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Discussion Starter #1
A while back my bike wouldn't start (1981 CX500C), and hasn't started since. So I sent my carbs to Larry, they came back perfect. I cleaned my tank and all the rust from inside and replaced the gas. I got a new fuel line, spark plugs, and charged my battery. And I also got an Ignitech CDI unit and a new petcock.

I put the new carbs in correctly but the bike just cranks. I tried spraying some carb cleaner in the carbs, but it just chugs a bit then backfires from the exhaust. I'm getting a good spark in both plugs, the battery is fully charged.

I know nothing about the electrical system of the bike, not sure where to start testing.
 

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Discussion Starter #4 (Edited)
open the carb drains and see if you have fuel in the bowls

if you had crap in your tank you vacuum petcock could be done and not letting fuel thru
I got all the rust out from the inside of the tank, and I bought a new non-vacuum petcock. The carbs came back from Larry in mint condition, and the fuel is definitely getting to them. Also, I have a clear fuel line so I can see the fuel going into the carb.
 

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If it isnt swapped coils.
Disconnect the bikes black/white wire from the Ignitech
see if that makes any difference
 

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A while back my bike wouldn't start (1981 CX500C), and hasn't started since. So I sent my carbs to Larry, they came back perfect. I cleaned my tank and all the rust from inside and replaced the gas. I got a new fuel line, spark plugs, and charged my battery. And I also got an Ignitech CDI unit and a new petcock.

I put the new carbs in correctly but the bike just cranks. I tried spraying some carb cleaner in the carbs, but it just chugs a bit then backfires from the exhaust. I'm getting a good spark in both plugs, the battery is fully charged.

I know nothing about the electrical system of the bike, not sure where to start testing.
Still sounds like it's not getting fuel. When you sprayed the cleaner in, it did more than without it. Could be something fairly obvious. Would it be possible to take a short vid of it cranking?
 

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Did you remember to put the o-rings between the intakes and the heads?

I missed the part where you said "it just chugs a bit", this sounds like it is running for a second or two on the starter spray. As Dan noted, it sounds like it is trying to run.
 

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Discussion Starter #12
Still sounds like it's not getting fuel. When you sprayed the cleaner in, it did more than without it. Could be something fairly obvious. Would it be possible to take a short vid of it cranking?
That's what I'm thinking.

Here's the video: [video]http://tinypic.com/r/x519xh/5[/video]
 

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I havent seen motorcycle fault finding 101 mentiioned yet
What did the plugs look like after repeated starting attempts?

Dry plugs its fuel
Wet plugs its sparks

Its not holy writ and there are exceptions but its a good rule of thumb
 

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Discussion Starter #14
I havent seen motorcycle fault finding 101 mentiioned yet
What did the plugs look like after repeated starting attempts?

Dry plugs its fuel
Wet plugs its sparks

Its not holy writ and there are exceptions but its a good rule of thumb
Yeah they're dry. I guess it's a fuel problem
 

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Yeah they're dry. I guess it's a fuel problem
Have you got the vacuum line connected to the right hand carb and to the furthest forward (toward the front of the bike) nipple on the petcock?
 

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Discussion Starter #16
Have you got the vacuum line connected to the right hand carb and to the furthest forward (toward the front of the bike) nipple on the petcock?
I replaced my vacuum petcock with a non-vacuum petcock, and I plugged the vacuum port. The fuel looks like its flowing alright.
 

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I replaced my vacuum petcock with a non-vacuum petcock, and I plugged the vacuum port. The fuel looks like its flowing alright.
And you have the O-rings in place between the manifolds and the heads?
 

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I replaced my vacuum petcock with a non-vacuum petcock, and I plugged the vacuum port. The fuel looks like its flowing alright.
Watched your vid. Sounds like it's turning over alright.

Have you checked for fuel flowing out of the carb drains?


Sorry, have to ask, are you using the choke?
 

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Yeah, but I noticed that the black boots are a bit cracked, not all the way through though.
It would take a fairly large hole in the manifolds to keep it from running. It might run lean.
 
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