Stihl FS 36 & FS 66 carb issues, Walbro carb swaps

[canucklehead]

Howdy everyone!! Great site. Whenever I google search small engine problems i always seem to find a thread on this site so i thought I should join.

I have a Stihl FS 36, good compression at 120 PSI. Replaced fuel lines, fuel filter and plug. Overhauled Walbro WT 160B carb with Walbro KAT20 kit. Never replaced welch plug, just the diaphragms and needle assembly. Also gave it a 5 minute hot bath in my ultrasonic machine. It seems to flood out once running. Took it to my smarter repairman pal and he says it floods after sitting.

Almost the same scenario with FS 66. It has a Walbro WT-45a carb, same kit, same overhaul as above on the FS 36. It seemed to start and run initially, but then crapped out and hasn't run properly since. Buddy says that one is also flooding while sitting. My expert friend says sometimes carbs just won't take a rebuild.

So now I look for replacement carbs. They are both way over-priced relative to the value of these units. The WT-160 is almost impossible to find and cheapest carb is around $60. The Wt-45 is about $40. I just bought carbs for a FS120 and 250 and they were $10-15 each!!

Can some other Walbro or Zama carb fit on these and work? Any other repair suggestions? These were home use and have great compression so it seems a shame to toss them. Also frustrated what I've wasted on them and don't want to give up.

THANKS!!

 

[heyduke]

Howdy everyone!! Great site. Whenever I google search small engine problems i always seem to find a thread on this site so i thought I should join.

I have a Stihl FS 36, good compression at 120 PSI. Replaced fuel lines, fuel filter and plug. Overhauled Walbro WT 160B carb with Walbro KAT20 kit. Never replaced welch plug, just the diaphragms and needle assembly. Also gave it a 5 minute hot bath in my ultrasonic machine. It seems to flood out once running. Took it to my smarter repairman pal and he says it floods after sitting.

Almost the same scenario with FS 66. It has a Walbro WT-45a carb, same kit, same overhaul as above on the FS 36. It seemed to start and run initially, but then crapped out and hasn't run properly since. Buddy says that one is also flooding while sitting. My expert friend says sometimes carbs just won't take a rebuild.

So now I look for replacement carbs. They are both way over-priced relative to the value of these units. The WT-160 is almost impossible to find and cheapest carb is around $60. The Wt-45 is about $40. I just bought carbs for a FS120 and 250 and they were $10-15 each!!

Can some other Walbro or Zama carb fit on these and work? Any other repair suggestions? These were home use and have great compression so it seems a shame to toss them. Also frustrated what I've wasted on them and don't want to give up.

THANKS!!

Welcome. I often just replace a carb rather than rebuild it, especially if I'm doing it for someone else and don't want to see it come back. I think the weed trimmers you're writing about have primer bulbs. That adds another level of complication since they usually have check valves that can be damaged and i've never figured out how to repair them. Did you clean these carbs with compressed air? That's how the check valve often get damaged. I usually check amazon and ebay for new carbs. You can usually get a good deal. Bonus, they usually come without limiters on the needles. Another thing, you didn't mention replacing fuel lines. That's important, especially if your dealing with a primer bulb.

 

[canucklehead]

thanks heyduke, yes, i replaced fuel lines & filters. I did blow some compressed air through afterwards but lightly, not high sustained blasts. DOH!! I'll be choked if my compressed air assitance ruined these.

I agree on replacement carbs when they're around $20-30. In this case, these are hard to locate and expensive relative to the value of the machines.

No primer bulb on the FS66, but there is a primer bulb on the FS36.

 

[heyduke]

thanks heyduke, yes, i replaced fuel lines & filters. I did blow some compressed air through afterwards but lightly, not high sustained blasts. DOH!! I'll be choked if my compressed air assitance ruined these.

I agree on replacement carbs when they're around $20-30. In this case, these are hard to locate and expensive relative to the value of the machines.

No primer bulb on the FS66, but there is a primer bulb on the FS36.

the problem i have with rebuilding carbs is that you spend time and money and it's a crap shoot. guy brought his non running wildthing to me. i bit on the rebuild kit, $20 from my local stihl shop. didn't work. i was out a fin and couldn't charge him for it. the saw was worth less than a new carb. i sold him a new (used) saw and took the wildthing in trade. good that the fs66 lacks a bulb they are an unnecessary complication and prone to trouble, especially with ethanol.

 

[canucklehead]

haha, i am finally splurging on premium non ethanol and also using Amsoil Saber 100:1 oil. I hear ya, if you're charging customer, a kit is a crap shoot and a waste of time. Just frustrating seeing carbs for $10-20 and then these old dinosaurs that are borderline ancient throwaways...I have to spend $40-60 per carb. I'd think it should be the other way around.

 

[gomoto69]

Check that the metering lever is adjusted correctly. I just rebuilt a walbro hd 6 carb for a jonsered 2171. Ran way rich when assembled. Went back in and found metering lever was too far above carb base, carefully bent lever till it was flush with carb body, runs good now

 

[heyduke]

haha, i am finally splurging on premium non ethanol and also using Amsoil Saber 100:1 oil. I hear ya, if you're charging customer, a kit is a crap shoot and a waste of time. Just frustrating seeing carbs for $10-20 and then these old dinosaurs that are borderline ancient throwaways...I have to spend $40-60 per carb. I'd think it should be the other way around.

you're not splurging. you're saving money using ethanol free fuel. i'm fortunate to have and ethanol free station within 15 miles. i use it mixed 50:1 and burn mix in my chipper and splitter too. even e-free isn't the same old liquid lizard that we used to get. it's a good idea to test it just to be sure it's e-free.

 

[canucklehead]

heyduke, how do you test to make sure it's ethanol free?

gomoto, how do I check/adjust metering? is that the tab on the fork that holds the needle? I don't see anything else adjustable.

I guess I hoped my experienced friend could fine tune beyond what I can't figure out.

 

[gomoto69]

The lever that holds the needle, the top end that sticks up should be level with the body of the carb when viewed from the side, or u can check by sliding a straight edge across it, lever should just touch straight edge, at least that is the proper setting for my carb, you should search 'metering lever adjustment' for your model in case it's different. If it needs adjusting, carefully (i remove it and use 2 pairs of needlenose pliers) bend the lever just above the where the pin goes thru it, so you don't distort the part that holds the needle. This adjustment is very important so you get the proper amount of fuel each time the needle opens. On my 2171, i had to turn the H needle to only about 1/4 turn out to stop 4 stroking, and still wasn't running crisp at all, lever adjustment cleaned it right up, H needle now about 7/8 out, idles and part throttles cleanly, good luck!

 

[canucklehead]

would bending upward = more fuel, and downward mean less fuel? funny thing is, these are brand new levers that came with carb kits so I would have thought no adjustment should be needed.

 

[heyduke]

heyduke, how do you test to make sure it's ethanol free?

gomoto, how do I check/adjust metering? is that the tab on the fork that holds the needle? I don't see anything else adjustable.

I guess I hoped my experienced friend could fine tune beyond what I can't figure out.

find a small skinny, tall bottle. this is a 10oz voss drinking water bottle from my local albertson's market. if you have access to labware a small graduate is really great but i like this because it has a lid.


fill to 10% capacity with water. mark the water level with a sharpie, grease pencil, rubber band or tape then fill the other 90% with gasoline. leave some space at the top so you can shake it.
put the lid on and shake. let it sit for at least an hour, over night is better. you'll have something that looks like this:


if the gasoline is contaminated with ethanol, you'll have more "water" and the level will be above your mark. no ethanol the level will be the same. you can't see my mark because i use the printing on the bottle that says, "10 fluid oz." for my mark.

my experience is that all gas has ethanol in it now. i think it gets contaminated in the tankers that deliver to stations. i left fuel in one of my saws and my trimmer over the winter and both have had carb problems, the wire mesh filters in the carb get clogged with schmutz even though the gas didn't have enough ethanol to show up in this test. so it's still a good idea to drain your saws before you store them. i used to do that before ethanol anyway.

hope this helps.

 

[gomoto69]

The lever is meant to be adjustable, it's really the only adjustment other than the needles. Give it a go, yes bending it down should lean it out, just set it till its flush with the carb body, if it's already there you may have some other issue.

 

[canucklehead]

thanks very much guys for your patience and help.

I picked up today from my mechanic buddy. he said my rebuild kit I installed had wrong lever. he put in another and it didn't seem right either. I will look for my old lever... I didn't throw it out. i will also try to clean the needle seat area. He head it running good and used it for several minutes but had to play with H & L while using it as fuel flowed too much he figures. it also flooded while sitting.

Other issue with premium vs. ethanol fuel is that they pump through same hose so you probably get 1st gallon or so of crap fuel before the good stuff flows. My buddy pumps into car first, before filling jug with the good stuff.

 

[gomoto69]

I use brake clean to blow out all the passages in a carb before installing new parts, although your ultrasonic cleaner should be an even better way of cleaning. Remove both H and L needles, metering needle, and direct the spray through each passage, then compressed air thru each to dry things out. Your new lever may be an updated design or something, just check that it contacts the diaphram in the proper place, and double check the kit is actually for your model carb. If the needles are identical you could probly use your old lever, but i would think the new one should work, if as i say, it's for that carb. (Is it a oem kit, or am chinese type kit?). Whichever one you use tho, check that it's properly adjusted! All your symptoms of running overly rich everywhere point to a lever set too high!