Blaster SBN46: When to change jetsize vs popoff?

[Quinc]

When do you increase jet size vs lowering pop-off; should I lower pop-off until the carb dribbles fuel, then increase from there until it stops and then put in bigger jets?

I am currently running a Pro-tec 46mm carb
165Main
125pilot
2.3 Needle and I think a 65gr spring. And she is running a bit lean. (spark plugs are white and only turning 6890rpms)

Should I increase to a 2.5 Needle with 65gr spring or increase jet sizes?

61x 718cc, porting, 180psi, coffman pipe, msd, a/m flame arrestor.

 

[wanderer1]

Refer to mikuni tuning manual. Increase in N/S will not flow more fuel larger jets will. A call to ProTec and inquire what's different in the circuitry would be a good idea also

 

[Quinc]

Refer to mikuni tuning manual. Increase in N/S will not flow more fuel larger jets will. A call to ProTec and inquire what's different in the circuitry would be a good idea also

I talked to Carl and he told me "You might consider getting a 2.5 N/S valve and the full selection of the pop off pressure springs. The larger N/S valve will richen your overall jetting"

 

[jri93]

Mikuni recommends using the smallest needle and seat possible to obtain your desired pop off, therefore i would say up your jet size. What makes you think its the pilot that is lean? You mentioned only turning 6890 rpms, so i assume your talking about top end. if it is running strong down low then i would say up your main jet. im guessing you already tried messing with the top end screw?

 

[Quinc]

Mikuni recommends using the smallest needle and seat possible to obtain your desired pop off, therefore i would say up your jet size. What makes you think its the pilot that is lean? You mentioned only turning 6890 rpms, so i assume your talking about top end. if it is running strong down low then i would say up your main jet. im guessing you already tried messing with the top end screw?

It has good bottom end snap with no hesitation so I think the pilot is ok, but I will try a 127.5 and see if it runs rich or better. I had the main screw 3 turns out.

 

[kevbo]

When do you increase jet size vs lowering pop-off; should I lower pop-off until the carb dribbles fuel, then increase from there until it stops and then put in bigger jets?

I am currently running a Pro-tec 46mm carb
165Main
125pilot
2.3 Needle and I think a 65gr spring. And she is running a bit lean. (spark plugs are white and only turning 6890rpms)

Should I increase to a 2.5 Needle with 65gr spring or increase jet sizes?

61x 718cc, porting, 180psi, coffman pipe, msd, a/m flame arrestor.

For a single carb setup, the N/S should have more area than all the orifices down stream. A 2.3 is plenty of area and with a 65G spring makes for plenty low popoff. Judge the pilot mixture by how much the engine sputters at steady 1/4 throttle, a 120 will sound clean but may tend to hesitate when snapped open. Larger pilots will sputter and chugg more but offer better response, especially when cold. Big singles with an open flame arrestor can require a huge main jet. Since you have a tach it is easy. Simply power tune the top screw and see where it ends up. Size the main so that the top screw is around 1 turn out.