New Carb not holding pressure

[WestCoastCanada]

Hello folks,

So i purchased an aftermarket carb on amazon for an old husqvarna 41
When i pressure test the carb it won't hold pressure
When i submerge it in gas and pressure test it there are no visible bubble or leaks

The saw starts with the carb, but it won't idle (chain is racing) and runs lean...
I tried tuning the carb, still can't get the chain to stop at idle...

What is my next step ?

further diagnostics ?
carb is faulty, buy another one ?
other ?

 

[L34]

Are you testing with the needle wet.
Can leak when testing dry.

 

[Chevboy0167]

What is wrong with the original carb? Same problem? I have very good luck on the originals with an OEM rebuild kit. I do run them through my heated ultrasonic cleaner for 20 mins. though. Using water based parts cleaner solution... kinda like Simple Greeen.

 

[Chevboy0167]

I have seen 3 aftermarket carbs on saws be junk. The owner buys them on Amazon or eBay for $10-12. I recommend new or used with a rebuild. Have one junk carb here that the drilling passage for the H circuit does not even exist!

Now, I did use a chicom carb on an old Mantis tiller for a guy once.... and it did work. Hit and miss I guess.

 

[Chevboy0167]

New updated ....

https://www.ebay.com/itm/402837376378?hash=item5dcafa8d7a:g:S3IAAOSwNSxU2BWF&LH_ItemCondition=3

 

[WestCoastCanada]

Are you testing with the needle wet.
Can leak when testing dry.

Are you testing with the needle wet.
Can leak when testing dry.

I'm testing the needle wet... no compression
I just installed a new a new clutch which fixed the chain rotating on idle issue
But the saw is definitely running erratic due to carb compression issue

 

[WestCoastCanada]

What is wrong with the original carb? Same problem? I have very good luck on the originals with an OEM rebuild kit. I do run them through my heated ultrasonic cleaner for 20 mins. though. Using water based parts cleaner solution... kinda like Simple Greeen.

Unfortunately i do not have the original carb... but from now on i will try rebuilding originals before buying aftermarket

 

[WestCoastCanada]

New updated ....

https://www.ebay.com/itm/402837376378?hash=item5dcafa8d7a:g:S3IAAOSwNSxU2BWF&LH_ItemCondition=3

Thanks looks good... i'll probably get it...

 

[atpchas]

When i pressure test the carb it won't hold pressure
When i submerge it in gas and pressure test it there are no visible bubble or leaks

If it's not holding pressure, the air has to go somewhere. If there are no bubbles, perhaps your tester is leaking.

 

[Jasonrkba]

I ran the gamet a couple years ago on the AM carbs and found myself throwing money away. Get back after the new carb comes in. That old 41 may need seals. I cant remember what type intake those have but it could be the boot or impulse. Id check those for cracks.

 

[rmh3481]

You need some jewelers rouge, a Qtip and a new Zama or walbro needle for that specific carb. Cut the cotton off one end of the Qtip. Use the shaft of the qtip and dip into the cutting medium (Jewelers Rouge, Valve Grinding compound etc). Slowly start to polish the seat where the needle seals. Clean up the seat until it seals. Dont use alot of pressure and stop as soon as it seals. Stay under 10psi on your thumb pump as the needle seals at 7 or less. Worry about getting a seal not a pop off. We use this procedure on the old walbro's that you cannot buy anymore and it works well. 8 out of 10 can be brought back to seal. Go slow on the carbs with brass seats.

 

[WestCoastCanada]

If it's not holding pressure, the air has to go somewhere. If there are no bubbles, perhaps your tester is leaking.

thanks... I'm quite confident the tester is ok because when i pressure tested the cylinder it held, so i don't think the tester is the issue, but i will take another look, and try dipping the carb in gas again and look for bubbles again.... in the mean time i will order a new carb kit for a spare walbro carb i have that fits...

 

[WestCoastCanada]

I ran the gamet a couple years ago on the AM carbs and found myself throwing money away. Get back after the new carb comes in. That old 41 may need seals. I cant remember what type intake those have but it could be the boot or impulse. Id check those for cracks.

Thanks, i will start getting oem carb kits from now on instead of AM cheap carbs. As for the cylinder, everything is good. New top end, new piston, new seals, new intake valve and boot... cylinder test holds pressure... its got to be the AM carb at this point.

 

[WestCoastCanada]

You need some jewelers rouge, a Qtip and a new Zama or walbro needle for that specific carb. Cut the cotton off one end of the Qtip. Use the shaft of the qtip and dip into the cutting medium (Jewelers Rouge, Valve Grinding compound etc). Slowly start to polish the seat where the needle seals. Clean up the seat until it seals. Dont use alot of pressure and stop as soon as it seals. Stay under 10psi on your thumb pump as the needle seals at 7 or less. Worry about getting a seal not a pop off. We use this procedure on the old walbro's that you cannot buy anymore and it works well. 8 out of 10 can be brought back to seal. Go slow on the carbs with brass seats.

Thats very detailed... thanks... i'll order a new carb kit first, and if i need to i will try your method.

 

[WestCoastCanada]

If it's not holding pressure, the air has to go somewhere. If there are no bubbles, perhaps your tester is leaking.

Hi... you were correct i put my MityVac tester under water and there is a leak in the plastic reducer connector that goes from 1/4" to 1/8".... i will replace the reducer with a brass one as soon as i can... thanks....