Walbro WJ39 on 394xp Throttle Shaft Leaking

[tallfarmboy]

Working on a very high hour 394xp... Had a cracked intake block, replaced that, but the saw still won't idle down like it should. I blocked off the outside of the carb, between the filter elbow and carb housing with Gorilla tape and pressure test found a big leak at the throttle shaft. Anyway, I know that throttle shafts will leak a bit... But, please tell me that this is excessive and would cause a fluttering idle... LOL
Video of the pressure test and soapy water.

 

[tallfarmboy]

I should add that if I moved the Gorilla tape to the other side of the carburetor, it passed vacuum and pressure test. No leakage.

 

[Big_Wood]

with the carb removed look inside the throttle side of the carb to inspect the throttle butterfly. the throttle spring that returns the throttle to closed can also cause the throttle shaft to pull to that side and wear the butterfly over time. it don't hurt a thing at high speed but you will notice on real high hour 39's that there will be a gap air can get through on that side cause some issues at idle. if yours doesn't have a gap there it's not as high hour as you thought or someone already repaired it.
you can block the intake of any saw and they would leak there so if your throttle butterfly is good i would say your looking at actual carb issues. you didn't mention if you rebuilt it or not and if you did it's not just assemble and go. not sure of your skill level so lets hear where your at.

 

[tallfarmboy]

with the carb removed look inside the throttle side of the carb to inspect the throttle butterfly. the throttle spring that returns the throttle to closed can also cause the throttle shaft to pull to that side and wear the butterfly over time. it don't hurt a thing at high speed but you will notice on real high hour 39's that there will be a gap air can get through on that side cause some issues at idle. if yours doesn't have a gap there it's not as high hour as you thought or someone already repaired it.
you can block the intake of any saw and they would leak there so if your throttle butterfly is good i would say your looking at actual carb issues. you didn't mention if you rebuilt it or not and if you did it's not just assemble and go. not sure of your skill level so lets hear where your at.

Thanks for the reply! I did rebuild the carb, so it has new internals. I removed the throttle butterfly and slid the shaft out a little to inspect. It did have a tiny little bit of play in it. The owner decided to just purchase a new carburetor, so I went on ebay and purchased a new WJ71. There were some selling for $40 with free shipping, so for that price, he couldn't go wrong.

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[Big_Wood]

Thanks for the reply! I did rebuild the carb, so it has new internals. I removed the throttle butterfly and slid the shaft out a little to inspect. It did have a tiny little bit of play in it. The owner decided to just purchase a new carburetor, so I went on ebay and purchased a new WJ71. There were some selling for $40 with free shipping, so for that price, he couldn't go wrong.

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Your missing what I’m saying. Doesn’t matter anymore since you ordered a new carb but I’m not saying that leak is cause by a worn butterfly. I’m saying that even with your throttle closed pretty well it’s getting the air through the worn spot of the butterfly. Seen more then a few high hour 39’s do that and it’ll mess you around when your tuning your low. There should be a number 192 on the throttle plate which is the same as a WJ69. The side of the throttle plate closest to the side the cable hooks too will be worn flat in side the cab bore. If it’s not it’s been repaired already and you have another issue or that carb is not as high hour as you think. If you want to send it to me that would be cool lol

 

[tallfarmboy]

Your missing what I’m saying. Doesn’t matter anymore since you ordered a new carb but I’m not saying that leak is cause by a worn butterfly. I’m saying that even with your throttle closed pretty well it’s getting the air through the worn spot of the butterfly. Seen more then a few high hour 39’s do that and it’ll mess you around when your tuning your low. There should be a number 192 on the throttle plate which is the same as a WJ69. The side of the throttle plate closest to the side the cable hooks too will be worn flat in side the cab bore. If it’s not it’s been repaired already and you have another issue or that carb is not as high hour as you think. If you want to send it to me that would be cool lol

I know that it's going to leak air passed the butterfly... I have the carb sealed off between the elbow and carb body. Pressurized the crankcase and it only leaks opposite of the throttle cable on the throttle shaft. It leaks pretty bad, in my opinion. When I start the saw and spray carb cleaner into that area, it will kill the saw. I know that a carb will leak a bit of air from the throttle shaft, I just don't think it should leak this much and I think that's where the problem is with this saw.

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[HarleyT]

If you are doing a leakdown test of the chainsaw, the carb should not be involved.

 

[HarleyT]

You block off the exhaust and intake ports of the engine, and test for crankcase leaks.

 

[tallfarmboy]

Guys, I know how to pressure test the crankcase... This saw passes a vac and pressure test 100%... But, it still didn't idle right... Fluttering and would slowly die... So, I decided to try to pressure the carb side of things. This was my result, seems like a massive air leak at the throttle shaft... I truly think that is the problem.

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[Big_Wood]

never said you didn't know how to pressure test. i read your post and can tell you know what your doing, i understand where you said you swapped the gorilla tape around. i occasionally put tillotson shafts in these which are slightly smaller then the WJ shafts and still don't have issues lol. i do believe your issue will be fixed with a new carb but not for the reason you think. i got an old ryobi weedeater out back with a WT out of an 028. swapped some ****** skinny shafts in there that worked but sloppy as hell. idles fine lol i wish i had a pic of an old 39 throttle butterfly to show you what i mean. what i'm talking about is completely unrelated to that leak you found and was since my first post cause i didn't and still don't believe that leak is your issue lol doesn't take much of any leak to make bubbles in soap like that. it's more likely that you are just dealing with an improperly assembled WJ39 then the worn throttle plate but since you said it was high hour i figured i'd mention it so you could check. did you even look? lol new carb will get you going. just don't toss the 39! i'll trade you something for it.

 

[tallfarmboy]

never said you didn't know how to pressure test. i read your post and can tell you know what your doing, i understand where you said you swapped the gorilla tape around. i occasionally put tillotson shafts in these which are slightly smaller then the WJ shafts and still don't have issues lol. i do believe your issue will be fixed with a new carb but not for the reason you think. i got an old ryobi weedeater out back with a WT out of an 028. swapped some ****** skinny shafts in there that worked but sloppy as hell. idles fine lol i wish i had a pic of an old 39 throttle butterfly to show you what i mean. what i'm talking about is completely unrelated to that leak you found and was since my first post cause i didn't and still don't believe that leak is your issue lol doesn't take much of any leak to make bubbles in soap like that. it's more likely that you are just dealing with an improperly assembled WJ39 then the worn throttle plate but since you said it was high hour i figured i'd mention it so you could check. did you even look? lol new carb will get you going. just don't toss the 39! i'll trade you something for it.

When I get the replacement, I will post again to share the results. If it fixes the problem, I will be very happy to swap it with you. I'm sorry if I sounded accusatory... It was more aimed at the comment of the person above. I don't ever include a carb on a pressure test, but I had eliminated all other options, in my mind... Which is pretty limited... LOL

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[HarleyT]

All carbs will leak some air at the throttle/choke shafts, worse of course when they are badly worn. Smear some grease over them and see if it affects the saw's performance....

 

[tallfarmboy]

All carbs will leak some air at the throttle/choke shafts, worse of course when they are badly worn. Smear some grease over them and see if it affects the saw's performance....

I don't plan on doing anything else with this carb as the saw is getting a new carb... But, when I sprayed the throttle shaft area while the saw was running, it would bog out and die. Wouldn't it make sense that it would be tough to tune with that big of an air leak?
More info... When I received the saw, it wouldn't run.. Needed a coil... Installed coil, ran but idled high... Found cracked intake block (spacer)... when reinstalling the spacer, realized that one of the bolts that held spacer in place was stripped... So, I tapped out to M6 and put a couple of Stihl bolts in, worked great, passes vac and pressure test... starts and runs but still won't idle properly... Installed a new carb kit into the WJ39... Still had flutterin idling issues. When I was trying to tune the carburetor, adding more fuel (CCW) on the L screw would make the saw idle higher, not flood it out.

Has to be an air leak in the carb??? Doesn't it??

 

[HarleyT]

What happens if you lower the low speed adj. screw? And how it runs?

 

[HarleyT]

My point being, to be honest, is that I have never actually tried to do a leak-test of the air/venturi passage, as any {pressure/vac} test of it would show a leak at the throttle/choke shafts, as they are not constructed to be air-tight.

And any slight air passage would be compensated for with the fuel/air adjustments.

The running issue that may arise from wear, would be an inconsistant air/fuel influx from an overly sloppy throttle/choke shaft, more likely on the throttle shaft, as that is the one with the majority of the movement/wear over time.

Also, is this new carb a real one, or aftermarket?

Is there any visible up/down slop on the throttle shaft of the old carb? Are the holes egg shaped?