# Walbro WT 199A air bleed problem



## tom tilson (May 1, 2006)

I am working on a blower with a Walbro WT. Air purge was catching air bubbles and now won't pump. I believe it to be caused by the main nozzle check valve because I can close both needle screws and it will start to purge air. I think fuel goes from the metering chamber into a small hole upper left of the metering lever and then passes by the needle valves to the respective circuit. I can not for the life of me see where the main nozzle discharges into the venturi, therefore I don't know whether to pull the larger welch plug which is to the upper left of the meter lever or a smaller one to the extreme right of the cavity. I may not even be on the right track. After the engine runs until hot, turning it off and then trying to restart is futile. I am thinking that fuel is perking out of the main nozzle because the check valve is stuck. Anyone out there give me some advice? Have a great Thanksgiving, Tom Tilson


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## 30yearTech (Sep 14, 2006)

IF the high speed check valve was stuck, the engine would not run long enough to get hot, so I don't think that is the problem.

Is it just a hot restart issue, does it run alright until then?


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## tom tilson (May 1, 2006)

*Walbro WT*



30yearTech said:


> IF the high speed check valve was stuck, the engine would not run long enough to get hot, so I don't think that is the problem.
> 
> Is it just a hot restart issue, does it run alright until then?


It all began with the engine running fine for aboit 15 min shutting off and then no start. After cleaning the carb, it will run fine until it is intentionally shut down and then fail to start, with hot fuel vapor coming out of carb intake. I see no reed valve so assume it to be a rothary valve on Homelite 250 blower. If the chechk were stuck open, I think it may run, but when stopped load up through fuel leaking into venturi However this is aa assumption. I sure do appreciate your reply, Tom


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## 30yearTech (Sep 14, 2006)

The purpose of the high speed check valve is to prevent back pressure from entering the metering chamber of the carburetor. If the high speed check valve was stuck open the engine would lean out and die, and it would not run good until it got hot and was shut off.

This is because when positive pressure enters the metering chamber, the diaphragm is pushed up and away from the metering fulcrum lever and then no additional fuel enters the metering chamber to be delivered to the engine. All 2-Cycle engines exhibit this blow back although it is more evident on ported engines. 

I would check and make sure that the mtg bolts, gaskets and insulator are in good shape and tight and that the cylinder assembly and crankcase cover are sealed good and tight. An air leak can cause symptom's similar to what you describe and may not manifest themselves until good and hot. Also have you checked that your not loosing spark when it's hot and won't restart?


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## tom tilson (May 1, 2006)

My first concern right now is that the air purge bulb is not drawing fuel. I think maybe I should address this first. I looked at my Walbro manual and it suggested that if the purge system did not draw fuel, to close both needles and if it drew then, that it was catching air through the faulty nozzle check. With carb off of engine, and needles closed, the bulb will pick up fuel from a long tube attached and stuck into a fuel source. With the needles open, it will not purge. As soon as I can correct this problem, I will apply about four psi to crankcase and check for leaks. Please keep comments coming and thanks for your interest. Tom
PS When I first attempted the repair, I saw bbles around the cylinder to case mount and found two of the three screws hand tight. Thinking that the cylinder was not vibrating around on the case that the seal would be ok I tightened them and moved on Think the seal may be damaged???


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## 30yearTech (Sep 14, 2006)

It's possible I have had many of these type blowers cylinders come loose and tear the mounting gasket.

Try just screwing down the low speed jet and leave the high speed jet at it's normal position, then check your purge pump to see if it will pump. Check valves were added to the low speed circuits of carburetors to facilitate operation of the purge pump, but are not required for the carburetor to function properly. There may be a problem with the high speed check valve leaking slightly when the purge pump is in use, I just don't think this is the cause of your hot restart issue. 

The reason I say this is that the check valve is designed to allow fuel to enter the carburetor venturi and prevent back pressure from entering the metering chamber, fuel will always flow out through it unless it is plugged or stuck closed. If there is any positive pressure in the metering chamber (i.e. metering needle set to high, needle not seating good etc..) then fuel may flow out when the unit is not running.

Let everyone know what you find and good luck! :wave:


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## tom tilson (May 1, 2006)

*30 yr tech*

OK I have spent two and a half hours on the blower today. 1) Press checked the case and saw small leakage bubbles arond cylinder to block. Diassembled and checked gasket. Resealed, bubbles gone and no crankcase leaks. OK. 2) primer still stays full of bubbles. Closed hi needle and it began to pump. 3) reran carb interior and found the metering gasket diaphram to be rather stiff and replaced same 4( hot or cold, good spark 5) Checked main nozzle chk valve and can still push pull air both ways. 6( Cranked right up and ran under load for twenty min with frequent intentional kills with instant restart. 7) Shut it off, put the filter element back on, waited five min and would not start. Removed plug and it was dry after repeated choking efforts. 8) Still feeling all of this has something to do with a stuck open nozzle check, after continual pumping and full of air bubbles, dry plug, Closed main needle valve fully, hit the purge bulb about three of four times, clear fuel in bulb, choked it twice and cranked right up and ran beautiful at idle. Backed hi out two turns and it ran great again. FACT everything is fine unless you wait about 5min between shutdon and restart. I really feel that the nozzle check is stuck open. Having never changed one, is this something I merely give the supplier a model # for.? Are they sold separately? Any other thoughsStay with me here now pardner, I feel the end is near. Thanks Tom


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## 30yearTech (Sep 14, 2006)

OK well the check valve assembly does not come in a kit, but it shows to list for $2.14 so it's cheap enough to try. 

Conventional logic tells me that if the unit runs good cold and until it gets hot, it's probably not the check valve causing the restart problem. Here is my way of thinking, I could be wrong, but the purge pump was added to carburetors to reduce the number of pulls required to draw fuel up into the carburetor. Since there still is a fuel pump on the carburetor the purge pump does not have to work in order for the carburetor to operate. If everything else is in order the fuel pump should deliver fuel to the metering chamber when pulling the rope a few times, and there should still be fuel in the carburetor if the engine was run in the last 5 minutes. If using the purge pump gets it started I would suspect a problem with the fuel pump not operating properly, but hey $2.14 is a pretty cheap gamble and one I would probably take, if for nothing else but to see if I was right or wrong. I have replaced H.S. check valves in the past but it has always been to correct a lean run condition not a hot restart, but there is always a first time for everything. This is how we all learn our lessons and it's the hard ones we remember most.

Have you had a look into the cylinder and piston area via the muffler? Borderline compression can cause hot restart issues. Also if you have not already checked the carburetor mounting gasket and the insulator and mounting gasket to be sure the fuel pump ports are open and aligned for the carburetor. 
Keep me up to date as I am very curious as to what you figure out.


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## tom tilson (May 1, 2006)

The original customer complaint was that It ran 10/15 min cutoff and no restart. That has now changed to runs great runs strong for as long as the tank has fuel. Shut it off and instant restrart. Shut it off wait a few minutes, and you cannot pull the cord enought to restart it until a long lenth of time(not measured). Wait for a period of time, restart and immediately shut it down, no start.
I have already examined the piston and ring condition through the exhaust hole and it looks great. Carb adapter gaskets aligned right. This particular adapter mounts with two screws and on its on being separate from carb mtg studs.
I have not taken an actual reading on the comp,but will do so in the morning. It however pulls over strong and runs likewise.
I don,t remember just where I read this, but it was a walbro or Tillotson manual that stated the nozzle check was to prevent the nozzle from drippling into the venturi while in idle and during idle progression. At that time the nozzle would be at atmospheric pressure and as the venturi air speed increased when accelerating, the carb inlet press dropped causing the chk to open and the main to contribute fuel until rpm was fast enough for it to take over. You gave me a real clue when you said to try the purge with the needles closed and the purge did begin. Later I read in the W manual that closing the hi needle was a way to check for air leaks into the purge system. I am now able to get restart by using that proceedure.
You used the word logic in your last reply. I too use logic and not guess when troubleshooting. When I do get one fixed, I want to know what I did to get it running and am not just satisfied that it does run.
I know the check is not working, but using the logic approach, can not figure how it can figure into this unless on shutdown, the open nozzle allows some air to migrate into the meter cavity. why unless lo


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## tom tilson (May 1, 2006)

One thing I forgot to mention is that I can .t see the tip of the nozzle in the venturi. Is it not normal to see the end of the tip? Frustrated Tom


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## 30yearTech (Sep 14, 2006)

Tom, I apologize if I made you think that you were not being logical in your approach to this problem. I in no way meant for it to come across that way.

I was simply referring to my personal experiences and working knowledge of carburetors in general. 

I did attend a factory Walbro carburetor clinic, but it was a long time ago before carburetors had purge pumps on them (16 - 17 years ago I believe) and we did a lot of hands on carburetor tear down and reassembly as well as theory. 

My understanding of the high speed check valve is to prevent positive pressure (back pressure from engine pulse) from entering the metering chamber at idle and mid rpm range as this would prevent any additional fuel from entering the metering chamber, which in turn would cause the engine to lean out and die. Now if the check valve were open all the time it should make the engine hard to start or possibly not start at all. Since your engine starts and runs good and idles good, but will not restart when it gets hot, I still don't think the H.S. check is the problem. Unless the heat somehow causes a complete failure of the valve until it cools down or possibly there is some debris that may somehow be preventing it from closing completely when hot. 

The check valve is not spring loaded it uses outside pressure to operate it, so fuel can flow out through the valve when the engine is not running (assuming air is vented into the metering chamber somehow). 

Do you think it's possible that the check valve in the purge body may not be sealing good when there is no pressure, allowing fuel to re-enter the metering chamber? That would not explain the dry plug on the hot restart however.

Oh and it's not unusual to see the tip of the nozzle in the venturi.


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## tom tilson (May 1, 2006)

You sure did read me wrong on that one. The logic was meant as a compliment, not an insult. I try to deal altogether with logic all though I have to admit at times I have to guess and then I am disqusted with myself. This one really bugs me for my logic is not working on it.
I have been a member for approx six months and always take exceptional notice to your well thought out remarks.
The engine does not have to even warm up, say run at idle two min. Shut down, will crank right back up. Shut it down and wait about four min and pull like crazy and then look at A dry plug, after purging and choking. Now here is what does not make sense about that. When you fully close the choke, there should be vacuum on the nozzle and draw fuel into the venturi.at least when in WOT.
When you ask about the purge chk, are you speaking of the duckbill immediately under the bulb? I did examine it and it appeared ok, but may try a new one tomorrow.
Keep this in mind. When I closed the hi needle, she drew fuel right into the bulb and she started. I want to take that as air leaking in through the nozzle or somewhere in that area. Since the nozzle does not do the actual metering and since I do not see the tip in the venturi, is it possible that it came out. I guess we would call this a dumb question but should'nt I be able to see the nozzle tip. When I get bum fuzzled, I have a tendency to grasp for straws while falling into the hole. Thanks for staying with me, Tom from upstate SC


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## 30yearTech (Sep 14, 2006)

Well as to seeing the nozzle in the venturi, it really depends on which check valve assembly is being used on your carburetor. There are several different types and not all of them extend up into the venturi. The reason closing off the adjustment needles allows the purge to draw is because this shuts down the possibility of air being drawn through the check valve and the only way it can draw is to pull fuel through the metering chamber (the path of least resistance). So if the suction is not sufficient to pull the valve closed tightly then air will enter and the purge will be reduced or not work at all.

With the choke completely closed and WOT the vacuum created by pulling the starter rope alone should be sufficient to draw fuel up into the engine even if the valve were not sealing completley (at least to my understanding) it no fuel is being drawn I would suspect that there is not sufficient vacuum and there fore must be an air leak. 

Is there any possibility that the pto bearing on the crankshaft is loose allowing play?

Just out of curiosity will it restart hot after the 5 min heat soak if you just use a prime?

One more thought, how is the throttle shaft? Is there any wear? Is it loose in the carburetor body? This could be a source of vacuum loss, as wear in this area would allow air to enter and bypass the venturi. Just a thought.

Don't worry about guessing, we all guess at times, they may be educated guesses but a guess none the less. In fact I am just guessing on what you should try next as I am just as befuddled as you are. Everything I know tells me it's not the check valve, but this would not be the first time I have been wrong and I am sure will not be the last...


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## tom tilson (May 1, 2006)

I stripped the ngine almost to barebones. The PTO is snug as can be. 
It will not start after a 5min hot start on just a prime. When the engine is cool, it will start right up and run great until you kill it. If you immediately pull the rope, she is purring again. If you wait2 or 3 min, Will not start, not even a pop and plug is perfectly dry. Check your email. I sent one via Hobby Talk. Tom


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## tom tilson (May 1, 2006)

FINALLY!!!!!!~ with the help of my 30 yr tech buddy, it is finished WOW!!!
Raised the metering lever about .022 and even with a slight air leak somewhere, the primer could overcome the weakened and taller metering spring and she runs like a scalded dog. Lots of nice people on this forum compared to another I joined a while back which provided more criticism than help. That is why I don't post there anymore. Tom


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## tom tilson (May 1, 2006)

Blower runs great but maybe I set the lever a few thous hi and the reset press is about the same as the residual fuel pump press resulting in a fuel wet throught the carb intake that wets a spot about 2" in dia before seating. I do not know the exact lever setting. How about it 30yrtech .


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## 30yearTech (Sep 14, 2006)

Well I actually have a gauge that I got from Walbro several years ago that I use to set the needles, on the WA and WT carburetors it looks like it's about .005 above the inner body of the carburetor when set with the gauge.

Did you replace the inlet metering needle, pin and fulcrum arm? Wear in any of these components can cause these settings to change. 

This brings to mind the original problem, perhaps the inlet metering needle was sticking closed when the engine got hot and was preventing fuel from entering the metering chamber. When you would close off the adjustment screws and operate the purge, it would force the metering needle to become unstuck and then the engine would start and run again. Setting the fulcrum arm up would apply enough extra lift to allow the needle to free itself and allow fuel to enter the carburetor.

What color is the tip of the metering needle?
If it's pink or has a thin pink line around the tip it needs to be replaced.


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## tom tilson (May 1, 2006)

Thanks 30yr, I presumed my son had put a kit in it before he gave up and sent it to me. I will check the needle tomorrow. 
You could be right about this being the problem from the beggining. The pink color is that what the core material of the needle tip is and as it wears through shows up as a wear indicator. 
Anyway the unit runs excellent and when you cut it off, I believe I have the needle set to a lower pop psi than the fuel pump press and the fuel pump press relieves its self through the venturi until it finally gets, to what may be a lower than spec pop press. It leaks about a table spoonful and stops leaking.
I believe that when I get the metering section right that she will run good and the leak will stop. Thanks again Ole Buddy. Tom


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## 30yearTech (Sep 14, 2006)

Yes, thats the color of the core material, the outer coating is something like a graphite that helps the needle seal and release freely. When the needle wears there is usually a little ridge on the needle tip and you can see the pink underneath and sometimes the entire tip is pink. I have found that when there is any pink showing or a ridge in the tip, they will stick, and I started thinking that we never addressed this possibility which could have been the problem all along.


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## tom tilson (May 1, 2006)

30yrtech Checked needle, had some sooty looking substance which I wiped off and used Qtip to swab out seat. Lowered lever just a tad. Runs great, no leaking fuel. Thanks


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