Kawasaki Vulcan Forum banner

1 - 20 of 24 Posts

·
Registered
Joined
·
12 Posts
Discussion Starter #1
Just did a bunch of carb and petcock work. After 20 minutes running like a champ bike died and gas is rushing out carb. Pulled the line off the petcock and gas is flowing freely. Question is, shouldn’t the carb be stopping it? What’s the difference between a failed vacuum petcock and a cheap open/closed one in the open position?
 

·
Registered
Joined
·
1,111 Posts
If the petcock is allowing fuel to free-flow then yes, the carb will get overwhelmed. Remember that the entire weight of all the fuel above the carb will be pushing downward in such a scenario.

I doubt there is any difference in a failed petcock and a cheap one in the open position. Flow is flow.

I think what has been proved here is that the flow of fuel from a properly vacuum operated petcock is less than that flow coming from a failed/fully flowing petcock. The carb can handle whatever amount the vacuum fed flow is but not a gravity full flow is. Then again, I'm just guessing it died (stopped running) due to too much gas. Regardless, once it died (therefore stopping the vacuum) and the fuel continued flowing, the carb got flooded in a real sense.
 

·
Registered
Joined
·
705 Posts
True but when the engine is running the the vacuum operated petcock is open the full amount of gas in the tank is pushing on the float and needle.
The fact that the float did not stop the gas flow means you have something lodged in there keeping the float from stopping the gas and flooding the carb.
OR the needle for whatever reason is not sealing as it should.
 

·
Registered
Joined
·
1,111 Posts
Ok that makes sense. I didn't know if the vacuum was enough to COMPLETELY open it or varied during the run time. Yeah, I can live with that reply.
 

·
Registered
Joined
·
27 Posts
Haven't had a bike for many years until a couple weeks ago. My 800 had a bad needle and bowl gasket. Mine was leaking too, but the petcock is good. Replaced the needle, float, and bowl gasket. If the needle and bowl gasket is good it shouldn't leak. We had full tanks of gas against the float and needle years ago and they didn't leak. My needle had a ring around it, and the gasket was flat when I took it apart. Don't know what they cost though as the dealer paid for them, I just bought the bike.
 

·
Registered
Joined
·
12 Posts
Discussion Starter #6
Yes im an idiot. I completely forgot that fuel coming through the carb was a float issue. The friend that came to pick me up gave the carb a little tap tap taparoo and she closed. Got her home and looked over again. With the needle seated the flow through the petcock was much less but still decent. Would the float being stuck open without the engine running create vacuum, opening the petcock more?
 

·
Registered
Joined
·
27 Posts
Yes im an idiot. I completely forgot that fuel coming through the carb was a float issue. The friend that came to pick me up gave the carb a little tap tap taparoo and she closed. Got her home and looked over again. With the needle seated the flow through the petcock was much less but still decent. Would the float being stuck open without the engine running create vacuum, opening the petcock more?
The petcock should NOT allow gas to flow in the on or reserve position. You probably have two problems.
 

·
Registered
Joined
·
12 Posts
Discussion Starter #8
Drained a little gas out the bottom of the carb, looked clean. Have her another good run and all seems good. The petcock rebuild was definitely a failure, there is always a little flow. Has anyone added an inline fuel filter? I guess there is one in the tank but thought it might not be a bad idea.
 

·
Registered
Joined
·
11,756 Posts
Rebuilds of fuel tap have a poor success rate.
Replacements always work.
If your fuel tap dribbles when it shouldn't, it will fill your crankcase with gas.
 

·
Registered
Joined
·
331 Posts
If fuel leaks thru in ON and RES, replace petcock w/OEM new. If your hose is not OEM but rather some rubber hose the PO got at a parts house, buy an OEM one. They are molded correctly for fit and flow and made of a compatible rubber like neoprene which ethanol will not degrade. Do not put a valve or a filter in the fuel line. Both restrict/plug/etc. I've seen many bikes with a rubber hose that is degraded on the inside, a little fuel valve and a little filter. All three contribute to problems down the road. Tiny flecks of rubber in the float valve and jets really suck! Fix it right if you are going to ride it. I agree with sfair and gas finds its way into places you don't want it, including rear cylinders. And rebuild kits for petcocks are hit and miss.

NOTE: If your carb is overflowing it is either from an obstruction in your float valve (like a tiny piece of degraded rubber) or your float is bent (or assembled wrong) and is hitting on something inside the carb. In both cases tapping on the carb can temporarily fix either.

Fix it right. You will be time and money ahead in the long run. Your bike is 18 years old and when we ride older bikes, some components just have to be replaced with new. Keep us posted!
 

·
Registered
Joined
·
11,756 Posts
As an add, there is not a carb float valve in the world that will hold fuel back on a long term basis. That is why the fuel tap is there in the first place.
 

·
Registered
Joined
·
12 Posts
Discussion Starter #12
Thanks all. I did get a new dealer fuel line and the carb was clean when apart. From the start the petcock rebuild was good but it didn’t take long for it to start leaking. I’m not sure about the carb not being able to hold back fuel, isn’t our vacuum design pretty rare? Tons of engines have a fully open petcock design. Or is it that unless you are religious about turning that type off when the bike sits it will flood?
 

·
Registered
Joined
·
331 Posts
Good question! I googled around to see what others were saying about vacuum petcocks. Many makes have them, BTW. Most of the bikers who have them, like the vacuum petcocks better than mechanicals one. Some are old school (like me) who want the mechanical one thinking they never go bad. (I like the vacuum!)

Also, many folks assume because they finally had to change out a failed vacuum petcock (after say 20 years) that a mechanical petcock never would have had to be changed out, and perhaps more than once. And all those petcocks that have failed (vacuum or mechanical), perhaps the owners did not take care of their fuel tank and gas as they should have?! Rust, goop, crap, dried up ethanol gas, water, etc. could have ruined them. Use fresh clean gas all the time and your petcock, any type, will stay good much, much longer. Here is what I found on the net as far as some reasons vacuum petcocks are used; I'm sure we could think of some other reasons:

1. User friendly, no need to turn to OFF all the time which is recommended if you do have a mechanical one
2. Easier on seats and valves that often leak minutely that you may not see unless bike sits long term. And as has been pointed out, will eventually leak into your engine.
3. More reliable. Personally, I've change more mechanical/gravity types than vacuum types, but in all cases the bikes were abused when I got them..
4. No fuel continuing to spill out of tank onto the pavement if ever in a crash or even if you bike gets dropped while you aren't there to see it. So a safety item too. (Many vehicles have 'fuel resets' after a crash.)
 

·
Registered
Joined
·
27 Posts
As an add, there is not a carb float valve in the world that will hold fuel back on a long term basis. That is why the fuel tap is there in the first place.
Not so sure I agree with you. I had many bikes in my younger years and NEVER turned off the petcock except during long term storage. Didn't have any leaking fuel back then. My golf car has a Kawasaki FE engine, carb is below the fuel tank and it has a fuel pump, no valve, and it don't leak fuel. My garden tractor has a Kawasaki 20 hp liquid engine with a fuel pump, NO valve and it don't leak fuel. Had snowmobiles for years, the tank was above the carbs, No valve, and they didn't leak fuel. If the needle and seat are good, it shouldn't leak being gravity fed. I'm fighting a carb leak on my bike right now. It has a new needle, float and pin, and a new bowl gasket. After sitting in the garage a few days I noticed a spot under it, looks like it's leaking around the parting line on the carb. Ordered another new bowl gasket, and will tear it down again when it comes in. There is quite a bit of fuel just in the line on a 800 if the needle is bad.
 

·
Registered
Joined
·
11,756 Posts
1. Any fuel system with a pump does not require a shut off. That is not what we are talking about.
2. I've had many bikes over the years and if the fuel tap was not turned off, they leaked, so where are we now? What happened for you is not necessarily the rule.
3. The manufacturers introduced the auto fuel tap to prevent fuel leaking into engine and anywhere else it might go. It's a liability issue, not because they had extra money laying around to spend on a more complex system.
4. In the carb, the fuel in the bowl will, over time, evaporate and the level drop just a tiny amount causing the float needle to open. The gas flows in at such a slow rate that it takes virtually nothing for the float to jamb, particularly if it is tilted on the sidestand, not move and you now have a leak.
5. Most float systems rely on vibration to function correctly.
 

·
Registered
Joined
·
27 Posts
1. Any fuel system with a pump does not require a shut off. That is not what we are talking about.
2. I've had many bikes over the years and if the fuel tap was not turned off, they leaked, so where are we now? What happened for you is not necessarily the rule.
3. The manufacturers introduced the auto fuel tap to prevent fuel leaking into engine and anywhere else it might go. It's a liability issue, not because they had extra money laying around to spend on a more complex system.
4. In the carb, the fuel in the bowl will, over time, evaporate and the level drop just a tiny amount causing the float needle to open. The gas flows in at such a slow rate that it takes virtually nothing for the float to jamb, particularly if it is tilted on the sidestand, not move and you now have a leak.
5. Most float systems rely on vibration to function correctly.
I suppose you do have a valid explanation. We do have a lot more evaporation with the fuel we have now a days, lot more than we had when we had good fuel. Maybe the fuel pump restricts the flow enough is why they don't seem to have any problems.
 

·
Registered
Joined
·
11,756 Posts
Two reasons for no shut off on fuel pump systems:

1. It is not needed.
2. If the tap is left in the off position, the fuel pump starves and, depending on the pump style, can cause damage.

Just realized I said a bonehead thing.
If the pump starves for fuel, engine quits and pump stops running.
I will go to my corner now.
 

·
Registered
Joined
·
126 Posts
It seems to me the owners manual of every bike I ever owned with a mechanical petcock told you to turn it to the off position when the bike was not running. This just makes sense, why risk it.
 

·
Registered
Joined
·
331 Posts
4. In the carb, the fuel in the bowl will, over time, evaporate and the level drop just a tiny amount causing the float needle to open. The gas flows in at such a slow rate that it takes virtually nothing for the float to jamb, particularly if it is tilted on the sidestand, not move and you now have a leak.
Well said. Now add ethanol to that recipe while the bike is sitting . . .
 
1 - 20 of 24 Posts
Top