KZ650 - gas mileage

bountyhunter wrote: [If the fuel levels are set too high (float adjust) you can have gas running out all the time.

When I first got the engine running (it was parked for 12+ years), there was overflow on the #2 carb with the accelerator. The problem resolved itself after a cleaning of the petcock. I figured the vacuum had something to do with it. Took the bike out on an easy road today for about 30 miles round trip and noticed the tank was very much full at the end. So I'm going to continue country riding and determine mileage on the next gas stop.

I need to do a few things here regardless. And make sure it's all to spec.

1. a clear tube test
2. valve clearance check
3. carb sync

A cracked or leaking overflow tube might be allowing gasoline to escape unnoticed through the overflow tube onto the road underneath the bike while riding.

When parked, any such discharge would stop when the manual petcock is turned off or the vacuum operated petcock automatically turns off.

Good Fortune!

Could be overflow. I'm thinking of taping a zip lock bag to the ends of the hoses and going for a short 1-2 mile test. Make sure it's not the cause.

Something is definitely wrong..... My 78 KZ650 since 1979 has pretty much mirrored the numbers Ed gave
For you to get only 25 I bet something is leaking somewhere....
Many of the things mentioned do have a negative effect on gas mileage, but I don't believe any of them would be that drastic......

Wouldn't a cracked or split overflow tube keep leaking till the carb bowl was dry or the fuel level went below the damage?? Even if the petcock is shut off??
I would think this should be noticeable under a parked bike

Yeah 25 is terrible. I run my 700cc built motor pretty hard and I get better.

Could be overflow. I'm thinking of taping a zip lock bag to the ends of the hoses and going for a short 1-2 mile test. Make sure it's not the cause.

Put your overflow lines into a small pop bottle and secure it somehow. Drive around a bit and see if you are running any fuel out the overflows. If you plugs are brown and the bike runs well, you've got to be leaking outside the engine.

I'll do the "clear pop bottle" test this weekend. Seemingly my bike runs smooth and has good power, however it's only now that I'm at the fine tune stage of the project with 100 miles of road time. Waiting on a carb sync tool and a compression tester, so far it's been a straight forward project.

Yesterday I noticed the #2 manifold was not attracting as much heat as the other 3 pipes. I tested spark and it is there, could be compression or a dirty jet/clog on the #2 carb. This is something that recently changed and I'm about to start looking for the cause. Hoping I don't have to get into the block for a ring job. The #2 spark plug looked equal to the other 3, with a very small trace of fluid (very small). I cleaned it up, checked the gap and placed it back in.

I'm guessing a carb clog because the tank is on the second tank of gas and had the chance to free up any small rust that was inside. The only filter cage is the stock petcock housing. I have an in-line fuel filter to install.

Might get on the road tomorrow morning for a short ride, otherwise it will be on Sunday.

ezrider714 wrote: Wouldn't a cracked or split overflow tube keep leaking till the carb bowl was dry or the fuel level went below the damage?? Even if the petcock is shut off??
I would think this should be noticeable under a parked bike

Depends on location and extent of the crack.
Discharge after shut-off might go unnoticed, but wouldn't hurt to check for discharge immediately after shut-off.

The point is to assure that there's no crack or joint leakage associated with the overflow tube, as fuel may be partially wasted via the damaged overflow system while riding when it won't be seen discharging from the overflow hose.

Besides visual inspection, a good way to check for an overflow tube crack or loose fitment is to remove the float bowl and fill it with fuel (or water or common household rubbing alcohol or whatever non-viscous liquid of choice), and see whether or not it leaks from the overflow discharge nipple.

Good Fortune!

Update: I'm on the road to better mileage. Firstly, after noticing a not so hot manifold pipe, I traced the problem back to a bad spark plug (after pulling the carbs and checking the #2 for blockage). Running on all 4's certainly placed a big smile on my face. I may have lost some gas into the engine with that valve not firing. Oil changed, new set of Plugs installed (Champion plugs were in there since I started the engine, went through some abuse, nevertheless I think they are junk and will only use NGKs)

Compression test reading 140, 132, 134, 138.
Clear tube test, all levels good.

Next up will be patching 2 small holes in the right side muffler. I think that will help the overall running and mileage. The one by the footpeg is the missing pop rivet size and pouring exhaust, the other is under the tail end of the muffle and about the size of a dime. Looking to use Permatex bandage tape on both. (Update, tried the bandage tape this morning, using a heat gun to avoid having the engine blow it out. Cooked it a few times and let is cool. After running the engine about 5 minutes the weld turned back to liquid and blew off = junk)

Did start going on longer rides in the country, taking it steady and easy on the throttle, mileage is up in the 34 range. I'll going to plan a longer country road trip and record the mileage. Do believe my 650 can be in the 40 range.

My new KZ650 in 1978 got 60mpg every fill for the first 2000 miles, then I reluctantly took it in for the mandatory 2000 mile service. After that it ran worse and got 40mpg. I never to this day figured out what they did wrong and it never ran as good again. I've had several other 650s and generally on a good running one you should see 40-50mpg, on one that is not just right you will see 30-40.

Most recent gas stop. 38.5 MPG, getting better with a few things left to do on the project before she becomes official.

Stock ignition system? If so, have you done the maintenance & adjustment on it?
Does the bike have the stock coils & spark plug wires?

When it's time for a new chain, you can probably go with different sprockets to improve the mpgs.

Muffler repair. From the KZRider archives okc-kent patched a couple of holes by using 18G stainless steel & JB Weld. The after photo is missing, but it did look good. If the patch doesn't hold, I'd probably redo it & use 4 small ss machine screws to secure it.
KZR topic --- Muffler patching with 2 pics
KZR topic --- see replies by okc-kent, as a follow-up to his original repair
nothing to do with mufflers, but see comment by scumbag. After doing a double-take before reading anything, the same thought came to mind. hee

Aftermarket option: Dunstall replica mufflers -->> Verner-650s bike.