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Hey guys.
have a Poulan Pro 442 backpack blower bought second hand which starts then dies. Atrempting to give it gas does nothing. Tried cleaning the carb but still same issue.
Probably easiest to replace the carburetor (at least for me) but having a hard time finding a replacement for it. Anyone know? It says Walbro 21-245 7-2 can’t find anything online. Thanks in advance.

Those numbers are not the Walbro model number. Look around on the cube for other numbers.

I think that is the first diagram that I have found that doesn't give the part number for the complete carb. Only individual parts. Anyway.. On Walbro the model number of the carb will be etched into the upper left corner of the carb cube. On one side or the other It may start with WT or something similar.

ILENGINE said:

I think that is the first diagram that I have found that doesn't give the part number for the complete carb. Only individual parts. Anyway.. On Walbro the model number of the carb will be etched into the upper left corner of the carb cube. On one side or the other It may start with WT or something similar.

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It is the first I have seen that too. Most times they only give their pn for the whole carburetor. It appears to be one of the Walbro HDA versions. Most of the pns are Kawasaki ones.

StarTech said:

It is the first I have seen that too. Most times they only give their pn for the whole carburetor. It appears to be one of the Walbro HDA versions. Most of the pns are Kawasaki ones.

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I grabbed a couple part numbers from the carb diagram and they showed HOP numbers but also showed NLA.

IF the tank does not vent and hold pressure it will not matter how many new carburettors you fit , the blower will not run
I replace far more faulty fuel caps than I do bad carbs

StarTech said:

Those numbers are not the Walbro model number. Look around on the cube for other numbers.

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I was primarily looking at the gaskets. Say the metering diaphragm showing Husqvarna 430282072 which is Kawasaki 43028-2072.

Actually many of the pns directly translate to the carburetor on the Kawasaki TE040D-AC52. Not all but most of them and that carburetor is a HDA-110A. Now of course the OP's PP442 has a primer setup which the TE040D-AC52 carburetor does not.

bertsmobile1 said:

IF the tank does not vent and hold pressure it will not matter how many new carburettors you fit , the blower will not run
I replace far more faulty fuel caps than I do bad carbs

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I have right the opposite problem here which I rebuild a lot more cubes than I find bad fuel tank vents. Actually I think I have only found one in the last 5 years.

Someone mentioned HDA earlier and they were correct. I believe it says 138A
Does that help?

bertsmobile1 said:

IF the tank does not vent and hold pressure it will not matter how many new carburettors you fit , the blower will not run
I replace far more faulty fuel caps than I do bad carbs

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How can I tell if it is properly venting?

HDA-138A is the carb model number. Not seeing any of that carb in stock at my normal suppliers. Calls for the K12-HDA carb repair kit.

Jbassman said:

How can I tell if it is properly venting?

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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

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

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.

@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.

ILENGINE said:

@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.

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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.

Thanks all for the help. Very impressed with the knowledge you all bring!

Reviving this old thread as I found the primer check valve to be torn. Anybody know where I can get a replacement?
Carburetor HDA-138A
Thanks in advance

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.