Gas mileage SUX

Just filled up for the first time. 47.4 miles/2.4 gallons = 19.75 MPG :ohmy: I could understand if I was hot rodding it but I haven't even been over 75 MPH and been driving it easy since I just got it running. Naked bike. No windshield etc. Compression good,valve clearence good, ignition good, carbs just done by WG and less than 20MPG. Heck I used to get 30MPG on my old KZ1000 back when I was a heavy handed kid back in 82.:blink: I'm starting to have vivions of a FOR SALE sign in the future.

Check your math?

Bluemeanie wrote:

Check your math?

OK, I checked. Came up with the same answer. 47.4 miles driven divided by 2.4 gallons used = 19.75 MPG. Am I missing something?

Some items to check ---

tire air pressure up to specs?

clean air filter?

anything blocking air filter?

leak in petcock or fuel line?

shaft drive properly lubed?

brake dragging (either rotor hot after a ride)?

free spinning front wheel?

crankcase oil level too high?

fresh properly gapped plugs?

Done a plug reading? (perhaps weak ignition is being overlooked)
possible ignition issues:

condition of plug wires?

functioning of plug caps?

good connections between plug wires to plug caps?

remembering to shift into fifth gear? (just kidding)


Then would re-check the fuel mileage --
fill completely
set odometer to zero
run on into reserve petcock setting
fill completely
do the math

Might be wrong, but thinking 35-40 mpg would be within reason at steady highway cruising speeds.

Good Luck!

Thanks Patton. I Just got her on the road so...Tire pressure checked,cleaned and oiled K&N air filter, New fuel lines and filter when installing carbs,checked for leaks,changed all fluids including rear diff.,brakes checked,checked front wheel bearings,new plugs and plug wires(automotive) with boots made on them and did the coil relay mod with 10ga wire.I haven't done a plug read yet but it runs sweeeeeet. I'll check plugs tomorrow if the weather permits.

Post edited by: 1982KZ1100D1, at: 2008/01/19 22:04

I vote for the pinhole in the petcock diaphragm theory.

Does this model have the vacuum petcock?

If there's even a pinhole, your intake manifold will suck gas into your cylinder.

Does the cylinder with the vacuum hose attached run richer?

1982KZ1100D1 wrote:

... cleaned and oiled K&N air filter....

Sometimes it takes running a few miles for a freshly oiled K&N air filter to start breathing freely again. If in doubt or poor mileage persists, could re-check fuel mileage using a new oem paper filter. And also compare plug readings with the different filters. K&N filter is supposed to flow more air (but with less filtration) than the oem paper filter.

And forgive reminder about possibility of brake drag or excessive oil in crankcase (which could cause engine drag and/or venting oil vapor from the breather into the air filter -- assuming crankcase breather vents to airbox)

I may try a OEM filter just for grins. I've never been a big fan of K&N anyway. It just came with the bike so I thought I would give it a try. I'm using new clear tubing for vaccum lines and no signs of anything in there. A plug check sure won't hurt but it sounds like it will be cold and windy tomorrow so it may have to wait until a later date.

You should have only one vacuum line connected to the petcock. Normally this line is black because the ID is only 1/8" I believe. The mileage you are showing is based on two gallons of gas? Bwhahahahaha Go at least a couple tankfulls. You topped the tank off exactly the same as the previous top off? You would have to in order to check after only two gallons. Did you rebuild that bike? Might take a few tankfulls to get things seated in. Mileage is pretty low after a rebuild. If you continue to have issues, drive by my shop one day when the weather is nicer. We can go over stuff...

are you sure the spedo is correct, also what about clutch slip, get it into one of the high gears and nail it see if the rpms come up and you dont take off

1982KZ1100D1 wrote:

Just filled up for the first time. 47.4 miles/2.4 gallons = 19.75 MPG :ohmy: I could understand if I was hot rodding it but I haven't even been over 75 MPH and been driving it easy since I just got it running. Naked bike. No windshield etc. Compression good,valve clearence good, ignition good, carbs just done by WG and less than 20MPG. Heck I used to get 30MPG on my old KZ1000 back when I was a heavy handed kid back in 82.:blink: I'm starting to have vivions of a FOR SALE sign in the future.

Interesting timing... My KZ750 twin used to average about 42 mpg in the city... got new headers and it started running lean and the mileage went up to 45. Did a rebuild on the top end and also jetted it in to the new headers... and it runs BEAUTIFUL and only gets 36 mpg.

Not sure where it will end up at this point, maybe the moral to the story is to stay away from MAC headers.

I have 3 vaccum lines. #2 carb to petcock, carb#'s 1&4 to the emissions valve up front. No re-build on engine,only checked over valve adjustment,compression, new plugs, wires etc. Thanks for the offer WG and I still may swing by sometime just to say Hi but I don't think it will be on the KZ. It's a neat bike and runs sweet but it's just not the type of bike I want to ride anymore.I wanted one sooooo bad back when they were new and when I saw this one listed 4 sale about a year ago I had to have it. Now that it's running I find it and my older body don't get along. :blush: I want something where I can stretch my legs more and not feel like my knees are beside my ears. I think I will sell it once the weather warms up and deposit the $$ in the savings account I set up to buy a 1600 Vulcan Nomad.