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Hey guys, I'm having a rather annoying issue with my '85 Vulcan 700. The bike is relatively new to me, but I'm (unfortunately) having to get quite intimate with it already. Let's start at the beginning:

When I bought the bike, It was running, but needed some petcock work/fuel lines. Simple stuff, right? Right. So, I rebuild the petcock and add some fuel lines and I start riding for a few days. However, I start to notice that the crankcase fills with fuel every time I let the bike sit for more than a few hours. My head goes to the floats, thinking that they aren't shutting off. So, why fix the problem when I can just add a fuel shutoff? So I consult the all-mighty VN750 forums and see the plethora of posts recommending the petcock for a TW200. I follow that to the 'T' and it works GREAT! I even got the bike out on the back country roads for the first time. Love it.

Here's where the fun starts- within the next couple of days, I'm stranded on the side of the road waiting for my floats to fill up. Eventually I limp it home and get to work. My first thought is obviously floats or needle valves, so I check those. Replace the needles and everything works as it should. Until I ride it. She'll idle forever, but as soon as I get a mile from the driveway, she's done. I've had to push it home 3 times now. Took the petcock apart, cleaned it, made sure all the ports and screens were clear, cleaned the jets, tried everything. Still no dice. It rides like it's draining the floats, but yesterday after some more tinkering and cleaning, it wouldn't even start after some time to fill the floats.

My buddy is convinced its either the coil or plug wires, and the floats aren't actually draining, but the bike is heating up, thus increasing the resistance of the wires or expanding a hairline crack in the coils. I'm not saying he's wrong, but I want a second opinion before I start throwing coils, wires, and plugs at the bike.

What do you guys think? Thanks!
 

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By needles, I assume you are referring to the float valves? Have you disconnected the fuel lines going to the carbs and checked for fuel flow? Be sure to catch the gas in clean containers so you can use it. It doesn't necessarily need to run a full tube all the time because the engine doesn't need that much gas, but it should have a consistent flow. Have you tried opening the gas cap and seeing if it will start up immediately when it dies? If it does, the fuel tank vent may be plugged, obstructed, or pinched, creating a vacuum and starving the engine for fuel. If you removed the tank, it's possible you pinched the line when you reinstalled it.

Good luck!
 

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Hey guys, I'm having a rather annoying issue with my '85 Vulcan 700. The bike is relatively new to me, but I'm (unfortunately) having to get quite intimate with it already. Let's start at the beginning:

When I bought the bike, It was running, but needed some petcock work/fuel lines. Simple stuff, right? Right. So, I rebuild the petcock and add some fuel lines and I start riding for a few days. However, I start to notice that the crankcase fills with fuel every time I let the bike sit for more than a few hours. My head goes to the floats, thinking that they aren't shutting off. So, why fix the problem when I can just add a fuel shutoff? So I consult the all-mighty VN750 forums and see the plethora of posts recommending the petcock for a TW200. I follow that to the 'T' and it works GREAT! I even got the bike out on the back country roads for the first time. Love it.

Here's where the fun starts- within the next couple of days, I'm stranded on the side of the road waiting for my floats to fill up. Eventually I limp it home and get to work. My first thought is obviously floats or needle valves, so I check those. Replace the needles and everything works as it should. Until I ride it. She'll idle forever, but as soon as I get a mile from the driveway, she's done. I've had to push it home 3 times now. Took the petcock apart, cleaned it, made sure all the ports and screens were clear, cleaned the jets, tried everything. Still no dice. It rides like it's draining the floats, but yesterday after some more tinkering and cleaning, it wouldn't even start after some time to fill the floats.

My buddy is convinced its either the coil or plug wires, and the floats aren't actually draining, but the bike is heating up, thus increasing the resistance of the wires or expanding a hairline crack in the coils. I'm not saying he's wrong, but I want a second opinion before I start throwing coils, wires, and plugs at the bike.

What do you guys think? Thanks!
Check the vacuum line from the petcock (center port) to the left carb. It should always be dry. If it's wet, or gas drips from the center port, the diaphragm in the petcock is leaking through.

If that's all dry, look at the floats, float level, sticking float valve, etc.
 

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Discussion Starter #4
Check the vacuum line from the petcock (center port) to the left carb. It should always be dry. If it's wet, or gas drips from the center port, the diaphragm in the petcock is leaking through.

If that's all dry, look at the floats, float level, sticking float valve, etc.
As I've moved on to the other petcock, this one no longer has the vacuum port.
 

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Ok, I misread the original post.

I wouldn't dive into coils until I checked for spark when it has stopped running..

If it has spark, then does it need gas, or have too much? Are the plugs wet, or dry, when it stops running.

As flitecontrol mentioned, could be POOGS. Will it restart if you open the gas cap?
 

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Ok, I misread the original post.

I wouldn't dive into coils until I checked for spark when it has stopped running..

If it has spark, then does it need gas, or have too much? Are the plugs wet, or dry, when it stops running.

As flitecontrol mentioned, could be POOGS. Will it restart if you open the gas cap?
The rear cylinder's plugs are wet when I pull them, the fronts are not. When the bike runs, it sputters on the rear cylinder until you get it up to about 4k, then it kicks on. As far as the vent goes, I wasn't finding where it's supposed to be on this tank. I have a spare tank that has a little 1/4" or so outlet on the tank right between the mounting screws for the gas cap, but the one on the bike doesn't have that. The cap has a small tube that fits right in the little outlet, so is that supposed to be on the tank?
 

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The rear cylinder's plugs are wet when I pull them, the fronts are not. When the bike runs, it sputters on the rear cylinder until you get it up to about 4k, then it kicks on. As far as the vent goes, I wasn't finding where it's supposed to be on this tank. I have a spare tank that has a little 1/4" or so outlet on the tank right between the mounting screws for the gas cap, but the one on the bike doesn't have that. The cap has a small tube that fits right in the little outlet, so is that supposed to be on the tank?
Think mine has the little rubber nipple sticking up out of the tank, under the cap. Then the cap closes down on top of the nipple, I need to look at mine though. But I'm thinking it's probably not POOGS, since you have wet plugs on the rear cyl.

There was some discussion over this winter about some tanks having different venting.

Do you think it's running on both cylinders when it runs? Wet rear plugs with dry fronts, and the engine dies. Makes me think the front isn't running at all, and it dies when the rear floods out.

Does the front cylinder get as hot as the rear? Were the jets cleaned when the carbs were worked on?

Need to know what the spark is actually doing, and if it loses spark anywhere when it dies.
 

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Discussion Starter #8
The rear cylinder's plugs are wet when I pull them, the fronts are not. When the bike runs, it sputters on the rear cylinder until you get it up to about 4k, then it kicks on. As far as the vent goes, I wasn't finding where it's supposed to be on this tank. I have a spare tank that has a little 1/4" or so outlet on the tank right between the mounting screws for the gas cap, but the one on the bike doesn't have that. The cap has a small tube that fits right in the little outlet, so is that supposed to be on the tank?
Think mine has the little rubber nipple sticking up out of the tank, under the cap. Then the cap closes down on top of the nipple, I need to look at mine though. But I'm thinking it's probably not POOGS, since you have wet plugs on the rear cyl.

There was some discussion over this winter about some tanks having different venting.

Do you think it's running on both cylinders when it runs? Wet rear plugs with dry fronts, and the engine dies. Makes me think the front isn't running at all, and it dies when the rear floods out.

Does the front cylinder get as hot as the rear? Were the jets cleaned when the carbs were worked on?

Need to know what the spark is actually doing, and if it loses spark anywhere when it dies.
The rear cylinder doesn't seem to run when the bike is running. Based on the noise from the exhaust and the pipes heating up, the front is doing most of the work. I've checked all of the plugs for spark, and they're all getting it. Sometimes the rear cylinder will kick on or "catch" at about 4k rpms.

Also, I tested the resistance of my plug wires today and got one wire that was waiting higher than all the others. Anyone have any idea what they're supposed to be?
 

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I recall reading that the spark plug cap has a resistor built in. Wolfie said he took his out of the caps.

Since you have spark, it's reading like a clogged pilot jet on the rear cylinder. But that doesn't explain it dying on down the road.

Need to know if the spark is dead immediately after it dies. If I didn't have a spark tester ($5 @ Harbor Freight), I'd carry an old plug to check it with. I guess the best plan would be to warm it up fully, and stay close to home.

When it dies, are you just riding straight down the road, or have you slowed down and making a u-turn? Just wondering if it could be a wiring problem in the headlight or neck plugs. Also, is there ever any problem with the switch not turning on? Like maybe needing to wiggle the key to get it lit up?

Seems like maybe two problems, a dirty rear carb and some electrical bug.
 

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Discussion Starter #11
I recall reading that the spark plug cap has a resistor built in. Wolfie said he took his out of the caps.

Since you have spark, it's reading like a clogged pilot jet on the rear cylinder. But that doesn't explain it dying on down the road.

Need to know if the spark is dead immediately after it dies. If I didn't have a spark tester ($5 @ Harbor Freight), I'd carry an old plug to check it with. I guess the best plan would be to warm it up fully, and stay close to home.

When it dies, are you just riding straight down the road, or have you slowed down and making a u-turn? Just wondering if it could be a wiring problem in the headlight or neck plugs. Also, is there ever any problem with the switch not turning on? Like maybe needing to wiggle the key to get it lit up?

Seems like maybe two problems, a dirty rear carb and some electrical bug.
Next time I have it running, I'll bring a spare plug and test it out. I actually have an issue with the ignition where I have to jiggle the key occasionally for it to run the starter, but it's never been an issue with cutting ignition while riding. I'm still able to spin the starter when it dies. As far as when it dies, it'll usually sputter while I'm going straight, then die either while I'm turning, or I pull the clutch in to stop.
 

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Next time I have it running, I'll bring a spare plug and test it out. I actually have an issue with the ignition where I have to jiggle the key occasionally for it to run the starter, but it's never been an issue with cutting ignition while riding. I'm still able to spin the starter when it dies. As far as when it dies, it'll usually sputter while I'm going straight, then die either while I'm turning, or I pull the clutch in to stop.
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Take note next time it stalls, while you're still rolling,.... Are the dash lights on or off? If your oil light etc. don't come on when it dies, you'll know it's the switch that killed it. That problem is usually the "puck" inside the switch needing cleaned and the springs stretched. There's a sticky thread on that I think.
 

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Discussion Starter #13
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Take note next time it stalls, while you're still rolling,.... Are the dash lights on or off? If your oil light etc. don't come on when it dies, you'll know it's the switch that killed it. That problem is usually the "puck" inside the switch needing cleaned and the springs stretched. There's a sticky thread on that I think.
All of the lights stay on, and everything still operates as normal, but the motor won't fire. It'll spin and spin to its heart's content, but won't even sputter.
 

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I'm no expert, but when I tuned my carbs for the ear shave on my 750 it was running lean and doing this after a little riding. If I was patient, after a while it would crank back up and idle fine. When it's running, does it run well at WOT? You said it idles good. Just curious if it was ever rejetted, stock jets? Stock air filter? I have converted my factory petcock to not use the vacuum port because mine was filling my crank case up too. I simply turn the gas off (when I think about it) and haven't had an issue since.

** Not sure if I'm helping but adding my .02 cents anyway.
 
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