miss-mixed oil / fuel ratio= Rough Idle?

[Sea_Sprite]

My 75 hp merc has never had any vibration in it at all. Lately the past 2 times I went out the motor seems to vibrate the boat quite a bit, it seemed to happen after I filled up.. and the lady screwed me up at the gas station, so long storry short I had put in enough oil for 7.5 gal of gas but only put in 5.5 or so. Is this mix off enough to cause the motor to run a little rough?<br /><br />I dont think i hit anything to bend a prop or anything, and its only at slow / no wake times I feel this vibe.<br /><br />Thanks!!<br /> Mike

 

[andy6374]

Re: miss-mixed oil / fuel ratio= Rough Idle?

Is is smoking? I wouldn't think it would run that rough. I have an 88' V6 200hp merc that I run 45:1, as my safety net, and it idles flawlessly. If it is too rich, then you could foul your plugs What's the ~ mixture?<br /><br />-andy

 

[JB]

Re: miss-mixed oil / fuel ratio= Rough Idle?

Modestly rich fuel mix shouldn't cause that, Mike. Even double oil shouldn't.<br /><br />You have some other trouble.<br /><br />Good luck.

 

[Sea_Sprite]

Re: miss-mixed oil / fuel ratio= Rough Idle?

humm<br /> I dindt think that was enough to cause issues either. Wonder what else it could be...<br /><br />Any way to check for a bent prop, i mean could it be bent just a little where I cant tell? and there are no vibrations at higher speeds..

 

[timmathis]

Re: miss-mixed oil / fuel ratio= Rough Idle?

Make sure the motor is not loose from boat!

 

[dajohnson53]

Re: miss-mixed oil / fuel ratio= Rough Idle?

Your mixture is probably around 36:1, if you intended to mix 7.5 gal at 50:1, but used the same amount of oil in only 5.5 gal. As most people said, it probably shouldn't cause rough idle.<br /><br />The simple things I've found that cause rough idle are fouled plug or loose spark plug wire eithier causing a cylinder to misfire or not fire at idle. First thing I'd do is check all of your spark plugs and make sure the wires are snug. After that, some other things that could do it, but are a little more complicated are a bad coil making a plug mis fire or not fire, contaminated fuel or a dirty carburetor.<br /><br />Just some simple thngs to check before going further. <br /><br />By the way, why not just add a couple more gallons to make the mix correct?