Some Stihl weedeater questions.

[JimL]

I got a couple trimmers I am fighting with. The first one is a FS55, not 2 months old. about a month ago I put on a new carb. Ran like a top on its way out. Got it back in this morning and the thing just wouldnt run at all. So i checked the usuals and poped in a new gas line set. I opened the carb (zama C1Q) and everything was good in there, cleaned it anyway. Presure tested carb and was good. Put it back on, still same thing. So I pop the carb off and go get another new one. hook it up and tighten everything down. Same thing. Spark is good, muffler and exhause ports are clean. Carbs good I think. So what do I check now? I tore it down and popped the nut and cup of the recoil side, looking at the crankcase seal I see what looks like a very small amount of oil and gas residue right around the seal. So I ordered a couple crank seals.

Anything else i should or should have checked?

Next one is a FS36, one of the pieces of ???? where you got to tear it completely in half to get to the carb. I put in a carb kit and cleaned fuel filter and got it to run. When adjusting it seems to be flooding out, and eventually dies. I spent an hour screwing around trying to get it adjusted. I tore the carb back down and cleaned it. That little brass thing with the check valve or what i think is a check valve, should i be able to spray carb cleaner through it both ways? I ordered another carb and am going to try it. This is a walbro carb...

thanks.

 

[stihltech]

trimmers

The FS55, make sure the compression is up to par. Is it flooding or getting nothing? Seals a possibility, but have not had any bad ones.
2 months old? Do you check spark with a large gap spark tester? I have found some coils that will spark a plug but not a tester. Does the piston look clean or brown? Had a gentleman that took out 2 pistons in a week with "milk jug gas".

FS36, my condolences. The valve/jet you mention is a good possibility. Remember the inlet lever must spin around the axle with NO friction. I spin the axle and if the lever comes around AT ALL, I clean or replace it until it stays still.

What brand are the carbs?

 

[JimL]

Now were getting somewhere, yes the piston is brown on the skirt of the FS55. Why is this? Bad gas? Running lean?
I tested compression at near 150. The cylinder walls dont look too bad, Ill have to open it up and take a better look.

The FS55 has a ZAMA C1Q carb and the FS36 has a WALBRO WT somethin carb.

 

[JimL]

Ok, the FS36 is fixed.
On the FS55, I put in new crank seals today. Put it all back together and it ran. Just on high RPM's not low. THe carb was already replaced once. So I went and took a new one off a new trimmer. It ran just the same, only high end. No adjustment so There still lies a problem. I replaced fuel line too. Ckecked today, Mufflers clean along with port again, plug is new, spark is real good, flywheels is in time, fuel filter is good, gas cap vents, compression is up around 150ish.

Still wont run right.

 

[stihltech]

FS55

The compresion doesn't sound bad, but I would still check for stuck rings and an air leak on the crankcase.

 

[sedanman]

When you say it won't run at low speed do you mean it will idle but not tansfer smoothly to high speed? My FS-75 had a bad case of the "wha wha's" (bogged on accell) until I swapped the carb out for a fully adjustable one. The carb swap required a LOT of arm twisting to get the dealer to go along. If the machine is that new keep bringing it back until they fix the p.o.s. EPA carb.

 

[JimL]

Originally posted by sedanman
When you say it won't run at low speed do you mean it will idle but not tansfer smoothly to high speed? My FS-75 had a bad case of the "wha wha's" (bogged on accell) until I swapped the carb out for a fully adjustable one. The carb swap required a LOT of arm twisting to get the dealer to go along. If the machine is that new keep bringing it back until they fix the p.o.s. EPA carb.

Bad thing is i work at the dealer, The main mechanic is gone for surgery and I am tryin to keep up on the 2 cycle.

ok.

Ill check it out again tomarrow. I need to get the vacuum and preasure test kit from stihl... all i have are the old tool books, not the new ones. they have a new test kit i think...

 

[JimL]

By not running low speed i meant, If i let it get past half throttle it dies...