Jonseed 2139t/Husky 338t very rich after rebuild

[93Dakman!]

Bought a used Jonsered 2139t last year and I'm just now getting around to working on it.

It was not a running saw. I put new fuel lines and primer bulb and rebuilt the Zama carb. The whole saw was filthy. I mean awful! But I only paid $5 for the saw, so I was okay with 2 hours of wax and detail service.

Due to the saw and carb being so dirty I took the long, skinny welch plug out of the carb to clean under it. I don't usually pop them out on a simple clean and diaphragm replacement.

After reassembly the saw is running rich. So rich that it is blowing black oil goo out on my wrist when it is running. It will only run throttle wide open. I've never had this issue before with any of the hundreds of carb kits I've done. I took the carb back apart and checked the needle/seat, the diaphragms, cleanliness, ensured that the mixture screw needles are in the correct hole, drove the welch plug in just a tad harder, but to no avail. It still blows heavy smoke and won't Rev to full speed due to the obscene richness. Any insight? Could it be the welch plug leaking around. I can run both mixture screws in until seated and the saw still starts and runs. It runs better than with the screws out, but it is still rich as heck.

Any ideas?

Clean under the needle/seat again? The check valve?

 

[mkinslow]

Check metering lever height, could have been enough difference in the little tit on diaphragm to make a difference and making it rich

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[Leonard Meehan]

This is what the Tillison manual said for the HS series. I am not sure which carb you have. I will upload the manual. It has very good diagrams.

CARBURETOR RUNS RICH WITH HIGH SPEED MIXTURE SCREW SHUT OFF
The 7/32 “ diameter nozzle welch plug, or nozzle check valve cage, is not sealing

 

[mbrick]

Did you used compressed air to blow out the carb passages by chance?

There is a plastic diaphragm in the main jet and it could have been damaged. The main jet be tested with a mityvac.

 

[Leonard Meehan]

It may not be worth any more of your time. I have had good luck with after market carbs. Of course if you are like me I hate to give up on any rebuild.
If you get it figured out please post the result.

I see where you said it is a zama carb. probably this one.
JONSERED 2139T Carb / ZAMA # EL33A-9ZB


Zama manual says this; WELCH PLUG • Under the extreme conditions of a clogged idle port and channel, it may be necessary to remove the welch plug. Do this operation very carefully. If the carburetor is equipped with the priming pump, do not attempt to remove the welch plug unless you are certain the check valve in the idle chamber is malfunctioning. • Use a small 2/32 to 3/32 inch diameter sharp pointed punch to pierce the welch plug. • Just below the welch plug there is a thin casting wall where the idle and secondary holes are located. Punching through this area will ruin the carburetor body casting. Let the punch just pierce the welch plug, then carefully pry the welch plug out of the body casting. • If the carburetor is equipped with the plastic filling in the idle chamber, it will be unusable when the welch plug is removed. So, replace the plastic filling. Note: It is often un-necessary to remove the welch plug. Test for plugged progression holes by spraying carb cleaner into the L needle hole. If cleaner sprays out the progression holes there is no need to remove the welch plug. LOCATION CHART FOR PIERCING WELCH PLUGS

 

[brad ruch]

Black oil goo??umm bar oil in the cylinder?been down this road had same senirio..

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[SteveSr]

Bought a used Jonsered 2139t last year and I'm just now getting around to working on it.

It was not a running saw. I put new fuel lines and primer bulb and rebuilt the Zama carb. The whole saw was filthy. I mean awful! But I only paid $5 for the saw, so I was okay with 2 hours of wax and detail service.

Due to the saw and carb being so dirty I took the long, skinny welch plug out of the carb to clean under it. I don't usually pop them out on a simple clean and diaphragm replacement.

After reassembly the saw is running rich. So rich that it is blowing black oil goo out on my wrist when it is running. It will only run throttle wide open. I've never had this issue before with any of the hundreds of carb kits I've done. I took the carb back apart and checked the needle/seat, the diaphragms, cleanliness, ensured that the mixture screw needles are in the correct hole, drove the welch plug in just a tad harder, but to no avail. It still blows heavy smoke and won't Rev to full speed due to the obscene richness. Any insight? Could it be the welch plug leaking around. I can run both mixture screws in until seated and the saw still starts and runs. It runs better than with the screws out, but it is still rich as heck.

Any ideas?

Clean under the needle/seat again? The check valve?

It is quite likely that the new welch plug isn't sealing properly. Best bet to reseal it is with THIN super glue. Clean everything out good with carb/brake cleaner. Let it dry completely. Run a bead of superglue around the welch plug. Now for the HARD part... Put the carb on the self for 24-48 hours to make DAMN sure that the superglue has hardened. You may see a little white haze around the plug. Cyanoacrylate is one of the few glues that will resist BOTH gasoline AND alcohol.

You can make a welch plug tester out of a generic clamp that you can buy at a big-box store as in the attached Stihl Tech Note. BTW, the Seal-All mentioned in the tech note is NOT resistant to alcohol.