# Sthil BG75 spark arestor



## shortlid (May 9, 2005)

I just got a old Stihl BG72 handheld leaf blower for free from a contractor. It is pretty beat but runs. I had to replace the gas cap for $10 but now is running good. Seems a little slugish. Was going to clean the spark arestor. If it is too plugged up can I just leave it out of the machine?


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## rotti1968 (Apr 26, 2009)

not recommended , thats to prevent a chance of fire. take it out and use a propane torch to burn it off I have yet to have one I cant clean.on a side note that from to rich of a mix should be 50 to 1 ratio and also not running the unit a full speed causes this.


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## geogrubb (Jul 28, 2006)

Create a mixture of 1/2 fuel mix and 1/2 Chevron Techron, enough for the blower to idle for 20-30 minutes, the carbon will start dripping out of the muffler,do not rev it up or the carbon will come loose in chunks and bad things can happen, when it is finished fill with regular fuel and let it idle for a few minutes and you are done. After doing this it will be spotless on the inside. Have a good one. Geo


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## shortlid (May 9, 2005)

OK, would Marvel Mystery Oil or Seafoam do the same??


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## geogrubb (Jul 28, 2006)

I don't know if they will work or not, I have never tried them, but I do know Chevron Techron works, give the others a try, I will say don't waste your time and money on the $.99 injector cleaners. Have a good one. Geo


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## shortlid (May 9, 2005)

*Kerosene*

Yep the injector cleaner is just Kerosene.


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## shortlid (May 9, 2005)

Well took the spark arestor and pipe out and it ran GREAT but was SOOOO loud!! Cleaned and blew it out with 100 psi. But when I put it in it does not run right??? Can I drill the hole for the outlet bigger?

It runs like the spark arestor is still pluged will idle but will not throdle up now? Has freash 50:1 mix in as well.


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## shortlid (May 9, 2005)

Should I try re adjusting the carb?


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## pyro_maniac69 (Aug 12, 2007)

did you burn out the muffler?


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## rotti1968 (Apr 26, 2009)

pyro_maniac69 said:


> did you burn out the muffler?


Good one to check , but can you see through the fire screen? sounds like it is still plugged


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## shortlid (May 9, 2005)

Yep, can see though the screen, and now like magic the blower is runing and throdleing-up OK?? Maybe some old gas in the lines and carb needed to be worked through. 

However when I got the owners manual from Sthil it shows TWO air filters the foam and and paper element this one only had the foam pre-filter, should I try to get the paper filter as well?


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## rotti1968 (Apr 26, 2009)

You should have filter's #4133 124 2800 pre filter and 4133 124 1500 main filter installed. That foam prefilter only prevents larger particles from getting through it willnot stop the smaller stuff that main filter will catch.


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## shortlid (May 9, 2005)

*Thanks for Part #*

Thanks for the part #'s I will pick it up.


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## shortlid (May 9, 2005)

*Has the devil in it this fall*

Well put both filters in felt one is $6!! Anyway Now it's will not run wiith out being on full choke. I can't figre the think out stalls when I release the trigger and only revs up wit full choke on how. It was running so good before I putthe right air filters!! in it. Pulled them both off again and still doing it


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## rotti1968 (Apr 26, 2009)

I would say you have a carburetor issue or an air leak on the unit . I would lean more towards the carburetor.


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## shortlid (May 9, 2005)

OK, should I try to adjust or just rebuild it?


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## rotti1968 (Apr 26, 2009)

I would remove the carburetor open and inspect, and also give a complete cleaning, then you can try to adjust. Was there alot of dampness around the carburetor? like it looks like the carburetor maybe leaking and there is debris around the carb.If so you should not even bother trying to clean or adjust and just replace. That shows signs of an internal leak in the carb that may not be repairable .


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## shortlid (May 9, 2005)

*Clean*

There is no debris around the carb I cleaned it good at the end of summer with small engine carb cleaner. I will try to disasemble, and clean, but got this unit for free if it needs a new carb I will likely trash it. It is REAL old and was used by a landscaper.


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## rotti1968 (Apr 26, 2009)

hows the compression ?


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## justin3 (Apr 10, 2007)

I have never seen an internal leak in a carburetor before, normally you can just rebuild the carb instead of replacing it. The rebuild kits are around $6-10. I would also replace the fuel line and filter if the unit is really old.


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## scrivokhad (Oct 29, 2009)

rotti1968 said:


> I would say you have a carburetor issue or an air leak on the unit . I would lean more towards the carburetor.


I'm very interested! I would love to find out more inforamtion related to this topic. Thanks in advance.
me too, I need more detailed info.:freak:


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## scrivokhad (Oct 29, 2009)

Great info! Really informative. It is helpful for me.


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## rotti1968 (Apr 26, 2009)

justin3 said:


> I have never seen an internal leak in a carburetor before, normally you can just rebuild the carb instead of replacing it. The rebuild kits are around $6-10. I would also replace the fuel line and filter if the unit is really old.


There are check valves etc inside of the these carburetors and at times the become stuck open or closed and cause an internal leak that will either supply to much fuel on the low side or not enough on the high side etc.... There is a testing procedure that stihl has trained us with that allows for testing of these check valves. In approx 10 minutes i can tell weather its worth rebuilding the carburetor or tossing it and installing a new one. Also if a welch plug has come loose or is leaking it will allow an internal leak in the carburetor. It has come to a point where it is at times not cost effective to put labor and kits into a carburetor and we just replace them as needed. The accelerator pumps also can become worn and leak as will throttle shafts and plates.
If you remove a carburetor and put a pressure tester on the inlet of the carburetor and apply pressure and it does not hold you have a leak. You can put that carb in a cup or tank of water and reapply that pressure and see where its leaking, sometimes its just the screws on the covers are loose but most of the time you will find that its leaking from the main jet or somewhere internal .
this test is not the one i ref above, that one is a little more complicated to explain and involves making a special tool for testing.


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## shortlid (May 9, 2005)

OK, that makes more sense I will pull it and check it.


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