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Post by lcmarky on Oct 13, 2020 17:40:03 GMT 1
Ran the 500 up today after finally getting around to fitting new brakes all round and cylinder #2 (Front lower left or nearside) wasn't firing. Swapped plug from cylinder 4 (front right hand side) and the same again.
Didn't follow up with any thinking about it as I had a couple of non RD things to do, so just starting to think what could cause one cylinder not to fire..
Will check spark and trace back I guess..
Anything particularly obvious I should look at first?
Cheers
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Post by rich on Oct 13, 2020 18:22:41 GMT 1
My guess would be carb related, does that cylinder kick in when you rev it or is it just on idle?
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Post by stusco on Oct 13, 2020 18:26:33 GMT 1
Ive not got a 500lc but do have a gamma ive had a similar problem it was fuel the needle valve had stuck not allowing any fuel into the carb,im sure ive read somewhere that there is a problem with fuel to certain cylinder on a 500 lc
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Post by lcmarky on Oct 13, 2020 18:28:43 GMT 1
Not firing at all. Strange as it's been fine up to now, so I'm sure it's something simple.
Carb's have been re-built too so easy enough just to bleed them too seeing as I have access.
#2 plug was wet when I chopped it, hence why I immediately thought spark seeing as the plug changeover didn't make any difference.
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Post by lcmarky on Oct 13, 2020 18:29:38 GMT 1
Not firing at all. Strange as it's been fine up to now, so I'm sure it's something simple. Carb's have been re-built too so easy enough just to bleed them too seeing as I have access. #2 plug was wet when I chopped it, hence why I immediately thought spark seeing as the plug changeover didn't make any difference. ..2nd one for fuel related. Will pull the carbs too, I'm a dab hand at it now! |
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richb
Thrash Merchant
Posts: 355
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Post by richb on Oct 13, 2020 20:21:42 GMT 1
Mine does exactly the same after being left for a while. It does eventually catch but then the carb just starts overflowing. Drop float bowls and normally a build of gummy shitty fuel - not good. Best to crimp fuel lines and run till stops so no fuel in carbs or drain out if standing for a while or empty tank and fill with aspen fuel
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Post by lcmarky on Oct 13, 2020 22:14:32 GMT 1
Mine does exactly the same after being left for a while. It does eventually catch but then the carb just starts overflowing. Drop float bowls and normally a build of gummy shitty fuel - not good. Best to crimp fuel lines and run till stops so no fuel in carbs or drain out if standing for a while or empty tank and fill with aspen fuel 3 for fuel. Will start with draining the bowls and refilling on prime. |
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Post by lcmarky on Oct 14, 2020 10:23:10 GMT 1
Spark is OK (well as weak/strong as the others... and not a patch on the LC now with it's big fat VAPE spark), so opened up the fuel bowl drain screws on the left side carb's and drained a bit of fuel out.
Manually set the carb slides as one was sitting high and biek started and ran on 4 fine for a bit. Choke off and cylinder 2 again starts to not fire, so will investigate the needle valve etc in the carb..
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Post by lcmarky on Oct 14, 2020 14:34:30 GMT 1
Traced to a broken choke plunger return spring on #2 carb'...
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Post by lcmarky on Oct 14, 2020 15:02:43 GMT 1
These springs are now unavailable as OEM Yamaha parts, but I have one of these in my garage and if you take the 5.6 x 38.1 and stretch it out a bit to get a similar no of coils, cut to length as per original and works a treat!  Springs by KTM Marky, on Flickr |
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