Poulan Pro 442 Backpack Blower Carburetor
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bertsmobile1
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Here is the actual Husqvarna technical school teachers videos
Joe Pace tank testing
Joe Pace carb pressure testing
Note the methodical nature of the job
Start with the tank then progress to the carb before you rip open the carb & do more damage than good
A bit of accumulated wisedom also helps
If it has been sitting unused for 3 or more months then varnish clogging becomes top of the suspect list.
If it was working fine last week then pressure failure moves up near the top
I am currently doing a 122LD trimmer
It has an external tank vent with a 2 way valve
This one was faulty
The owners just paid another shop 2 hours of labour + a new genuine carb & coil when all that was bad was a 10¢ check valve
Slipped an Echo one in there and the trimmer ran like a champ so I sent it back then it boomeranged a week latter.
Because I did not check everything I failed to notice the previous tech had installed the new fuel lines wrong way round so the H jet is now partially clogged and the carb internal filter was packed solid
bertsmobile1
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And the other three Joe Pace videos are here just for the record
Fuel Line & Filter
primary & secondary Compression
Most workshops do not bother checking the filter, so just replace them & pressure test the line while doing it as the test takes 4 times the new filter price in labour cost
And once I get through the 200 I bought bulk ages ago I will only use porex filters except on the very flat tanks that require the use of a long butterfly filter so on those you do have to pop the felt off & check the internal screen / membrane
Fuel Line & Filter
primary & secondary Compression
Most workshops do not bother checking the filter, so just replace them & pressure test the line while doing it as the test takes 4 times the new filter price in labour cost
And once I get through the 200 I bought bulk ages ago I will only use porex filters except on the very flat tanks that require the use of a long butterfly filter so on those you do have to pop the felt off & check the internal screen / membrane
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There seems to be a misunderstanding how a fuel tank vent works here. Most do not prevent fuel tank pressure buildup here in the USA, there are limited number that does vent externally; although, the EPA frowns on this practice. They only prevent the fuel tank from creating a vacuum in most cases. The tanks having some pressure actually help the 2 cycle cubes and rotary carburetors move the fuel. Many times it is the metering diaphragm getting stiff that causes idle only problems as it the engine's impulses can not pull the diaphragm down to open the needle valve. Also when this diaphragm gets replaced along with metering lever and needle, lever height needs to set to the correct height so the carburetor does not run over rich at idle or lean out at high speed. Again a stiff metering diaphragm will cause lean out at high speed demand as it can't open the metering needle valve the right amount.
Another problem I have seen is the internal filter screen on some models is super tight (very low microns) and clogs easily. Most repair kits don't this filter but instead a have lower filtration rate screen. IE: the super tight one can't be seen through and replacement most times can be seen through. These tight filters can not cleaned either.
Plus if the kit has a new needle valve then replace the old one as they tend ring the rubber tips leading to leaking. Note most Walbro does not include the metering lever spring so don't lose the spring.
Of course I pressure test these carburetors to make sure the needle are not leaking before I install the rebuilt carburetor. You can only pressure test the fuel pump side of the carburetor. The metering side can not be tested by pressure or vacuum due to design of the carburetor.
As a side note don't use normal carburetor cleaner, forced air, or wire probes as they can damage the internal not replaceable check valves of the carburetor. Here all I use is soap and water in an ultrasonic cleaner. Then once out use only light air pressure to blow off most of the water. Now Walbro does have their own carburetor cleaner but I have never tested it as to be honest why do it when soap and water is cheaper. Most time I use a non residual soap but there are times I just use Dawn dish soap if I will installing the carb right a way.
Another problem I have seen is the internal filter screen on some models is super tight (very low microns) and clogs easily. Most repair kits don't this filter but instead a have lower filtration rate screen. IE: the super tight one can't be seen through and replacement most times can be seen through. These tight filters can not cleaned either.
Plus if the kit has a new needle valve then replace the old one as they tend ring the rubber tips leading to leaking. Note most Walbro does not include the metering lever spring so don't lose the spring.
Of course I pressure test these carburetors to make sure the needle are not leaking before I install the rebuilt carburetor. You can only pressure test the fuel pump side of the carburetor. The metering side can not be tested by pressure or vacuum due to design of the carburetor.
As a side note don't use normal carburetor cleaner, forced air, or wire probes as they can damage the internal not replaceable check valves of the carburetor. Here all I use is soap and water in an ultrasonic cleaner. Then once out use only light air pressure to blow off most of the water. Now Walbro does have their own carburetor cleaner but I have never tested it as to be honest why do it when soap and water is cheaper. Most time I use a non residual soap but there are times I just use Dawn dish soap if I will installing the carb right a way.
@StarTech I have used the Walbro carb cleaner and can confirm that it is not rubber safe. It will swell the check valves. Seems to be less harsh on the carb than the normal off the shelf carb and choke cleaners but is not fool proof.
And most tank filters are around 150 micron whereas the internal screen in the carb is roughly 75 micron. so it will catch stuff that will go right through the tank filter.
And most tank filters are around 150 micron whereas the internal screen in the carb is roughly 75 micron. so it will catch stuff that will go right through the tank filter.
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That what I suspected but I played it safe with something I know will not harm these rubber parts. Usually I clean the outside of carburetor before putting them in USC using the same fuel mix the equipment runs on as I know it should be safe to use for the carburetor and of course not good for the user; unless, you take precautions.
But Walbro knows there is a demand for the spray type cleaner among DIYers and they don't mind those having to buy replacement carburetors because they damage these rubber parts.
But when you have NLA carburetors to work on it is better to play it safe.
As carb screens I agree they catches a lot things the bypass the filters and they are definitely needed if the in tank filter falls off the line to prevent clogging of tiny passages of the carburetors. It just that screens that so tight that you can't see though even when new are problem causer. Probably why you don't seen them in the repair kits much at all.
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Primer bulb is PN 188-13-1. Check with local shops as they will usually be cheaper than online dealers (shipping is killer) if they have one in stock. I am showing list price is $1.45 and that I personally have two in stock but these are for my local customers.