Flat spot! (yes another!) and high fuel use

[bikerfox]

Hey everyone, I have a flat spot around 5k to 6k, and at 6k in 5th the bike just launches, like its got all its original power and THEN some!

Acceleration through 5k is pretty good, though nothing like 6k through red line!

The bike also seems to get about 20mpg and getting worse. It pops on deccel more than it ever has, and thats getting worse too (rather quickly)

The bike is my only transportation to work right now Could it be the plug wires are bad? They felt kinda leaky last time i came in contact with them
Would that cause abnormal fuel use?

The carbs have been cleaned, and i havent yet checked the valves, though compression was decent when i checked that

Thanks in advance!
Mike

[Nessism]

What kind of bike and any mods?

[psyguy]

and i though my 30mpg was bad!!!

what do you do to it, ride it exclusively in the red tach area?

[trippivot]

re-set your points

[bikerfox]

completely forgot the model, sorry!

1980 GS850G

[ryonker]

Yeah, 20 mpg's is really low. Now that mine is tuned and running well, I consistantly get 45 to 48 mpg. I have a 79 so I am not sure if I can help you.

I found doing the valves is really key...also the coil relay mod.

Good luck!

[badbrown]

What are your mods? Check my new thead on my fixes. Alot of my flat spot issues were because of my mods, wrong settings, partial neglect of the electrical, and ignition. My high fuel consumption was beacause of wrong float height ( set it to stock), and too large main jets. On the VM carbs.

[bikerfox]

oh yeah, that too! nah, no mods, i dont like to mess with em much

Anyway, i took it out to try messing with the choke, and remembered some relevant information! I dont really notice the flat spot in first or second, 3rd its kinda there, but not really a problem, 4th it gets bigger but still responsive, and 5th is where the wall of nothing is.

It will still accelerate through the flat spot to get to that 6k+ boost, but its veeeeery slow. I -CAN- however, sneak past it in 4th.

When i choke it while idling, it dies, completely. If im moving, it tries to die until it gets past that and then revs up and fast idles while im moving

While im on the highway, if i yank the choke in the flat spot, it doesnt really change much, but it feels like it loses yet more power.

As for the plugs, as far as i can tell its a little lean, but not major

Thanks again,
BF

[badbrown]

I'd say if you use the choke and it dies you are too rich. Check them plugs. Also the lower gears are enough to mask a problem because you can rev through the flat spot. Your carbs then should be set to completly the stock setting. Stock pilot jet. Stock needle height. Stock main jet. Sock turns on the air and fuel screws. Carbs clean synced and plug chopped. Check all air seals and ignition voltage eith the volt meter.

[bikerfox]

Ok, news!

Compression test shows 120 after 3 cycles on all 4, 3 and 4 got up to 145 a little slower after that.

Plugs: 1, 3 and 4 are lean on idle, and here is where some of my fuel goes...
2 is completely rich on idle. I pull the vacuum hose off the carb and sure enough, wet with fuel! Though not leaking any more when not under vacuum.

Did some plug chops, couldnt get enough road to break past that wall, but around 5,000 to 5500, 1 and 4 are lean, 2 and 3 are rich, 3 is even slightly wet with fuel. Below that, 1 and 4 are still lean, 2 is still rich, and 3 is good!

Thanks for the help, folks

[psyguy]

those compression figures are good

the results you posted on the plug chops are not consistent enough to suggest wrong jetting, so most likely dirty carbs and/or problems with the spark

it sound like you have a bad fuel tap so, i'd replace that first and then get onto thoroughly cleaning the carbs (meaning taking them appart, etc, there's a tutorial on the home page)

make sure the plug caps are in good shape and have a good contact with the coil leads

measure the voltage at the coils


btw, plug chops are better done at a given throttle position (rather then at a given rpm)