carb question
07-31-2010 | 10:42 PM
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From: Salem,
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carb question
I've got a carb question, it's still in weedie form and I need it for that purpose... it's an Echo 21 with a Zama two needle carb. For one, the tank vent seems to cause a vacuum in the tank, I have two of these engines and have tried both of the vents I have with the same result. Sometimes it'll lean out then if I open the tank cap it'll run fine again for another few minutes. Then when it gets to half tank (always half tank, clunk still fully submersed, no bubbles in fuel line) the carb seems to suck air and it's not through the fuel line or fuel inlet. Pushing the primer bulb you can hear the air being sucked but it's hard to tell from where. I've put a different metering diaphragm in and checked the fuel pump diaphragm with no noticeable change. the other echo 21 I have didn't come with the carb, so I can't steal it. fuel lines are routed right.
the thing runs great when it gets fuel... any ideas are appreciated, thanks!
the thing runs great when it gets fuel... any ideas are appreciated, thanks!
07-31-2010 | 11:25 PM
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RE: carb question
fuel line is one piece from carb to clunk, replaced fuel line last time I worked on it because I thought the same thing.
I'm thinking I just need to completely pull the carb and clean out everything... then put new diaphragm's in it along with any other parts I can find, I know I have enough single needle carbs around for spare parts...
I'm thinking I just need to completely pull the carb and clean out everything... then put new diaphragm's in it along with any other parts I can find, I know I have enough single needle carbs around for spare parts...
07-31-2010 | 11:33 PM
#4
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RE: carb question
With the tank empty and your thumb over the end of the clunk, see if you can suck air through the fuel line at the carb
I suck on the fuel line and stick my tung over the end of the tube. If it is tight, it will hold my tung against the fuel line
I suck on the fuel line and stick my tung over the end of the tube. If it is tight, it will hold my tung against the fuel line
08-01-2010 | 07:45 AM
#5
RE: carb question
ORIGINAL: rangerfredbob
I've got a carb question, it's still in weedie form and I need it for that purpose... it's an Echo 21 with a Zama two needle carb. For one, the tank vent seems to cause a vacuum in the tank, I have two of these engines and have tried both of the vents I have with the same result. Sometimes it'll lean out then if I open the tank cap it'll run fine again for another few minutes. Then when it gets to half tank (always half tank, clunk still fully submersed, no bubbles in fuel line) the carb seems to suck air and it's not through the fuel line or fuel inlet. Pushing the primer bulb you can hear the air being sucked but it's hard to tell from where. I've put a different metering diaphragm in and checked the fuel pump diaphragm with no noticeable change. the other echo 21 I have didn't come with the carb, so I can't steal it. fuel lines are routed right.
the thing runs great when it gets fuel... any ideas are appreciated, thanks!
I've got a carb question, it's still in weedie form and I need it for that purpose... it's an Echo 21 with a Zama two needle carb. For one, the tank vent seems to cause a vacuum in the tank, I have two of these engines and have tried both of the vents I have with the same result. Sometimes it'll lean out then if I open the tank cap it'll run fine again for another few minutes. Then when it gets to half tank (always half tank, clunk still fully submersed, no bubbles in fuel line) the carb seems to suck air and it's not through the fuel line or fuel inlet. Pushing the primer bulb you can hear the air being sucked but it's hard to tell from where. I've put a different metering diaphragm in and checked the fuel pump diaphragm with no noticeable change. the other echo 21 I have didn't come with the carb, so I can't steal it. fuel lines are routed right.
the thing runs great when it gets fuel... any ideas are appreciated, thanks!
It seems to be an obvious thng, but your tank vent needs to be open to the atmosphere. When you say it runs ok after you remove the tank cap, it suggests that the cap is not vented, or the vent line is clogged. Check for clogs.
Regards,
Richard
08-01-2010 | 12:38 PM
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From: Salem,
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RE: carb question
at the half tank point where it won't run at all, it doesn't matter if the tank cap is off it still pulls air through the carb. I got tired of loosening the cap yesterday and ran with the tank vent off, still did the half tank thing. I'll take the carb apart tonight and see what that does.
08-04-2010 | 12:26 AM
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RE: carb question
carb is screwed somehow, doesn't make any sense... both gaskets/diaphragms are in good shape, nothing causing them not to seal, needle is in good shape. When you release the primer bulb it pulls air instead of fuel even cold now. going to dig thorough my carb pile and try to find something else.
08-04-2010 | 11:59 PM
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RE: carb question
hoping I figured it out tonight, replaced the fuel pump diaphragm with another used one and it started pulling fuel, also found I fudged on the regulator needle spring, wasn't seated right and forced the needle down. Still haven't found anything real reason, just guesses. We'll see when I run the thing again on sunday. Did find something odd though, being a Zama carb the pulse hole is at 45* from the bolt holes instead of 90* like a Walbro, the gasket had the holes at 90 and somehow it ran fine most of the time, that is now fixed but I found it odd.
08-08-2010 | 06:34 PM
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RE: carb question
the running problem was the weak pulse signal to the carb... I ran a complete tank through it today (from full to dry) with no real issues, I have no idea how it ran so good before with the pulse port mostly blocked off... the primer still doesn't work perfect, but it runs good now.
