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Discussion Starter #1
Have lurked here for a bit. This site has been an amazing resource filled with tons of knowledge. Thanks to all the people who have shared knowledge over the years.
My brother and I are working on some intermittent problems with my bike. I know people have discussed problems similar to this; fact is most of the advice I've followed has been from this site. Nonetheless, the problem isn't resolved.
Bought a '99 Vulcan 500 off craigslist, ran great for a few weeks, then bogged down and died on the freeway. I could make it up to high speeds, but when the engine was hot, if I let off the throttle then opened it again, it failed to accelerate and the engine would die.
First, I thought it was a malfunction in the fuel tank venting causing Phantom Out of Gas Syndrome. Took it apart, cleaned the hell out of it. Not fixed.
Checked the petcock, it functioned as it should.
Pulled the plugs to read them. Electrodes were worn, and, based on the condition of the plugs, it looked like the bike was running rich.
Replaced the air cleaner because the old filter (probably the one from the factory) was disgusting and slimy and broken down.
At that time, we tested both ignition coils. I can’t remember the exact readings, but both tested to within spec as various people had described it on this site and in a Vulcan manual.
Bike sat for well over a month while I waited for a carb rebuild kit.
We also replaced the pulse coil, because it tested out of spec.
Rebuilt carburetor smoothly (thanks in large part to the excellent walkthough on this site!) and replaced pulse coil.
Lo and behold, it did not jump up and go, it had trouble starting, then it had trouble idling. After we tweaked the idle speed to work, upon acceleration it would stumble and die.
Now we've figured that it was a rich condition giving us all the trouble, so we tweaked the mixture screws on the carb and found an agreeable ratio. Managed to get it going, and, driving over to the gas station to replenish the nasty old gas, I could accelerate but it needed to consider for like half a second, then it would go.
Took it out for a cruise, and the thing ran like a dream for the night and many high fives were had to celebrate a job well done.
Well

I took it out the other day for a low speed cruise, no freeways just in case, stop and go traffic and it drowned like a snitch in cement shoes. Had a hell of a time getting it home, as I couldnt get it to idle, then I couldnt get it to accelerate for more than 20 yards. The weird thing is switching to reserve seemed to help, and topping off the tank allowed me to put petcock back on regular. Now it purrs nicely when I start it, but who knows when it's going to crap out next, and where.

To reiterate:
  • -Carb rebuild, New jets, mixture screws, etc.
  • -New air filter
  • -New pulse coil
  • -fresh plugs properly gapped
  • -ignition coils testing within spec
The problem still at least seems to be like the bike is running rich, and I would have wagered dollars to donuts there was a jet sticking or clogged in the carbureter. However, having addressed every air/fuel trouble spot, and in light of the intermittent nature of the problem, perhaps there are electrical issues. If there are electrical issues, it’s a weird one because the bike does not die outright, it stumbles. To me, that rules out a bad ground or anything, because that would be more likely to cause the bike to die completely than it would cause running rough. Also, we have checked all the main chassis grounds we can find, and they are solid.
Are there any electrical issues that mimic air/fuel issues like this?
The bike came with a li/ion battery, which has never failed on starting. However, I wonder if perhaps the li/ion battery doesn’t play nicely with the remainder of the bike’s electrical system.
I do not want to replace the IC igniter, at least not yet, because it is untestable except by replacing with a known good part, and $300 for an aftermarket unit.
I could replace the regulator rectifier, because I have heard that voltage issues can cause funky problems with the ignition system because of how the IC igniter works. Maybe that is the next stop.
It's dreadfully confusing, I feel as if I've done everything I need to do, yet the problem persists. If any of you guys have insights I’ll be grateful.
 

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First the mixture screws have nothing to do with the way the bike runs when its moving down the road.
They are for idle only.
Second the tank vents through the gas cap as well, and these can get plugged.
If it whistles when you get back after a ride, its working correctly.
And most of the time when the bike bogs down its a jet problem.

Check the voltage on the battery after sitting over night, and again when your starting it, and again at a high idle.
I agree that a 1999 bike and a new battery chemistry setup might not be the best, but voltage is voltage.
If you'll give us the three readings above we can determine if the charging system is working.
 

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Discussion Starter #3
Upon reading, yeah I found that the mix screws are for idle only
We've also taken apart the tank cap and cleaned it all out, so that shouldn't be an issue.

As far as the jets are concerned, these are brand-new OEM jets, which is what has me completely stumped. Are there differently sized jets which would function differently, like a narrower/wider inner diameter?

Will look into the battery readings though
 

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From the way you describe your issues, it sounds to me like you're having carb/fuel delivery issues.

As far as the jets are concerned, these are brand-new OEM jets, which is what has me completely stumped. Are there differently sized jets which would function differently, like a narrower/wider inner diameter?
When it comes to jets, there are 2 basic schools used to measure to get the number they assign. Each company uses one of the two, the problem is knowing which one they used.

Measurement type 1: This is a direct measurement of the inside of the hole, represented as a number (a 105 jet might be 1.05mm, or .105 inches, depending on the manufacturer and intended use. 1.05mm and .105 inches are not the same physical size).

Measurement type 2:
This is a measure of how many CCs of fuel will flow through the jet in 1 minute. A 105 jet would flow 105 CCs of fuel. Generally this is a metric thing.

Confused yet? It gets better...

A 105 jet measured by type 2 is a totally different size than a 105 jet measured by type 1.

You said you used brand new OEM jets, so we will assume they are correct.

On to the next questions...

Did you replace the needles on the diaphragm? If so, were they installed in the correct position? Some kits have needles with several grooves to adjust your fuel flow to compensate for different intake and exhaust systems. Also, look over your diaphragms... stretched, stiff, or torn, replace them.

Check your tank as well. There is a chance you could have some rust or general crud in it that could be making it's way through the system. That will play all sorts of games until you figure it out. Trash in the lines is another area to watch for. A recent customer at the shop had us seal the tank on his old CB1000. Then he rebuilt the carbs, new (NOS new) petcock, etc. Then he couldn't understand why he couldn't get it to stop flooding. A couple hours into it, I found the issue. He replaced everything except the rubber line from the tank. A mud dauber made a nest inside the line. The fuel then washed the nest right into the carb bowls....

Pull your plugs again and post a picture. Please do not touch or clean the part inside the engine. Remove and take a pic. That'll let me see how they look.

Speaking of plugs, what brand and number did you use?

That'll make for a good start, along with the battery info requested by vulcandoc.
 

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Discussion Starter #5
Gas tank is sparkling clean, we looked in there a few times upon disassembly. Yeah, I did replace the needles when I rebuilt the carbs, and the diaphragms are in perfect health, still supple and flexible.
As far as electrical goes, voltage readings (taken by multimeter across the battery terminals) are:
After Sitting Overnight – 13.58V
At idle – 14.5V
Revved up – 14.24V
Seem to be in the healthy range. There are never any problems with starting power or anything like that.

I took it for a ride today and went on the freeway, full throttle, closed and opened it no problem, everything was really running nicely, until I got off the freeway.
As I turned onto my road, it stumbled, and hesitated on acceleration, then it wouldn’t accelerate at all, so I pulled over and idled it (it did fine) but still couldn’t get it to rev. So I switched it to reserve and after 30 seconds it was going fine, as if it had run low on gas and needed switching to reserve. To test, I switched it back on regular, whereupon it bogged down again 30 seconds later; back to reserve, same result. The trip meter I reset when I filled the tank said 50 miles, and there was plenty of gas in the tank when I opened it up and looked inside. I highly doubt I only get 50 miles before switching to reserve, as the consensus on this forum seems to be that a full tank should last between 130 and 150 miles before hitting reserve.
Further, my brother (who used to have an EN450) has been on the bike when it bogs down, and he thinks it doesn’t feel like running out of fuel. He thinks a low fuel condition would cause stuttering and coughing that would start and stop as the float bowls run dry; whereas this is really predictable and seems more like the bike is running wrong. He’s never had a bike that feels like this when it runs out of gas.
Like I said before we had thought it was an evap and tank ventilation system problem, and folks on here talked about phantom out of gas syndrome (POOGS). However, the way I understand POOGS caused by an obstructed tank vent, it occurs where the tank cannot ventilate properly. This leads to essentially a vacuum condition in the tank, which prevents fuel from flowing freely. If that were happening, it should not matter if the petcock was set to RES or ON, because the vacuum condition would still exist regardless of petcock position. We have dismantled the entire system and cleaned every line. We dismantled the fuel cap too (which was perfectly clean inside) and cleaned it thoroughly just to be on the safe side. Finally, at one point when it was running really poorly, it ran poorly with the gas cap wide open! Thus, I have a hard time suspecting tank ventilation issues.

At one point, we wanted to replace the vacuum petcock just to be sure. We ordered an affordable aftermarket unit on eBay, but it didn’t actually fit because, although the petcock could be mounted to the tank, the gigantic lever couldn’t be turned to reserve without interfering with the tank! In any event, we had eventually ruled out a petcock problem because it had been running rough with the petcock in all positions, but I suppose we could try replacing the vacuum petcock with a manual model. It would be annoying, and run the risk of walking out to a puddle of gas if I forget to turn it off after riding, not to mention the risk of a crankcase full of gas and an impromptu oil change; but if the petcock is the problem, then it would be a super easy fix. It’s also easy to undo if it doesn’t fix the problem and I don’t like it. Further, if the manual petcock (inexpensive) provided a solution, I might be willing to pony up the $95 for an OEM petcock, which is available from some retailers.
Does anybody know of an aftermarket petcock that has been proven to fit this bike? I searched the forum and could not find a thread identifying a proven manual petcock. One thread suggested any 34mm manual petcock would fit. I would like to avoid ordering a random eBay model, dismantling my tank, and then having the replacement unit not fit.
 

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This may sound odd, but take a moment and check all your carb boots and vent hoses. I reread your original post and noticed you're working on a 500. Those boots can be a real pain to get on fully, and the hoses (including the vacuum line to the petcock) can age and the end gets stiff and doesn't seal well all the time.

My 500 started running rough on the way home from work today, much like the way you have described. The vacuum line to the petcock had come partway off it's fitting on the petcock. When I looked under the tank (inspection mirror), I noticed it. When I just got my finger on it, it came the rest of the way off. The end was stiff, not supple or squishy feeling. The whole hose had taken a set to it's particular position. Hopped in my truck, made a quick trip to my local parts house, bought several feet of vacuum hose (didn't need that much for this job, but I like to have extra around), and seems to be fixed. Probably this weekend I'll pull the tank and check the rest of the lines...

My bike is an '08, so a few years newer than yours... it's worth looking into on yours, and cheap to fix too...
 
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