What is the point

[Guest]

What kind of changes should I expect going from a 130 to a larger main jet on my 80 gs1100 4 v motor w/pods & pipe? Strictly a top end power increase? I know some are running up to a 150 main. I assume they're also running a big bore kit & cam? I guess the real question here is how large can I go & should i also look at the needle? Bike currently runs awesome, just looking for more power as I want to hit the drag strip before the season is over.

 

[Steve]

If it currently runs "awesome" and your plugs are showing the right colors, you will not add any power by simply changing jets.

The reason some are running larger jets would be because they have made modifications that allow more air through, requiring the extra fuel that larger jets would provide.

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[Nessism]

This info came from a test performed by Joe Minton and published in Motorcyclist magazine back in the day. He used a dyno and checked the fuel mixture to select the jetting, but the jetting itself was not fine tuned for each pipe. Regardless, this graph provides real world info on how much power you have to gain.

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This second graph shows another test published in Cycle World (I think), and shows greater gains, although the bike itself was pretty tired in general.

 

[MisterCinders]

But the data in those graphs is not related to upping main jet size, but from changing the total air/fuel package (e.g., pods v. airbox, different pipe configurations, etc.).

I think the answer to the OP is that a main jet size is either right or wrong. The right size will maintain proper mixture at WOT. Too small will be too lean, too big will be too rich. Changing the main jet only, should not yield more power except maybe a lean mix that boost power while it burns up the engine.

Or did I miss something along the way?

 

[posplayr]

if your bike is stock other than pods and pipe you are probably already a little too rich. The DJ kit is 132-138 so you are at the high end of that with 130 Mikuni.

 

[Guest]

Are you running stock needles?

 

[Guest]

Yep Bill,

Stock needles set to the middle.

I think my mods of a pipe & pods is pretty common, so what are others running this combo using for a main jet size?

 

[posplayr]

Yep Bill,

Stock needles set to the middle.

I think my mods of a pipe & pods is pretty common, so what are others running this combo using for a main jet size?

DJ 3133: 138 main, 47.5 pilot, needle 3rd grove from top
4:1 with K&N Pods or equivalent (not emgo)