Poor Gas Milage

thlillyr

thlillyr

XS400 Addict
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The manual says my bike should get about 56 MPG. Currently I'm getting 20-25. Thats bad for a bike. I usually rev it to about 7-8000 rpms when i get up to speed so fairly aggressive launches but then I'll drop it to 3-4000 when at speed. Bike seems to run pretty good. Except bike will hesitate below 2000. Sometimes for like 5 seconds.

Jets are 125
Idle screws are at 4 turns
Floats are propaly high. Had a mechanic clean my carbs and he said he raised the floats a little to help with high RPM hesitation.

Am I getting the proper MPG? Is my driving style? Or am I tuned wrong?
 
sounds bad, get those floats down to the correct level, probably needs a good clean inside too
 
As Drewpy said, when the carbs are properly cleaned and adjusted and if fuel supply is good, you should not experience any performance issues. If the setup is stock, you should not have to mess with float height or jet changes. Doing so only invites trouble.
 
Word to the wise, you never know if your carbs are clean unless you see it with your own eyes. These mikunis are VERY sensitive.
 
Are you sure your calculator is not broken? Even when my float was stuck and gas was pouring out of my intake, i still managed 41 MPG.
 
Yeah....I don't see how an XS400 can run anywhere near decently and get 25 mpg unless it's sitting around leaking gas.

How did you figure the mileage?
 
If it is running good you should not have to rev it up to 8k this won't help ether. I shift at like 4500
 
Not going to say how I know this, but also make sure the petcock is "ON" and not "PRI."
 
i mile each tank. about 100 miles I have to turn on my reserve. Pump puts in almost 4 gallons exactly each time.I drop my gear around 4500 i but I shift into second third etc at 8000 for fun. I'm one of those guys i know i know. I've seen the inside of my carbs when I rejeted them. The look like new. But an awful lot of gas poors out of them when i removed them. Is it normal to have about half a cup to a cup of gas just sitting in the carbs? Petcock is set to ON and the vacuum works.
 
If the vacuum is working, then no, it's not normal. It was always my understanding that without the engine on, the vacuum keeps gas out of the carb which is why it doesn't need to have an off switch. That's what the vacuum is for. My guess would be maybe a petcock rebuild? Anyone else have any ideas?
 
The petcock appears to be fine. Gas won't flow out unless in the PRI position or a vacum is applied. Both RES and On positions behave normaly. Tested this with a bottle and starting the bike.
 
Have you looked at the color of your plugs? Sure both cylinders are firing? Did an ohms test on you coil? Checked the resistance of spark plug caps? Compression? Valve shims? Timing chain tension adjusted? Enrichment or choke working properly, on when you want, off when not? Lots of possibilities.
 
This is what both spark plugs look like. Is sooty and rubs off on my fingers.

EDIT: Using this chart.http://www.verrill.com/moto/sellingguide/sparkplugs/plugcolorchart.htm It says it's carbon fouled due to overrich mixture. Likely causes are bad air filter, high float level, bad Needle or stuck choke.

It's got to be my float level then cause thats what the mechanic adjusted to enrichin it when it was running lean. I rejetted it cause it had 95s now its to rich. Any body know how to adjust a float level?

full
 

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