OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Trimmers and Brushcutters Two Stroke Trimmers & Brushcutters Stihl FS66 over-fuelling

Picked up an FS66 straight shaft brushcutter the other day. It had been sitting in a shed for a while , and didn't want to play at all.
I put a carb kit through it (Walbro), and a new fuel line, and it fired up almost straight away.

I ran it for about 45 minutes the next day. It was bogging down a bit under load, so I was going to tweak it the following day (I had purposely left it a bit on the rich side for safety sake).

When I went to start it the next day, it wouldn't fire at all. Pulled the plug out, and it was dripping wet. Pulled it over with the plug out, and you can see large drops of fuel flying out the plug-hole!

I've re-stripped the carb and made sure diaphragms and gaskets are right way around and everything is clean.

Tried searching through the forum here, but everything seems to deal with a lack of fuel, rather than an over-abundance.

Please help before I go (more) insane!!

Don

Did you adjust the hi and lo speed mixture in line with the Walbro manual? If the mixture is right, it sounds like it might be a fuel pressure problem. The Walbro manual is the best source of information I know of.

Don,

the bet is that you need to replace the diaphragms as well as the fuel filter in the tank before you tune.

Aren't the diaphragms part of the kit he bought, Bruce? If he hasn't replaced them, he certainly needs to before going any further.

Replaced the diaphragms and gaskets, (didn't replace the in-tank filter - I could blow back through it, and it didn't seem restricted). New metering needle, rocker arm and pivot rod. Blew carb cleaner through every orifice I could find, double (and triple) checked the diaphragm/gasket order both sides.

The only gray area, as far as I can figure, is the height of the metering rocker arm. If that is too high, could it cause this over-fuel situation? Everything I've read so far says the end of the arm should be about level with the face the gasket sits on. Took a fair bit of bending (from stock) to get it high enough, (you'd think they would be closer than that from the factory).

Igor, I doubt it was necessary to bend the lever significantly - I think about 9 people out of 10 would just install it and use it. However I could be wrong.

I agree Chris.

Igor, my point on the metering lever is that you may have caused the problem with the adjustment you made. According to the Walbro manual, the leading cause of flooding is "Metering lever set too high". Since you have flooding, and you massively bent the metering lever to make it higher, we have a possible hypothesis that you should put it back the way you found it in the kit.

I'm not trying to be an after-the-event critic here Igor, what you did is what I would have done before I spent decades doing everything incorrectly and learning by the experience. I've done the equivalent of what you did many times on various parts of cars, including float levels. The important thing is to do each wrong thing as few times as possible. (Unfortunately, I was always good at forgetting past mistakes and repeating them. I still do that.)

Bent the lever back to somewhere around halfway between the bottom of the metering chamber and the gasket face. Dried the plug, and disconnected the fuel line. Pulled it over, and it ran for about 45 seconds with no fuel line connected! Must of been a heap of fuel still in the crankcase from previous efforts
Started with 1 1/4 turns out on the low speed - ended up at about 1 3/4 turns and idling well. High speed is close to the same.

Grumpy - all after-event criticisms are welcome I spent part of my youth cursing over Strombergs, SU's and even the odd Tillotson. Life is nothing if not a learning curve

Thanks all for your input! Buy youse all a beer one day!

Igor, it sounds as if you just may be slightly off in the other direction with that lever, since you ended up with the mixture screws open a bit further than normal. However if it's running well, that's nothing to worry about. If you start to have trouble with transients (e.g. it stalls when you drop the throttle from high rpm, or when you first open the throttle, etc.) you might try a small lever adjustment.

I'm sorry if I got a bit critical there - you've come through a Walbro rebuild practically unscathed, so you are a decent carburetor mechanic. Glad to have you aboard.

I'll close this thread.