Topic: i have been getting 32 miles on my bike--1980 cb650..ways to improve mileage.

[cb650 bobber]

ways to improve or that I should be looking at on my bike that might not be set up right.....I am running seafoam right now...1980 cb650

[Soos]

Is your cb650 using CV carbs, or the Mechanical slide(the same as the '79650, and all the 750's)

The first thing I would do is after warming her up, do a valve adjustment.(read on Hondamans recommendations as to why he recommends increasing the exhaust valve clearance to 0.005)
then set your timing.
check all hoses coming from the motor.
Check your aircleaner.
Check the condition of your spark plugs(verify all wires are securely attached, and gap is corect, color is not too rich or lean)
Then I would synchronize them.

With stock carbs, you should be able to AT LEAST be able to get 45.
The best I have ever gotten was around 60's MPG.
I average at the moment about 47-52 mpg, depending on whether i use fifth gear on the highway or not. 

A properly tuned 650 will get very good gas milage.


l8r

[eurban]

Are you running stock front and rear sprocket sizes?
Are you going into 5th gear?
Are your brakes grabbing /  wheels spinning freely?
Fuel leak?
Have you modified your carbs?
Have you cleaned / adjusted your carbs?
Air cleaner condition?
Ignition timing / air gap correct?
Condition of spark plugs,  plug wires, and ends?
Valve clearances properly adjusted?
Cylinder Compression?

[cb650 bobber]

I have modified nothing replaced spark plugs and oil in the last month...air cleaner looks like it in good shape not to much dirt in it...

[Soos]

Concerning cylinder compression, how many miles on the bike?
If it's a bike that has not set for too many years without running it should be ok, but you may want to check just in case.
But if the PO had it sitting for more than 5 years(without running), you want to get that checked.

Definately check/adjust valve clearances.

The cb650 is a electronic timing, so there is no air gap to speak of.

Does your advancer unit work properly?

Definately check the float bowls as eurban stated. if there is sediment, you will need to pull the slow jets, and clean them thoroughly(if you can) as well as the main jets/emulsion tubes.


One other question... do you have a manual, and how well are you at wrenching?

If you are mechanically adept, all the adjustments you need to do are possible. If not.... get ready to contact a local bike shop, or hope there is a member here close to you and willing to help you tune that baby up.
You may need to buy a few tools, but 100.00 will buy all specialized tools you should need for a good tume up, assuming you already have a set of metric wrenches and sockets, and a few good screwdrivers.



l8r

[eurban]

The cb650 is a electronic timing, so there is no air gap to speak of.

Yes it does have an electronic iginition and there is indeed an "air gap" between the spinning sensor and fixed pickup that is has a spec in the manual and is adjustable.  Probably not his issue though.

[Soos]

I stand corrected.

And after refering to my manual on this...
Electronic ignition is the correct term, and according to my manual, only the CB650 Custom models would you need to check the air-gap.

After reading this, i though since I own a '79cb650, amnd a 80(title says '81)cb650Custom, I though I would check the difference if any.

My '79 cb650 has no adjustment for side to side play for clearance adjustment between the pulse generator and the projection of the crankshaft. the plate they are attached to is a very close fit, so adjustment there would only be about  0.005 of adjustment.

My '80cb650Custom however, you can move the pulse generator enough to have it off center  or to adjust it so it has the same gap on both pickups.
My custom has roughly about 0.020-0.030 of play to adjust with.

Sloppy castings? Either that of looser fitting parts. didn't measure the OD of the pulse generators on both bikes to check.

l8r



Any luck getting your bike to do better MPG wise?

[super pasty white guy]

Have you gone through and done a full tune-up?  That'd be the first place to start before digging deeper.

dave