Raising the jet needles

[ccs]

Hello All;

I've been advised that I need to raise the jet needles on my GS-850G (I put an aftermarket exhaust on the bike).

Am I correct in presuming I can do this with the carbs on the bike (it looks like I can remove the gas tank and gain access to the tops of all 4 carbs)?

Also... after I remove the tops of the carbs, do I need some sort of sealer or gasket when putting the tops back on?

Any other advice would also be appreciated!!

TIA.

Charles...

 

[mark]

What year is your bike? VM carbs?

 

[ccs]

It's an 82 with CV carbs -- Mikuni BS32SS.

 

[t3rmin]

On my 750 you can indeed get the slides out without removing the carbs. No gaskets/sealer required -- the slides have a diaphragm which acts as its own gasket. Just make sure to line up the notches (you'll see what I mean when you open them up).

 

[80GS750]

hes right, just pull the tops off, dont damage the diaphragm and you can pull the pistons right out..

if no one put in a jet kit, you will need to put in spacers under the needles cause your needles will not have adjusting notches in them.

 

[Nessism]

hes right, just pull the tops off, dont damage the diaphragm and you can pull the pistons right out..

if no one put in a jet kit, you will need to put in spacers under the needles cause your needles will not have adjusting notches in them.

Actually, to raise the needle you need to reduce the thickness of the plastic washer ON TOP of the needle clip since there is a spring pushing up on the needle - by reducing the spacer thickness the needle is push higher up thus effectively raising it.

 

[ccs]

Thanks guys -- I'll be working on this over the weekend -- I hope!

Charles...

 

[80GS750]

Actually, to raise the needle you need to reduce the thickness of the plastic washer ON TOP of the needle clip since there is a spring pushing up on the needle - by reducing the spacer thickness the needle is push higher up thus effectively raising it.

that is correct!

 

[ccs]

Actually, to raise the needle you need to reduce the thickness of the plastic washer ON TOP of the needle clip since there is a spring pushing up on the needle - by reducing the spacer thickness the needle is push higher up thus effectively raising it.

Wow... I've been riding my GS850 all summer long (got the main jets changed, but have not fooled with the jet needles) -- time has just flown by (this post is from Mar and now it's August).

Anyway, I took apart one of the slides and am wondering how to reduce the thickness of the plastic spacer??

1) Should I use some sandpaper -- that might be tough to get all four the same.

2) Should I find some little metal washers and "build" my own spacer? Or, will several washers interfere with smooth operation of the slide?

3) Is there somewhere to get thinner plastic spacers?

Your tips/advice appreciated.

TIA.

Charles...


BTW is anyone riding in the Cincinnati Fire Museum's Memorial Ride (http://www.cincyfiremuseum.com/2007 poster mailer.pdf)?

 

[Guest]

This is what I did until I bought a Dynojet. Go to radio shack and buy some washers that look just like the one under the E clip on the needle. Put washers on the needle until the last one is even with the top of the needle. From there if you take off one washer it's like raising the needle 1/2 notch. Two washers = one notch ect....

 

[ccs]

This is what I did until I bought a Dynojet. Go to radio shack and buy some washers that look just like the one under the E clip on the needle. Put washers on the needle until the last one is even with the top of the needle. From there if you take off one washer it's like raising the needle 1/2 notch. Two washers = one notch ect....

OK... I got my washers at Radio Shack!!

However, the little plastic bushing on the top of the needle does not go all the way to the top. The bushin is only 4 washers thick and the needle will take 2 additional washers to come to the top.

So... I used 3 washers -- thereby raising the needles 1/2 notch -- as far as I can tell.

However, I still have a "flat" spot around 5500-6500 RPM under load -- the engine has that great Suzuki whine until these RPM's are reached and then you can hear the engine sound turn to a "uuuuhhhhh" and the power drops off some, but the bike still pulls OK. Depending on the load and whether I back off the throttle some I'll get "whine", "uuuuhhhhh", "whine", "uuuuhhhhh", "whine", "uuuuhhhhh", "whine", "uuuuhhhhh" until I settle in at whatever speed I want.

Also, I noticed, with the throttle WIDE open, in 4th gear, after about 10-15 seconds of this "uuuuhhhhh" sound, the whine returns and the engine power just JUMPS and I accelerate amazingly fast.

I know re-jetting is more art than science... so any advice on what to try/do next would be appreciated.

TIA.

Charles...

 

[khardrunner14]

Do a plug chop during the "duuuuhhhhh" phase just to be sure you are running lean. If you are a magician at reading plugs, you may even be able to tell how lean/rich you are.

just a thought....

 

[Guest]

I hope you don't have any intake or airbox leaks. Keep taking washers off until you find that sweet spot. I NEVER get it right the first time.
Is the flat spot at wide open throttle? We can't help you jet with RPMs. It totally depends on the throttle position. Idle - 1/8 throttle or less is the pilot circuit. 1/8 throttle to 3/4 or more is the needle circuit. Wide open throttle is main jet only and they do overlap.
If you have an airbox leak these CV carbs depend on air flow to raise the needles and you could have a problem.

Do a search for plug chops. Mark the throttle at 1/2 throttle. Then 1/4 and 3/4. Do plug chops with these markings.

 

[ccs]

I hope you don't have any intake or airbox leaks.

I pulled the aribox and carbs to replace the main jets. Took the airbox apart and soaked the pieces in soapy water (very greasy and dirty), wiped them down, then re-assembled. The intake boots between the airbox and carbs are very supple and I did not see any cracks. Pretty sure I don't have any leaks there.

However there appear to be some *very* minor cracks on the boots between the carbs and the engine. Is there some way to test for air leaks?

Keep taking washers off until you find that sweet spot. I NEVER get it right the first time.

Yep, know I might have to do this -- but was hoping someone with more experiece than me could point me in a direction other than just keep taking washers off.

Is the flat spot at wide open throttle? We can't help you jet with RPMs.
Do a search for plug chops. Mark the throttle at 1/2 throttle. Then 1/4 and 3/4. Do plug chops with these markings.

The problem occurs when I open the throttle *quickly* (and the engine hits 5500-6500 RPM) -- pulls great and sounds great until these RPM's are reached.

I presume it's between 3/4 and full throttle. In 1st and 2nd gear it's not very noticable. In 3rd, 4th, and 5th it's very noticable.

I'll try and do some plug chops over the wekend.

 

[Guest]

If the needle was suspect and you hit the throttle quickly it would bog right way. If it's doing it during full throttle the main jet is suspect.