Topic: Fun with jetting

[JS550]

So over the last little while Ive been trying out different jetting on my bike. I didnt really gauge the mileage, but its not hard to guess that its better with the smaller size. Anyway, my bike is 75 750K, unknown mileage, but runs good, doesnt smoke or burn oil. It has a 4 into 1 that could use a repack(maybe later), K&N with airbox modded a little, a Hondaman ignition, & I just put in fresh set Denso plugs a few weeks ago. Stock was #105s, I swapped in #120s last year & rode a little with them this year. I put #110s in & drilled out the top four holes in the emulsifier tubes, then retried the #120s. I just went back to the #110s, my bike seems to like them better. The #120s seemed to have a bit of an un-eveness in the mid to upper RPM range, where as the #110s are smooth all the way through. It also seemed like it was loading up a bit at lower RPMs. With the #110s its good. But, if its loading up at the lower RPMs, isnt that the slow jets? Plugs loo great with the #110s, light brown/tan and were dark grey/black with the #120s. Another good thing that came out of this is that I know my carbs are clean!

[Laminar]

Did you do plug chops at specific throttle openings to determine which fuel circuits are running lean/good/rich? There's more to tuning than just main jets.

[razor02097]

If it is lean with the #110; have you tried switching to the #120s and adjusting the air or fuel screws (depending on the type of carbs you have) leaner?

[Laminar]

If it is lean with the #110; have you tried switching to the #120s and adjusting the air or fuel screws (depending on the type of carbs you have) leaner?

...

Plugs loo great with the #110s, light brown/tan and were dark grey/black with the #120s.

[JS550]

Didnt do a plug chop. Im not getting that far into it right now. The plugs look better with the 110s & the bike runs better with the 110s. Maybe do a chop later this summer. If I were taking it to the track I might worry more about getting every last bit outta it. But for now its running great for an old bike. I did adjust the mix screws as I went, tried different settings. Just kinda sharing my findings. But, I did have a question about what RPM the slow jets are working in? I understand there is more to tuning then jetting, but Im not looking for that last pony hiding in there! Im not knocking anyone or trying for a big long discussion about tuning. No offense.

[razor02097]

If it is lean with the #110; have you tried switching to the #120s and adjusting the air or fuel screws (depending on the type of carbs you have) leaner?

...

Plugs loo great with the #110s, light brown/tan and were dark grey/black with the #120s.

Good job you can use quotes

too bad your post gave nothing constructive.

[TwoTired]

If you are tuning for the street by just experimenting with main jet sizes, you are kinda in self defeat mode, as the mixtures for throttle position between 1/4 and 3/4 are dominated by the slide needle position, and throttle valve jet.

FYI

[JS550]

If you are tuning for the street by just experimenting with main jet sizes, you are kinda in self defeat mode, as the mixtures for throttle position between 1/4 and 3/4 are dominated by the slide needle position, and throttle valve jet.

FYI

aaaaahhh.......thats info I can use! Thanks.

[Laminar]

If it is lean with the #110; have you tried switching to the #120s and adjusting the air or fuel screws (depending on the type of carbs you have) leaner?

...

Plugs loo great with the #110s, light brown/tan and were dark grey/black with the #120s.

Good job you can use quotes

too bad your post gave nothing constructive.

+0 is better than -10

[razor02097]

If it is lean with the #110; have you tried switching to the #120s and adjusting the air or fuel screws (depending on the type of carbs you have) leaner?

...

Plugs loo great with the #110s, light brown/tan and were dark grey/black with the #120s.

Good job you can use quotes

too bad your post gave nothing constructive.

+0 is better than -10

That doesn't even make any sense 

[Laminar]

If it is lean with the #110; have you tried switching to the #120s and adjusting the air or fuel screws (depending on the type of carbs you have) leaner?

...

Plugs loo great with the #110s, light brown/tan and were dark grey/black with the #120s.

Good job you can use quotes

too bad your post gave nothing constructive.

+0 is better than -10

That doesn't even make any sense 

Which of your posts in this thread wasn't either derailing or a result of poor reading comprehension?

[JS550]

Come on guys, no bickering. Both helpful, happy riding!

[Ayrity]

not to hijack your thread or anything, but so if I understand this correctly, I need to adjust my slide position to try to get the bit of heasitating dead spot I have around 5500rpm to go away?

[razor02097]

Come on guys, no bickering. Both helpful, happy riding!

Sorry I just need to learn to ignore people.

I think after stock parts are replaced one tinkers with carbs forever.  I know I do. 

[flybox1]

I was always under the impression main jet sizing should be determined first, buy plug chops, at WOT.
up-sizing the jet and changing needle clip positions as necessary.
white plug, clip down, black plug, clip up.

once main jet size has been determined,
a plug chop is done at mid rpms to determine pilot jet sizing, and again needle clip setting.

please correct me if i'm misunderstanding the process

[TwoTired]

I was always under the impression main jet sizing should be determined first, buy plug chops, at WOT.
up-sizing the jet and changing needle clip positions as necessary.
white plug, clip down, black plug, clip up.

once main jet size has been determined,
a plug chop is done at mid rpms to determine pilot jet sizing, and again needle clip setting.

please correct me if i'm misunderstanding the process

That's the essence of it.  The difficult part for the home mechanic is that the mixture demands change with the load placed on the engine.  More load usually requires a richer fuel delivery.
The WOT tests load the bike with whatever the rider weight is.  A heavier rider/uphill would need a slightly richer fuel delivery, as more work is required to move the specified mass.

Same is true for mid throttle testing.  But, you seldom ask for max power at a mid-range throttle setting.  Certainly maximum heat is not generated at cruise power and that effects the plug's ability to self clean.

I'm not saying it is impossible.  I'm just noting that there are more variables to juggle during the process.  The process tends to bore the tuner well before optimum settings are achieved, certainly for all but WOT settings.

It is much easier/faster to re-jet on a Dyno where the load can be varied along with the throttle position, and the exhaust can be sniffed/tested for unburned hydrocarbons.  Then you are tuning the bike only as opposed to a bike/rider combination.

[flybox1]

thanks TT!

[JS550]

I was always under the impression main jet sizing should be determined first, buy plug chops, at WOT.
up-sizing the jet and changing needle clip positions as necessary.
white plug, clip down, black plug, clip up.

once main jet size has been determined,
a plug chop is done at mid rpms to determine pilot jet sizing, and again needle clip setting.

please correct me if i'm misunderstanding the process

That's the essence of it.  The difficult part for the home mechanic is that the mixture demands change with the load placed on the engine.  More load usually requires a richer fuel delivery.
The WOT tests load the bike with whatever the rider weight is.  A heavier rider/uphill would need a slightly richer fuel delivery, as more work is required to move the specified mass.

Same is true for mid throttle testing.  But, you seldom ask for max power at a mid-range throttle setting.  Certainly maximum heat is not generated at cruise power and that effects the plug's ability to self clean.

I'm not saying it is impossible.  I'm just noting that there are more variables to juggle during the process.  The process tends to bore the tuner well before optimum settings are achieved, certainly for all but WOT settings.

It is much easier/faster to re-jet on a Dyno where the load can be varied along with the throttle position, and the exhaust can be sniffed/tested for unburned hydrocarbons.  Then you are tuning the bike only as opposed to a bike/rider combination.

So, because Im fat, my bike needs to be richer?