Export thread

I don't know why... me and 2 strokes do not click. I can do 4 cycles all daaay long with no problems... give me 1 frickin 2 cycle and i can't do sheet with it.
The aformentioned weed trimmer is my personal one.... started running bad lately, after the usual yearly tune up, fresh fuel ,filter, making sure exhaust wasn't plugged ETC, i figured the carb may be tired so due to time constraints i bought a new ZAMA/STIHL carburetor from the local dealer. (cant remember PN) installed but i can't get it to run right still. new intake gaskets installed as well.
If i get it to idle good and rev up good, when i let off at full throttle it dies upon reaching idle. If i tune it to where it doesn't die when going back to idle, it will not reach full throttle... I've gone back and forth back and forth,little turns at a time... i even copied the turns of the old carb to new one... nope..... Anyone know of the "factory setting" where it *should* run....
Help.

Found some factory settings that fish posted on here, 1.5 turns out, H, 3/4 turn out L.... did that... ran somewhat better, revved with no hesitation... idled poorly and inconsistently.

If you put on a new OEM carb with the proper starting settings and it runs poorly i would pull the muffler and check for scoring and if P&C is good may have a leaking crank seal. When it won't rev up does it sound strained lean or rich blubbering?

Most two carburetor are tune at idle first and then at high speed as the idle circuits also feed during high operations.

This is from the 2022 tune up guide from Stihl.

Note these are initial settings, final tuning may vary.

P&C checks out good... will run and rev from mixed fuel sprayed into carb.... 108psi compression.
I went to the stihl dealer... talked to the parts guy.... he went in the back for a few minutes, came out with another carb, said "try this"..... I get home, new carb will not prime... verified lines installed correctly, fuel never makes it to the bulb, but it does pressurize the tank. It almost feels like the bulb builds up air pressure...
Experts?

Scrubcadet10 said:

P&C checks out good... will run and rev from mixed fuel sprayed into carb.... 108psi compression.
I went to the stihl dealer... talked to the parts guy.... he went in the back for a few minutes, came out with another carb, said "try this"..... I get home, new carb will not prime... verified lines installed correctly, fuel never makes it to the bulb, but it does pressurize the tank. It almost feels like the bulb builds up air pressure...
Experts?

Click to expand...

The bulb does build up pressure
Pull the input line off the carb & pump the primer
Fuel should gush forth
If not the line or filter are blocked

Is fuel filter good? Not clogged?
Pressure test the carb.
Verify carb tries to pull fuel when bulb is pumped. Remove carb and install fuel lines on inlet and purge nipples. Put line to pump side bn in a cup with fuel in it and pump bulb. Should suck fuel and spit it is out the purge line.

Just had a similar failure here with a Walbro carb on FS74. I had to get pass the initial problems with carburetor as it needed new kit so cleaned it via USC. Welcome it primer was just sucking air and filling the tank. In this case it turn out to be a stuck main nozzle check valve. A piece of trash got stuck in it, keeping it from sealing on vacuum. Once I got it out things started working.

First check to see if the carburetor inlet is pulling a vacuum, if it is then the carburetor is fine. Otherwise try submerging the carburetor in fuel mix and prime it as this might loosen a stuck check valve. But as Bert said it can be clogged fuel inlet pickup line. Water in the fuel tend to corrode and clog the fuel filter [depending filter design].

For some reason Zama carburetors lately are giving more problems than usual. I have several primer carburetor mounted bases to fail on Stihl equipment. These cost as much as some of the carburetors when it comes to Stihl products since Stihl controls them.

Note: the initial complaint here from the customer was fuel pouring out. Well that was because the metering diaphragm had ripped. At least they didn't mess with the carburetor. Just got wait on new fuel lines with grommets.

Hammermechanicman said:

Is fuel filter good? Not clogged?
Pressure test the carb.
Verify carb tries to pull fuel when bulb is pumped. Remove carb and install fuel lines on inlet and purge nipples. Put line to pump side bn in a cup with fuel in it and pump bulb. Should suck fuel and spit it is out the purge line.

Click to expand...

Filter is new OEM Stihl.
Will do.

Submerged the carb in mix fuel, let it sit for awhile, then pumped the bulb with it submerged, it filled the primer bulb.... put it back on the whacker and it ran momentarily until the bulb was empty.
With the carb installed, when i press the primer, the fuel bubbles in the tank....
I'm stumped.....

Hammermechanicman said:

Verify carb tries to pull fuel when bulb is pumped. Remove carb and install fuel lines on inlet and purge nipples. Put line to pump side bn in a cup with fuel in it and pump bulb. Should suck fuel and spit it is out the purge line.

Click to expand...

Put a line on the pump side, pumped the bulb, in about 6 pumps (which is the recommended number on the plastic shroud) it pulled fuel up to the carb, but the bulb never filled and it never spit fuel out of the purge nipple.

Either bad check valve in purge assy or bad check valve in carb or possibly fuel pump valve. It would help if you had a way to pressure check the carb.

i have a pressure tester, i just never have taken the time to learn how to use it... but no time like the present.

Not much use for the carburetor can only test the fuel side and metering needle seating. No way to pressure or vac test the metering side. Vac testing the metering side is nearly impossible with the mixture ports bleeding air. Pressure don't work either as main nozzle opens on pressure.

It does sounds the primer is working as it can n\more than 6 pumps, Initially there is a lot of air to get rid of.

Was the carb from the dealer a new one?

Apply no more than 10 psi to the fuel inlet. Should hold pressure. If it doesn't the diaphragm needle not sealing. Press the purge bulb and pressure should drop a little each time you press it.
Connect tester to the purge port and pump the purge bulb. Should build pressure slowly and hold. If it doesn't one of the purge system valves is bad.

Fish said:

Was the carb from the dealer a new one?

Click to expand...

Yes, Zama C1M-S267A

Hammermechanicman said:

Apply no more than 10 psi to the fuel inlet. Should hold pressure. If it doesn't the diaphragm needle not sealing. Press the purge bulb and pressure should drop a little each time you press it.
Connect tester to the purge port and pump the purge bulb. Should build pressure slowly and hold. If it doesn't one of the purge system valves is bad.

Click to expand...

Thanks Hammer. will do

Hammermechanicman said:

Apply no more than 10 psi to the fuel inlet. Should hold pressure. If it doesn't the diaphragm needle not sealing. Press the purge bulb and pressure should drop a little each time you press it.
Connect tester to the purge port and pump the purge bulb. Should build pressure slowly and hold. If it doesn't one of the purge system valves is bad.

Click to expand...

Needle held at 8 PSI. pressure did not drop when purge bulb was pushed. The bulb will fill with fuel about, just a little across the bottom and no more.

One thing I thought of and tried, if I press the primer bulb down, plug the fuel inlet nipple with my finger, and let go of the primer bulb, shouldn't the bulb stay sucked down, due to no air being able to come in?

Press the purge bulb down and then put finger over the purge nipple and release the purge bulb. If it sucks fuel into the bulb the check valve in The purge assy is bad.

Hammermechanicman said:

Press the purge bulb down and then put finger over the purge nipple and release the purge bulb. If it sucks fuel into the bulb the check valve in The purge assy is bad.

Click to expand...

Yep... it's pulling some fuel into the bulb.not filling it up, but fuel is coming in.

Do same test with carb turned with purge bulb on the bottom snd see if bulb fills. Pump it a half dozen times or so.
I think what is happening is the check valve on the purge outlet is bad and the engine runs pulling fuel from the purge bulb then pulls air when the bulb is empty.

Hammermechanicman said:

Do same test with carb turned with purge bulb on the bottom snd see if bulb fills. Pump it a half dozen times or so.
I think what is happening is the check valve on the purge outlet is bad and the engine runs pulling fuel from the purge bulb then pulls air when the bulb is empty.

Click to expand...

Same result as earlier.

Picked up a stihl carb at another dealer today, this one is made in the Phillipines..... Trimmer fired right up and runs great.