Gas Mileage, Carb Floats and Colortune

I've been digging around the forums and can't find the exact answer to my problem so I figure I'll ask. I just filled up again after 50 miles! 2.5 gallons! With gas at $3.64 right now and rising, I'd prefer to get this fixed quickly. So here goes.

I put in the colortune and I can't get the bike to go lean. It seems the pilot screws aren't changing the mixture enough to matter. The carbs are CLEAN. I followed Rick's guide to the letter to get the bike running and run it does. Even got them bench sync'd before putting them back on. Only thing I wasn't able to do was adjust the float levels. I measured with them off the bike and they looked ok. I didn't measure with fuel in them just with the "turn them 60 or 70 degrees method" in the Yamaha book.

I was having a problem with the petcock (imagine that) until I used Rick's 19mm socket "adjustment" and that fixed my leaks, but I noticed when it was leaking that I'd get fuel pouring out the overflow tubes onto the garage floor.

So now I'm wondering, if my floats are set too high (so they never shut off the fuel flow) could I be filling up the bowls to the point that my fuel is just running out the overflow on the road? Could this explain the poor mileage? What about the mixture screws? I spun one all the way down and I swear the cylinder didn't hesitate one bit. Pretty blue color on the colortune the whole time! At one point I had the screws 3.5 turns out, I turned them in to 2.5 turns and I don't get a really bad fuel smell in my exhaust anymore.

I read somewhere that if the air filter is clogged, it can cause you to run rich. Is it possible to clean this filter so I can test while I wait for my dealer to order one for me?

I'm not sure it matters but the bike purrs like a kitten. Runs fantastic but gets horrible mileage. I'm at a loss on this one.

Wow that's a lot of questions.

 

Floats that are set physically too "low" will allow a "high" fuel level and will cause an engine to run rich.....with the higher fuel level in the bowl, the same amount of engine vacuum will pull more fuel.

Of course, I assume that all of your fuel and air jets (and main jet needle) are the proper size?

Yes, a clogged air filter will cause it to run rich also. Trying blowing it out with compressed air (from the inside out) and see if that doesn't clean it a bit.

BTW, of course I offer the stock and replacement (aftermarket) 700 air filters, and do keep them in stock:


AIR FILTER ELEMENTS:

af1) OEM and aftermarket stock PLEATED PAPER AIR FILTER ELEMENT. Original factory and reproduction air filter elements lets your engine breathe all the good, clean air it deserves. Dirty, oil or fuel soaked elemtns dramatically reduce the flow of air into the engine, thus resulting in a very rich fuel mixture to the carbs. Aftermarket stock type elements look, fit, and perform just like the factory filters, although some versions may have molded plastic end cases rather than the thin stamped sheetmetal caps as on OEM filters.

HCP692 OEM pleated-paper stock Air Filter Element, fits all XJ700 models.
$ 37.00


af2) Aftermarket K&N high-flow, re-usable HIGH-PERFORMANCE AIR FILTER ELEMENT. Made from 4-6 layers of a tough cotton gauze material bonded between aluminum retainer screens, K&N air filters flow more air than stock pleated paper filters, and can be cleaned, re-oiled, and re-used almost indefinitely, while also fitting inside your stock airbox. Each filter contains two 15ml tubes of filter oil and cleaning/re-oiling instructions. Large 6-ounce spray cans of re-oil fluid and 32-ounce bottles of cleaner are also available below. You normally DO have to re-jet your carbs when replacing a stock paper element with a K&N filter, but individual situations will vary. Always check your plug insulator colors after installing any intake or exhaust modifications to insure proper mixture conditions and settings!


HCP5786 K&N high-flow Air Filter Element, for all 1985-86 XJ700 and XJ750-X models:
$ 40.00


af2) Aftermarket UNI re-usable FOAM AIR FILTER ELEMENT. Made from an open-cell polyurethane foam material, these filters flow more air than stock pleated paper filters, can be cleaned, re-oiled, and re-used almost indefinitely, and fit inside your stock airbox. As contrasted with K&N filters, you normally will NOT have to re-jet your carbs when replacing a stock paper element with a UNI foam filter, but individual situations will vary. Always check your plug insulator colors after installing any intake or exhaust modifications to insure proper mixture conditions and settings!

HCP6476 UNI high-flow Air Filter Element, for all 1985-86 XJ700 and XJ750-X models:
$ 26.00

 

>I put in the colortune and I can't get the bike to go lean.
The idle mixture screws just regulate part of the mixture from the pilot jets.
If you screw them in all the way and it's still too rich then too much is coming in some other way.
Could also be leaking float valves but if the float level is correct then maybe someone replaced the pilot jets with larger ones or drilled them out so they admit too much fuel or they put washers under the tapered needles to raise them up.

 

UPDATE - Ok, so I checked the jet sizes and they are all correct for my bike. I do not however know if some PO didn't drill them out. From the looks of the carbs when I cleaned them I would guess not, but I really have no way of checking. I went back into the carbs and checked the float height, it was a little off so that got adjusted. I can now literally pour fuel into the input pipe and after the carbs fill up, it stops flowing. But I'm still running into the same issue as before. I can screw the pilot mixtures down all the way, completely bottom them out and no change in the engine sound or the colortune plug. I am going to blow out the air filter tomorrow when I get the chance but I ran the bike with the filter off and it was STILL rich!

I'm pretty frustrated and was angrily toying with the idea of trading it in, but I'm going to stick it out. I may even take it to a local shop and beg them to work on it (they refuse to work on anything older than 1990). Is there any other place I can be getting fuel? I have done the clunk test, cleaned the carbs to pristine condition, set EVERYTHING I can find and I'm out of ideas (and running out of patience). I had an excuse for not working on it the past couple of weeks (final exams and a remodeling project in my master bedroom) but it's getting more into riding season and I'm itching to go. Heck, if anyone is in my area, I'll even kick some cash your way to come out to my place and give me a hand.

 

Had a dumb thought this morning. The bike ran horribly when I first got it, which led me to cleaning the carbs. During that process, I found out that the main and pilot (fuel) jets were reversed by the PO. I took a picture of the top of the carbs.

http://picasaweb.google.com/TJames1979/ ... 5378024306

I'm wondering if they managed to swap the air jets as well. What position are they supposed to be in? In the picture, the top is 210, the bottom is 70.

 

i believe that is correct at least thats how mine are

 

From digging around on the site...

http://www.xjbikes.com/Forums/viewtopic ... r+jet.html

Gives the sizes of the jets

http://www.xjbikes.com/Forums/viewtopic ... rt=15.html

Gives the locations of the jets

Unfortunately, mine are correct. That still doesn't solve my problem.

 

Well, from jetting my XR650, I know when you get no change at all with the pilot screw.... That means to big of a pilot jet.

 

Ok, so here's the bottom of the carbs. I think this is the right size. 36.5 for pilot and 107 for the main. From what I can tell, those are in the right place.

http://picasaweb.google.com/TJames1979/ ... 3967958946

 

not to hijack.... but nice BIKE!

are those mufflers, or auto exhaust tips?

 

Thanks for the compliment Zookie. They are mufflers. I have no idea who makes them, they came with the bike. I pulled one off tonight and there's no manufacturer name stamped on it, so I'm going to try the other one. I need to polish them up but that's after I get it running well. They do have a pretty throaty growl to them and if you get on the throttle, it sounds really nice.

But, back to the point. I FINALLY got my cylinders to quit after screwing down the pilot screw. I cleaned the heck out of the air filter and that leaned out the mixture enough for the pilot screws to have an effect. Colortuned it and took it for a ride. It's not perfect but it's driveable again. I'm going to try taking it to work and around a little tomorrow to see if I can get over the 56 miles per tank thing. I'm also going to look into a replacement air filter for it. I know chacal sells them, and I am going to be doing fork seals soon too so I might as well combine it all into one order. I'll keep this updated with the progress.

 

i have the same trouble
i get 68 miles to a tank
i need to check the the things that you have on your posts and see if i can squeeze some more mileage out
im running a 650 seca tturbo in the city

 

Any update to this? I have a 750 Seca that does the same thing. I set the float height and cleaned the carbs in the fall but didn't get a chance to tune the bike. Now I balanced the carbs but I get 25 mpg and very little power (nearly full throttle at 75 mph and won't hole it on an incline).

 

I haven't had the time to work on it in a little while. My wife and I just got back from our honeymoon (about time, been married two years now) and I also had final exams for college and a load of stuff at work taking up way too much time. I'm hoping to get to it either this weekend or early next week. I did add a new air filter (stock replacement) and it seemed to be running better. I need to sync the carbs and colortune one more time. That should tell me how I'm doing. Gas is now $4.07 here and I would like to get riding this summer some time!

 

UPDATE: I sync'd the carbs one more time and colortuned again. It's way better than before. I didn't get the chance to run through a tank of gas to figure out mileage. It's now down to the little turns that will tweak it out. So to summarize, what I've learned from this ordeal.

If the bike is getting bad mileage here's a list of stuff to do.
1) Clean the carbs following RickCoMatic's instructions.
2) Check the airfilter, replace if it's bad.
3) Sync the carbs
4) Colortune
5) Repeat 3 & 4 till running well.

I guess some people would have done that from the start but I'm slow sometimes.