Author Topic: jonsered 670 champ carb  (Read 288 times)

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Offline ub54

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jonsered 670 champ carb
« on: August 25, 2016, 11:37:05 am »
OK, so i bought my son a champ for x-mas . I knew it needed some repair , no big deal I've done it all on saws ... I thought . Anyway after getting it cleaned up , it needed a fuel filter and a carb kit. Got that done and fired it up . Realized why they called it a champ , the thing ran super and cut great .... for a while then died . But it would start right back up and die . So I refilled the tank and it started and ran great again ... for a while . Same thing. I figured the fuel line was cr acked where it goes through the tank , and replaced it . It wasn't bad . So I fired it up again and it was fine ... until my son used it for a bit and the same thing happened. I told him to switch the position of the impulse line and the one to the carb thinking I'd switched them . Anyway that wasn't the problem either , but the thing runs great if the tank is full . Use it a bit , and it will die . What am I missing ?









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Offline Cut4fun .

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Re: jonsered 670 champ carb
« Reply #1 on: August 25, 2016, 02:24:59 pm »
WAGS

tank vent plugged. 

coil going out when it gets hot warmed up.

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Offline ub54

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Re: jonsered 670 champ carb
« Reply #2 on: August 25, 2016, 04:20:45 pm »
Could be the tank vent, doesn}t really run long enough to get coil hot

Offline Cut4fun .

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Re: jonsered 670 champ carb
« Reply #3 on: August 25, 2016, 07:23:44 pm »
I had a stihl here that would run great for 3-5mins then coil go out.

I put the old school spark tester between plug and lead to watch it happening when testing.  Could see the spark light flutter then go out.

Just one of the two ideas.
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Offline ub54

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Re: jonsered 670 champ carb
« Reply #4 on: August 26, 2016, 09:11:53 am »
Thanx , I'm gonna check today

Offline oldpro

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Re: jonsered 670 champ carb
« Reply #5 on: November 07, 2016, 04:45:43 pm »
When it dies immediately check it for spark,being sure to have the spark plug grounded on engine metal somewhere.Open the gas cap listening closely for any sound of suction or pressure. Not a bad idea to just replace the tank vent for the little they cost. Did you replace the fuel filter?

Offline Eccentric

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Re: jonsered 670 champ carb
« Reply #6 on: November 08, 2016, 02:43:44 pm »
If you're bringing an old saw back to life for use as a work saw you should replace the crank seals.  Like the fuel line and carb diaphragms, the crank seals are rubber parts with a finite lifespan.  Sometimes crank seals will leak (or leak more) when hot.  When they leak, the impulse signal to the carb gets weak.   That will cause the saw to lean out.   A weak impulse signal afects the ability of the pump section of the carb to consistantly pump fuel from the the tank to the metering sectiion of the carb.

People often 'tune out' an air leak by richening the carb settings (often without even knowing that they are compensating for an air leak).  This can work for a while (until the leak worsens), but is bad practice and will eventually lead to damage.

Contrary to popular belief, a 2 stroke engine often does not 'race' or refuse to slow to idle speed when it has an air leak.  Those symptoms do happen sometimes, but not always.  Same goes with changing tune/idle speed with tilt.  That is a good indicator of a leaking crank seal.......but it does not always happen when a seal leaks...
-Aaron

For older saws:
Tune the H side so that it 4-strokes (burbles) at WOT unloaded and just cleans up when under load.
When you lift cutting load, the saw should immediately revert to 4-stroking.  Fine tune the transition point for the wood you're cutting.
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Offline oldpro

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Re: jonsered 670 champ carb
« Reply #7 on: November 14, 2016, 03:23:52 pm »
When it comes to crank seals I will replace them just like tune-up parts if the saw has quite a lot of running time or if the saw is more than a few years old. I can replace them in less time that it takes to pressure test the motor. They are fairly cheap and easy to replace.
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Offline farmboy

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Re: jonsered 670 champ carb
« Reply #8 on: November 14, 2016, 08:57:22 pm »
Just bought a doz from Jacks.  They were actually cheaper than AM's from Northwood.  I change them all the time too.
Shep

 

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