bad gas mileage & slow(ish)

[Erik the Red]

So here are my two issues: Rhona's only getting about 26 miles to the gallon and won't break 100 mph. What gives?? I synched the carbs (haven't Colortuned) last fall. She's got 4-1 Jardine pipes, stock airbox, and I believe the main jets are up 1-2 sizes. And she's naked, too.

I read over in the Member's Lounge that Tod and planedick are getting 120+ mph with full fairing. She pulls real well in the main jet rpm range, but just won't produce the zoom at the end.

And 26 mpg just seems way the heck too low. Granted, I'll get lower gas mileage when I'm trying to hit top speed, but this low??

Any suggestions on what to do about each of these problems? I'm scratchin' my head here.

[egsols]

Clutch slippage? Brakes dragging? Both?

[planedick]

Answer

As everyone knows, "stock is best". Modifications like aftermarket pipes will always make it slower. It has been a long time since the carbs were synched too. I think that the jetting is such a PITA if it is done correctly, which means lots of spare jets, many attempts with dyno runs to test the effect. Too many times taking the carbs off and back on for me. I would get too frustrated. Of course I also realize that stock pipes are no longer available so one has few options. I did have good luck with Jardine 4 - 2 slip-ons on the '79 without hurting the top end which is still over 130 with fairing and bags. That engine is especially good with 150 psi compression straight accross and the bike only has about 50k on the clock.

[81xsproject]

Not quite. I run pods and 4-1 and have NO problem getting to 100 real quick like. The only power loss from those mods would be on the low end. Stock is nice because it makes it Barney-simple with no questions. After market pipes aren't the problem as he has already increase the mains.

[mro]

because it makes it Barney-simple

26 mpg is way to low, should be over 30 even riding it on the hard side.
If not sure which way to adjust carbs.
Would get a couple sets of new spark plugs and do the "throttle chop" at a couple different RPM's to see if your running rich or lean.


mro

[DiverRay]

Check the float levels, gas cap, and then check the fuel lines. If the floats are off by just 1 mm, you can drop a few MPG. Make sure the vent in the gas cap is NOT partially plugged, this will cause you to starve for fuel at high RPMs. make sure you don't have a pinch in the fuel lines when the tank is installed. I run mine under the intake side of the carbs too the opposite side bank. Left petcock feeds carbs 3&4, right feeds 1&2. Also check the vents on the carbs. The early models, '78 and '79, vented to the airbox. If the airbox nipples are not drilled, or are plugged, you won't get fuel at high RPM.

[mason79]

when i moved my needles up a notch the gas mileage went down from 33 to 27, runs very well, but i'll eventually go with what ray said, needles back down and lower the floats 1mm see if that fixes the pinging, which with the needle adjustment it did, but the 27 mpg inhales. then again i don't ride that much, i'm just a poser.

[Erik the Red]

Thanks for the replies, all. I just re-did the front brakes, and one is a bit warmer than the other two on the bike, so that'll be taken apart this winter to double check and re-lube. No clutch slippage noise, though.

I'll try getting new plugs and seeing what color they're getting colored in the different rpm ranges. Just to be clear, is this the procedure? 1. get the bike warmed up, 2. run at a particular RPM output for a bit, 3. pull in the clutch, and stop as quick as I (safely) can, 4. pull the plugs on the side of the road and make a note of what color the ceramic is. Also, can I get away with one set of new plugs and just run for longer in an rpm range? I guess that'd tell me if I needed to raise or lower the needles in midrange... right?

The airbox nipples? I don't remember noting any last time I had it apart. Are you talking about where the different air vent lines attach? I'll make sure to double check all the venting, elsewhere too.

[mro]

How to read plugs

click link
http://www.xs11.com/forum/showthread.php?s=&threadid=85

Would first check what Ray said.


mro

[Dragon Tamer]

Don't want to point out the obvious but have you checked the air filter? Last summer I noticed the mileage dropping and noted that the mufflers were running a little dark, power was also dropping a little, resynced the carbs (the Dragon does NOT like to stay in sync) and showed little improvement. Then I had an epiphany, when was the last time I checked the air filter???? WOW, what a difference a little more air made. I am still running at just a little over 36 MPG and I know that she will go well over a hundred very quickly, I do not know if she will still go over the 140+ mark as she used to do (did it on an airport runway BTW) and probably will not find out. This is due to the fact that the air in Wisconsin has gotten to the point over the last few years that it starts to scare me when it gets going past me at any speed over about 90. I think this has something to do with global warming. My wife has another theory but I will not embarass her by bringing it up here.

[morticiaann]

gas mileage & fast

I only got 42 miles on the last tank. It seemed a little faster and I don't see any leaks or anything wrong with it.