Does needle affect main jet size?

[ptnov]

Hi,

Would different needles have different optimum main jet size or is optimum main jet the same for all setups?

Thanks!

 

[maleko89]

Needle impacts main and vice versa...especially during the transition from one to the other. This is why main jet is always set by WOT tests from 7500 rpms to redline.

 

[Rusty McNeil]

Well, its just me or the way I think but there's two answers.

When you say optimum then I say NO needle does not matter. Optimum is when the slide is open all the way and you are running ONLY on the main. At 7500rpm up WOT.
This is the only correct way to select main, and should be the first needle/jet adjustment on a carb.

The main will effect just about every ckt in the carb, so its needs to be done 1st.

Does needle "effect" the main and vice versa. Yes like Mark stated in that, by intended design. The needles job is to interfere with the main jets flow rate at lower than high rpm WOT openings. according to how much the slide is open

But selecting needle and spring setting around the main you have is doing it out of order. Main first always.

 

[Sweetwilliebrownjr]

Different needles might require larger mains, so if you select the correct main with 1 set of needles, and then switch to a different set, then the main may no longer be correct. On my bike, stock needles needed a 162.5, stage 1 needles needed a 160, and stage 7 needles needed a 155. That was all verified with a wideband, and shooting for a 13 to 1 air fuel ratio.

 

[Rusty McNeil]

Different needles might require larger mains, so if you select the correct main with 1 set of needles, and then switch to a different set, then the main may no longer be correct. On my bike, stock needles needed a 162.5, stage 1 needles needed a 160, and stage 7 needles needed a 155. That was all verified with a wideband, and shooting for a 13 to 1 air fuel ratio.

This is where I must disagree somewhat.

A proper main is selected for maximum power when "on the main" only, Meaning the slide is all the out and the needle is not doing ANY metering, allowing the main to flow its max rate. This is usually at 7500 and over with the throttle held wide open. No other settings are in play here except a proper float level.
Done this way because the mains job is to work completely on its own, so its gotta be right for that job, the rest of the settings are built around that, and in order on the following setting in order of throttle openings.

When "on the needle" its working with the main too, but since the main has to work on its own at higher loads, then the needle needs to be selected to work with the main, not vice versa.

If you change mains to make needle settings work then your compromising somewhere else.

You CAN end up with a setup that works fine but you'll be leaving something on the table somewhere.

Hate to sound like a know it all but this is basic CV carb gospel.

Check out factory pros tuning guide or the carb bible sticky on this forum.

 

[one2dmax]

Actually, he is correct! Our testing does show that the stage seven needs a much smaller main then the stock needles with our jet kit anyway.

 

[maleko89]

I ran 175 mains with stock needle and Morley air box and now run 152.5's with stg 7 needles. Dyno showed I was still a bit rich up top.

 

[Sweetwilliebrownjr]

This is where I must disagree somewhat.

A proper main is selected for maximum power when "on the main" only, Meaning the slide is all the out and the needle is not doing ANY metering, allowing the main to flow its max rate. This is usually at 7500 and over with the throttle held wide open. No other settings are in play here except a proper float level.
Done this way because the mains job is to work completely on its own, so its gotta be right for that job, the rest of the settings are built around that, and in order on the following setting in order of throttle openings.

When "on the needle" its working with the main too, but since the main has to work on its own at higher loads, then the needle needs to be selected to work with the main, not vice versa.

If you change mains to make needle settings work then your compromising somewhere else.

You CAN end up with a setup that works fine but you'll be leaving something on the table somewhere.

Hate to sound like a know it all but this is basic CV carb gospel.

Check out factory pros tuning guide or the carb bible sticky on this forum.

Theory and application don't necessarily go hand in hand. With stock needles I had to use larger mains to achieve the same power/ air fuel ratios. I would guess that the stock needles being so blunt on the end is creating some amount of hindrance to the flow of the main.

 

[Rusty McNeil]

Actually, he is correct! Our testing does show that the stage seven needs a much smaller main then the stock needles with our jet kit anyway.

I'm not arguing, trying to learn and understand now on how my thinking is wrong..,,,

How is needle size relevant to proper main jet size when the bike is "on the main" only and receiving fuel from the main while the main it is unimpeded by the needle? Slides fully open, needle not metering, main jet at max design flow rate?

I thought this was the only parameter for proper main selection, in that if the bike is to ever make Max power "On the Main" at WOT high rpm that the main should be selected for that condition only, or else a compromise is made in WOT high rpm condition its adjusted trying to correct issues at lower throttle openings where the needle is in play, subsequently sacrificing something up top?

I realize a smaller main can be used to hide/correct issues created by too aggressive of a needle or too quick of an opening slide, and that the end result can be a very well running bike, but doesn't that sacrifice something when the bike is "in the main" only?

 

[Rusty McNeil]

I would guess that the stock needles being so blunt on the end is creating some amount of hindrance to the flow of the main.

Ok....I can accept that, since the needles tip is still in the hole just a tiny bit, in reality it is STILL having some effect on the function of the main....so your comment makes sense.....

In any case tho I still believe in picking proper main...period....if I had to change needles afterwards, and I believed your above statement (which I do), then I would THEN go back and redo the "on main" test for the needle I had changed to...

I use a DJ WideBand for my testing as well.....,

I guess if I was going to state my "new" position it would be say I think the main needs to be picked exactly as I said before, but with whatever needle we're using, but still be chosen for the "on the main" segment of testing.....In light of what y'all have taught me, if I understand correclty, I believe that if you change to a different type of needle, or even adjust the needle clip position much, then the main needs to be reconsidered as well in light of what y'all are saying.....

Does that sound right?

 

[thor_eyerdhal]

Yes even at high RPM WOT the tip of the needle is still in the hole, so the needle is metering a bit regarding to his diameter tip...

 

[Rusty McNeil]

Thanks guys. Learn something new everyday.

 

[marsmax85]

Thanks guys. Learn something new everyday.

That saying goes to a lot of us on here . LOVE THIS FORUM !!!!!