Diagnosis of fuel petcock or vacuum problem

[Doug650L]

My 83 650l sat unused for 2 winters after it no longer ran at idle unless choke was out. Fuel also came out of carb overflow. This spring I fixed the sticky float ( pin was stuck) and rusty tank. Upon reassembling the tank, fuel did not come out of the petcock when in PRI position. Took apart the petcock and reassembled. Fuel now flows freely when in PRI position. Got engine to start in PRI position and then when in ON position but dies when choke is pushed in. Not an experienced technician but I can make do. Read that vacuum carbs can be difficult. Where do I start to solve this?

[Doug B.]

My guess would be either a vacuum leak at the manifold boots or clogged jets in the carbs. After sitting two years they are probably just in need of a good thorough cleaning. It doesnt take much to block up the little pilot jets.

[sedelen]

Sounds like plug a plugged pilot circuit, 2 years sitting surely needs a good cleaning.

[gustovh]

Pull and clean your carbs, replace all the O rings with new, probably floatbowl gaskets as well, replace the carb mount O rings while the carbs are off. That ought to get you in the ball park. Check carb cleaning in search.

To check to see if the gas valve is working properly in the on pos, while the carbs are off run the gas line into a can from the tank, connect the vac hose to the valve and give it a suck, gas should flow.
V

[tom203]

Sounds like plug a plugged pilot circuit, 2 years sitting surely needs a good cleaning.

Absolutely. unfortunately on this model the carbs are no fun to remove, but this is what needs doing. I'd also opt for new petcock and not worry about it again.

[Doug650L]

Have more to add: left the tank valve on PRI overnight accidentally and fuel was coming out of carb overflow (into container). Is that supposed to happen or does that indicate anything about the fuel petcock?

[tom203]

Have more to add: left the tank valve on PRI overnight accidentally and fuel was coming out of carb overflow (into container). Is that supposed to happen or does that indicate anything about the fuel petcock?

Yes, left on PRI the float needle valves can't hold back gravity forever- they will leak and overfill bowls and then flow into carb throats; depending on angle, fuel will flow towards engine or out to airbox.

[Steve]

You have more problems than you realize.

Fuel also came out of carb overflow.

Have more to add: left the tank valve on PRI overnight accidentally and fuel was coming out of carb overflow (into container).

These carbs do not have an "overflow".

.

[Doug650L]

Please explain. I think I meant one of the two ventilation tubes.

[tom203]

If carbs are on bike (are they??), overflowing fuel bowls will send gas into carb throats BEFORE it rises up thru vent hose nipples (see attached pic). Typically , fuel will run down throats towards intake valves, washing down the cylinder walls, and falling into crankcase oil- bad news!

[Doug650L]

Ok. Thanks for the explanation. Carbs on bike and nile is on center stand. So anyone who mistakenly leaves the valve on PRI has a high chance of contaminating the motor oil? From what I have read, my tank valve is operating as it should and a carb cleaning could take care of the problem of engine cutting out when choke is in.

[BassCliff]

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Help! Your Bike Won't Start
DON'T DO THESE THINGS
Help! Your Bike Won't Run Well
Oh God! Pods!


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Thank you for your indulgence,

BassCliff

[Doug650L]

This appears to be an add-on. Is it an in-line fuel filter? Is it needed and can it be cleaned?

[tom203]

This appears to be an add-on. Is it an in-line fuel filter? Is it needed and can it be cleaned?

Add-on bandaid, inline fuel filter- really don't need, I'd plan to remove it in near future, cuz it might cause fuel restriction at hignway speeds.

[Doug650L]

Butterfly valve o

Reading a post from a while back, someone quoted a manual stating the butterfly valves should be open a small amount in order to idle. Mine are closed completely at idle. Should I use the idle control screw to adjust them?