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Discussion Starter #1
Hello All,

Sorry I haven't been doing a lot with the "social" side of the site - the fire, the accidents (yikes!) and so on. I've been swamped at work lately.

So - I started work again on the project bike. I did the ear shave, the degoat, the rejet/carb clean, etc. The bike kept flooding, then stumbling and dying when I tried to ride her.

Turns out, in addition to replacing the float needles, what I really needed to do was replace the diaphragms on the side of the carbs. They had significant cracks and holes in them.

Changing them out was easy - don't even have to take the carbs off the bike. Just unscrew the cap, pop the new valve, tiny O-ring, and spring in, and screw the cap back on. This also makes them easy to check.

The replacement parts can be found on ebay if you search for "diaphragm" or "air cut off valve". I'm not sure what they do exactly, but apparently having holes in them means flooding and stalling and uneven idle.

Now she fires right up and will maintain a steady idle.

Time to change out the coolant and the gas corrupted oil. Then maybe a ride today - hot damn.
 

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Love My Baby
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Time to change out the coolant and the gas corrupted oil. Then maybe a ride today - hot damn.
What was ut that gas-corrupted your oil? I'm sure you fixed the cause before you changed out the oil.
 

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Discussion Starter #5
Slim has it.

Unfortunately, it started flooding again after a Great test ride. I suspect the float needles have some kind of trash on them.

Can someone explain the physics of this? - shouldn't the petcock just shut off without vacuum? Meaning, how can I have a steady flow of gas out of the tank through the petcock, and into the carb?

I mean, that's what's happening, but I thought there couldn't be flow through the petcock without vacuum.
 

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The Professor
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3,147 Posts
Slim has it.

Unfortunately, it started flooding again after a Great test ride. I suspect the float needles have some kind of trash on them.

Can someone explain the physics of this? - shouldn't the petcock just shut off without vacuum? Meaning, how can I have a steady flow of gas out of the tank through the petcock, and into the carb?

I mean, that's what's happening, but I thought there couldn't be flow through the petcock without vacuum.
Petcock will shut off, but the carbs will drain. Unless you have a pre 89' and petcock is set to "PRI: :doh:
 

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Love My Baby
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1,165 Posts
I thought gas flow was gravity feed and the vacuum helped suck out the gas faster than gravity alone during times of higher demand. If that is true then any leak post petcock will allow gas to flow by gravity through the petcock, unless the petcock is turned to OFF. Am I wrong, as my wife likes to tell me constantly?
 

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Discussion Starter #9 (Edited)
Well, not to muddy the waters, but I have an 86 petcock (as far as I can tell - the bike's an 86, and I don't know if any of the POs did anything with the tank.).

I replaced the petcock diaphragm because of flooding earlier. Now I wonder if the petcock diaphragm is the wrong one or something. It fits, but is the petcock diaphragm the same for an 86 and a (for example) 92?

When I shut the bike off, I had gas leaking out of the right emigo filter (the new bike is shaved). It was like the tank was draining straight out into the carb with nothing stopping it. I am certain that the petcock was on the regular setting, not PRI. I toggled it between Res and regular just to see if anything would happen. Nothing did.

So I opened the drain on the bottom of the right carb, put a piece of vinyl tubing on it, and let it drain into a gas can. What a mess by that point though!

Anyone have any thoughts on why my tank is just draining through the right carb?
 

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The Professor
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hey lance...that isn't entirely true... mines a 92 with on, off and res.
Sorry dude but it is entirely true!!! By your own admission your petcock does not have the "PRI" setting that was pre 89'. Pre 89's had a "PRI" setting instead of "OFF" which means "prime" it was a function to prime the carbs before you statted the engine. It bypassed the vacuum diapram and would let fuel flow.

They have the same diaphram and 0-rings but the selector is different. Just went through this last week with Hyper.


http://www.vn750.com/forum/showthread.php?p=111269#post111269




 

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The Professor
Joined
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3,147 Posts
Well, not to muddy the waters, but I have an 86 petcock (as far as I can tell - the bike's an 86, and I don't know if any of the POs did anything with the tank.).

I replaced the petcock diaphragm because of flooding earlier. Now I wonder if the petcock diaphragm is the wrong one or something. It fits, but is the petcock diaphragm the same for an 86 and a (for example) 92?

When I shut the bike off, I had gas leaking out of the right emigo filter (the new bike is shaved). It was like the tank was draining straight out into the carb with nothing stopping it. I am certain that the petcock was on the regular setting, not PRI. I toggled it between Res and regular just to see if anything would happen. Nothing did.

So I opened the drain on the bottom of the right carb, put a piece of vinyl tubing on it, and let it drain into a gas can. What a mess by that point though!

Anyone have any thoughts on why my tank is just draining through the right carb?
If it drained through the right carb at the jet drain "rear" carb, this means your front carb float bowl or petcock selector valve or the diaphram o-ring is NOT shutting off the fuel flow and that's why it came out the right Emgo filter. The fuel lines are higher than the breather and gravity prevailed. Did you drain the left carb ???
 

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Discussion Starter #12
No, the left carb wasn't flooding. There was fuel in the line to both carbs (transparent fuel lines).

This is my working hypothesis.

1) The right float needle is not sealing. If it was, it would stop the fuel flow, regardless.

1a) I must pull the carbs and check out the right float needle situation.

2) There's something wrong with the petcock. If it was working OK, only the fuel in the petcock-to-carb line would drain into the right carb.

2a) I should replace the petcock and or refinish it.

2b) I recently replaced all the petcock gaskets. I ordered the petcock diaphragm part of the internet. Does anyone have any idea if the petcock diaphragm is the same for the res-on-pri and for the res-on-off petcocks. I'm thinking if it's not, whatever one I have in there is resulting in the carbs being more or less constant flow.

I have a spare petcock - I will try and see if that works.
 
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