What rpm range to certain jets affect.

[nisom512]

what rpm range do certain jets( main, pilot, and needle height) get used at.

I guess I dont really know how to ask the question. so does a larger main jet effect the lower rpms or the higher?

I am running lean and I put in larger mains and pilots and I didnt raise my needle height. I am still running a little lean so I think I should raise my needle height.

how do I raise the needle height? can I just go to ACE and buy a washer to put in or what?

i am asking for my 81 gs850 so it has cv carbs

[crapwacker]

It's more about throttle position that RPM. I think there is something posted on here somewhere about which circuits work where and check Mikuni website. Most needles have a clip with several slots cut into them. move the clip down to raise the needle

[man8woman]

It's a reference to throttle position rather than rpm.
3/4 to full throttle is main jet. 1/4 to 3/4 needle and needle jet and there is overlap between them.

[crapwacker]

http://www.mikuni.com/pdf/vmmanual.pdf

[nisom512]

sorry this is for cv carbs not the vm ones they are on my 81 gs850

[maro]

http://www.factorypro.com/tech_tuning_procedures/tuning_carbtune,CV,high_rpm_engines.html

[Steve]

As mentioned, it has more to do with throttle position than engine speed. What's the difference, you ask?
How much throttle does it take to hit 5,000 rpm on the centerstand, in neutral?
How much throttle does it take to hit 5,000 rpm in fifth gear, going up a hill?

On your BS carbs (the BS-series carbs are a CV-type of carb), the idle mixture is preset by the pilot air jet in the carb intake and the pilot fuel jet in the float bowl, near the main jet, under the rubber plug. How much of that mixture is allowed to flow is controlled by the idle mixture adjustment screw, which is on top of the outlet of the carb. This is what supplies most of the fuel mix during idle and low-throttle running. As the throttle is opened, this circuit can not keep up with demand. The slide starts rising, lifting the jet needle out of the needle jet (confusing, isn't it?), allowing more mixture to flow. As the throttle is opened far enough for the slides to lift the jet needles all the way up, the fuel is going to be controlled by the main jets. All of the fuel has been going through the main jet up to this point, anyway, but the other jets flow less fuel and limit their own circuits. In the end, it is the main jet that does all the limiting.

This is why you have to mark your throttle grip to do plug chops. You need to have a specific, repeatable throttle opening to do consistent checks.
Here is how I marked my wife's bike:


The markings are, from top to bottom:
idle
1/8
1/4
1/2
full

.

[ryonker]

As mentioned, it has more to do with throttle position than engine speed. What's the difference, you ask?
How much throttle does it take to hit 5,000 rpm on the centerstand, in neutral?
How much throttle does it take to hit 5,000 rpm in fifth gear, going up a hill?

On your BS carbs (the BS-series carbs are a CV-type of carb), the idle mixture is preset by the pilot air jet in the carb intake and the pilot fuel jet in the float bowl, near the main jet, under the rubber plug. How much of that mixture is allowed to flow is controlled by the idle mixture adjustment screw, which is on top of the outlet of the carb. This is what supplies most of the fuel mix during idle and low-throttle running. As the throttle is opened, this circuit can not keep up with demand. The slide starts rising, lifting the jet needle out of the needle jet (confusing, isn't it?), allowing more mixture to flow. As the throttle is opened far enough for the slides to lift the jet needles all the way up, the fuel is going to be controlled by the main jets. All of the fuel has been going through the main jet up to this point, anyway, but the other jets flow less fuel and limit their own circuits. In the end, it is the main jet that does all the limiting.

This is why you have to mark your throttle grip to do plug chops. You need to have a specific, repeatable throttle opening to do consistent checks.
Here is how I marked my wife's bike:


The markings are, from top to bottom:
idle
1/8
1/4
1/2
full

.

Wow. Nice explaination Steve. You are are master GS teacher!

Rick (friend of Jakes)

[Steve]

Wow. Nice explaination Steve. You are are master GS teacher!

Thanks, Grasshopper.

I don't know if it's because of, or in spite of the fact that about a year ago, one of the newbs pretty much accused me of being one of the most worthless posters on the board. And, I'm more of a hands-on guy that does not mind some details, so I try to show you what I'm talking about.

.

[chef1366]

Thanks, Grasshopper.

I don't know if it's because of, or in spite of the fact that about a year ago, one of the newbs pretty much accused me of being one of the most worthless posters on the board. And, I'm more of a hands-on guy that does not mind some details, so I try to show you what I'm talking about.

.

What's changed?

[TheCafeKid]

Thanks, Grasshopper.

I don't know if it's because of, or in spite of the fact that about a year ago, one of the newbs pretty much accused me of being one of the most worthless posters on the board. And, I'm more of a hands-on guy that does not mind some details, so I try to show you what I'm talking about.

.

Woah woah woah... Hands off the Newbs there buddy...there's been enough Teacher/Student scandals of late

[Steve]

What's changed?

I haven't seen any posts from him lately, and I'm still here.

[Steve]

Woah woah woah... Hands off the Newbs there buddy...there's been enough Teacher/Student scandals of late

.....................................

[nisom512]

well that is werid then cause I have a 130 main on right now with a 45 pilot and I was wondering why I am still back firing. and running lean. Yonker and I are gunna get the timing just right cause it wouldnt turn to the point we needed it at the first time so we are gunna do that and sync the carbs tomarrow and hopfully that will help. I did bench sync them so a full sync shouldnt change much.

so raising the needle wont help in the higher rpm or any for that matter? cause even tho you say the main does all the work which I know and understand if you have the needle a little bit higher that would there fore allow more fuel to flow in at any given time. here is an equation to explain

A=air
1=needle at stock hight
2=needle raised up
(use numbers as actual numbers and representations of the needle hight)
with a raised needle Mixture=A+2x
with needle at stock hight Mixture=A+1x

the amount of fuel is going to be larger with the needle raised in my theory

Thank you
Jake

[chef1366]

Go to radio shack and get the assorted small washer kit.
Find the washer that is the same size as the one above the spring on the needle.
Take off the spacer on the top of the needle and replace the same space with the washers. Remove 3 washers and I bet this richens the needle circuit.