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Discussion Starter #1 (Edited)
I bought a used '06 Vulcan 500 last week (@ 6k miles), and took it on the highway for the first time this past weekend. Everything was good, until I was reaching around 70-73mph. When I tried to give it more throttle to up the speed (was in the slow lane getting passed by most cars), the engine power would completely cut out, I'd feel an immediate drop in power (to zero), but it would immediately come back on as I ease off the throttle.

This was in 6th gear (I didn't try it in lower gears or at idle). I don't think I'm hitting the rev limiter because most people say top speed is 90+ (unless I have a really weird sprocket configuration? I'm planning to change the sprockets to 17-40 to lower the RPMs anyway). Even if I keep the throttle high, as I slow down the engine doesn't come back on. I get no issues at slow speeds, bike starts up immediately, etc. I've already put about 300 miles on the bike with no issues.

Maybe this is relevant, but the previous owner had it since 2012 and only put around 100 miles on the bike during these past 2 years. He says he added fuel stabilizer in the tank and all that. He seemed to know his way around bikes - had a few in his garage he was working on.

What do you guys think the issue could be? I'm planning on taking it to a mechanic and getting it checked out, but I'd love to hear your opinions first (to make sure I don't get screwed over with pricing and all that lol). Thanks!

EDIT: I do get about 50 mpg on it, so that seems fine. Also, I have no windshield (not sure if that's relevant).
 

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It is not the rev limiter as it will not kill the engine. Besides mine will do 95 easy, have not tried a higher speed on it yet because that is pretty fast. I have the windshield which helps. I am getting 54 to 60 mpg depending on how I ride. Sounds like the problem is electrical. Is there much vibration at the cut out speed?
 

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Discussion Starter #4
I don't think it's the battery as the starter motor runs quick, not sluggish at all.

I also don't really remember noticing much vibration, at least not much more than it would have at 50-60 mph. The wind pull was the only thing that became powerful once I get past 60. I'll take it out tonight for a test run on the highway and see if this happens in lower gears too, and maybe really open up the throttle at 50 mph before I even get to 70. It was during the day so it's hard to say if the whole electrical system would drop or just the engine.
 

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I ask about the vibration because the kickstand safety switch could be acting up causing the engine to turn off. Run the engine up past the rpms you would be turning in 6th gear in first and second gear and see if the engine dies. Could be a loose connection that happens when the vibration gets up there at speed.
 

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Most likely battery connections. Happened to me as well. Vibration causes connections to lose contact and bike to cut out.
 

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It happened to me too. Make sure the battery posts, ground and connections at the relay box under the left side cover are clean and tight. I had recurring gremlins till I did this - no more problems since.
 

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Try running a Sea Foam through a fresh tank of gas. That alone may help. It does look like it's not getting enough fuel.
Did you do any regular maintenance on the bike since you got it?
If not, I would go through schedules maintenance items according to the owner manual.
Check air filter, battery connections etc.


Sent from Motorcycle.com Free App
 

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Discussion Starter #11
It's the JETS!

Thanks for the replies guys. Turns out the issue is with my main jets. Took it to a mechanic and he said it's running too rich. I know stock mains are #102, and I opened up the carbs last night (dat service manual!). Everything looks shiny and clean, but what I have installed is size #136 jets. Big difference there from stock. So I have to get smaller main jets...

Now I do have aftermarket pipes on it (trying to figure out from previous owner exactly what exhaust system it is), so I am guessing that means I would need jets bigger than sock (right? higher exhaust flow = bigger jets needed?), but I am not sure what size to get. What do you guys think? I am thinking to order #105 and maybe #110, but I really have no idea what sizes to try to see what works best, and I don't want to order more than 2-3 sets of jets ($$$).

Now I understand the main jet only comes into play at 3/4 to full throttle, and I can smell gas when I'm at stop lights... so this must means the bike still runs rich when throttle is from closed to 3/4 (needle jet?). Do I have to adjust the needle as well to get a more balanced air/fuel mixture? Lower the needle 1 click (bring that "thing" closer to the top of needle)? Or try and play with air/fuel mix screw first?
 

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I was going to say, sounds like a loose or large main jet problem but I see you have gotten that far.

First get the jetting as close to the factory settings as possible.

IIRC
#35 pilot jet. Keihin jet series N424-25B. N424-25B-035(note HD and Kawi use .6mm bleed(cross) holes, if the jet is smaller you can enlarge them)

#102 main jet, Keihin jet series 99101-393-102

The last 3 digits of the part numbers for both the pilot and main jet series # I listed are the jet size.

For the main 098, 100, 105, 108 were optional sizes from Kawisaki.

I also recall the stock needle is not adjustable. If yours is adjustable(other than with shims), if it has grooves for clips. It is likely someone has put a jet kit in it, Cobra or Dynojet...... Often times the aftermartket jets from these companies do not follow the carb manufactures jet number sizing, some times due to the replacement needles having a more aggressive taper and the manufacture chooses to shift the jet numbers in relation to actual size in a attempt to not freak the customer out at the new size.

Example for Keihin a #102 main jet = 1.02mm, a #105 main jet = 1.05mm and so on.
#35 pilot jet = .35mm.....


As I said the aftermarket jets don't always follow this path, though it has gotten better over the years. For aftermarket jet EBC does follow this pattern and are readily available if you search for the Keihin jet series number and size, usually at a lower cost to OEM or Keihin jet prices.

A handy PDF for anyone who has to do carb work often.
http://www.keihin-na.com/assets/1/7/jetlist.pdf

I have found a #35 pilot jet fine for virtually all set ups when the mixture screws are set appropriately or a custom #36(.36mm) to also work well with after market exhaust.

For the main, a #102 is a touch lean even in a stock bike when getting wound out, especially if you are in an area that is dominated by E10 fuels. A #105 does quite well with both stock exhaust and more open mufflers.

Altitude will also play a roll in what I have found to work well. For reference I'm basically at 1,000'.

Float height( 17mm +/- 2mm)(shorter = higher fuel level(remember this is measured upside down for all practical purposes)) will have an influence too on the in service(suspension setting and rider weight) fuel level (from the float bowl gasket surface(carb body not bowl) +1.5mm, -.5mm is spec limits. Higher fuel level = richer.

If yours has had a jet kit installed it is also likely the slide vent hole has been drilled to allow the slide to lift sooner/faster. This can also have an influence on the main jet size you need.
 
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