Where should I look to fix misfires in my Vulcan 750?

Question

My Vulcan 750 misfires, especially at hi speeds and usually around 4000 rpm. I can't accelerate and often start slowing down if I'm over 50mph. If I change gears, it usually goes away. I've changed the plugs and plan to check and make sure the new ones are still good. What else should I check?

Answer 1

You own what may be THE BEST Japanese cruiser to ever be sold. At one time I would buy all that I could and had two rental companies that would buy them from me sight unseen for use as rentals. The reason was that they never break ! The problem you're having can only be carbueration. The valves are hydraulic and never need adjusting. Spend a few bucks and have a good mechanic clean and adjust the carbs.

Answer 2

Always give year, make, engine size and model # when asking questions. We need all of that info to give an informed answer.

Depending on the year, some Vulcan 750s had a problem with the pulse coils (on the engine down by the flywheel) shifting their position which would affect the ignition timing.

Shifting gears will change the RPMs of the engine which will alter the timing advance at the moment.

The "air gap" of the pulse coils had to be adjusted.



Edit

Before getting to involved with electrical trouble shooting, check mechanical things first.

Adjust the valves - it's probably never been done.

Remove and clean the carbs - dirty carbs could gum up the throttle slides, preventing them from raising smoothly.

The throttle slide diaphragms could be cracked or leaking.

Could have water in the gas.

Look in the fuel tank for rust (not good).

Check for intake manifold leaks - especially if the carbs have been removed.

Check for exhaust leaks at the heads and muffler joints.

Answer 3

Definately check your plugs and plug wires first. If those are fine, check out the coil. You can find out how to test that using a multimeter online. It's really easy. If your coil is fine (input and output), check out your ignition system. Your ignition module is usually in the nose cone on the bottom right side of your motor (formerly known as the points cover). Make sure there are no shorts or anything like that. And make sure everything is grounded properly. My guess is you probably need a new coil or plug wire. Hopefully it's not your ignition. That could be a pain. My ignition has an option for dual fire or single fire. If you only have one coil, make sure you choose dual fire if you have the option. I doubt you have that option but I thought I'd include that just in case.

Answer 4

The very first thing to check is the oil level. My motorcycle (1985 Virago 700) misfires on the rear cylinder if the engine has been overfilled with oil. Set your motorcycle on its center stand, let it settle a couple of hours, cool, and check the oil level. The level must be between the two marks. If there's too much oil, you need to drain some until it is between the two marks.

Answer 5

check coil for spark power, should be blue, and bracket for cracks.......

Answer 6

firing module, i.e. coil