5 Series carburetor run issues

[Stump Shot]

Some run issues with carbs and what the fixes were.

Problem, saw runs eradic and eventually dies. Also passes a crankcase pressure/vacuum test and is fine mechanically and has good spark.
Leaving the fuel system suspect.
Carburetor passes a standard fuel inlet pressure check.


However, it fails when a light vacuum is applied to the primer outlet, with the inlet blocked off.


Upon disassembly it was found that one of the little flaps on the fuel pump side was lifted up with some crud growing under it on the carburetor body due to the use of ethanol fuel. This allowed a short circuit to the main nozzle, which makes it uncontrollable.
Carburetor was cleaned along with a new gasket and diaphragm kit and reinstalled. Tests were now passed as well as running confirmed saw was back in proper condition.

 

[Stump Shot]

Another start and immediately die situation with direct opposite test results.
Vacuum to the primer outlet side without the aid of blocking the inlet pulled a vacuum, which it shouldn't. This told me that an inlet problem was apparent. Needle and seat checked out, that left the inlet screen, which was found to be plugged with fine debris. A new screen took care of the situation and saw was back in working order.

 

[big_eddy]

I’ve had the latter several times. Saw will idle all day long, but pull the trigger and put it into a log and it dies almost immediately.
Clean the screen and back to normal operation.

 

[Bjorn]

Hello. I find this on youtube.

What is he doing, changing?

 

[Stump Shot]

Hello. I find this on youtube.

What is he doing, changing?

That's a good question.

 

[Stump Shot]

 

[Stump Shot]

On the 550's most problems are either the inlet screen and or the fuel pump side diaphragm having internal leaks.
The Mark II's have the new spiral kit installed and have synthetic gaskets. One trick I have done is install the old paper gasket on the fuel pump side to eliminate leaks. I had one a while ago that the little flapper valve got all kinked up, how, I have no idea, but these seemingly small things make for big run issues.

 

[Stump Shot]

Also to note, there's a new inlet lever gauge from Walbro for the spiral inlet diaphragm that you will need to get it set right when working with them.

 

[hacskaroly]

On the 550's most problems are either the inlet screen and or the fuel pump side diaphragm having internal leaks.
The Mark II's have the new spiral kit installed and have synthetic gaskets. One trick I have done is install the old paper gasket on the fuel pump side to eliminate leaks. I had one a while ago that the little flapper valve got all kinked up, how, I have no idea, but these seemingly small things make for big run issues.

So far the only carb to really cause me grief in troubleshooting has been for a 562, it looks similar to 550 one you are showing. Pushing the purge bulb only results in minor fuel spit into the bulb and a high pitch whistle (sucking air). I connected the purge bulb directly to the fuel tank fuel line and it cycles fuel like a champ. I even swapped to a different purge bulb and got the same issue, cycled fuel when direct connected, but somewhere an air leak in the carb. All fuel lines are in good shape (relatively new, no cracks or pinholes - pass vacuum test). I have replaced all of the gaskets and diaphragms, screen, needle...etc with new after cleaning the carb with cleaner. I am still getting the whistle. I painted clear fingernail polish all around the seems of the fuel pump cover and metering cover let it dry and am having the same issue. I am not sure where it is pulling air from, any ideas from your experience?

 

[Stump Shot]

So far the only carb to really cause me grief in troubleshooting has been for a 562, it looks similar to 550 one you are showing. Pushing the purge bulb only results in minor fuel spit into the bulb and a high pitch whistle (sucking air). I connected the purge bulb directly to the fuel tank fuel line and it cycles fuel like a champ. I even swapped to a different purge bulb and got the same issue, cycled fuel when direct connected, but somewhere an air leak in the carb. All fuel lines are in good shape (relatively new, no cracks or pinholes - pass vacuum test). I have replaced all of the gaskets and diaphragms, screen, needle...etc with new after cleaning the carb with cleaner. I am still getting the whistle. I painted clear fingernail polish all around the seems of the fuel pump cover and metering cover let it dry and am having the same issue. I am not sure where it is pulling air from, any ideas from your experience?

Pressure/vac test it as described above. If you need to, under pressure drop in a clear jar of water to find leak/s.

 

[srcarr52]

That's a good question.

Idle air bleed screw. It's essentially the same as opening up the butterfly a little. It forces the computer to richen up the idle mixture to maintain the target idle RPM which will help with the off idle stumble.

 

[Sawponder]

Anyone know what to set the metering lever height to on these 572xp at carbs?

 

[Stump Shot]

Anyone know what to set the metering lever height to on these 572xp at carbs?

https://www.sawsalvage.co/products/...gauge-500-528?_pos=3&_psq=walbro&_ss=e&_v=1.0