Bogs When I Gun It Real Hard/FAST from 0 to ¼ Throttle

[Tomkay44]

I'm Still trying to tune my Nibbi PE28FL on my 2021 TBR7.
I'm at 69' above sea level SO, as you guru/motor gods seem to be suggesting, I currently have the JETS at:
-38 pilot
-112 main
OTHER MODS are:
-I just put a fresh NGK Ridium IX SPARKPLUG in
-I've got the yellow Nibbi Racing COIL on her
- The MSD SPARKPLUG BOOT
-STOCK EXHAUST (one thing at a time)
-I'm trying to keep the STOCK AIRBOX but I have chopped a lot of the top open for more air and put a 1' sleeve in the intake hose to keep it good and open.
-The AIR SCREW'S at 2 ¾ turns out.
I've been playing with the AIR SCREW, adjusting it at ¼ turn intervals down to 2 turns out and up to 3 turns out. It doesn't seem to make a difference on the bog.
QUESTION 1:
Since at 0 to ¼ THROTTLE involves the PILOT JET and, as most you all seem to suggest, that's what I need to get right first, do you all suggest I go UP TO 40 OR DOWN TO 36 ON THE PILOT JET (I don't believe there's a 39 or 37) in order to to lose that O TO ¼ THROTTLE BOG? (Or do y'all suggest something else is causing it?)
QUESTION 2:
When I'm doing "PLUG CHOPS" trying to achieve that carmel colored porcelain, DO I NEED TO USE A NEW PLUG EVERY TRY/CHOP or will the black (or white) burn away to the new, carmel color once I've gotten it right?
It seems like a new plug every chop might be costly. Especially on the Ridiums.

[dirtbkr188]

Continue turning the air screw IN (to richen it) a 1/4-turn at a time and see if it improves. You can go all the way to a !/2-turn from being fully seated before you need to go UP one size (#40) on the pilot jet.


Are you riding the bike after an adjustment, or just blipping the throttle from idle to WFO on a bike stand?

[Tomkay44]

Thanks for the help dirtbkr188. I really appreciate it.
I don't even have it on a stand right now besides the kick stand. I haven't been running WFO though. Just 0 to a bit over ¼ throttle trying to get the pilot jet right before I button it up to run it to see what else needs tweaking. Is that okay.
It sure is good to have somebody that knows what they're talking about saying it's okay to turn the air screw in so that it's less than two turns out. I've had a lot of people tell me it has to be between 2 and 3 turns but I never can get an answer as to whether it's okay to be less than 2 turns out.
Maybe it eventually lands there once you get the rest of the carb tuned.

[krat]

The air/fuel mix is supposed to be done with the engine running. You will need one of these before you can accomplish it properly. They hide the a/f screw in that well where it is unreachable with a straight screwdriver and it results in all these guesses and searching for the "right setting" formula. There isn't one.

https://www.harborfreight.com/hand-t...set-93916.html

The screwdriver set has a flex shaft that goes around and up into the well where the screw lives.

Start the engine, adjust the fuel screw until you have the fastest possible idle. If you move the screw in or out it will slow or bog.

When you get the fastest possible idle you set the idle speed using the idle screw on the side of the carb. It should be set at 1500rpm.

After you set the idle properly if you are still bogging you need to shim the needle, then readjust the a/f screw.

[Tomkay44]

Thanks for your input krat but this is a Nibbi PE28FL carb so it's an easy to get to with a small flat head air screw before the fuel intake, not a hard to get to air fuel screw.

One thing at a time starting with the pilot before I do any needle adjustments (no shims involved)

[bigdano711]

All I was looking for with the pilot was for the RPM's to come right back down to 1500 and settle after a blip on the throttle. If it idles high for a few beats and then comes down, it's too lean. If it drops below 1500 and comes up, it's too rich. Once you get it idling right, your pilot has been set and tuned.


The issue your describing is what I am battling. For me, it's time to begin needle adjustments in the lean direction.

[bigdano711]

I have been adjusting like a maniac the last few days. Here's where I'm at and it feels close, just not quite there.


Pilot: 40
Main: 100
Needle: JJH in middle position


In 2nd gear idling down, when I open up the throttle it lags for just a moment then gets rippin'. Does that mean rich on needle and main? My head is buzzing with adjustments and I forget what means what....

[Deckard_Cain]

Also do know that "gunning it hard from 0 to 1/4 throttle" and experiencing a hesitating or bog before it picks up RPM is completely normal in most cases. Especially without a pumper carb.

So your testing methodology may be inherently flawed here. You're treating the 0-1/4 throttle action as if you'll be drag racing it. That's typically not how you'll be riding it.

[bigdano711]

I moved the JJH needle to the number 4 position or one notch towards rich. After doing so, I could not get the idle to come down below 2000 rpm, so I went back to the 38 pilot. Massive improvement. I will bring the main jet back up to 105, possibly 108 and I think it will be dialed.


I'm not trying to drag race it. Someone on these forums told me to do this test, I did not come up with it all on my own. Point being, it's running lean and I struggled mightily to understand where/why. With the 40 pilot being too rich, the stock needle positions didn't make much difference at all. Changing to the JJH gave me more positive feedback where the idle is concerned. Then I remembered looking at the plug when I had to find TDC to change out the head gasket. The plug showed rich, which it had never shown before. After putting on the new head gasket and running it a bit, I decided to change the oil. The plug showed lean, like it always did. This confirms the pilot was too rich because I mostly idled it and shut it down over the winter. I did run it a few times, but mostly idled and shut down.


Current settings on Nibbi PE28FL:
Pilot: 38
Needle: JJH in #4 position
Main: 100
Elevation: 6,824'