TT TBR7 carb question

[BrandonT]

As always thx in advance to everyone for the info. I just got my replacement carb and jets. I have a 110, 115 and 120 main jets, as well as a 25 and 27.5 pilot jet. I cracked open the carb and swapped out no problems. But the pilot jet included in the carb was a 40. Now I’ll be the first to admit I don’t know anything about anything when it comes to bikes and small engines. But everything I’ve seen said that they replace the pilot jet for a LARGER 25 or 27.5 pilot. Mine seems to be going in the other direction. Can anyone help clarify please?

[Megadan]

Originally Posted by BrandonT

As always thx in advance to everyone for the info. I just got my replacement carb and jets. I have a 110, 115 and 120 main jets, as well as a 25 and 27.5 pilot jet. I cracked open the carb and swapped out no problems. But the pilot jet included in the carb was a 40. Now I’ll be the first to admit I don’t know anything about anything when it comes to bikes and small engines. But everything I’ve seen said that they replace the pilot jet for a LARGER 25 or 27.5 pilot. Mine seems to be going in the other direction. Can anyone help clarify please?

That is simply because for the longest time all of the Mikuni clones only came with a 20. Now a few are coming with a 40, which is too big. So simply replace larger with smaller.

[NzBrakelathes]

Almost all clone or carbs from China come randomly jetted and kits included.
Kinda just have to bite the bullet and order jets you need and ignore what is in it to be sure you end up with a range that suits you.

[BrandonT]

I guess I’m overthinking it. Just seemed like a big jump from a 40 to a 25. But I will of course listen to those who know infinitely more about it than me. Where should I set the fuel air screw as a good starting point to begin tuning the carb? I am at sea level if it matters. Also, I’m just past the first 6 hours of engine time. What oil should I change to? 15w40 as suggested in your post?

[Megadan]

Originally Posted by BrandonT

I guess I’m overthinking it. Just seemed like a big jump from a 40 to a 25. But I will of course listen to those who know infinitely more about it than me. Where should I set the fuel air screw as a good starting point to begin tuning the carb? I am at sea level if it matters. Also, I’m just past the first 6 hours of engine time. What oil should I change to? 15w40 as suggested in your post?

What jetting depends on if the bike has mods, what mods, or if it is just stock.

For a stock bike I always recommend a 25 pilot, 105 main, needle in 3rd or 4th slot. Being at sea level, this may change slightly - a 107.5 or 110 main may work better.

If you have an exhaust and pod filter or intake mods you might want to start with the 27.5 pilot and a 115 main, needle in the 4th notch.

No matter what, start with getting the pilot jet sorted. Tune the idle mixture so it is more than 1 turn out from seated, but less than 2. If less than 1 turn out, go down a size. If more than 2 turns out, go up a size.

I do know that some members at sea level have ended up with a 30 pilot jet in the Mikuni clones, so it isn't out of the realm of possibility for you. On my last Hawk I ended up with a 27.5 with just a hair over 1 turn out with exhaust and a pod filter for upgrades because the 25 was just over 2 turns out and had a slight lean stumble with light constant throttle and my main was a 115 in hot weather (85 and above), and a 117.5 in cooler weather. Needle was comfortably in the 3rd slot (middle) with that combo and I managed to get fairly impressive fuel economy too (averaged mid 60's, with low 70mpg crusing at 50-55mph.

Two things I stress a lot with people. 1. Use genuine jets. They cost more, but they cost more for a reason.
2. I am a huge fan of "half" sizes for really dialing in a carb tune, especially with climate changes. If you run the 115 and you end up being a little lean, but a 120 causes a rich bog, then the 117.5 going to really get you close to where you need to be. That was the exact scenario I was in when I had the 115 main in cooler weather, but the 115 was perfect in the middle of the summer (117.5 would load up slightly wide open).

[Ariel Red Hunter]

Originally Posted by Megadan

What jetting depends on if the bike has mods, what mods, or if it is just stock.

For a stock bike I always recommend a 25 pilot, 105 main, needle in 3rd or 4th slot. Being at sea level, this may change slightly - a 107.5 or 110 main may work better.

If you have an exhaust and pod filter or intake mods you might want to start with the 27.5 pilot and a 115 main, needle in the 4th notch.

No matter what, start with getting the pilot jet sorted. Tune the idle mixture so it is more than 1 turn out from seated, but less than 2. If less than 1 turn out, go down a size. If more than 2 turns out, go up a size.

I do know that some members at sea level have ended up with a 30 pilot jet in the Mikuni clones, so it isn't out of the realm of possibility for you. On my last Hawk I ended up with a 27.5 with just a hair over 1 turn out with exhaust and a pod filter for upgrades because the 25 was just over 2 turns out and had a slight lean stumble with light constant throttle and my main was a 115 in hot weather (85 and above), and a 117.5 in cooler weather. Needle was comfortably in the 3rd slot (middle) with that combo and I managed to get fairly impressive fuel economy too (averaged mid 60's, with low 70mpg crusing at 50-55mph.

Two things I stress a lot with people. 1. Use genuine jets. They cost more, but they cost more for a reason.
2. I am a huge fan of "half" sizes for really dialing in a carb tune, especially with climate changes. If you run the 115 and you end up being a little lean, but a 120 causes a rich bog, then the 117.5 going to really get you close to where you need to be. That was the exact scenario I was in when I had the 115 main in cooler weather, but the 115 was perfect in the middle of the summer (117.5 would load up slightly wide open).

I just want to re-enforce what Megadan said. Start with the pilot jet. It effects the fuel mixture all the way from idle to wide open...ARH

[JayWolf]

Is there a carburetor you can buy already jetted for a stock tbr7 probably a stupid question

[Biker_Andy]

Originally Posted by JayWolf

Is there a carburetor you can buy already jetted for a stock tbr7 probably a stupid question

Unfortunately no, unless someone here has a spare their willing to get rid of. Fortunately there is a wealth of knowledge here and some nearly professional carb tuners with lots of free advice.

[JayWolf]

Ok so in running 25 idle jet and a 115 main ripped off that big factory airbox it seemed to just starve my tbr7 from air now it seems its getting to much air with a stumble at 1/4 throttle cant seem to get that hiccup outta the equation needle is in the fourth slot any ideas guys

[Kenstogie]

wow this is very close to what i just did to my tbr7....i have a non cat after market exhaust at about 300-400 asl........ my mikuni clone also came with a 40 idle jet... which i replaced and that confused me at first too waht seemed like a big drop to a much smaller one...

stock airbox for now anyway....

--did you adjust the fuel air mix? mine is at 1 and 1/2 turns out
--i have 27.5 idle jet actual mikuni from jetsrus
--needle e clip is 4th down
--main is 112.5 but may go to 115-120 after air pod install....
---mine still has a very slight hesitation at the initial crack of the throttle to about 1/16 so i "blip" it ...but it works so well through the rest of the throttle i can live with that....


couple things to watch out for...

make sure your carb needle retainer clip goes on top of your Needle e clip ( ask me how i know ) and make sure the throttle cable end is fully seated in the carb piston....test the throttle and make sure it snaps back prior to reassembly

if you take off the intake manifold (which is easier than taking the carb off of the intake manifold imho) make sure the o ring stays in place. ( ask me how i know ) make sure the intake manifold doesnt have any cracks etc......

also don't over torque down the jets ....i believe they seat into something on the softer side (brass maybe)

many much smarter people than i around here but that all worked for me.....

good luck!

[JayWolf]

Thanks for the info I'll see what changes I can make

[kb21guru]

Originally Posted by JayWolf

Thanks for the info I'll see what changes I can make

The 25 pilot and why.
There are actually a few reasons but I'll only touch on two main ones.

1) These carbs are for smaller 125cc engines, smaller engines require smaller main jets, 88-98 mains so the 20-ish to 30ish pilots are required to yield a smooth transition from half to wot.

2) Why does a 230cc engine come with a carb for a 125cc engine?
It is because of the very restrictive airbox, and exhaust header, this set up simply can't supply/purge enough air/waste to warrant a larger main. This is why ppl say to use a 110/115 with stock set up. It's about the max the air box and header can handle.

When we up the main to a larger 115/120 and keep the smaller 20-ish pilot jet, the engine will bog/hick up, at around half throttle going to full throttle (basically every time we change gear and throttle back up it will hick up and then take off as it burns the flooded fuel). This is because when the main jet comes on, it throws a bunch of fuel into the engine that is not at the correct rpm being it's a small 20-ish pilot.

Running a 38-42 pilot with a 115/120ish main, at half throttle the engine is running at a high enough rpm for the added fuel of the 115/120ish main to have a smooth transition between the two jets.

With a tiny pilot and large main, it's like flooding the engine when the main pilot kicks in, so it takes a few revolutions to catch up with the added fuel.
Hence the momentary hick up/bog.

Now if you were to use a 130 main (yes you can) you would need a 46ish size pilot jet to keep a smooth transition.

Don't let anyone tell you to run a 25 pilot in a 230cc engine with a main higher than a 88.