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Post by xl130 on Nov 18, 2020 19:27:17 GMT -5
I was wondering if the needle seat can wear on a Tillotson HS series carburetor?
I recently rebuilt two HS series carburetors and they both leak pressure around the needle. I have not really seen this particular problem too often.
Is it possible that there is a very small amount of debris that is hard to see built up on the seat causing the to needle to not seal properly? Spring tension loss?
I use carburetor cleaner usually but possibly a sofa blast would help remove stubborn deposits?
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Post by fossil on Nov 18, 2020 21:33:16 GMT -5
Does the saw run OK? A carb is one giant air leak. As long as the leaks are consistent they are tuned out.
On the other hand, if the PO cranked down on the needle to hard the seat will be damaged and the carb is done.
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Post by edju1958 on Nov 18, 2020 21:37:04 GMT -5
What I've done on really dirty carbs is to take a Q tip & remove the cotton from the end & use the stick with cloth wrapped around the stick,then dip it in Seafoam & go into where the needle seats & swab it around till the cloth comes out clean.You'll be surprised at how much crud you'll remove from the seat.The cost is minimal & doesn't do any harm to the seat.I remove the cotton from the swab because I've seen it come off in the seat & then it's a pain to remove.It can also leave bits of cotton behind that you can't see,defeating the purpose.I find an old white sock works well.
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Post by xl130 on Nov 18, 2020 21:58:20 GMT -5
Does the saw run OK? A carb is one giant air leak. As long as the leaks are consistent they are tuned out. On the other hand, if the PO cranked down on the needle to hard the seat will be damaged and the carb is done. I didn’t bother trying to run the first carb. It would not hold pressure when tested. Second carb had the same issue.I stretched the spring out a bit. It worked to hold the pressure but now I’m thinking that it may cause a lean condition if the spring pressure is higher that it needs to be.It does seem to lean out at sustained WOT. Haven’t cut with the seal much though. I went as far as to pull the high needle soft plug and install a new screen due to build up of crud throughout. Both were carbs that had not been run in a looong time. Lots of remnants of old fuel and moisture. |
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Post by edju1958 on Nov 18, 2020 23:36:15 GMT -5
If it's leaning out on you,can you compensate by turning the needle out a bit more?I've gotten to the point that I can tune almost every saw I work on by ear.Maybe it's because my eyes aren't worth a hoot so I've come to rely on my ears moreso.
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Post by fossil on Nov 20, 2020 11:52:30 GMT -5
Does the saw run OK? A carb is one giant air leak. As long as the leaks are consistent they are tuned out. On the other hand, if the PO cranked down on the needle to hard the seat will be damaged and the carb is done. I didn’t bother trying to run the first carb. It would not hold pressure when tested. Second carb had the same issue.I stretched the spring out a bit. It worked to hold the pressure but now I’m thinking that it may cause a lean condition if the spring pressure is higher that it needs to be.It does seem to lean out at sustained WOT. Haven’t cut with the seal much though. I went as far as to pull the high needle soft plug and install a new screen due to build up of crud throughout. Both were carbs that had not been run in a looong time. Lots of remnants of old fuel and moisture. Make sure that little screen under the welch plug stays clear. That's a capillary main nozzle check valve. Anything that blocks that could hamper fuel flow. |
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