Terrible Gas Mileage

[p_s]

What else could it be? The throttle slides are fine. I just don't get it...

Brake drag?

[Norseman]

I don't think so - I just went out and checked. Front spins freely, and rear spins with a little resistance (I assume from shaft drive). But I definitely don't feel any drag from calipers.

[themess]

With a drive shaft the rear wheel won't spin.

The magazine tests from 1981 and 1982 reported 4 seconds for 0 to 60, and a 13 second quarter mile. Sounds right to me. I once pulled a wheelie using throttle alone - no pulling back or dumping the clutch. If your 650G doesn't accellerate quite briskly, there are serious tuning problems. Of course, with that mileage, you already know that you have serious problems.

I think that testing compression is next. Sears sells testers starting under $30. Harbor Freight starts at $10. Ebay has a KD one for $10. White smoke is a bad sign.

How many miles on it?

[jadesystem]

While you are at the carburetion topic, and you decide to remove and inspect the carbs again, try to check the pilot and main jets for the
value vs the correct stock value in the manual. Check the seating of
the Needle Valve.

You can use a 8-10mm metric hose to the gas inlet nipple, and blow
thru the hose into the float bowl with the bottom float bowl removed.
Move the float up and down to verify it seats and cuts off. Once the
float is level it should cut-off whereas you cannot blow air thru it as
the needle valve is seated. If not, bend the tang on the float so it
cuts-off at level. Check all the varbs this way. You are simulating the
gas and verifying the needle valve is adjusted correctly. Otherwise
gas will overflow and become wasted - the metering function of the
needle valve will be defeated.

You can read your plugs too to see if they are heavily carboned. It
could be running too rich. Seat the air/fuel mixture screws CW, then
CCW 1.5-2 turns. This is a static adjustment. It is better to run slightly
rich than too lean.

When you do your compression test, take out all of the plugs so that
the engine turns over easier. Make sure your battery is fully charged.
The compression results should be within 20-25psi from each other on average. if it is way off, something is wrong with your rings or valve
seats. One way to isolate this to point to rings or valves is to pump
it up with compressed air with both intake and exhaust valves closed.
If air seaps to the bottom thru the PVC valve, it is rings. If it leaks at
the top, it is the valves. Of course, the valve cover must be off to
hear and see it (bubbles thru some excess oil).

Good luck to you :-D

[Norseman]

Much appreciated, Tom and Jadesystem. Tom, after reading the info on acceleration I definitely don't have that kind of power on take-off! I did a compression test and got: #1=135, #2=165, #3=160, #4=130. Not the greatest on outboard cylinders, and I will eventually re-bore/hone/new rings, but that alone shouldn't cause excessive fuel use or dramatic power loss. So I guess I remove carbs and clean again, and check the jet numbers.

Now, one more piece of information - once in awhile, during drving, suddenly the bike will abruptly really out white smoke - I mean a real cloud. Stop the bike, shut it down, wait a few seconds, and start it up again, and it will be fine.

Any ideas on this?

[jadesystem]

The carbs are usually the culprit regarding performance and fuel efficiency. The electronics (other than the RR), engine, and
everything else is bulletproof. 95% of the time. it is issues with
the carbs. That is where everything gets mixed, metered, and
tuned for optimum performance together with the subsystems
of the electronics and the mechanical aspects and synchronization
of the engine.

You probably will have to rebuild the carbs again. The best carb kits
for any GS series bikes I've experienced is with George Fix on Ebay
AND on thise GSR website. His carb kits are complete and not just
a few O-rings. Don't be fooled by junk kits out there made in China.
George only sells the best !! I've gotten very good at rebuilding
these carbs.

Check the carb bodies too for hairline cracks. You'll see it all when
you replace everything with these complete kits. Don't buy half kits
with just a few gaskets and O-rings - buy the complete kits. I've
always wanted to make my own clear float bowls with a level line
drawn so I can see the gas level in each bowl. You can also see dirt
inside or blockage.

Good luck on your project.

Talk to you soon :-D

[GQROD]

Auto Zone has one that is the cheapest i have seen for $40.00, and it has the correct size adapters for motorcycles which should have a 12mm and even a 10mm, the higher numbered ones are for auto spark plugs. Sears carries one but is $60.00, They usually have it behind the counter so ask the salesperson. Normally you would take three readings from each cylinder and use the average of the three readings as the compression figure for each cylinder, but other members could provide clearer direction.

[chef1366]

Did this bike sit for a long period of time?

[daverx1]

hole in the vacuum pet cock diaphragm. check the plug color on #2 cyl. of it is darker than the rest the petcock is to blame.