CRAPPY MPg?!?!?!

[tbcfreerider]

so now that i have a fuel sending unit, i noticed that, my stock 82 jx11 get ****ty gas mileage... it currently is running a bit rich( bad exhaust fumes, some black puffs of smoke) would that be the cause? I also notice that the fuel level display is constantly fluctuating... like it made it 12 miles or so after a fill up at the local gas station then it show 3 bars vs 4. when i filled up i was at 32,186. Im now sitting at 2 bars on my display and at 32,218ish. what gives? im commuting on the bike, ALOT of L.A. stop and go traffic.

[petejw]

Check your air filter isnt blocked and dirty.
Also check there arent any blockages in the air intake.
Replace your plugs and check/adjust your mixture screws.

[XSokieSPECIAL]

You need to pull those carbs! Rebuild time.

You've got a float adjustment problem or a float needle leak/float needle O ring leak problem.

Sounds like to me. IMHO

Buy kits and do it right. That IS experience speaking.


BTW make sure there isn't gas in the oil. You don't want to kill your engine.

[Ken Talbot]

You could just start with a carb sync, but you would only have to go back into the carbs later anyway.

Take off the carbs, strip them down, and start with checking the float levels. At this point, it doesn't really matter what they are, just make sure they are all the same. Make sure all the jets and orifices are squeaky clean. Put it back together with a bread-tie sync just to get it running again.

Then, sync the carbs, colortune them with a colortune or be ear, then re-sync. Ride it for a tankful or two to see what kind of mileage you are getting and check the plugs. Only then can you start homing in on what the problem may be.

If you start right in with changing jets and changing float settings, you will be just chasing your tail because you will have no baseline for reference. Follow the steps above, see where you are, then come back for some follow-up.

[tarzan]

I'm not familiar with the XJ, but the miles you gave are what 32 miles?
And you have 3 bars?Is that 3/4 full?So 136 miles out of a tank.
My special got just under 120 miles out of a tank and I got right at
40 MPG.I don't know how many gallons you hold,but if I were you, I
think I would run a whole tank through it keeping track of miles and
fuel and find out the exact figures and then make a determination.
I think somewhere between 34 and 41 or 42 could be normal from a lot of the posts I have read.Comparing to what others get.
Obviously too, type of riding,quality of gas, altitude, load carried as well as other factors could be variables to consider.
BTW,how does it run?
I would try adjusting the mixture screws before tearing carbs apart
if it runs good but a little rich.
JMHO
Rick

[81xsproject]

You need to pull those carbs! Rebuild time...

Buy kits and do it right. That IS experience speaking.

Nothing personal, but you're dead wrong! Kits are not only a waist of money but quite often lead to VERY poor performance and hard to diagnose issues.

Other than float valves, and bowl gaskets there is ABSOLUTELY NO REASON to put new parts in there. What's there simply needs cleaned. 98% of carbs don't need rebuilt, they need to be cleaned.

[tbcfreerider]

thanks everyone!

[DiverRay]

Th XJ uses the "O" ring type seat for the float valve. If you don't know the last time this was changed, it is probably a good idea to replace them. I DO think a kit with the PROPER parts would be the way to go, as getting just the few you need from the dealer would cost more money. I get kits from georgefix on ebay, and they ALWAYS work well. You don't need everything in the kit, but I would replace the mixture screw, float needle and seat, and gasket with new parts.
Just my $0.02, and worth everything you paid for it!

[dbeardslee]

Just to add to what's already been said, there's a pretty good tech tip on improving gas mileage.

[81xsproject]

Approximately $12 for 4 bowl gaskets, pennies for the o-rings, $30 for float needles. Show me ANYWHERE you can get kits for anywhere near $45 for all four. 80's carbs don't typically have the problems that 70's do with smashed and damaged mixture screws. For a few extra bucks you can get an entire box of like 300 various o-rings from Harbor Freight and never worry about o-rings again. Yes, all this would cost much more from the stealership .... which is why I take my money elsewhere. There are never any question marks when you run Mikuni parts.

[rpgoerlich]

I believe the XJ11 uses the clear tube method for verifying/setting fuel levels in the float bowls. You might check them before you take them off. Would give you a little insight if you have one or more set too high.

[81xsproject]

The standard method can still be used, set them to 23mm. The clear tube works fine, but is 3 times the work without any better results.

[XJOK2PLAY]

tbcfreerider,
I own an XJ, and have gone through my carbs a couple of times. I've also added a Dynojet kit as well. The reason I added the kit? Poor fuel economy.

First, don't put a lot of faith in the accuracy of the fuel bar gauge.
1 bar does NOT necessarily equal 1/4 tank. It should, but I've noticed on mine the first bar goes out way before a quarter tank has been used up.
Then, it goes a lot farther than 40 miles before I drop the next bar.

I went the cleaning method, checked all 4 floats to make sure they weren't sinking or defective, reset all float levels... (remember - the XJ's set up a lot leaner than any other XS...) then guage synched. It ran & started fine, but 30-32 was the best mpg I could get.

After researching, I found these things used to get between 40-45 stock when new! At that point, I decided to try a Dynojet kit, on the advice of a few of my 11 buddies here that had tried one w/ great results.

After the initial install, I saw -0- change in mpg, but a big increase in torque and performance! I was much surprised! But disappointed in the mpg.

But the cool thing about the DJ kit... adjustable needles! XJ's don't have those... (the Specials did...) so we pulled the carbs again, and I lowered the needles to notch 1. (my kit was for stock, unmodified by the way. You can use the other parts in the kit if you have mods done..ie: exhaust, cams...etc.)

Instantly, my mpg's jumped to 40! That was way cool! Now the darn kit pays for itself, and I get the extended range I was after! Now, instead of low fuel warning light @ 120, and out at 150... I get warning light @ 155, reserve at 175 or so, and out @ 200! Way better!

The needles / needle jets wear... usually in the region where they rest in the jet at cruising speed... and that extra space causes the mpg loss.

But... proper synching was a bit of a challenge... we used the 4 guage synch tool method. Main thing we learned was to start w/ carb 3... GET YOUR HIGHEST READING ON THIS ONE FIRST... and tune it by ear carefully... then synch the other 3 carbs to your highest reading you get on #3. Listen carefully to idle quality, and tune each carb to it's sweet spot.

The XJ uses a vaccuum device under the tank that generates a voltage it sends to the ECU under the seat, which in turn electronically controls the timing to the coils. If the vaccuum is low... you'll have all kinds of idleing issues...DAMHIK...

Trick to getting the idle speed properly set lies in proper synching... and higher vac reading is the key to success! Idle speed should be 1200 rpm, and should return there instantly when the throttle is released or blipped. Mine wanted to hang, work right sometimes, stick @ 3200 sometimes... a real drag!

You might want to consider investing in a DJ kit. For me... it was well worth the cost, once I got it dialed in. 8 mpg increase for me was well worth the cost and effort, and might be the answer you're looking for as well to get your mpg's up.

Hope this helps. Good luck w/ your project.
Regards,
Bob

[DGXSER]

Bob, Excellent write up and great info there. However, the needles stopped being adjustable in 1980, the 90-81 Specials and I believe Stds also did not have adjustable needles.

As to checking float level with the tube on the drain bowl, I use both methods. I set my floats by measuring to 23 mm and then verify the level with the tube. So far, the tube method has only proven my measurements to be spot on.

[XSokieSPECIAL]

Nothing personal, but you're dead wrong! Kits are not only a waist of money but quite often lead to VERY poor performance and hard to diagnose issues.

Other than float valves, and bowl gaskets there is ABSOLUTELY NO REASON to put new parts in there. What's there simply needs cleaned. 98% of carbs don't need rebuilt, they need to be cleaned.

I rebuilt mine and I don't think it was a "waist".

There was 3 mixture screws broken off that needed to be replaced and they came in the kits.

These are the kits I used and my bike runs perfectly;http://cgi.ebay.com/ebaymotors/4-YAM...Q5fAccessories