Small Sneeze While Idleing

[rekogniz1]

What would cause my 91 Evinrude 150xp to sneeze while idleing aprox every 5 secounds or so? It idles fine and then kinda misses but hesitates like it sneezing. Checked timing and it is set properly. Runs fine when throttle is advanced from idle but does continue to miss till about 2000 RPM then goes away. I have new plugs with less then 4 hours on them but seem to be darker then they should be ......seems to be running a little rich.

 

[bktheking]

Re: Small Sneeze While Idleing

Dirty carb(s) will do it, have you cleaned them? What plugs were installed, was the issue present before you changed plugs?

 

[rekogniz1]

Re: Small Sneeze While Idleing

Carbs where just rebuilt, plugs purchased and they gap'd them for me. The problem litteraly just started while on the muffs last night while I was setting my idle speed. Maybe a fouled plug?

 

[bktheking]

Re: Small Sneeze While Idleing

You can't set your idle speed on muffs, first problem found. Has to be done in a lake or a large test tank, not enough backpressure on muffs. What make and # plug was put in the motor?

 

[Dennisanoka]

Re: Small Sneeze While Idleing

You should really set the final idle speed when the motor is in the water. It will idle faster when it doesn't have the exhaust back pressure. Not sure that it would cause the sneezing though but I'd drop it in the water to be sure. If it's not that then I'd go back to whatever was changed before it developed this condition and re-examine them.

 

[rekogniz1]

Re: Small Sneeze While Idleing

Let me clairify! I did adjust the idle on the lake the other day but was adjusting the slack in the cable and pressure on the throttle cam as it was causing it to idle high sometimes depending how the cam returned to rest. My idle is set by the timing not by and idle screw. Nothing was changed prior to this happening, it had been running fine the last few times I took it out after the plugs where changed and carbs rebuilt. The plugs I am using are Champion XXXXJYC (I dont have the boat avilable to look at right now). The plugs are what is recomended and what was in ther priviously so I am sure they are the correct plug. I have not owned the boat very long so have never experienced a missfire and am wondering if it could just be a fouled plug.

 

[d.boat]

Re: Small Sneeze While Idleing

Have you checked for air leaks throughout your fuel and oil system?

I had an idle sneeze on a previous outboard of mine and I'm pretty sure it was caused by a tiny air leak in the fuel system, because identifying and fixing an air leak made the sneeze go away.

That engine had a VRO/OMS fuel pump that had been converted to gas only by capping the oil inlet. The previous owner had used a - I don't know what they call it - a simple rubber nipple over the oil intake and it had degenerated/rotted and was leaking air. I replaced it with a little piece of good strong fuel hose, properly clamped to the inlet and plugged at the end with a stainless steel bolt and clamped. Sneeze went away immediately. Frankly, I don't have the expertise to say this was the one and only cause of that sneeze, but an OB mechanic I know said it made sense to him.

An easy thing to check and cheap and easy thing to fix if you find one.