Poor Fuel Mileage - ZX-11

I'm getting poor mileage with my '94 ZX-11. Many reviews from when it was new and other information I can find all have praise for its excellent mileage - often 45 MPG and better on long trips. A local owner I asked confirmed that he gets that around town. When I first bought it, it had stock jets, a needle shim kit, and a Kerker pipe & igniter. Mileage at that point was really poor - about 23-28 MPG and it was obviously running too rich.

I bought it mainly for a sport/touring ride and so have been restoring it back to OEM status. It now has a stock exhaust, jets & needles, and igniter, but the mileage still isn't that great. My brother's '91 ZX-11 gets much better. On a trip we took to San Antonio in December, his consistently got 8-10 MPG more than mine. I did not adjust the float settings when I had the carbs apart - I haven't ever set the float level on a motorcycle and I wanted to avoid an embarrasing trip in to a repair shop to have it fixed correctly. So the needle settings and conditions are an uknown.

It was running hot in traffic - so much so that I had to shut it off at lights if there was too much of wait. I traced this problem to a bad thermostat which I replaced last month. At some point, one of its former owners appears to have tinkered with the idle needle valve settings (which are clearly marked FACTORY ADJUSTED - DO NOT ADJUST in the service manual) with an ice pick. Idle RPM is unsteady below 1500 so I keep it there.

I need to take it in and have the valves timed and the carbs synchronized and I haven't tested the compression, but it doesn't seem to be burning any oil (it has about 18K miles on it). I have a stock timing wheel ready to install in case an aftermarket one is in it (were those ever replaced with kits?).

Beyond that, does anybody have any suggestions as to what may be the cause?

Edit: Also, what symptoms should I look for if the fuel tank is not properly venting?

UPDATE 3/12/05 - I was pleasantly supprised by 41 MPG on the ride up to Llano today. Maybe it's the new fairings?

If your valves are out of adjustment, fixing those will go along ways in tuning for the bike.. Ive never heard of that causing milage problems but it can make a big difference in the way the bike is running/tuning. Is it showing any semptoms of running rich, any black smoke, strong smell of fuel in the exahust. Have you checked to make sure you not leaking the fuel from anywhere, petcock carb fittings ect? The idle problems below 1500 along with the other issues you list sounds like you need to have a once over on the carbs again, make sure you check all your vaccume caps and any other sources for air leakage.

I dont really have any other suggestions. Good luck and keep us posted.

If you get stuck, I recommend Johnny Cheese Performance in Pflugerville or AF1 Racing. Both do excellent tuning with dynomometers. Johnny uses a dynojet which seems to be the industry standard and AF1 uses a Factory Pro dyno. Johnny probably has actual experience with the Kwak from his days at Woods years ago.

I was just perusing brd's post about the float needles when he mentioned the fuel venting problem. When I open the tank for refuelling, there is an obvious release of pressure and after shutting it off, I can hear the slow leak from the tank as the fuel is heated by the engine. How normal is that?

This poor thing looks like its first owner cared well for it, but was subsequently trashed by later owners. Overall it's a good platform for restoration and hopefully it isn't serious mechanical trouble - just leaks and adjustments like you suggest.

Thanks for the feedback and I'll keep you posted.

Edit - My calibrated nose tells me that it's still running rich at idle, but others disagree. The plugs look darker than I'd like.

Edit 2: Thanks for the dyno contact info.

I would first beg, buy, borrow or steal a carb sync gage. Beyond that, a good carb cleaning and adjustment might be in order. At 18k, the valves are probably due for adjustment as well. Not hard to do. Per the manual, I do mine every 6k. It's coming up due again as I also just turned over 18k on mine.
Lots of info on ZX11 here:
www.bigbikeworld.com

Whistling Kwaks are normal. Mine have all done it even as the temperature in the garage rose and fell. A venting problem would starve it for fuel. I have got synch gauges if youd like to borrow them.

If you are experiencing this at more or less constant highway speeds, my guess is that you may have worn emulsion tubes, mis-set needles too large of a pilot jet, or mis-set a/f screws. Find the stock sizes and settings for all of them and reconfirm it all. While you are there, emulsion tubes are cheap.

Next things to confirm would be valve timing, valve lash and condition of the cam chain and tensioner. Dark plugs tell you a lot. Are you sure it still has the stock cams? A dyno run is $40 at Johnny Cheese's and will be invaluable in saving time and money. He will make recommendations on where to go.

Because of all the performance type work done (jets, pipes, exhaust, etc) and then your taking it all off, I would recommend taking the bike to a shop that has a dyno and gas analyzer. Running the bike on a dyno and checking the exhaust gas levels is the only way to ensure that the bike isn't running too rich or lean. A dyno run may also point out other items that may need to be fixed or adjusted. It may sound like a lot of work, but it will probably be worth it in the long run.

But, before doing any performance type changes, do a complete basic tune-up to ensure that basic engine and carburation issues have been addressed. Adjust the valves, check out the ignition system to ensure that it is working correctly (especially check the plug wires to ensure they don't have too much resistance), syncronize the carburators, check the intake manifolds for air leaks, ensure that the carb's float height is correct, clean the air filter, replace the spark plugs, etc.

Carl

Thanks everbody for the input! I'll keep you all posted.

Oh, and TXMedic - the old emulsion tubes were OK, but I had oredered a new set along with the jets and needles just in case - forgot to mention that. Overall condition of the carb castings (except the aforementioned mangling of the idle air adjust screws) is OK.

CMC - My older brother's '91 ZX ran really well after the valvetrain adjustment and timing - I'm going to have that done in the next few weeks. The exterior condition of the plug wires looks OK, but you're right - until they're tested I won't know for sure. After all, they're over 10 years old.

So tell me - after what % of newly installed parts is a bike considered "new" again?

Add float height to the list of things to check. I have a gauge for that as well.