Help me understand carbs

Genius

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I find myself pulling my hair out on carbs quite often. When it comes to homeowner saws like the 290's, 250's etc Chinese carbs are so cheap that a lot of times it isn't worth my time buying a rebuild kit, USC cleaning a carb and going through it.

Lately I've been working on more pro saws and older saws where either aftermarket carbs are not a option, or if they are, I'd rather keep a OEM carb in. Plus, I want to better understand carbs.


When you guys are rebuilding carbs, how are you going about it besides putting in a kit? I always USC clean the carb, then blow it out with compressed air from one of those cans that they use for cleaning computers etc. seeing I don't have a compressor in my saw shop they seem to work pretty good, and they are not very high pressure. I pull the metering lever and needle and put a new one in every time FWIW.


A few issues I am having are (mostly idle issues)
1: I can't get the saw to even pop, and after several pulls, it's flooded
2: The saw won't properly idle or idles real rough.

In these two instances I've put a known working carb in and the saw works fine. The saw passed pressure and vac test just fine. New fuel lines and filter were installed already.


I do set the metering lever with the Zama or Walbro tool FWIW
 

rocketnorton

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r u takin out welsh plugs? u need more air. 100 psi wont hurt a bare carb body. think the cans are 10ish. no usc here, just industrial cleaner, soak em, rinse w/gas. don't want that cleaner on anything you care about & air.
 

Red97

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I find myself pulling my hair out on carbs quite often. When it comes to homeowner saws like the 290's, 250's etc Chinese carbs are so cheap that a lot of times it isn't worth my time buying a rebuild kit, USC cleaning a carb and going through it.

Lately I've been working on more pro saws and older saws where either aftermarket carbs are not a option, or if they are, I'd rather keep a OEM carb in. Plus, I want to better understand carbs.


When you guys are rebuilding carbs, how are you going about it besides putting in a kit? I always USC clean the carb, then blow it out with compressed air from one of those cans that they use for cleaning computers etc. seeing I don't have a compressor in my saw shop they seem to work pretty good, and they are not very high pressure. I pull the metering lever and needle and put a new one in every time FWIW.


A few issues I am having are (mostly idle issues)
1: I can't get the saw to even pop, and after several pulls, it's flooded
2: The saw won't properly idle or idles real rough.

In these two instances I've put a known working carb in and the saw works fine. The saw passed pressure and vac test just fine. New fuel lines and filter were installed already.


I do set the metering lever with the Zama or Walbro tool FWIW

FWIW

I have done 6-8 "old saw" carbs Walbro/Tillotson

Always used OE kits

I pull the carb down everything but the welch plugs. spray carb cleaner through all the passages blow out with compressed air. I pay close attention to the needle/seat when setting the lever, have to make sure it stays seated while making adjustments.

As long as the gaskets are in the right order I haven't had many issues with the carbs ive put kits in.

Now I have got 2 Chinee replacement carbs and neither have worked correct out of the box.

Carb 1 wouldn't pop/ run after fighting with it for 30min it got tossed, checked lever height adjusted the needles all over and nothing.

Carb 2, Had low speed/ idle issues, this one may be cure able, never took the time to pop it apart.

carb issues are no fun, hopefully someone is willing to shed some light on this subject.....
 

Genius

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r u takin out welsh plugs? u need more air. 100 psi wont hurt a bare carb body. think the cans are 10ish. no usc here, just industrial cleaner, soak em, rinse w/gas. don't want that cleaner on anything you care about & air.

I havent popped the welsh plugs. I am curious when these warrant being pulled or not.
 

Red97

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I havent popped the welsh plugs. I am curious when these warrant being pulled or not.

If the carb still doesn't work after a kit????

Im sure some people pull them every time, but I figure ill just screw something up in the process of removing it.
 

rocketnorton

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I havent popped the welsh plugs. I am curious when these warrant being pulled or not.

If the carb still doesn't work after a kit????

Im sure some people pull them every time, but I figure ill just screw something up in the process of removing it.

if carb looks clean, ill skip them. sometimes works, sometimes ya get to do it 2nd time round. I use a jewelers finger drill to drill plugs & not f up the body. I don't use any kinda sealer on the new ones. don't flatten them, either. couple taps w/small drift & tack hammer.
 

leeha

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I've done a ton of saw carbs and others as well and
never used an USC. I don't have one and feel i don't
need one. If the carb looks clean when disassembled
i skip the welch plugs and leave them. I use CRC carb
spray cleaner soak the carb a few times and spray into
all the passages. This way you can see where the carb
cleaner goes. Then blow dry through all the passages.
Assemble carb per carb specs and go. It's also important
to pay attention to diaphragm and gasket orientation and
if it's a vintage carb it could very well have the wrong
gaskets and diaphragms in it.


Lee
 

DSS

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I've only got a baby USC and don't use it much. Spray good carb cleaner through every passage, like a lot of carb cleaner. I don't usually put a lot of compressed air either, just enough to dry it. I've only ever had a couple that defeated me.

Make sure you assemble the gaskets and diaphragms the right way. If you're not sure, the walbro and tilly websites have good diagrams of most of the carbs. I printed a bunch off and put them in a binder.
 

trx250r180

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Great thread ,seems like if i take one off and apart twice and it still does not work ,i could have bought a new carb for the time invested ,Maybe Scott will chime in to this thread and give some tips ,he is the carb god
 

Genius

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Thanks guys. I forgot who, but someone told me to not spray carb cleaner through cause it's a good way to ruin seats from the pressure. That's why I always ran canned air after a USC cleaning.

I'll give a good shot of carb cleaner after the USC.
 

fossil

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It generally thake many pulls to pull fuel into a freshly kitted carb. I use and eye dropper off mix squirted into the carb throat with high idle set and choke off. It usually takes 2 or more primes to get the carb drawing fuel on it's own

Watch using high pressure air on carbs with mechanical check valves. That can ruin the check valve.

Sea Foam Engine cleaner is great stuff to soak dirty carbs and poorly acting carbs in. I recycle it.

Here's good info on Walbro carbs.

Good stuff here.

http://www.walbro.com/media/21936/SERVICEMANUAL.pdf Well worth the read for how they work.

Carb specific

http://www.walbro.com/servicemanuals.aspx



Tillotson Carbs.

Google Tillotson and the model number. ie Tillotson HS


Zama

http://www.zamacarb.com/pdfs/TechGuide_2007.pdf

http://www.zamacarb.com/images/techsupport/DisassemblyC1U.pdf
 

DSS

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It generally thake many pulls to pull fuel into a freshly kitted carb. I use and eye dropper off mix squirted into the carb throat with high idle set and choke off. It usually takes 2 or more primes to get the carb drawing fuel on it's own

Watch using high pressure air on carbs with mechanical check valves. That can ruin the check valve.

Sea Foam Engine cleaner is great stuff to soak dirty carbs and poorly acting carbs in. I recycle it.

Here's good info on Walbro carbs.

Good stuff here.

http://www.walbro.com/media/21936/SERVICEMANUAL.pdf Well worth the read for how they work.

Carb specific

http://www.walbro.com/servicemanuals.aspx



Tillotson Carbs.

Google Tillotson and the model number. ie Tillotson HS


Zama

http://www.zamacarb.com/pdfs/TechGuide_2007.pdf

http://www.zamacarb.com/images/techsupport/DisassemblyC1U.pdf
Look at you going all circus bear on us
 

trx250r180

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Thanks guys. I forgot who, but someone told me to not spray carb cleaner through cause it's a good way to ruin seats from the pressure. That's why I always ran canned air after a USC cleaning.

I'll give a good shot of carb cleaner after the USC.

It can cram the dirt further in the passage too ,:banghead:
 
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