stihl trimmer issue (similar a saw, lol)

[Mike G]

hey guys,
Not sure of how to search for this, so im just going to ask it. No yellin please! I have an old sthil string trimmer that has some issues staying running. I have adjusted and readjusted the carb countless times. it starts and runs ok, untill a few days ago. It was all warmed up, runnin good. I let off the throttle, back to idle, but instead of staying running it throttled all the way down to a dead stop, almost like the fuel has been cut off for some reason? ignition looks good when it shuts itself down, so it seems to me that a carb issue might be at hand. after a 10 or so minutes, i could get her started again and go back to work untill it decides shut down again.
Thanks for any advice, there are a countless number of 2 cycle genious here as AS!
~Mike

 

[Lakeside53]

What's the model number?

 

[yellowhammer]

Stihl Trimmer Issue

Clogged exhaust screen? Clogged vent?

John

 

[Mike G]

Model No. : FS-51 AVE, I have yet to check the exhaust screen, the fuel cap has a large crack in it, (only 1 yr old, factory part ) so i assume it vents ok (that was one of my first thoughts). When i first got it, i messed around with cleaning the carb, and if i remember, somthing was wrong with the little lever that moves the needle (i think i tried to bend it ......i was young then...........)? it was a while ago tho, perhapes a carb rebuild could help? i also tightend up the four cap screws on the crankcase (also holds the fuel tank bracket inplace) as they were slightly loose. Looks like some fuel may be leaking from around that gasket, I think one is homemade (perhaps by me............. )

 

[Lakeside53]

I just parted out a bunch of 051's and thew most of it in the garbage... I might have an old carb you can have.. What's your carb number?

 

[Mike G]

its a Walbro carb, only no. i could find was WT38A? Ill send a photo if necsarry. I cant tell now if the fuel and oil on the carb is from the leaky cap or bad gaskets somwhere. Do they still make a kit? The more i think of it, i could never get her adjusted quiet right. If i set it so there was no lag when the throttle was opened wide, then she would never restart when warm. she starts ok now, but sorta lags when stepin on the gas, and now she randomly started the dieing problem. Thanks for the offer as well Lakeside!!! :rockn: I guess most folks would just go buy a new trimmer, but i kind of like this one, old and all metal.....im off to try to cut some more and see if i can better diagnose the problem.

PS, have any fuel caps? the damn factory replacement cracked apart in 1 yr, tryed to jb weld her, but no luck.

~Mike

 

[Lakeside53]

Fuel caps are not longer available, so...

The WT38B is correct. Just rebuild it with a standard K10-WAT walbro kit. Really simple carb, and change your fuel filter...

 

[Mike G]

ok, thank you lakeside, i tore the carb apart tonight and discovered that the lever wouldnt even budge the needle when pushed the whole way down. Rebuild kit it is!

 

[Mike G]

ok, got the new carb kit in. Doesnt stop running randomly now, however acceleration sucks. Ive tried to adjust her, but it just bogs down when the throttle is squeezed. if u fuss with it enough to get her to full speed, she runs fine. correct me if i am wrong, its the Low speed screw that affects acceleration????? im going down to look at the fuel filter, but if she runs ok at full, would this affect acceleration? Thanks!

 

[Lakeside53]

Yes, it's your low screw that affects the accel. Make it slightly richer. Check your meeting needle height.. Assuming you don't have a walbro guage, make it level with the bosses around the arm.

 

[scottr]

Gas Cap

Mike , I used Seal-All to repair the broken gas cap on my old Stihl trimmer . http://www.eclecticproducts.com/sealall.htm

 

[Mike G]

ohh, does that have to be adjusted following a rebuild? i was assuming it came factory correct. I did that to my old carb, but it made things worse (i just made it open the needle more, but too much i think) so just make it level with the surrounding casting when the little lever is depressed fully? I fooled with that low screw like crazy, and opening her had barely, if any affect on acell.

Scott, thanks for the tip, i guess JB weld couldnt fix everything, lol, ill give ur suggestion a try (right now some elcetrical tape and a gum band is helping, LOL)

 

[Lakeside53]

Is meeting needle tech talk for metering needle or is it just a typo?

Dan

Sharp beady little eyes you have my fine-feathered friend.... yes, a typo the spell checker "corrected"...

 

[Lakeside53]

ohh, does that have to be adjusted following a rebuild? i was assuming it came factory correct. I did that to my old carb, but it made things worse (i just made it open the needle more, but too much i think) so just make it level with the surrounding casting when the little lever is depressed fully? I fooled with that low screw like crazy, and opening her had barely, if any affect on acell.

It should be level with the casting bosses when the metering arm is back in its normal position (not depressed). Don't just bend it... hold down one end while you gently pry up the other, or vice versa. Factory is often close, but it depends on your valve seat wear etc.

 

[Mike G]

thanks Lakeside,
looked at the carb tonight and saw the bosses u were talking about, i guess i never noticed them before. I made the lever level when it is in its original position, holding the needle valve shut. We'll give her a shot tomarrow and see how she runs!

 

[Mike G]

Sweet,
She now accelerates properly, thanks to lakeside! however......................she has one more issue :bang: i start her up cold, and get her warmed up a bit. I got the carb all adjusted to where she runs, idles and accelerates good. I started to cut some weeds, and a good while in i let of back to idle, At which point it fizzeled out just like fuel had been cut off. It seems to be related to temp, because the thing runs ok at first, but then no amount of adj. can keep her idleing. Its not the coil, i checked the spark right away after it fizzeled out. When this occurs, the trimmer will run good at high throttle, but die out when returned to idle. I think im going to end up wearing out the damn screws, for all the stupid problems ive had!

 

[Lakeside53]

I don't remember how the tank vents on that model ,but try loosening the gas cap while it's running..

A much worse potential problem is that if you over lean the engine either by excessive lean (don't "peak" the rpm with the H screw), or, too much load (string too long), it might not idle because it's trying to seize! Seen it may times..

Sometimes seal swill get flaky when the engine gets hot.. maybe your carb mount block is slightly loose?

 

[Mike G]

i did make a gasket for the crankcase cover a while ago, looks oily all around it, so perhaps that is the issue? carb and block is on there nice and tight, but ill look again. as for the high setting, i have her set so she just begins to 4 cycle. It was damn hot out today as well............. another thing that ive notice when foolin with screws, is that she will idle at times with the low screw closed?

 

[Lakeside53]

............. another thing that ive notice when foolin with screws, is that she will idle at times with the low screw closed


Hmm, that often a loose welch plug.. the little aluminum disks in the carb that cover the 3 low progression, but can also be damages needle seats from over zealous tightening of the mixture screws.. or a leaking metering needle. Did you pressure test the carb though the fuel line?