idle (slowest speed I can put her in) and she idles just fine.

As I said, can't give you help on the motor, but it doesn't sound like mine.


That doesn't sound normal at all. I had to say it, but it sounds like your dealer doesn't reallyy know what the problem is and is giving you a line of BS to cover it. I would call Merc and see if they is any truth to it. I had a caller dealer one time tell me that my Lumina was pulling back and forth due to something called "memory steering" LOL Never buy from them again! I didn't bother telling him that I knew it was the rack & pinion. Unfortunately, some dealers only want your business once. I hope your's is not the case. But find out, if it is, post it in the dealer report card. Good luck.


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