Trying to tune this bloody Flo Jet carb on an old 11hp Cox ride on. Great machine but I can't tune the carb.
It has what I can assume is an idle adjustment a high adjustment and another random adjustment.
If anyone could give me a 'how to' on these carbs I would be bloody greatful! At the moment I've got it reving high and the mower responds well but it won't shut off, I have to pull the fuel line.
I've taken a photo with the adjustment screws circled to provide further clarity from my rambling.
This might help ,the last one I tuned needed the emulsion tube to be removed so all the small jet holes could be cleaned out, this was to stop the engine hunting.
Can you post the model and type number of the engine? I don't see a small one piece Flo Jet with an adjustment at the fuel bowl in the service manual so I need to look up your setup.
Its worth noting that the new flo jet carb I purchased has an additional screw adjustment next to the idle screw that the original carb did not have. Unsure why..
This might help ,the last one I tuned needed the emulsion tube to be removed so all the small jet holes could be cleaned out, this was to stop the engine hunting.
Ok, if it is running badly, there are a few things i would check first. Are the bolts that hold the carb on tight, and is the gasket ok? if there is a problem here it will draw air in and run lean.
valve clearances can make it a problem too, also if the flywheel key is sheared or half sheared it will run badly.
So by the sounds of it you are using a new carburettor, so throttle shaft wear shouldn't be an issue. What is the engine doing exactly that it required tuning?
The screw under the float bowl is the high speed mixture screw. the one up on the very top is the low speed mixture screw, then you're idle adjustment is on the throttle shaft itself.
I always start with both screws at 1.5 turns out, get it started, then adjust high until it runs properly. (clockwise on the screw on the bottom will lean it out and make it pop and or start to die, counterclockwise will make it rich, blow black smoke and die, you want it about halfway between rich and lean.
once it is running nicely start low, it is usually easier to have the idle screw in a fair way so it doesn't just die. same as before, lean will make it hunt up and down, rich will choke it. once you find the mid way start lowering you're idle speed until its idling nicely at i think approx 800rpm
you may have to adjust high again after low, as they do affect each other.
Now all of this will have to be done likely with the air filter off. once its running nicely sit the filter on, and you may need to lean both down a little bit as the filter will restrict the intake flow a little bit.
If it will not shut off it is not a tuning problem, it will be something to do with the stop switch. is it on a key or is it just on the throttle control at the back? it should stop regardless of rpm.
Thanks for such a detailed reply Nath. It should be stickied in the Briggs motor thread!
As for the motor not turning off; I had it 'tuned' (I use that term loosely) to a point where it would idle well albeit, high but smooth, but not blowing smoke.
At full revs under load with the deck turning it was also very responsive and not blowing smoke. However it was revving very high. I was concerned that it is revving too high and I could cook the engine - even though in regards to smooth idle & responsiveness it was tick all the boxes.
Its a key turn ignition.
Im good with chainsaws & diesel engines however small 4 strokes are a bit of a grey area for me!
Kill switch wire should be on the carby or cable some where close, small black wire. All that does is short out the magneto. The black wire may also go up to the ignition switch where it is earthed out up there somewhere.
Ok cool. So it is not a tuning issue then. Tuning these carbs adjusts the mixtures, It will not affect the stopping nor the full speed revs. The revs are governed by the Governor and its spring. Being that you have changed the carburettor, it is always a good idea to adjust the governor. Simple process, you will probably have to remove the throttle control at the back of the motor where the throttle cable goes. loosen the nut on the governor arm and hold the throttle wide open. while holding that twist the shaft the same way until it stops and tighten the nut.
If it still over revs and the spring doesn't look modified or shortened, try bending the bracket it attaches to, some people fiddle with these to try and get more power from the motor. They do, but the engine also goes bang.
As norm said stop switch wire will go from under the cowl to the throttle control at the back of the motor. usually to an insulated bolt. there is then usually a wire from there to the key switch. check something hasn't fallen off or been cut somewhere.
I just found you're pictures!. so the brass coloured screw on top should be wound all the way in. I do not know why these have a spring on the aftermarket carbs. Also by the way there isn't a kill wire attached to the motor that i can see. check for a loose wire lying around.
