whats the proper setting on idle screws?

[Af4408]

I just purchased a 40EL 2 cyl. Mariner and it idles rough, I want to try and adjust the idle screws but not sure how. I've always heard turn them in all the way then back them up to the highest idle, is this right? or how many turns back would suffice? It runs perfect above idle.

 

[Silvertip]

Re: whats the proper setting on idle screws?

There is no magic one setting fits all. Adjust inward in 1/8 increments until the engine begins to bog or gag, pausing 10 seconds between each adjustment. Note the screw position. Then back it out in the same manner until the engine begins to die. The best idle quality is then somewhere between those two settings. The final setting is then about 1/4 rich from best idle. And make sure you make these adjustments with the engine in the water, not on muffs as there is no exhaust back pressure.

 

[Af4408]

Re: whats the proper setting on idle screws?

Thank you very much, I understand this motor was made in Japan by Yamaha and I talked to my local dealer, gave them the SN but they can't figure out what year model it is, 420706 they say they can't even find the number. Any ideas?