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Discussion Starter #1
Hey Folks,

This seems to be a theme here with no clear answers. My particular issue I need some help thinking it through. I recently got this 05 Vulcan, the problem I have is that the L cylinder doesn't work all the time. Today I think I found out exactly when and how it cuts out. Basically it pumps fuel at idle (to cyl 1) but at wide throttle angles the engine vacuum surpasses the ability of the L carb to pump fuel and so it starves.

Basically I've been in the habit of opening the tank before I ride because it seemed to clear up the issue for awhile - but not for more than a mile or so. But I think the tank vent is a red herring. Today on the ride home, good power - had both cylinders firing - about halfway home one cuts out - loud choppy noise, crummy power, you know. So I pulled over and pulled the vacuum hose off the L carb. It came back; so I said that's it. Some problem with the vent - and maybe there is. But of course a mile later it does it again. I pulled over in a lot and just held the bike upright and idled for about 20 seconds. That's it. Then the power came back for another mile.

On chainsaw carburetors the fuel pump is built into the carburetor; there's impulse coming from the crankcase that operates the small diaphragm (pump). If those get clogged or stiff or break or whatever then fuel doesn't get pumped into the carburetor. You get starvation. Seems like exactly the same thing is happening here... In Cyl 1 only.

My question to those that know more than me is; where do the carburetors get impulse from; is there a fuel pump or is it operated by crankcase pressure & vacuum (up & down movement of the piston a la 2 strokers) and is the systems separate and distinct for each carburetor? I'm looking at the IPL for it, don't see a "fuel pump" anywhere, so that makes me think it's simply vacuum operated. Is this part of the venting system? Of course it's all connected but is the pump directly connected to the venting system?
The carburetor definitely operates, what appears to be happening is that it's running out fuel and not replenishing.
 

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The fuel delivery is gravity feed, no fuel pump. Both carbs receive fuel from a single hose to a tee between the carbs. Same setup with the carb vents.

The left carburetor supplies the vacuum that opens the fuel petcock from the tank. Sometimes the diaphragm will develop a leak allowing excess fuel into the vacuum hose and into the left cylinder.

Try disconnecting the left vacuum hose, cap the nipple, and turn the fuel lever to PRI. If the bike runs better for longer there is a problem with the petcock diaphragm. Replacement kits are available from ebay for about $25.
 

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Discussion Starter #3
Thank you so much for the reply. So it sounds like you're suggesting the L cylinder may be flooding from a leak in the tap diaphragm? I did pull the vacuum hose off the L carb while it was running and could feel the carb pulling a vacuum, if that means anything. I'm going to try that, Bill - thanks again for the reply. I really love this bike, but I love it even more when the whole powerplant works!
 

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Discussion Starter #4
So that made absolutely no difference in how long it took for the L cylinder to cut out; less than 1 mile. That seems to rule out the tap. I tied a piece of plastic film over the vacuum port on the carburetor, set the tap on PRI and the hose from the tap was just hanging there.
I'm no expert on float style carburetors (diaphragms I can work on all day) but it's starting to sound an awful lot like a sticking float needle. Probably stuck shut since it gets enough in there at idle or if it sits for awhile to run - I'm thinking long enough to drain the bowl - and then it's back out. Thoughts?
 

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Sam,

Float carbs aren't much different than diaphragm carbs except that they only work 'right side up'. :)
They have a vent hose that must be clear. Your carbs are fed fuel by gravity so there is no fuel pump. The float level is analogous to the meter lever setting. Disassemble only one carburetor at a time to ensure you always have a spare for reference. Do you have a Service Manual? If not it is a GREAT tool to have.

Continuing with the fuel delivery testing, disconnect the fuel hose from the petcock nipple, attach a length of hose, and direct its flow into a container. Turn the lever to PRI and observe the fuel flow. If it flows with a full stream then it is flowing well. Anything less will not deliver enough fuel. Is there an inline fuel filter in the hose? A clogged filter can restrict fuel flow.

Hope this helps.
 

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Discussion Starter #6
Thanks for the reply, Bill. Those are good suggestions. I'm going to take it into the shop tomorrow where I work and that's a test I'll add, the fuel flow test.
I've cleaned and rebuilt many float carbs but it's probably a 10th of diaphragm ones that I've done.
There's not a fuel filter as far as I know unless it's under the tank, but I doubt it.

On thinking of it some more I feel pretty confident it's a fuel delivery issue such as restricted line or gunked up carb. It's almost 15 years old with 15k miles which means it has sat for long periods of time, perfect set up for ethanol and stale gas to do its damage. I see it daily on the outdoor power equipment people bring in.
 

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Discussion Starter #7
Well I want to report back what I found today, now that I had time to work on it.

In the problematic, left carburetor I found that the tang on the float assembly was bent just enough that even at the open or down position the float needle wasn't unsealing from the inlet line. Ridiculously simple fix. I also cleaned up the jets and sprayed out all the ports with carb cleaner, cleaned the bowls. Now both cylinders run 100% of the time. I can hear clicking from the valves - rocker arms I suppose - and so that's coming up. It also leaks coolant. Needs new brake line on the front and rebuild the forks. But it now RUNS correctly - SO much more power!

Thanks for the advisement on that Bill, carb was exactly where to look for the issue.
 

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Bill has helped me many times since i have joined the forum, he is spot on when it comes to the Vulcan 500. So glad i joined !
 

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Well I want to report back what I found today, now that I had time to work on it.

In the problematic, left carburetor I found that the tang on the float assembly was bent just enough that even at the open or down position the float needle wasn't unsealing from the inlet line. Ridiculously simple fix. I also cleaned up the jets and sprayed out all the ports with carb cleaner, cleaned the bowls. Now both cylinders run 100% of the time. I can hear clicking from the valves - rocker arms I suppose - and so that's coming up. It also leaks coolant. Needs new brake line on the front and rebuild the forks. But it now RUNS correctly - SO much more power!

Thanks for the advisement on that Bill, carb was exactly where to look for the issue.
The rockers tighten & get quieter as miles go on....If you can hear them clicking your fine.
 

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Discussion Starter #10
The rockers tighten & get quieter as miles go on....If you can hear them clicking your fine.
I've read that, but it sounds a little slappy to me, which makes me think they are not quite right -- plus it's at 15k miles which is about where the book says to check & adjust them. Could be I'm just new to this and don't know how motorcycle valves are supposed to sound.

Ordered a fork kit and master cylinder rebuild kit for the front brakes. Do you have a suggestion on AM steel braided lines or is the much more expensive OEM rubber line superior?
 

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Another possibility for a ‘slapping’ noise is a loose timing chain. While irritating to the ears it poses no problem with performance or longevity.

Regarding brake lines, the stock brake hose has served me well. However I did have a stainless line made up once but never installed it.
 

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Discussion Starter #12
Okay, thanks again Bill. Think I'll probably get in there and pull the valve cover and check/adjust them since I now know it's no big deal to get the tank off. Plus the previous owner bought the plugs and never got around to replacing them.
The reason I ask about the brake line is that OEM is over 100 and I believe most AM ones I've seen are quite a bit less than that.
 

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Discussion Starter #13
I think carburetion had its day, and I think there's still a place for it but damn it if they can't be persnickety as you-know-what.

My bike sat for about a week since the rain and being out of town - filled up the reservoir for coolant to try and find a leak, lo and behold nothing is coming out this time; so I figure I better warm it up see if it's on the engine side of the thermostat maybe. I go for a short ride - ostensibly toward the shop - get about 3 blocks and the engine starts losing power big time, popping & even backfired a time or two during acceleration. Idled so low it almost couldn't keep going.

I'm thinking it's related to the carb adjustment I did before, since I don't have a way to check make sure I got the float height exactly right that or the mixture screws. Any thoughts on that?
 

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Some on here think that float height has to be set ever so right.
One millimeter one way or the other is NOT going to make your bike run differently.
I bought my 500 with 12,000 miles and now has 30,000 miles and have not opened the carbs yet.
Are the floats right where the specs state they should be? I'd guess not, yet the bike runs flawlessly.

And the idle screws only come into play at idle.
When your going 30mph down the road the mixture screws have no effect on the running of the engine.

Check and maybe replace the vacuum hose to the petcock, this can cause problems if the hose is old and brittle.
Check the carb boots on both sides. They need to be flexible to make a seal and prevent air leaks.

And try some Seafoam in the tank and see if that might make a difference.
 

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Discussion Starter #15
I have the repair manual and it gives a spec but I really wasn't sure how to measure it. That said, I been giving it a think over the weekend and there's a couple things I feel I can deduce based on the conditions.
First the bike ran fine the last time I rode it: which was about a week ago, prior to going out of town for my Uncle's last service (God rest him). When I got back I put coolant in the reservoir with the intention of seeing where it was leaking: the leak didn't make itself known immediately so I thought donuts to dollars the leak is after the thermostat. At this point I actually fired it up and it seemed to sit there and idle okay. (In fact today I looked and the reservoir is still full, phantom leak).
Right after that I hopped on it with intent to ride over to the shop where I work to get it good and warmed up and spot the leak. I got about 4 blocks before it started to pop, lose power & get really sluggish/crummy idle - I'd say somewhere in the 400 RPM range, it was BARELY putting along.
So my thought is the sudden onset of the issue to me suggests some kind of electrical issue. Perhaps brought on by the introduction of coolant to the system and the leak is in fact somewhere in the head or where it can get on exposed wiring. I looked at the oil through the oil-checker hole on the side of the crankcase and it looks well, not milky white as is the case when it absorbs coolant. So I really hope it's not a blown head gasket; initial observations don't suggest as much anyway. Then again really low compression introduced by a head gasket would also describe some of the symptoms; low power, poor idling, hard starting.

That said, I've decided I just don't have the time to work on it since I barely have any free time as it is and I didn't buy this bike to be a fixer upper - I'm taking it to the local H-D dealer (we don't have Kawa here) and let them give me a diagnosis and from there I'll decide if it goes up for sale on CL or if it's worth fixing... But I'll be honest, I've had this bike a month and it hasn't ran well in all that time; the threshold for fixing it is VERY low now.
 

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I get it, hate it when I have to fix something and I have other things I wanted to work on.

Yet why did you buy it if you knew it wasnt working right and needed work??
An old bike will most likely not be an easy fix.
 

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Discussion Starter #17
I get it, hate it when I have to fix something and I have other things I wanted to work on.

Yet why did you buy it if you knew it wasnt working right and needed work??
An old bike will most likely not be an easy fix.
I didn't. It was advertised as a good running bike. It passed muster for me at the time, and ran good pretty much until I got it home. Actually that I say that the non-firing cylinder issue was probably present when I bought it but since it's my first bike I had no real frame of reference for how powerful a 500 should be nor how exactly it should sound. I also don't believe the previous owner misled me in anyway, I think when I started fiddling on it to fix the to-now minor issues I probably exposed other weaknesses in the system. Today I had it towed to the shop & so now I wait to hear what they find.
 

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I didn't. It was advertised as a good running bike. It passed muster for me at the time, and ran good pretty much until I got it home. Actually that I say that the non-firing cylinder issue was probably present when I bought it but since it's my first bike I had no real frame of reference for how powerful a 500 should be nor how exactly it should sound. I also don't believe the previous owner misled me in anyway, I think when I started fiddling on it to fix the to-now minor issues I probably exposed other weaknesses in the system. Today I had it towed to the shop & so now I wait to hear what they find.
What was the end result?

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Discussion Starter #19
It's still in the shop. I called them up after a week - which was this past Tuesday - and they told me it's scheduled to be looked at next Wednesday.
I tell you, for that month I had a bike it was a lot of fun. But if this works out to being more than 2-300 bucks it's going to the scrapyard. I think then I'll wait until I finish school and buy a brand new one or wait until I have my own house with a garage where I can more easily do my own work.
 

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I rescued mine from sitting out in a backyard under a tree for 3 years. Still needs aesthetic work, but other than that she's running great. These bikes are pretty simple. You can do just about everything with a decent mechanics tool set and a torque wrench. Don't give up on her yet. Shop time is expensive.

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