Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums - Reply to Topic
Carbs and Fuel System
From the gas tank to the carbs
All fuel system discussion

Thread: Fuel in oil Reply to Thread
Send Trackbacks to (Separate multiple URLs with spaces) :
Post Icons
You may choose an icon for your message from the following list:

Register Now

In order to be able to post messages on the Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

Once registered, your User Name"cannot be changed". We can make exceptions within 7 days, but after that, it is set in stone.

User Name:
Please enter a password for your user account. Note that passwords are case-sensitive.


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:


  Additional Options
Miscellaneous Options

  Topic Review (Newest First)
03-04-2018 11:41 AM
Spockster Good point ... If the front cylinder had much gas sitting in it, the starter is likely to act really sluggish at first. Think, hydrolock.

It cost me a couple of oil changes to get busy on the petcock. I thought turning it off all the time would save me from the leak, d'oh, I was wrong again.
03-04-2018 11:25 AM
Originally Posted by Spockster View Post
The leak through the petcock bypasses the float, and goes directly to the cylinder. It's flowing through the vacuum port on the front carb. The front carb is angled toward the front cylinder, so the gas just runs downhill into the cyl.
D'oh--that makes sense! I haven't had that happen to me, so didn't make the connection.

I was thinking, too that if OP just got the bike and is replacing the starter it might be a little premature to be deciding whether the carbs need to be pulled or not. They may need to be cleaned anyway. . . .

Sounds like OP has a project!

03-04-2018 10:31 AM
Spockster The leak through the petcock bypasses the float, and goes directly to the cylinder. It's flowing through the vacuum port on the front carb. The front carb is angled toward the front cylinder, so the gas just runs downhill into the cyl.

Edit: Also, with a blown diaphragm, turning the petcock off won't help, gas will still seep through the vacuum hose.
03-04-2018 09:05 AM
GDI Yeah, it's really the failure of two separate systems--a) vacuum petcock, and b) float valve in the carbs. If either one of those things had worked correctly you wouldn't have had the gas in the oil problem that you've got.

Pulling and cleaning the carbs is a major undertaking on this bike as the designers jammed those carbs in there with a shoehorn (after greasing them up first!). That's why it's probably much easier to fix the petcock instead. I've never actually fixed a vacuum petcock myself. Many people will just replace the petcock with an aftermarket style when the diaphragm fails, which is what I have done in the past. The aftermarket petcock will have an "off" position, which serves the same purpose as the vacuum shutoff. The thing is that you'd have to remember to shut off the petcock and turn it back to "on" every time you stop and start your bike as long as the float valve is sticking.

The easy way (may not always be effective) to free up your float valves is to empty out that old gas and then put some fuel additive in there to help clean up the carbs. Lots of people swear by sea foam, but I've never had much luck with it. I prefer the "Berryman's B12" additive, myself. The best remedy is to run a few tankfuls of gas through the carbs for everything to get cleaned out like it should be!

Then you'll always want to use a fuel treatment like Stabil (or even sea foam is probably fine for this) whenever you store the bike for extended periods. I always treat my fuel when it's sitting over winter.

good luck,

03-03-2018 11:55 PM
Spockster Check the vacuum port on the petcock, if it's wet, the petcock needs a new diaphragm. Gas will leak through the vacuum line and flow to the front cylinder, then past the rings into the oil.
03-03-2018 11:08 PM
flitecontrol Did you happen to check the oil level before draining the oil? Fuel in the oil usually results from a stuck float valve. The Vulcan comes with a vacuum operated petcock, which should prevent the flow of fuel unless the engine is turning over. It's possible the petcock is faulty. That can be checked by removing the lines to the carbs when the petcock is turned to the on position and seeing if they leak gas.
03-03-2018 05:01 PM
Fuel in oil


So my father-in-law is giving me his 750 Vulcan. Yay!!!! Today we attempted to replace the starter. Once we removed it a vast amount of fuel came out along with oil. So now I am here on this forum praying someone can help me understand why fuel is mixing in with the oil and what it will take to get it fixed so I can ride please.

Thank you

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

For the best viewing experience please update your browser to Google Chrome