Gas mileage and no to end speed

[BhamminXS]

So I've gone and done the second gear fix but before I began that I noticed I want getting the gas mileage I thought I should on a full tank I'm getting less than 100 miles and the bike well to out at roughly 80 mph give or take, I have synched the carbs, got no back fire or any of the other issues I was having to me the bike seems dialed in yet 100 miles on a standard tank fill up(that's over five gallons) doesn't seem right and I know that to speed for these bikes I'd around 130 mph or so I've heard and read, any idea why I might be having these issues.

[motoman]

So I've gone and done the second gear fix but before I began that I noticed I want getting the gas mileage I thought I should on a full tank I'm getting less than 100 miles and the bike well to out at roughly 80 mph give or take, I have synched the carbs, got no back fire or any of the other issues I was having to me the bike seems dialed in yet 100 miles on a standard tank fill up(that's over five gallons) doesn't seem right and I know that to speed for these bikes I'd around 130 mph or so I've heard and read, any idea why I might be having these issues.

Well, at his point, kinda' hard to speculate since you haven't stated what you have or haven't done engine/carb wise. My initial guess would be since you've stated that bike is weak on the top end and gas consumption is high, that it is running to rich. either float levels are to high or main and pilot jetting has been changed to larger size. Without more info, just an initial guess at this point.

[BhamminXS]

The carbs were gone through thoroughly, I set the float bowls at 22mm if I'm not mistaken, ava the jets were replaced but with oem bikini jets recommended by manufacturer in reflection I haven't gone back in and pulled th he plus again this time after solving the sputtering back fire issue, I wonder could those being either foul or the gap being off cause any of those symptoms.

[IanDMacDonald]

There are so many factors, it's crazy! Brakes dragging? Carbs out of sync? A/F ration not dialed-in? Rings not sealing? Coils out of spec, or not firing 100%? Plugs not gapped properly?

My best guess is a combination of A/F ratio, and bad sync. Just because you don't hear popping, does not mean your carbs are spot-on. Everybody has their method for tuning. Truest method is a dyno, with an O2 bung welded-in, connected to a A/F monitor. Second best in my opinion is a plug chop.

[BA80]

No matter what I do unless I ride at 55 - 65 mph a hundred miles is about as good as it gets. This IS a 40 year old carbureted bike.

Depending on how I've ridden I've gotten as good as about 42 mpg and as bad as 18 without doing anything but ride differently.

[IanDMacDonald]

The carbs were gone through thoroughly, I set the float bowls at 22mm if I'm not mistaken, ava the jets were replaced but with oem bikini jets recommended by manufacturer in reflection I haven't gone back in and pulled th he plus again this time after solving the sputtering back fire issue, I wonder could those being either foul or the gap being off cause any of those symptoms.

Wait a minute, what bike are you talking about?

[TopCatGr58]

Wait a minute, what bike are you talking about?

His Profile says an 80 XS11, but doesn't specify Standard or Special, however he does say a "standard tank fillup of 5 gallons", so I'm guessing it's a standard.

Bhammin, you need to edit your Signature to add your XS11 to the list, and verify it's model style/type.

Aside from what has already been stated, have you done a compression test on the engine? OEM spec is ~140 psi at sea level. Also, if the bike hadn't been run for a long time, and you've just now gotten it back into running condition but have not put very many hundred miles on it, then the rings may not have reseated as well.

Give us a rundown on the things you've worked on, fixed, etc., and we can possibly give you more pointers as to where to go next to tweek better mileage from it. Glad you were able to get the 2nd gear problem fixed!

T.C.

[BhamminXS]

Looking to see how to edit my signature, until then it is a1980 standard xs1100. I've juror it pretty much stock including keeping an airbox instead of pod filters. I've put a couple hundred miles on the bike and once I complete the second gear fix a compression test was the next step on my list so I'm glad you second that thought. I may have to live with the gas mileage the way it is but I just want to be certain I've done everything feasible to assure that that is what it is gonna be. I know it hasn't ran in a year before I got it how long before that I couldn't tell you. While I had the exhaust off for the second gear fix I noticed a couple of exhaust leaks and fixed those, I checked the gap on the plugs and they were within specs but the number three was a lot leaner than the other three not sure why that is but will entertain any ideas from you guys as how to ascertain the cause. You mentioned the compression range at sea lever but as my signature says I'm a little higher than sea level any idea what those ratios would be here?

[TopCatGr58]

Hey again,

Well, according to an online pressure calculator, it says that 140 psi at sea level would be 115 at 1 mile high/5280ft. Wow, didn't realize it would be that big of a drop!?

Okay, there's a good chance that your engine just needs a few more hundred miles to reseat the rings. But, with leaks in the exhaust....they wouldn't happen to have been on the #3 pipe....that could contribute to the leaner reading on your plug, and may change now that you've fixed the pipe. But could also be an off setting of the float on that carb, or could be a vac. leak on that carb....either the intake boot to engine mating, or the vac. synch port cap...they harden and can seem like they are tight, but will leak around the brass tube and the hard rubber cap, or could be the butterfly shaft seals....not sure how you cleaned the carbs....but soaking the bodies in caustic carb cleaner can damage them. Also, the exhaust leaks could have caused the engine to burn an exhaust valve which would let it leak and not create adequate compression?

SO....a good compression check will help to some degree in analyzing the engine's health, but putting a few more hundred miles on it may also help/increase the compression as the rings loosen up and reseat. Remember, to turn the fuel off, remove ALL of the spark plugs, and unplug the TCI or coils as well. Then be sure to have the throttle/carbs WIDE OPEN during the cranking compression testing. Do it dry, and then repeat with a teaspoon of oil in each cylinder after hand turning it around a few rpms to get the oil down around the rings. IF compression increases, then rings may be worn, if pressure doesn't increase AND if it's very low, then would indicate leaky valves.

So...I wouldn't worry too much about the mileage specs right now. Getting the engine up to proper running condition will then help give you the performance and mileage you may be more happy with down the road.

T.C.

PS, I edited your Signature/profile to reflect the 80 G.