2020 tbr7 pz30 carb tuning

[Captcj68chris@aol.]

Hi all Chris here. As title states, stock carb with aliiexpress pilot jet, Amazon main jet kit.
PILOT JET K42, fuel/air 2.5 turns out (do not have k44 in my kit,)
MAIN JET K125 (chart for comparison I saw. K125= mikuni110??)
MY PROBLEM bike will pull healthy from low RPM full throttle till upper RPM 6000ish?
(I have no tach) then bike starts to sputter/buck,cut out.
Changing main jet to any other size, up or down will just exaggerate the issue!
I'm in bowling green k.y. altitude <1000 foot max?
Bike will start and idle from cold with no choke or throttle.
Do I need a half size jet adjustment? (Are these engines that sensitive?)
Spark plug has good color.
Bike is not registered, not ridden on open ,road, or off road, just in my neighborhood and mostly no more than 1\2 throttle
am I looking at a fuel issue, or an ignition problem?
Thank you
Christopher

[Thumper]

Based on your description of easy start and good acceleration including full throttle, I think your pilot and needle heights are fine. The main jet might be the next thing to adjust for high rpm, high throttle (3/4 to full) open position, but you say up or down jet size there is bad.

Soooo, how about float bowl height (seems unlikely, but might be filling too slowly). Or fuel line causing a vacuum (minor flow issue).

Or, not getting enough air when it needs high flow at high rpm. For a quick test, remove the air filter. If this fixes it, get a new filter.

Originally Posted by Captcj68chris@aol.

Hi all Chris here. As title states, stock carb with aliiexpress pilot jet, Amazon main jet kit.
PILOT JET K42, fuel/air 2.5 turns out (do not have k44 in my kit,)
MAIN JET K125 (chart for comparison I saw. K125= mikuni110??)
MY PROBLEM bike will pull healthy from low RPM full throttle till upper RPM 6000ish?
(I have no tach) then bike starts to sputter/buck,cut out.
Changing main jet to any other size, up or down will just exaggerate the issue!
I'm in bowling green k.y. altitude <1000 foot max?
Bike will start and idle from cold with no choke or throttle.
Do I need a half size jet adjustment? (Are these engines that sensitive?)
Spark plug has good color.
Bike is not registered, not ridden on open ,road, or off road, just in my neighborhood and mostly no more than 1\2 throttle
am I looking at a fuel issue, or an ignition problem?
Thank you
Christopher

[krat]

I have to agree with Thumper. You have messed with the carb before you opened the air box or the exhaust.

Strip the cat, punch the exhaust and open the air box at the minimum. You will not believe what they use to block your exhaust flow! It is restricted about 75%

Also shim the needle.

[Megadan]

Originally Posted by Captcj68chris@aol.

PILOT JET K42, fuel/air 2.5 turns out (do not have k44 in my kit,)
MAIN JET K125 (chart for comparison I saw. K125= mikuni110??)
r

What mods to the bike? Without knowing this the jetting advice is going to be hard to give properly.

For the pilot jet - The Keima jets (what the K stands for) are sized a bit weird compared to Keihin I have found that with any significant modifications a K45 size is more ideal. In Keihin terms it's roughly close to a 38 and in Mikuni terms a bit smaller than a 27.5. Both of those sizes are just about perfect for modded CG250 engines

Main jet - If that jet does have a K on it then it is also a Keima size so there is no telling what the equivalent is. As far as jetting size comparisons go between the Keihin 99101-393 (what most PZ clones use) and the Mikuni N100.604 (Proper VM26 clones use these) is actually identical in terms of numbering. Generally this isn't the case wither other styles of jets when it comes to Mikuni vs Keihin but this is the one exception.

Assuming the Keima jet size also compared directly then I would say your main jet is way big. I was running a Keihin 125 main jet with full bolt-ons and a very ported head. If your bike is mostly stock it shouldn't need anything bigger than a 110 and with an exhaust upgrade a 115.

The reason it seems to pull ok until you hit around 6000 rpm is because of the intake velocity across the jets starts pulling much harder and more fuel is being drawn in relative to the air and it's so rich it can't ignite. If you have other Keima jets try dropping down to a K120 and see how it responds.

[Captcj68chris@aol.]

Hi all Chris here thanks for the quick responses, forgot to mention. Stock exhaust. With cat in place.
AIRBOX lid removed, paper element replaced with green foam 1 inch thick cut with a razor to the
Exact shape of the original paper element, foam then mounted in the cradle that screws to the top of the air box. (green foam bulk air filter material ).
UPDATE. Checking ignition, spark plug, and electric grounds right now. Spark plug looks a lil. More black than tan than would aim for, however this bike putts around, low RPM, low throttle, low MPH.
Gonna remove air filter and test ride in a lil while.
Thank you. Ttyl
Christopher

[Captcj68chris@aol.]

Hi all, hi dan, bike has 1500km on Speedo. = 800 miles???? I saw a chart listing main jet comparison, kehin,= delorto,=mikuni. That's what I went by. Is it possible that I am so far off on my main jet that stepping down from a 125 to a 120, even though it seems worse ,
it Is only masking the possibility that I am indeed heading in the right direction? If these
Alliexpress jets are indeed sized correctly, I should aim for a 110 main size that. Most people here use regardless of brand? That does make sense to me
thanks all

[Captcj68chris@aol.]

Hi all, the main jet kit that I am using is the one on amazon. N100.604. Has a sloppy looking graffiti style K outline stamped on it. Not a crisp letter K like on my original. k36 pilot jet.
Thanks

[Captcj68chris@aol.]

Hi all, took your advise put in the 110 main, left pilot at k42, 2.5 turns out. Took wee bit longer to start cold, 2 tries with the start button as opposed to one push before. Bike pulls all the way through clean
Right up to the point anyone with out a tach would shift. Slight cut out when wrung all the way out.
However I would normally never be up that high anyway. At that Rpm it's just revs anyway, these bikes don't have much top end power stock, like everyone else plan on making some upgrades down the road
4° flywheel key, nibbi coil, cat delete with stock muffler (I like my bike quiet). Head work maybe when I get it registered. Right now the bike is DEFINITELY running much better!
Thank you to all
Safe riding
Christopher

[buzz]

Drill out jet just a little bigger,and make sure air cleaner is clean

[Captcj68chris@aol.]

Hi buzz, I'm gonna leave it like this, I am happy with it. The point where I starts to cut out slightly, is WAY beyond any rpm I would normally be near. I just revved it up that high to test it.
I just tried starting it up again in my garage, motor 3 hours cold, 1 push on starter, no throttle, no choke, fired right up and idled by itself. I'm gonna call this a good tune.
Once again this forum and the members have proven why it was created
Safe riding
Christopher

[Megadan]

The point where it is cutting out now is likely the rev limiter in the cdi, which usually comes in around 8500rpm, which is well beyond peak power anyway, which is usually around 7000 to 7500, and drops off hard beyond 8000