Hello!
I have a 1981 cb650 that I just got up and running after a bit of carb work. I changed the plugs, it has new gas, new air filter is on its way, and new stock size 120 jets. I've been running it every morning to get the seafoam that I put into the gas to run through the carbs.
I also removed the vacuum operated fuel shut off (with the help of this forum). Anyways, the bike idles fine at between 1100 and 1300 rpm with all cylinders working and then it dies after a couple of minutes. After some testing I figured out that if I turn the petcock to "off" the engine doesn't die. I can run it 10-15 minutes with the petcock on "off", I haven't tried doing it any longer (Not really riding the bike right now as it is on planned non op and not yet insured.) If I'm idling it and I switch the petcock from "off" to "on" then the engine will stall out after about 1 minute. Just seconds after it stalls fuel will begin dripping from the carbs as if the bowls were overflowed.
Anyone have any idea what's going on? Like I said the air filter is on its way but I wouldn't think that it's absence would have this kind of effect on the engine. Seems like the issue is with the carbs or the petcock, not sure which one.
Edit: I just realized that my issue could perhaps be that the bike is on the side stand? Not sure but I will put it back on the centerstand and test the issue shortly.
Turning petcock to "on" kills the engine
Re: Turning petcock to "on" kills the engine
Check your float needles and seats. There may be some gunk in there that is keeping them from functioning properly.
PS: These are air cooled engines. Make sure that if you have it idling for long periods of time that you have a plan for keeping the engine cool.
PS: These are air cooled engines. Make sure that if you have it idling for long periods of time that you have a plan for keeping the engine cool.
Have a problem with your CB650? Have a technical question? Click here!
My Current Bikes: 2005 HD FLHTCUI Electra Glide Ultra Classic, 2007 Yamaha Vino,
My Current Bikes: 2005 HD FLHTCUI Electra Glide Ultra Classic, 2007 Yamaha Vino,
Re: Turning petcock to "on" kills the engine
Thanks for the reply. I don't idle it for more than a few minutes at a time, about the time it would take to warm it up. A quick google search says that tapping the back end of a screwdriver on the bowls might free up the floats, I will try this. I'm trying to avoid having to pull the carbs again but ultimately it seems like that's what I'm going to have to do.
Re: Turning petcock to "on" kills the engine
Follow AS Folsoml mentioned.
You can check fuel bowl level with clear tube on the bowl drain.
attach the tube and hold it up against the side of the bowl and watch the level when you turn the fuel off and again when on.
Put a clear tube on each Bowl and hold them together on one side to check all at once.
See it for yourself.
You can check fuel bowl level with clear tube on the bowl drain.
attach the tube and hold it up against the side of the bowl and watch the level when you turn the fuel off and again when on.
Put a clear tube on each Bowl and hold them together on one side to check all at once.
See it for yourself.
Re: Turning petcock to "on" kills the engine
Do you have a clean tank for sure?
Check out your petcock by blowing it through. Especially it should be tight in "off" position.
Besides the floater valves (sticky floats or dirt at seat), also the legendary "vacuum tees" might cause fuel leakage when cracked.
Check out your petcock by blowing it through. Especially it should be tight in "off" position.
Besides the floater valves (sticky floats or dirt at seat), also the legendary "vacuum tees" might cause fuel leakage when cracked.
Cosky's great (free) online manual: http://cosky0.tripod.com
forum links to common technical issues
If you really like this site and you would not like to see it vanish soon, have a look there: Urgent: Future of HondaCB650.com Forum
forum links to common technical issues
If you really like this site and you would not like to see it vanish soon, have a look there: Urgent: Future of HondaCB650.com Forum
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Re: Turning petcock to "on" kills the engine
Sounds completely opposite of what a good petcock does.
My first guess is that you have your directions mixed up. Some petcocks use the lever to point, some petcocks actually have a triangle "arrow" opposite the end of the lever to point.
True "off" should kill the engine in one minute. True "on" should let the bike run for 15 minutes-to as long as it takes to empty the tank. Since there is no more vacuum assist, remove the fuel line, put a temporary line from the petcock to a catch container, and retest the petcock "directions" to see when fuel flows freely.
The only problem with this though is if you think it is "off" when you pull the fuel line, you won't get a chance to put the temp line on, LOL.
My first guess is that you have your directions mixed up. Some petcocks use the lever to point, some petcocks actually have a triangle "arrow" opposite the end of the lever to point.
True "off" should kill the engine in one minute. True "on" should let the bike run for 15 minutes-to as long as it takes to empty the tank. Since there is no more vacuum assist, remove the fuel line, put a temporary line from the petcock to a catch container, and retest the petcock "directions" to see when fuel flows freely.
The only problem with this though is if you think it is "off" when you pull the fuel line, you won't get a chance to put the temp line on, LOL.
Buy New, Wire Right. BNWR. LOL
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