Cleaning carb idle drillings without removing welch plug

[tomalophicon]

I have a Zama C3m that was filthy - the strainer was completely blocked with crud. The fuel pump diaphragm is stiffer than a 2 dicked billy goat.
I cleaned it up and have ordered a carby kit which doesn't come with a replacement welch plug.
Is there a way to ensure the idle drillings and other internal passageways are clean and clear without removing the welch plugs?
Does boiling them actually work?
Cheers.

 

[Joel D'Angelo]

How hard is it to remove a welch plug? Also, If a carb is naughty, soak it in a gallon of commercially available carb cleaner. It is available in the states for like $35.

 

[tomalophicon]

How hard is it to remove a welch plug? Also, If a carb is naughty, soak it in a gallon of commercially available carb cleaner. It is available in the states for like $35.

Hi Joel, the removal isn't difficult but the welch plug is destroyed in the process.
whatever you have available over there will be at least triple the price here unfortunately.

 

[SteveSr]

I have a Zama C3m that was filthy - the strainer was completely blocked with crud. The fuel pump diaphragm is stiffer than a 2 dicked billy goat.
I cleaned it up and have ordered a carby kit which doesn't come with a replacement welch plug.
Is there a way to ensure the idle drillings and other internal passageways are clean and clear without removing the welch plugs?
Does boiling them actually work?
Cheers.

C3M is a pretty simple carbFirst I would verify that you actually had clogged passages. Remove the "L" needle and spray some good carb cleaner into the "L" hole and check for flow in all of the idle holes. If that doesn't work I would go to the ultrasonic with liquid carb cleaner. Once that you have verified that it is clean I would re-seal the existing welch plug with thin super glue and let it cure for a day or so before reassembling.

You may also need to change the main nozzle as the integrated check valve is known to leak and cause erratic idle / engine performance.

 

[tomalophicon]

C3M is a pretty simple carbFirst I would verify that you actually had clogged passages. Remove the "L" needle and spray some good carb cleaner into the "L" hole and check for flow in all of the idle holes. If that doesn't work I would go to the ultrasonic with liquid carb cleaner. Once that you have verified that it is clean I would re-seal the existing welch plug with thin super glue and let it cure for a day or so before reassembling.

You may also need to change the main nozzle as the integrated check valve is known to leak and cause erratic idle / engine performance.

Thanks for your reply SteveSr.
I have sprayed the L and H passages but will go in again and see what I can see.
Can you confirm what the main nozzle is? Is that connected to the metering lever? If so I have one coming in the carb rebuild kit.
Saw starts perfectly every time but dies soon after starting (won't idle) and any throttle input bogs it down and stalls straight away.
I don't have an ultrasonic cleaner and was hoping boiling is an alternative.

 

[SteveSr]

Thanks for your reply SteveSr.
I have sprayed the L and H passages but will go in again and see what I can see.
Can you confirm what the main nozzle is? Is that connected to the metering lever? If so I have one coming in the carb rebuild kit.

The main nozzle feeds fuel through the "H" circuit of the carb into the venturi. The back side is that 3/16" round brass thingy in the metering chamber. It does NOT come with the kit. If you change it be sure to REMOVE the "H" needle first or you may destroy it.

BTW, I hope that you are using an OEM Zama kit.

Saw starts perfectly every time but dies soon after starting (won't idle) and any throttle input bogs it down and stalls straight away.

This could be main nozzle but you won't know until you fix the rest of the carb.

You should also clean the needle seat with a Q-tip stem dipped in carb cleaner and twirled around. Get out your magnifiers to inspect the seat when you are done.

Be sure to check and probably set the metering lever height. The old one might be usable and correct but should be checked. A new one MUST be set.

Once the carb is reassembled you should pressure test the fuel input to verify no leaks. It should hold 7-10 psi indefinitely.

BTW, what model saw is this on?

 

[tomalophicon]

The main nozzle feeds fuel through the "H" circuit of the carb into the venturi. The back side is that 3/16" round brass thingy in the metering chamber. It does NOT come with the kit. If you change it be sure to REMOVE the "H" needle first or you may destroy it.

BTW, I hope that you are using an OEM Zama kit.


This could be main nozzle but you won't know until you fix the rest of the carb.

You should also clean the needle seat with a Q-tip stem dipped in carb cleaner and twirled around. Get out your magnifiers to inspect the seat when you are done.

Be sure to check and probably set the metering lever height. The old one might be usable and correct but should be checked. A new one MUST be set.

Once the carb is reassembled you should pressure test the fuel input to verify no leaks. It should hold 7-10 psi indefinitely.

BTW, what model saw is this on?

Thanks for the advice regarding the nozzle. I'll have a look and see what I can find this afternoon.
This is a new saw to me. In the interests of ensuring it's been put together in the first place, is the L screw the longer of the two?

The kit is still in the post. Not sure if genuine or not.

I'll follow your advice when cleaning.

The metering height was set quite high but making it level with the carb body (not sure if that's correct) didn't seem to make a difference.

I pressure tested it previously and it was fine but will do so after the rebuild.

The carb is on a 2001 Husky 365 Special. Not sure if it's original or not but I believe Aussie Specials continued to have Zamas and open port cylinders at least for a while after the US got the Walbro and closed port cylinders.

Thanks again, very helpful.

Tom.

 

[Mad Professor]

This might be helpful?

Note you can ruin carb if you poke the carb body removing welch plug

 

[tomalophicon]

This might be helpful?

Note you can ruin carb if you poke the carb body removing welch plug

Helpful is an understatement. Thanks for that.

Yes thanks, almost ruined a Walboro drilling into the welch plug.

 

[Chevboy0167]

Only used this kit twice so far but much smoother and safer...

https://www.ebay.com/itm/224300495471?epid=2312767745&hash=item343959f26f:g:7RAAAOSwH8NggVGD

 

[tomalophicon]

Only used this kit twice so far but much smoother and safer...

https://www.ebay.com/itm/224300495471?epid=2312767745&hash=item343959f26f:g:7RAAAOSwH8NggVGD

Looks great but too rich for me unfortunately

 

[tomalophicon]

I have sprayed carb cleaner through the L hole and the idle holes are clear.

The main nozzle is clear but not sure if it's working correctly. I performed the test outlined in that Zama manual by blowing through it with a straw. The guide said I should be able to blow through it but not suck. Well I could blow and suck so that might indicate a broken check valve?

I also noticed this plug that's not flush. I assume it's the low nozzle as it's above the L screw?

And finally the high screw taper is not as sharp as the low. Is this a potential issue?

Thanks all.

 

[Mad Professor]

Did you use high pressure air blowing out the carb? Some check valves don't like that. Might try a fine wire to see if ball is stuck

 

[SteveSr]

I have sprayed carb cleaner through the L hole and the idle holes are clear.

Then leave the welch plug alone

The main nozzle is clear but not sure if it's working correctly. I performed the test outlined in that Zama manual by blowing through it with a straw. The guide said I should be able to blow through it but not suck. Well I could blow and suck so that might indicate a broken check valve?

Possibly... this test is hard to do as you have to seal off the other feeds into the "H" circuit. With this carb it looks like closing the "H" screw should be enough. Use generic fuel line squared off with a sharp razor blade to apply pressure and vacuum for the "straw" test. You should hear the valve click and flow much more in than out.

This looks like a "bypass" carb where most of the fuel goes through the jet in the main nozzle and only about 25% goes through the "H" screw. This provides a limited range of adjustability but much less sensitivity.

I also noticed this plug that's not flush. I assume it's the low nozzle as it's above the L screw?

Probably.

And finally the high screw taper is not as sharp as the low. Is this a potential issue?

No. They were designed like this. As you can see the screws are different with different screw threads to keep from getting them mixed up.

Keep in mind that the saw may have other air leaks that need to be fixed which is why it may have burned up in the first place. A main nozzle check valve usually won't cause this. If it sticks closed the saw won't rev up (no fuel). If it sticks or leaks open it will create an internal air leak and will stall at idle or the "L" screw will have to be open much further than spec to get it to idle. Symptoms can also be erratic which is why the rest of the saw has to be pristine to rule-in the carb.

I also found the Zama metering lever adjustment. It is interesting that they were too lazy to put the correct "bump" on their gauge for some of their carb models. File this under "Watch Out With Zama!" i.e. don't trust the gauge!

 

[SteveSr]

Did you use high pressure air blowing out the carb? Some check valves don't like that. Might try a fine wire to see if ball is stuck

I don't believe that this is a ball type valve... too new. Most that I have seen are a disc of fiberglass laminate. If the fibers come loose it can lead to sticking.

 

[tomalophicon]

Did you use high pressure air blowing out the carb? Some check valves don't like that. Might try a fine wire to see if ball is stuck

No but I've only just bought the saw and it's 20 years old

 

[tomalophicon]

Then leave the welch plug alone


Possibly... this test is hard to do as you have to seal off the other feeds into the "H" circuit. With this carb it looks like closing the "H" screw should be enough. Use generic fuel line squared off with a sharp razor blade to apply pressure and vacuum for the "straw" test. You should hear the valve click and flow much more in than out.

This looks like a "bypass" carb where most of the fuel goes through the jet in the main nozzle and only about 25% goes through the "H" screw. This provides a limited range of adjustability but much less sensitivity.


Probably.


No. They were designed like this. As you can see the screws are different with different screw threads to keep from getting them mixed up.

Keep in mind that the saw may have other air leaks that need to be fixed which is why it may have burned up in the first place. A main nozzle check valve usually won't cause this. If it sticks closed the saw won't rev up (no fuel). If it sticks or leaks open it will create an internal air leak and will stall at idle or the "L" screw will have to be open much further than spec to get it to idle. Symptoms can also be erratic which is why the rest of the saw has to be pristine to rule-in the carb.

I also found the Zama metering lever adjustment. It is interesting that they were too lazy to put the correct "bump" on their gauge for some of their carb models. File this under "Watch Out With Zama!" i.e. don't trust the gauge!

I'll try the fuel line test again tomorrow and play with H screw. I had it open 2 turns as suggested by Zama but will try closed and see what happens.

I have pressure tested the case and intake boot twice now and can't detect a leak anywhere. My assumption based on advice from this board is the saw was revved hard cold or run without enough oil - the scoring was on both intake and exhaust sides of the piston. (Additionally I have cleaned the spark screen, replaced fuel line, pickup filter and impulse line, new plug, gapped coil, blown-out the air filter, replaced piston and ring, cleaned the vent line, used fresh fuel and played with the idle and screws).

Backing out the low screw makes it run longer which makes me think that it's looking likely it's this nozzle as you suggest.

Thanks for the assistance re metering adjustment. I also pressure tested the metering needle/seat and seems to operating correctly.

 

[frank_]

sounds like the carb is ok, and its the blowback that is causing the laggy hesitation ?

 

[Okie]

I did not read all of this but in answer to your question about removing welch plugs or clearing idle passages.
When I'm first flogging a carb of any kind, small to large I do not remove welch plugs.
I clean them good, and now days use a Usonic. I use low pressure air (from a air compressor) and/or spray can air to check the [passages.
If the carb indicates it's not right after doing a performance test on the eq I then go back and very carefully drill a itty bitty hole in the center of the welch plug and if it's aluminum I can usually persuade the plug out with a ice pick or a o ring pick, if steel I may have to casrefully use a sharp pointed small screw as a puller.
After the plug is out I can then reform the plug using a soft leather backing and a round punch or a ball bearing from my stock pile. I also save welch plugs and keep both the ball bearing and welch plugs in same place.
When I re-install the welch plug I have some really good strong slow set non runny epoxy about consistency of margarine (24 hours to fully cure) and coat the complete out surface of the plug to the edges. Mine is actually Brownells acraglass gel and can be mixed with aluminum or metal particles.
About $22 at this ebay linkhttps://www.ebay.com/itm/264504234121?epid=1700207420&hash=item3d95ae5089:g:w7YAAOSwKFlfU-BD
This stuff stores really good, but if you open the white cap jug and it's kinda grainy months or years later, just get some hot water and set both of them into the water for few minutes then slowly stir as the plastic container warms and they will become the proper consistency again. Do not get water into the epoxy. Also using warm water will result in a faster cure time, but the warmer you get it the thinner it becomes, but it will still not flow freely.
Very good stuff. I've use it for lots of piddling projects and it will glue rubber to metal.
Mainly use for glass bedding gunstocks. You can review release agents if you have a place you do not want it to bond to paint the surface with the release agent. Kiwi Neutral shoe wax is a good release agent. (their are others)

Fast set epoxy is not as good as my slow set type and I do not trust any JB weld stuff for long term bonding use of carb welch plugs.

 

[tomalophicon]

sounds like the carb is ok, and its the blowback that is causing the laggy hesitation ?

Hi frank, not sure what blowback is. Can you explain please?
Cheers
Tom.