rich idle

[4speedfury]

I have a simple question. If the idle circuit needle should be open 1 1/2 turns on a 10 hp, will running it way too rich, say 5 turns out, make it backfire quite bad cold and to a lesser degree warm?
thanks

 

[Nate3172]

Re: rich idle

it's possible i suppose if you are putting too much fuel into her. Does it backfire out the exhaust or the carburetor? The 1 1/2 turns is just a starting point. Altitude, change of fuel grade, change of oil mixture, barrometric pressure, temperature of the day, alot of things come into play when adjusting the idle mixture on your engine. For you, depending on all these things, your engine may run best at only one turn out. Why is it at 5 turns out though? that seems way too excessive. Usually it only takes an 1/8 to a 1/2 turn to come into the right setting from the initial setting.

 

[4speedfury]

Re: rich idle

I bought the engine a couple of weeks ago as a replacement for the 1955 fleetwin that gave up the ghost. It's a 1976 model. I removed the carb yesterday under the recommendation of a forum member to check for a dirty condition causing surging at high RPM due to a fuel restriction (spotless, by the way...). upon disassembly, I counted the turns in first so that I could have an idea where it was before I took it apart. Also I suspected something because it smoked like something fierce when idling yesterday. It was the first trip out with it. So it was like this when I got it .... really.
I suspect that the surging was due to the possibility that it was over revving and the main jet was not large enough to handle those RPM's. You see, I needed to reseal the crank case halves before I could use it, and I guess I set the linkage incorrectly. I think it may be going past the governor. At least that makes sense to me.
As far as where the backfire is happening, I'm not posotive, but I think out the exhaust. What would this tell you?

 

[4speedfury]

Re: rich idle

bump

 

[bowhuntrrl]

Re: rich idle

First of all, backing the idle needle out leans the mixture and will definitely cause what is called a lean sneeze .The adjusting screw allows air in for the idle, not fuel. The more turns open, the leaner you are running it. This makes it stumble off idle, possibly stall going into gear and would cause it to spit when trying to accelerate off idle. If it won't run where it's supposed to be set, then it needs a carb overhaul.

 

[eurolarva]

Re: rich idle

That mixture screw regulates gas not air. 5 turns out is way too rich. Typical carb setting would be about 1 1/4 turn counterclockwise from totally seated. To adjust you want motor in as low an idle in forward gear as possible so that it will keep running. Slowly turn clockwise in 1/8 turn increments every 20 seconds till it starts to race. Go back the other way and do the same thing till the motor stumbles. Half way between race and stumble is the correct setting. I am pretty sure that motor does not have a governor.