My bike cuts out under load above 3500rpm but if I put it in neutral it'll rev up to redline. I've had the carbs off twice. Once to clean and once to adjust float level. The spark plugs are light tan in color and the bike idles great. The spark looks good and I've checked for vacuum leaks. The tank is clean and the petcock checks good. I've yet to check compression and electrical components.

Anybody have this problem? What's the fix?

fuel??? drawing more under load and starving? not sure about safety but how about using spare key in cap and when starts to die out pop that baby open and see what happens.just a guess from me though as I'm still learning this bike.

disclaimer: trying my idea could be hazardous to your health!!!

Done it...nothing

humm... tan like early fouling, or tan like plug is burning?

humm... tan like early fouling, or tan like plug is burning?

Tan like good plugs. They are a little lighter than the good plugs I have in my other bikes. I put in some new plugs I had and they didn't make any difference.

I had an S10 that had the same characteristics, but it was because the plugs got too hot. I replaced them and it runs fine.

The kicker is all of a sudden this bike started acting this way and that is what makes me think it is electrical.

Just a thought.... you say you took the carbs off to adjust floats?? are they not suposed to be adjusted on the bike??? if so they may be set too low and you are running too lean.

I may be wrong here, but it is a thought.

I'd say the floats are set too low, as 93VN750 says, the float level should be checked with the carbs on the bike. As Trashlord says, there will be less fuel demand in neutral so the problem may not show up until it's under load.
Also, may be worth checking to see if any of the fuel lines are getting pinched under the tank somewhere & restricting the fuel flow.
Will be intersted to hear what the problem was when you finally get it sorted.

What I've done to date (to no avail):

Checked float level (checks at the correct level according to Clymer)
Synchronized carbs
New spark plugs (plugs have excellent color)
resistance check of the pulse coil (330 to 530 ohms, mine checked at 520ohms)
New hoses
Petcock and fuel filter check good
No vacuum leaks that I can find
Engine compression test (150 psi both cylinders)
Checked electrical connections
Voltage and current test of charging system

What I'm doing tonight:

Look at vacuum hoses again
Run the bike without carb air intake boots
Resistance check coils and igniter
Check sidestand switch connection

If all else checks good I need to find someone with a good running Vulcan and then swap electrical components one at a time. If that fails, I'll check the carbs again. If that fails....Bonfire!

Before you do all that, put the bike on the center stand, get on it, start it, and run through all the gears. This is a slight load, but you will know if the problem is truly with the engine or something with the drivetrain.

Last night I was able to coax it into running above 4000rpm by gettin up to speed in 2nd or 3rd gear and then shifting down so the revs got up to about 6500rpm. The bike would run all the way to redline with some slight hiccuping, but as soon as I brought the revs down to 4000 again, the misfiring would take over.

So if you can ride it, then put some Seafoam in your tank. We all use it, it has magical properties. If there is anything wrong with your fuel system, besides an adjustment, SeaFoam will fix it. You can get it at an auto parts store, such as NAPA, Autozone, Advance Auto Parts, Pep Boys, etc...

http://www.vn750.com/photopost/data/502/seafoam.jpg

Almost sounds like you have some water in your fuel try putting some alcohol in your fuel tank.Every you have checked sounds right.

Or try SeaFoam. It's great for all gasoline engines, even lawnmowers. The important ingredients are Naptha, Pale Oil, and IPA (isopropyl)

Thanks for all your input fellas! Last night, after checking all ignition components, I decided to see what would happen if I took the intake boots off the carbs...the bike ran good all the way to redline. As soon as I restrict the air into the carbs, it starts running worse. Putting the boots back on and removing the air filters and covers resulted in rough running around 5000rpm at low speeds of 20-40mph, but as soon as I get my speed up above that it clears out (Ram air effect). As soon as I put the covers on, or the air filters on, it runs rough like before.

So, it is back to inspecting the carbs. I'll be back to tell if I get it running good!

It should run bad with the boots or filters off. Sounds like your jets aren't stock, or have been drilled out. You bought this new, right? I'd take it back to the dealer, as I'm sure it's still under warranty.

Sonds like a restriction in the air system, Look for a bent pipe or mouse nest.

Maybe you should consider an ear shave? Sounds like it may want to be that way. I just found the thread where you say you bought it used, and it's got 21000 on it. OK. So if the original owner thought it was carb related, then he tinkered with it, right?

Maybe you should consider an ear shave? Sounds like it may want to be that way. I just found the thread where you say you bought it used, and it's got 21000 on it. OK. So if the original owner thought it was carb related, then he tinkered with it, right?

Yeah, the original owner had the carbs apart three times. It started running rough for him and he discovered some gunk and rust. It fixed the problem for 500 miles then started acting up again so he cleaned the carbs AND the gas tank, then the carbs started flooding a bit so he took the carbs apart again...and that's when I bought it. I'm taking the carbs off again tonight. I blew air thru all the holes I could find in the carbs when I first bought the bike, but I didn't probe them. Maybe something is still plugged up.

I'll keep you posted! And I'll look into that ear shave.

Maybe you should consider an ear shave? Sounds like it may want to be that way. I just found the thread where you say you bought it used, and it's got 21000 on it. OK. So if the original owner thought it was carb related, then he tinkered with it, right?

Remember Photohap? I have his bike!

All this troubleshooting and 3 carb pull/clean/reinstalls later and it all came down to something simple, discovered by accident!

The issue I had this whole time came down to the vent tube coming from the 2 carbs. The tube had the 45 degree cut and was in place inside the right air box...well, the bike doesn't like that! As soon as I pull the tube out and face it forward, the bike runs perfect. If the tube faces backward, or is placed in the air box hole with the cover off there is slight hesitation (not as bad as with the air box cover on).

Who'da thunk that hose was so picky. I figured as long as it wasn't plugged, the bike would run fine.

I just happened to be riding the bike and pulled the tube out of the air box hole, and noticed that messing with its position affected how the bike ran.

I love easy fixes!