Bike seems to stumble in low RPM

[Anonymous]

My 81 GS650G is now running after a good cleaning, and tweaking od the mix screws.

My question is this:

From idle to 3K RPM it seems to be unresonsive. It takes alot of throttle to get her moving, but she doesn't really seem to accelerate quickly. Once i hit 3K, or about 1/3 throttle, she almost literally jumps out from under me and roars off.

I have some limited work tuning in a carb, but this is the first time I've worked on a multi-carb system.

My first impression is that the pilots are either too small, or have built up lacquer, etc. clogging them.
Secondly, I wonder if just synching the carbs would solve this. Would a sync tend to affect the lower end?

I lean towards pilot jets since it seems this way in all gears, but depends on throttle position.

Currently my mix screws are set at about 3.5 turns, give or take a slight "tweak".

[earlfor]

Re: Bike seems to stumble in low RPM

I would put new plugs in it, clean the air filter and then synch the carbs before considering any carb jetting changes.
I would also check to see how much voltage I had at the coil + terminals. You could have some corrosion in the electrical system and consequent resistance in your ignition wires to the coils. As rpm comes up, available voltage increases and it could be simply increasing enough to overcome resistance resulting in a normally operating ignition system at higher rpm. Only alter the carbs when you are sure everything else if correct.

Earl

My 81 GS650G is now running after a good cleaning, and tweaking od the mix screws.

My question is this:

From idle to 3K RPM it seems to be unresonsive. It takes alot of throttle to get her moving, but she doesn't really seem to accelerate quickly. Once i hit 3K, or about 1/3 throttle, she almost literally jumps out from under me and roars off.

I have some limited work tuning in a carb, but this is the first time I've worked on a multi-carb system.

My first impression is that the pilots are either too small, or have built up lacquer, etc. clogging them.
Secondly, I wonder if just synching the carbs would solve this. Would a sync tend to affect the lower end?

I lean towards pilot jets since it seems this way in all gears, but depends on throttle position.

Currently my mix screws are set at about 3.5 turns, give or take a slight "tweak".

[Anonymous]

Thanks Earl. What voltage would be good? And do I ground to the negative terminal and check the positive? Or ground to the frame and check the positive? I'm not very experienced with a voltmeter if you couldn't tell!

[earlfor]

Take the orange and white wire off the coil + terminal. That is a hot/positive lead. Turn the ignition key to on. The wire will be energized. Put the + lead of the meter into the connector on the wire end and the neg lead of the meter on the bare metal of the engine. That will give you a voltage reading of what is going to your coil. Do this for both coils. The voltages should be the same. Now, put the voltmeter leads on the battery terminals. If you have a fully charged battery, it should read about 12.5 (more or less, depending on condition of the battery) If you have 12.5 at the battery and the meter only shows 11.1 (or whatever) at the coils, you know you have a problem. If the wiring is in good condition and the harness connectors are clean and the switches inbetween are in good condition, all the readings should be about the same. I have about 1/4 volt drop in voltage on my 750 due to wiring harness resistance. Or in other words, my battery reads 12.5 at the terminals and the orange and white leads that power my coils read 12.25 volts available.

Earl

Thanks Earl. What voltage would be good? And do I ground to the negative terminal and check the positive? Or ground to the frame and check the positive? I'm not very experienced with a voltmeter if you couldn't tell!

[Anonymous]

Once again, thanks Earl. You Da Man! I'll give that a try later today and let y'all know.

[Anonymous]

Earl,

I tried to read the voltages from the orange/white wires. The only time i got any numbers was when I started the bike. With just the ignition on, I get nothing. With the bike running, I get numbers that flucuate, wit hthe high point being almost 13.

But with just the ignition turned on, nothing is going on the orange/white.

[earlfor]

Something is very strange here. With the ignition switched to on, the ignition system must be energized. The engine couldnt run if it wasnt. Try doing the test again, but this time with the voltmeter negative lead wire connected to the battery negative terminal. Maybe you just didnt have a good ground.
Be sure the kill switch is in the ON position. If still nothing with the ignition switch on and the kill switch on, try flipping the kill switch back and forth while holding the + test lead on the orange/white coil wire.. If you get a fluctuating meter needle, then the problem is in the kill switch. If you still get nothing, try bridging the kill function. This will eliminate it from the loop for test purposes. To do that, in the headlight shell you will find a 3 wire white plastic connector bar that measures about 1/2 x 1/2 x 1 1/2".
There will be three wires going into it and three wires coming out of it.
from left to right, the colors on one side of the plug will be orange, orange/white, green/yellow. From left to right the the opposing colors will be orange/white, orange white, green/yellow. On the orange/white, orange/white. green/yellow side, put a jumper wire between the two orange/white wires. This will remove the kill switch function from the circuit. Then switch the ignition to on, and check for voltage at the coils on the orange/white wires.

Let me know whatcha get.

Earl

Earl,

I tried to read the voltages from the orange/white wires. The only time i got any numbers was when I started the bike. With just the ignition on, I get nothing. With the bike running, I get numbers that flucuate, wit hthe high point being almost 13.

But with just the ignition turned on, nothing is going on the orange/white.

Earl,

I tried to read the voltages from the orange/white wires. The only time i got any numbers was when I started the bike. With just the ignition on, I get nothing. With the bike running, I get numbers that flucuate, wit hthe high point being almost 13.

But with just the ignition turned on, nothing is going on the orange/white.