Very Bad Mileage - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 11 (permalink) Old 05-28-2013, 09:27 PM Thread Starter
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Very Bad Mileage

Hi,
Just recently started riding. Bought a 750 Vulcan as a starter bike. It has 17,000 miles. Runs good, but can tell it's running a little rich, but problem is bike getting horrible gas mileage (only about 15 mpg). Any suggestions? Thanks
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post #2 of 11 (permalink) Old 05-28-2013, 09:36 PM
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Quote:
Originally Posted by rasams View Post
Hi,
Just recently started riding. Bought a 750 Vulcan as a starter bike. It has 17,000 miles. Runs good, but can tell it's running a little rich, but problem is bike getting horrible gas mileage (only about 15 mpg). Any suggestions? Thanks
That's a LOT rich! Unmodified bike should see around 50MPG!

Pull the spark plugs and let us know their condition. They will prolly be jet black from running rich.

First place I would start is the petcock. Pull a fuel line off the petcock and see if it drips any gas. If so, it is allowing excess fuel into carbs. If the petcock is tight and not flowing any gas with engine off, I'd then check the floats.

There is a nipple under each carb with a hex screw to open and close bowl drain. Get a piece of rubber tubing and attach to nipple and drain the gas out of the bowl into a safe container. Next, blow into the rubber tube into the float bowl and listen. You should hear air escaping. Do this for the other carb and go test drive the bike and see if the mileage improves.

You may want to drain the oil, too. If the floats are allowing gas to flow, there is a good chance gas has overflowed into the crank case mixing in with the oil. This is not good.

Let us know what you find.

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post #3 of 11 (permalink) Old 05-28-2013, 09:58 PM
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I would check out the floats and the rest of the carb. A working float should be able to control any amount of flow coming from the petcock.

Look at the plugs first, they may tell you which carb has the problem, and if you're lucky it's only one carb needing attention.

If you can get the float off, shake it and see if there's gas in it. There shouldn't be any.

Make sure the slides are coming all the way back down after opening the throttle.

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post #4 of 11 (permalink) Old 05-29-2013, 09:57 AM
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If your getting 15mpg, you're leaking fuel somewhere. Check your oil to see if it smells of gas.

Only time I've heard of this bike getting an mpg figure like that wasn't leaking fuel, it was running on only one cylnder.

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post #5 of 11 (permalink) Old 05-29-2013, 10:29 AM
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Mileage

My bike has just under 18000 on it and I just rode from Sacramento to Reno (just about 110 miles from my house) and ran out of gas after 105 miles. I was averaging about 85 miles an hour. I couldn't go over 95 through the turns because of the grooves in the pavement(causes a bad wobble) At normal speeds my riding style only averages about 40-45 mpg. Your spark plugs must be dripping with gas. Is either cylinder worse than the other or do all your plugs look the same? Is your choke lever working? I don't see how it can even run and use that much gas so I agree it must be leaking somewhere and hopefully not into the crankcase.
Good luck and let us know what you find.

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post #6 of 11 (permalink) Old 05-29-2013, 11:11 AM
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Is the bike stock?
What type of exhaust do you have?
What type of fuel are you using?

the above info will help us understand your setup and then we can give better advice on what to look at other than what was stated above.

even with the ear shave, open exhaust and re-jetting the carbs performed, the mileage should still be better than 25mpg....and that is even a bit low IMO

Last edited by kc2dgq; 05-29-2013 at 11:14 AM.
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post #7 of 11 (permalink) Old 05-29-2013, 09:02 PM
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If needed i can provide a guaranteed way to check a float for pinholes. It takes some time though.
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post #8 of 11 (permalink) Old 05-30-2013, 05:02 AM Thread Starter
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I put new plugs in it. I believe the guy I bought it from had put wrong plugs in it. Seems to be much stronger. Riding to work today. I'll see. Thanks
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post #9 of 11 (permalink) Old 05-31-2013, 10:16 AM
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Don't disregard what was mentioned about the petcock. I said to look at the carbs, but the petcock can leak through to the front carb and cause it to flood, gas can pass through the vacuum line if the petcock is bad.

Quote:
First place I would start is the petcock. Pull a fuel line off the petcock and see if it drips any gas. If so, it is allowing excess fuel into carbs. If the petcock is tight and not flowing any gas with engine off, I'd then check the floats.

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post #10 of 11 (permalink) Old 05-31-2013, 11:07 PM
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But at 15 mpg I doubt the engine would even run it would be so rich. I'm betting on a fuel leak to somewhere outside the engine, maybe a cracked fuel like that mainly leaks when the engine is running (vibrating) and evaporate quickly off the warm crankcase. At 15 mpg excess fuel through the carbs and cylinder rings when the bike was sitting would cause the rods to slap the excess fuel/oil mixture blowing more gas through the surge tank further enriching the fuel mixture.

Try filling up and either immediately ride an hour before refueling to check mileage or at least turn the petcock off when stopped for more than a minute to elimate excess fuel drain past the floats and petcock. Would be interested in the results. Since replacing the fuel lines is a simple 30 minute job I'd try that first.

You may still have a leaking petcock and float valve (I had both) but 15mpg is pretty bad. Even with a leaking petcock and leaking float valve (1 leaking float valve) when parked a few days before refueling I still got 40 mpg and a slightly raised oil level. Enough float valve/petcock leakage to give you 15 mpg would cause MAJOR rod/oil slap if the excess fuel got into the crankcase.

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Last edited by Spencer1; 05-31-2013 at 11:10 PM.
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