TBR7 Adventures in Pilot Jets fuel Mixture Screw

Articulas · 05-01-2022, 03:08 AM

Just like everyone else, the stock carb is poop. The main jet is a dog and it dont idle worth damn. So I buy the VM26 generic from Amazon. There are dozens of videos and posts stating a stock bike will be happy with a main jet between 100 and 110. I settled on 105. Worked fine.

But first I needed the bike to idle. Neither the stock carb nor the new carb has any markings to tell you what is on it. Jay So LoI Hertz has a YT video stating he uses a #38 Thats because he has a modified exhaust and air intake. The new carb does not idle even with the idle screw all the way in. Soooo I install a 37.5 pilot jet and it runs way to rich, and the motor gets hot. I install a #35 PJet and it is still running way to rich Iinstall a 32.5 and yep it is still running way to rich.... I am getting frustrated at this point.

So I say F#&% it and decide to go for a #25, and now the thing is way way way way lean.... I mean way to lean, wont idle and hard starting...

WTF! I throw some wrenches around and continue to keep fiddling with the fuel/air mix screw and idle screw for an hour. So now I get the idea something is wrong, a human error... I go through all my pilot jets from the kit and come to realize the one missing is a #12.5.... Yep I saw the 25 and assumed it was a #25, yep I was trying to start on a #12.5....

Sooooo I popped in a #22.5 and have now found idle bliss!!!!! The reason I tell the whole story is to help others who like me are very confused by no marking on stock jets and have no baseline to start with . None the less I am at 100 ft above sea level and the #22.5 works like a charm. Good place to start if your new and unexperienced!!!!!

Also I purchased an extended air/fuel screw with a big knob on it from Amazon made for a CRF250X on Amazon. OMG it makes the adjustment so much more convenient!

Hadaveha · 05-03-2022, 12:42 PM

I’m at sea level, I put a 110 main jet in my Amazon carb, Needle in the middle slot, and fuel adjustment screw at 2 turns out, seem to be the perfect match but now I’m at sea level

Hadaveha · 05-03-2022, 12:44 PM

Allso I ment to say I have to adjust the idle screw up when cold and ease it of as she warm, and I never have to use choke

Articulas · 05-04-2022, 07:37 AM

Quote:

Originally Posted by Hadaveha

I’m at sea level, I put a 110 main jet in my Amazon carb, Needle in the middle slot, and fuel adjustment screw at 2 turns out, seem to be the perfect match but now I’m at sea level

Being in NY our temp jumps up and down. Yesterday the morning temp was 42F and by 3pm it was 72F. when it warms up the bike is idling rich again. So I may drop two sizes on the pilot jet. Though it don't stall like before.

Also once it is hot out the bike sputters at the tail end of full throttle.

This has been a learning process. But I like wrenching almost as much as riding.

One thing I noticed is that the airbox wraps half way around the muffler. I personally believe this is a problem as the it must be heating the air in the box at full running temperature. Gonna experiment with a unit pod filter.

Thumper · 05-04-2022, 09:18 AM

We rejet a new (2021) TBR7 a couple of months ago. We are at ~700feet elevation. It came with a #88 main jet, and we replaced it with a #108. The pilot jet was a #36, and we replaced it with a #38 and set the pilot screw at 2.5 turns

But we didn't buy a carburetor and rejet the new carb. We just rejet the PZ30.

You could always try the original carb again. I am surprised that a pilot jet marked 22.5 worked at all. We didn't modify intake or exhaust. You can get a set of pilot jets from Aliexpress for under $10...
https://www.chinariders.net/showthread.php?t=30694
It runs great with #38 pilot, but needs a slightly longer idle adjustment screw (the slide height adjuster).

Jerryhawk suggested shaving the slide height screw post so the end can go further in and lift the slide a little more. Excellent idea. Before doing that, we might try a "NIBBI Idle Adjustment Screw (PE28mm)" from Amazon. It has the rounded end that is on our PZ30 OEM carb on the TBR7 and it is $8!

Megadan · 05-04-2022, 01:37 PM

This comes down to the issue with Chinese carburetors in general. All of the VM26 jetting advice out there for them that say to use a 25 (ish) size pilot jet are under the assumption that it is running a Mikunki pilot jet.

For a while this was never an issue, but then somebody else starting importing "VM26" carbs that use Keihin style pilot jets. Keihin jet numbers represent very different fueling from the Mikuni numbers.

The biggest thing to look out for is what type of pilot jet they are using, the actual style NOT the number.

The other thing to remember, and the biggest issue I have with the groups on Facebook and elsewhere, is that there are a bunch of overnight carb tuning "experts" who give terrible tuning advice to others because they fumbled around blindly and got lucky. Their advice is along the lines of adding a bigger main jet because a persons idle is rough. etc.

Basically, the lack of attention to detail and generic (reads BAD) advice lead you down that path that made you want to quit. This is why I am so focused on detail. Details matter! Someday, that ignored detail will destroy somebodies engine, or possibly get them hurt.

Megadan · 05-04-2022, 01:42 PM

Quote:

Originally Posted by Thumper

You could always try the original carb again. I am surprised that a pilot jet marked 22.5 worked at all.

The pilot jet on his Mikuni clone is an actual Mikuni jet. The sizing is way different in terms of number. More than likely it runs either the VM28/486 or an N224.103 style pilot jets. This is the style of Mikuni most of us used to run, so all of our jetting suggestions for a 25, 27.5, etc. are based on THOSE jets.

The carbs may look the same, but there are small differences. Most easily identified is the 4 bowl screws vs. the 3 of the PZ carbs.

Otherwise, the actual style of the jet is different as well and needs to be noted. When a person says Mikuni, they mean Mikuni jetting, not Keihin jetting. A 38 Mikuni jet is flipping enormous compared to a Keihin 38

kyle · 05-04-2022, 11:26 PM

I've had good luck jetting four of these using the chart as a starting point. 2 on stock carb and 2 on the clone:
Tbr7.com/upgrades/fuel-system Has a chart for a starting point.

Thumper · 05-05-2022, 09:07 AM

Of course. I missed that. Tripped up again!
I am sure it doesn't help that a pilot jet isn't labeled when you open up the carb!

Megadan · 05-05-2022, 01:11 PM

Quote:

Originally Posted by kyle

I've had good luck jetting four of these using the chart as a starting point. 2 on stock carb and 2 on the clone:
Tbr7.com/upgrades/fuel-system Has a chart for a starting point.

Your chart needs a little refinement to differentiate between the clone carbs as there are some that come with Mikuni style jets, and others that come with Keihin style jets. Sounds dumb, but it happens. I have a PZ30B carb that says Mikuni on it and uses Keihin jets.

kyle · 05-06-2022, 02:56 PM

Quote:

Originally Posted by Megadan

Your chart needs a little refinement to differentiate between the clone carbs as there are some that come with Mikuni style jets, and others that come with Keihin style jets. Sounds dumb, but it happens. I have a PZ30B carb that says Mikuni on it and uses Keihin jets.

I agree, unfortunately the chart is only as good as the information fed to it via the form. After we get enough info I'll build actual charts that give great starting points for individuals using the average best configuration and include great detail.

As for 'clone' for us we go with the Keihin as that's what we suggest on the page and what the majority of us end up with if we go clone: https://tbr7.com/upgrades/fuel-system/

05-04-2022, 01:37 PM	#6
Megadan Join Date: Apr 2017 Location: Omaha, NE Posts: 8,110	This comes down to the issue with Chinese carburetors in general. All of the VM26 jetting advice out there for them that say to use a 25 (ish) size pilot jet are under the assumption that it is running a Mikunki pilot jet. For a while this was never an issue, but then somebody else starting importing "VM26" carbs that use Keihin style pilot jets. Keihin jet numbers represent very different fueling from the Mikuni numbers. The biggest thing to look out for is what type of pilot jet they are using, the actual style NOT the number. The other thing to remember, and the biggest issue I have with the groups on Facebook and elsewhere, is that there are a bunch of overnight carb tuning "experts" who give terrible tuning advice to others because they fumbled around blindly and got lucky. Their advice is along the lines of adding a bigger main jet because a persons idle is rough. etc. Basically, the lack of attention to detail and generic (reads BAD) advice lead you down that path that made you want to quit. This is why I am so focused on detail. Details matter! Someday, that ignored detail will destroy somebodies engine, or possibly get them hurt. __________________ Hawk Information and Resource guide: http://www.chinariders.net/showthread.php?t=20331 2018 Hawk 250 - Full Mod list here. http://www.chinariders.net/showpost....62&postcount=1 2024 Royal Enfield Shotgun 650 https://chinariders.net/showthread.php?t=34124
	0

05-01-2022, 03:08 AM	#1
Articulas Join Date: Feb 2022 Posts: 7	TBR7 Adventures in Pilot Jets fuel Mixture Screw Just like everyone else, the stock carb is poop. The main jet is a dog and it dont idle worth damn. So I buy the VM26 generic from Amazon. There are dozens of videos and posts stating a stock bike will be happy with a main jet between 100 and 110. I settled on 105. Worked fine. But first I needed the bike to idle. Neither the stock carb nor the new carb has any markings to tell you what is on it. Jay So LoI Hertz has a YT video stating he uses a #38 Thats because he has a modified exhaust and air intake. The new carb does not idle even with the idle screw all the way in. Soooo I install a 37.5 pilot jet and it runs way to rich, and the motor gets hot. I install a #35 PJet and it is still running way to rich Iinstall a 32.5 and yep it is still running way to rich.... I am getting frustrated at this point. So I say F#&% it and decide to go for a #25, and now the thing is way way way way lean.... I mean way to lean, wont idle and hard starting... WTF! I throw some wrenches around and continue to keep fiddling with the fuel/air mix screw and idle screw for an hour. So now I get the idea something is wrong, a human error... I go through all my pilot jets from the kit and come to realize the one missing is a #12.5.... Yep I saw the 25 and assumed it was a #25, yep I was trying to start on a #12.5.... Sooooo I popped in a #22.5 and have now found idle bliss!!!!! The reason I tell the whole story is to help others who like me are very confused by no marking on stock jets and have no baseline to start with . None the less I am at 100 ft above sea level and the #22.5 works like a charm. Good place to start if your new and unexperienced!!!!! Also I purchased an extended air/fuel screw with a big knob on it from Amazon made for a CRF250X on Amazon. OMG it makes the adjustment so much more convenient! __________________ --------------------------- Stay Cool and Hang Loose -Articulas 1986 Kawasaki Vulcan 750 Tao TBR7
	0

05-03-2022, 12:42 PM	#2
Hadaveha Join Date: Apr 2022 Location: Alabama Posts: 14	I’m at sea level, I put a 110 main jet in my Amazon carb, Needle in the middle slot, and fuel adjustment screw at 2 turns out, seem to be the perfect match but now I’m at sea level
	2

05-03-2022, 12:44 PM	#3
Hadaveha Join Date: Apr 2022 Location: Alabama Posts: 14	Allso I ment to say I have to adjust the idle screw up when cold and ease it of as she warm, and I never have to use choke
	1

05-04-2022, 09:18 AM	#5
Thumper Join Date: Feb 2021 Location: Kansas City Posts: 2,771	We rejet a new (2021) TBR7 a couple of months ago. We are at ~700feet elevation. It came with a #88 main jet, and we replaced it with a #108. The pilot jet was a #36, and we replaced it with a #38 and set the pilot screw at 2.5 turns But we didn't buy a carburetor and rejet the new carb. We just rejet the PZ30. You could always try the original carb again. I am surprised that a pilot jet marked 22.5 worked at all. We didn't modify intake or exhaust. You can get a set of pilot jets from Aliexpress for under $10... https://www.chinariders.net/showthread.php?t=30694 It runs great with #38 pilot, but needs a slightly longer idle adjustment screw (the slide height adjuster). Jerryhawk suggested shaving the slide height screw post so the end can go further in and lift the slide a little more. Excellent idea. Before doing that, we might try a "NIBBI Idle Adjustment Screw (PE28mm)" from Amazon. It has the rounded end that is on our PZ30 OEM carb on the TBR7 and it is $8!
	0

05-04-2022, 11:26 PM	#8
kyle Join Date: Jun 2021 Posts: 110	I've had good luck jetting four of these using the chart as a starting point. 2 on stock carb and 2 on the clone: Tbr7.com/upgrades/fuel-system Has a chart for a starting point.
	0

05-05-2022, 09:07 AM	#9
Thumper Join Date: Feb 2021 Location: Kansas City Posts: 2,771	Of course. I missed that. Tripped up again! I am sure it doesn't help that a pilot jet isn't labeled when you open up the carb!
	0