Can't get bike over 23MPH

[DAMIEN1307]

the BoFeng runs so perfectly on these engines, and just works.... I have ditched the pumpers on a few builds for the Bofeng.

I will never run an NT again after running the BoFeng...Its a night and day difference from using an NT...lol.

 

[BrainPain]

The kit I have now came with a Bofeng carb I had to switch to a older style NT to get over 19 mph. I have a raceing carb on my bike now bigger jets it really doesnt seem to do as much as the regular NT carb and I put a cone filter on the NT it did help the torque a little and if the weather was right I could get to 28 mph on flat ground I weighed about 195 pounds. The point there is no magic Carburetor or part.

 

[DAMIEN1307]

The kit I have now came with a Bofeng carb I had to switch to a older style NT to get over 19 mph. I have a raceing carb on my bike now bigger jets it really doesnt seem to do as much as the regular NT carb and I put a cone filter on the NT it did help the torque a little and if the weather was right I could get to 28 mph on flat ground I weighed about 195 pounds. The point there is no magic Carburetor or part.

There has to be something or many things that are overlooked or not adjusted correctly then...Even my cheapest Flying Horse or Seeutec motors were much more capable of producing more power and speed in totally stock condition than what your reporting.

There is no magic carb is correct...There are many more variables than just the carb that helps make all the difference in the world and taking the time and effort of optimising everything to its full potential, even if stock, is paramount to a healthy output of power and speed despite being fairly stock systems.

My slowest bike ever was ten years ago when its top end, really straining it, was only 33 MPH and it was totally stock back then including the air filter.

Ps...My bikes always weigh in at around 80 pounds and my lard butt adds another 217 pounds to that mix...lol.

 

[ImpulseRocket]

The JRL one is a BoFeng. Yes, its miles better than the typical NT carbs in every way. Other than jet selection being a bit more limited and not as available, but you may not need to re-jet. The stock jet in the BoFeng is a 70.

Jet's are just as easy to find and purchase as the ones for the NT. You can get cheap kits on Amazon or go spendy and order Keihin replacement jets from Jets R Us. Pick a size any size... https://jetsrus.com/a_jets_by_carburetor_type/jets_keihin_99101-124_and_99101-ZF5_air.html

 

[ImpulseRocket]

The kit I have now came with a Bofeng carb I had to switch to a older style NT to get over 19 mph. I have a raceing carb on my bike now bigger jets it really doesnt seem to do as much as the regular NT carb and I put a cone filter on the NT it did help the torque a little and if the weather was right I could get to 28 mph on flat ground I weighed about 195 pounds. The point there is no magic Carburetor or part.

There has to be something or many things that are overlooked or not adjusted correctly then...Even my cheapest Flying Horse or Seeutec motors were much more capable of producing more power and speed in totally stock condition than what your reporting.

There is no magic carb is correct...There are many more variables than just the carb that helps make all the difference in the world and taking the time and effort of optimising everything to its full potential, even if stock, is paramount to a healthy output of power and speed despite being fairly stock systems.

My slowest bike ever was ten years ago when its top end, really straining it, was only 33 MPH and it was totally stock back then including the air filter.

Ps...My bikes always weigh in at around 80 pounds and my lard butt adds another 217 pounds to that mix...lol.

To interject myself into this little conversation... There does seem to be some hit or miss quality issues with the Bofeng style carbs. If that is due to manufacturer differences or whatever other variables are at play I can't say but I do know that there is a wide array of quality issues with them.

Case in point. Some people have many issues with the Bofeng carbs leaking or flooding out due to float needles not sealing. LA Hover is a great example of this as he doesn't like the Bofeng carbs for those reasons. Yet I have not had a single issue with the Bofeng that came with my Phantom 85. I've even done bad things like left my bike sitting for several days without draining the fuel from the bowl and even forgetting to turn off the petcock more than once because I am forgetful. Zero issues.

My own personal opinion on the "best" carb for these engines when performance is a goal but it still needs to be useable as a daily - aka minimal headaches and tuning issues - the Mikuni VM-18 or the Keihin PZ19. They are 4 and 5mm larger in internal bore diameter than the 14mm Bofeng but not so large they suffer much from "too big" carb syndrome and are easy to get intakes for that work without hodge podge fabrication.

My main reason I love them is that they have independent idle mixture, pilot jet, and main jet which gives you the ability to really dial in fueling all all points of the throttle sweep. This is something that the single jet NT and Bofeng lack.

 

[TheWizzerd]

To interject myself into this little conversation... There does seem to be some hit or miss quality issues with the Bofeng style carbs. If that is due to manufacturer differences or whatever other variables are at play I can't say but I do know that there is a wide array of quality issues with them.

Case in point. Some people have many issues with the Bofeng carbs leaking or flooding out due to float needles not sealing. LA Hover is a great example of this as he doesn't like the Bofeng carbs for those reasons. Yet I have not had a single issue with the Bofeng that came with my Phantom 85. I've even done bad things like left my bike sitting for several days without draining the fuel from the bowl and even forgetting to turn off the petcock more than once because I am forgetful. Zero issues.

My own personal opinion on the "best" carb for these engines when performance is a goal but it still needs to be useable as a daily - aka minimal headaches and tuning issues - the Mikuni VM-18 or the Keihin PZ19. They are 4 and 5mm larger in internal bore diameter than the 14mm Bofeng but not so large they suffer much from "too big" carb syndrome and are easy to get intakes for that work without hodge podge fabrication.

My main reason I love them is that they have independent idle mixture, pilot jet, and main jet which gives you the ability to really dial in fueling all all points of the throttle sweep. This is something that the single jet NT and Bofeng lack.

I have seen this jet argument on the BoFeng before and it isn't exactly true.

The jet issue needs some clarification as there is some discrepancy and seems to be some variance in the jet that comes in the BoFeng. This may also be an indicator that the "hit or miss" of the BoFeng may be 2 factories, and them using different jets, and differing quality.

The jet in the 3 BoFeng carbs I have are NOT the typical M5 thread Keihin jets. They are an M7x.75 thread. Yes, Keihin does use the M7x.75 jet in some carbs, but they are not the more common ones. Of course you can get them, but the common places people are going to buy from looking for a kit with appropriate sizes, the selection of M5 vs M7 jets is like 1000:1.

So maybe a more appropriate statement would be "relatively" less common.

I have not had a 5mm one, but it seems they do exist.

I machined an adapter to allow me to use the 5mm jets. Simply an M7 to M5 thread adapter.

So it seems there are some that use the 5mm jets. Maybe those are the "iffy" ones. I have not watched LA Hover to see what his was.

I agree having full tunability is nice for people like us, "sometimes" , but a good BoFeng is the ideal carb for most people that dont want to tinker much and just have a decent running bike.


EDIT: This is where all 3 of my BoFengs came from. With these carb/reed/filter combos. https://www.amazon.com/gp/product/B0B1J1XVFF

 

[Greg58]

I don’t buy jets, I solder and drill mine as needed, I have a bofang on one of my 48cc bikes that is a #72 bit size, stock was too rich. Other than the improvements already noted the fuel line connector is much better also.

 

[FrizzleFried]

All I can say is that my experience with the BoFeng carb is that it sucks. I want it to not suck... but it does. I get nothing but 4-stroking when I go higher than 1/2 throttle... period... out the door.

The NT style carb works much... MUCH better.

Trust me... I want it to be different. I paid good money for the carb... then better money for the jets... but for whatever reason... it just aint' happening. Of course, my new Phantom 85 has the same carb. I hope IT works well..

 

[DAMIEN1307]

I paid good money for the carb

How much exactly did you pay as "good money"???...My BoFengs have always been by JRL, all worked perfectly, better than I expected, and they only cost me $11.19 cents with the tax included and free shipping...lol, and I never had to even change the jets and I'm at a 4500 ft altitude where that is the expected norm...lol.

 

[noah9988]

Of course, my new Phantom 85 has the same carb.

Yet I have not had a single issue with the Bofeng that came with my Phantom 85

You guys got a bofeng with your phantom? I got a speed carb.