Gas Mileage Problem?

Bought my first motorcycle last week (1981 xj760 seca) to ride to work figuring would save some money on gas since I have to go 35 miles one way to work everyday. But when I ran through my first tank of gas and checked the mileage I got 24 mpg!!! I am thinking this cant be right?? It ideals fine, and goes down the road good (60-70mph). Carbs were cleaned, air filter looks good, ran some seafoam though this last tank (24.5 mpg). Any Ideas why it is getting such bad gas mileage? My 93 sonoma gets 25 mpg so I am going to drive that till i get this figured out.

 

A little info to be found here:

http://xjbikes.com/Forums/viewtopic/t=7 ... leage.html

 

Another Minnesota XJ'er!

So I'm not the only one!

 

You may also want to examine your tire inflation, wheel bearings and brake calipers. If your tire isn't properly inflated, your rolling resistance will increase rapidly. Wheel bearings will kill gas mileage if they are toast. And a sticking brake caliper is a really bad thing. As a second guess, you may want to change out your air filter even if it looks "ok". Clogged air filter will suck fuel too. Check your plugs, if they are rich, I'd swap out that filter.

 

Thanks for the info. I know tire inflation is good, but will check the bearings and brakes out. It must be running rich though cause the plugs have a black soot on them. I also noticed that the rubber boots that go to the carb are cracked. Would that cause poor mileage?

 

Give her some new plugs and an oil change too. Also make sure your battery is nice and healthy. Does the idle RPM's climb drastically when the bike is warmed up? If so, then yes, the boots may be cracked badly enough to cause an air leak. However, this would not hurt gas mileage, it would slightly increase it (the bike would be running too lean).

Chad
1981 XJ750R

 

The spark plugs and battery are new this spring and oil/filter was changed. I did lift it up last night and the front wheel didn't spin freely. Sounded like the brakes were rubbing. It is running rich because I cleaned the spark plugs and then drove to work and back and they were black again. So I don't know if putting a new air filter in and adjusting the brakes will get the mileage back up? Is there any adjustments that can be done for it running to rich?

What kind of mileage does anyone else get with the xj750??

 

Sounds like you and Hess need to get together and hold a carb clinic. The colortune plug will help reset the rich mixture but it only works at idle. I would change the air filter and check the valve clearances.

 

Bryan, my 82 750 seems to average right around 36mpg.

 

I'd change that air filter then ride for a short bit and check my plugs again, if still rich (dark soot) then your carbs need to be leaned out.
To find those adjustments look at the link below
http://www.xjbikes.com/Forums/viewtopic/t=1586.html
Hope that helps.
Be careful when drilling out the screw caps

Mike

 

I would replace the air filter, do a brake flush, and clean that caliper out. I would also suggest sealing up any cracks in your carb boots. and then i would get your carbs synced and tuned. If it's STILL getting terrible gas mileage.... well then it beats me.

my 81 xj 750 seca gets between 38-44mpg
check your math perhaps??




just for the record:
running lean, does not increase your gas mileage because there is less gas in the mixture. if you spent a lot of time idling this may be true. But under normal load it is the opposite. less than optimal fuel/air mixture means you have to use more throttle to get the same amount of power from the bike, so you infact get a lower MPG.

granted lean is better then rich as far as the MPG thing goes.

 

Ok I think I have some time to work on the bike. Just wondering where anyone usually gets their parts, online or dealer? Right now I am looking for an air filter and then fork seals. Any particular brand that I should go with?

 

I've used BikeBandit.com with good results. You could also check out OldBikeBarn as well. Their link is listed under our stealership/shop forum if I remember rightly (and I hope I did). Google them if you need too. Parts-n-More is another place for the old bikes. They just have lousy customer service. All the online places have good stuff, just a bit cheaper than the stealership and you usually get the parts faster anyway.

 

The adventurous one may of course make his own air filter

http://fj600.blogspot.com/2006/05/air-filter-deed.html
http://fj600.blogspot.com/2006/05/air-filter-update.html

I've been using my high throughput air filter since then and it seems fine so far.

Best wishes,
Relu

 

I've built three air filters using the methods described by the fellow in the link you provided Ohmega. A few points of difference: I purchased a sheet of UNI foam for my applications. I use RTV to bond the pieces of my foam together. Any color will work but I use clear. I cleaned just as he did but I use the UNI or K&N foam filter oil so I don't have the problems he described. I don't glue the entire sheet into place, I purchase long springs and use them to hold the element in place. I need to post some pictures for you all.

 

That guy is me Robert ... that's my journal of repairs. I'd buy the Uni oil, but I just couldn't find it here in Toronto. From what I understand the K&N oil (spray) is for cloth, not for foam; but if you say it works, I think I'll get a can and use it.

I too wanted to buy the Uni foam. But then I asked myself what properties such foam should have. And found this "dense" type of foam at work, so I thought I may as well give it a try.

 

I'm not aware of the different characteristics of the foam in question but I will say this. Some foam cannot endure exposure to hydrocarbons and oils so I made the $14 USD investment in materials I knew would stand up to the rigors of a motorcycle. I've built three filters with the one sheet and have enough left over for at least two more (got one to build right now too). You might have a perfectly useful chunk of foam there, I'd just watch it rather close for a few months for breakdown of the media. Best of luck on that one!

 

http://cgi.ebay.com/Yamaha-XT550-XJ700- ... dZViewItem
Here's the fork seals

http://cgi.ebay.com/ebaymotors/Yamaha-H ... enameZWD1V
Heres the filter

Prices seem in line

Good luck
Mike

 

I just got some carb rebuild kits to see if that will help me w/ my gas mileage problems. Got a couple questions though. The new kits that i got don't have the screen on the end of float seat and the end is smaller then the ones that I had so the screen will not fit on there. Do i need the screens? Also was wondering about the Pilot Screw Blind Plug. I can not see where that would go, do i need it?

While reading through some of the forms too guys were talking about the washer for the main jet. Mine has it and is running rich, if I take that out will it lean out or am I reading them wrong?

 

Bryan:

I recently cleaned the carbs on my baby Seca.

After cleaning, I originally set the pilot screws about 4 turns out. The bike made awesome power, but my fuel mileage went down about 25% (from 50mpg to 38 mpg)!

I then adjusted the pilot screws to about 2 1/2 turns out, and the gas mileage returned to 50 mpg. Not as much fun riding, but definitely cheaper on the pocketbook.

Given your rich condition (as indicated by the sooty plugs), you may want to check your pilot screws and see if they are backed out too much.

Just one more possibility...

Herb