Gas mileage

I have been riding with my son and his bike is running great but we checked his mileage yesterday after a long ride and he is only getting around 30 mpg on a 78 KZ650 :whistle: compared to me getting 46+mpg on my 78 KZ1000 .

He's a new rider so I'm leading and only going 55 to 60 mph tops on curvy country roads.

My bike is purring at around 3500 rpm's and his is somewhere around 5200 rpm's with a stock chain and sprocket.

Is this normal ?

I did step up the main jets one size from 102.5 to 105 because he is using a Vance and Hines 4 to 1 now but he still has the stock air box.

I was hoping for much better mileage.

JD

Not normal at all. Should be in the mid-40s, depending on his riding style, of course. How do the plugs look?

Agree, not normal. Rpm's sound high for his and low for yours if gearing is stock. I'm at 3,500 with 18/38 gearing with the 180-55/17 tire between 55 and 60 mph, gps isnt all that consistant. I'm up to around 35 mpg on my turbo.

Les

Not normal.

If his KZ650 is a B or C model it should have 16 / 42 sprockets. The D model is different; maybe Martin can provide correct sprocket sizes for that. In either case, at 60 mph the rpm should be right around 4500. At 5200 rpm the bike should be traveling 69 mph. From the rpm / mph you gave I suspect his clutch is slipping. Adjust it using the instructions in the manual and see if the rpm moves to 4500 at 60 mph. If not, check the number of teeth on each sprocket to see if someone made a switcheroo. If the sprockets are correct and adjusting the clutch does not bring the rpm down it may be time to replace the clutch. What oil is he using? If it's not JASO-MA compliant it may have coated the clutch plates with moly. Ed

One other thought, is it possible someone worked on the clutch and didn't properly tighten the clutch pressure plate bolts (the ones the springs wrap around)to the specified torque settings? They really must be tightened using a torque wrench and the factory torque specs.

According to the diagrams at Kawasaki.com, the stock 650D SR sprockets are 16T Fr & 40T Rr (40/16=2.5). For the B/C models: 42/16=2.625. The sprockets on my 81 650-CSR are 13-33 (33/13=2.538). I don't know if there are any differences in the transmissions?

81 650-CSR. With a stock airbox, KZ750 exhaust system, & 92.5 main jets, I typically get 45-52 mpgs.
Other stuff: the tires are correctly sized & properly aired up. Stock electronic ignition system w Dyna green coils & spark plug wire set. The spark plugs are a good tan color. The fuel is 10% ethanol & my fuel economy is the same w 87, 89, or 93 octane.

OK, it looks like a bad/fouled plug on # 2 cylinder .
I swapped it with a good plug and it is sparking fine on # 2

It looks like the other three plugs are running too hot, Z1E sent us NGK B6E S but the book calls for NGK B7E S , are the B6E's hotter then the B7E's ?




Also checked the rear sprocket and it is a 42 tooth, Zach said that he made a mistake when he told me the RPM's vs MPH, turns out it is as Ed says at 4500 at 60 mph.

After we get fresh plugs and change out the oil I'll take it for a spin and see what I come up with,
When I rode it before I really hammered it and took it way passed the speed and RPM's that Zach will go hopefully for a long time and it had no clutch slippage. B)as a matter of fact she screamed , this bike is probably quicker off the line and much better handling then the 1000

B6ES is too hot to use in the KZ650. You should use either NGK B7ES or ND W22ES-U plugs. They are the correct heat range for the engine. Personally, I prefer the ND W22ES-U plugs. Ed

Thanks Ed that's just what I needed to hear, time to take a ride into town