Brozz too lean fix - Page 2

JohnC · 01-03-2021, 12:52 PM

Hi,

I live in Southeast Michigan, about 600 feet elevation. I have my 2020 Brozz 250 currently with a 120 main jet, one washer on the needle and always 87 octane, no ethanol fuel. I started with a 105 main, and moved to a 115 for a few hundred miles, and it seemed it was still a little on the lean side, looking at the plug. I am currently finishing up a port and polish, so I got a real good look a the head, ports and piston. It is running a little rich. I guess I'll wait until I see any impact from the head work. I would rather a little rich, than lean. I would think 115 would be in the ball park for 1000 feet.

Thanks,
John

TheChairman · 01-04-2021, 02:34 AM

Quote:

Originally Posted by putterputter

What is making think it is too lean is that i always have use a full choke no matter what the temperature is outside, and have to run it for about a minute before it will idle with the choke off. I have my idle set at 1500 rpms

You're close, then. You might try notching the sealed idle air screw, removing it, and replacing it with the adjustable one to see if that makes the choke a little less needed. That is going to richen up your idle mix before replacing the slow jet completely.

Another note about gas, octane aside. Some stations sell "top-tier" gasoline, and some don't. The octane doesn't matter. It either is, or it isnt. If you want better gas, you have to go to the stations that sell it.

https://toptiergas.com/

Megadan · 01-04-2021, 06:15 AM

People are putting too much thought into octane with these bikes. A standard CG250 engine from any of these machines found on this site would likely run on horse piss if it was flammable. These engines are fairly low compression with extremely modest ignition timing. Heck, my Hawk has run on 87 WITH the compression increased (pre CDI or ignition advance flywheel key). I was in a pinch and I didn't like it, but I never experienced any knock/ping of any kind. In fact, the equivalent US octane these engines are actually rated to run on would be 85 octane, something not really found here unless you start to get into the higher altitudes.

The only thing I do recommend is to try your best to avoid the E10 fuels. You can't avoid ethanol in modern fuel though. Even "No Ethanol" gasoline can have up to 9% ethanol in it and they don't have to tell you about it (more common than you think). One thing I always recommend with these bikes is to add either a couple ounces of MMO to a full tank, or the same with marine grade fuel stabilizer. Doing this has the benefits of lubricating the moving parts of the carburetor as well as putting a film of oil inside the steel of the tank to help stop corrosion from forming. Some would also claim it can reduce wear on the intake valve face, but if it does it would be minimal. Plus, MMO mixed gas just smells so good when burned lol.

putterputter · 01-04-2021, 10:46 AM

The gas station is Marathon, which is supposed to be top tier and also has some STP in it , so i could drop to a low octane rating, and i use the Star Tron to combat this ethanol in the gas and also stablize it , maybe the Marvel Myestery oil would do the same thing.

Is the Keihin stock carb just as good as the Minuki VM 26 and are both just as easy to work on and rejet? I want to get a second as a backup , just not sure whether to get another KeiHin or Mikuli ? What do you guys think?

TheChairman · 01-04-2021, 11:22 AM

I have experience with both. They are both excellent carburetors. They rejet almost exactly the same way, with the exception of them taking different jets. As you progress, you'll notice that basically all small engine carburetors are the same.

grumpyunk · 01-06-2021, 11:08 AM

If you want ethanol-free fuel, you can buy it that way, or make your E10 free by adding water. The ethanol mixed with gasoline can be forced to precipitate out of the mixture by adding water. You can watch it being done on youtube if you want.
The fuel in a video was placed into a glass(?) jug, and a measured amount of water added. Within a short while, the ethanol started to fall out of solution, and gather at the bottom. This example waited some time, an hour or more, and then decanted the ethanol-free fuel into his gas can. I do not remember the proportion or amount of water needed for each gallon.
You can also calculate the Exx ratio in your fuel using calibrated glassware. I don't remeber the name, but you add specific amount of water to a specific amount of fuel and then wait. The level(amount) at the bottom of the tube tells the percentage ethanol in the fuel.
Premium, high-octane, fuel just prevents or slows the combustion of fuel due to higher compression pressure. The flame front starts as the spark plug rather than than having more than one ignition point inside the combustion chamber. The single flame will burn smoothly while two flame fronts colliding will cause ping/knock/pre-ignition. Premium fuel actually burns slower than regular. From what I understand.
Using premium fuel provides no performance advantage unless the engine is designed to use it. These engines should tolerate ethanol fuel, they may not, as it has been on the market for quite some time and they don't like to pay for repairs caused by its use. Keep the fuel fresh, drain as needed, and adding some MMO or 2T lube to a tank of gas won't hurt anything, and may prevent rust on the inside of the tank and corrosion of the float bowl & associated parts.
IMO
tom

cycleway4 · 01-06-2021, 02:02 PM

Probably 20 years ago,..I attended a Turbo Motorcycle Owners Group Rally. As in many rallys of this type, there were seminars that were able to be attended. I went to one such seminar on tuning the Kawasaki 750 Turbo, led by at the time, the #1 Kawasaki 750 Turbo drag racing guru in the country. The subject of using high octane premium fuel/its advantages on stock bikes came up (not necessarily turbo bikes, just stock)....our instructor explained that there was no advantage at all using a higher octane than a motor was designed for,..or needed...that higher octane fuel actually burned slower, was less prone to pre-ignition/spark knock, etc. The higher octane in fact offered no power gain when not needed,..in fact the opposite. As an example, he offered the following story to prove a point: at a recent drag race event, the bike his team used as a pit-bike (a 50cc Honda) ran out of fuel...all they had with them, was 105 octane fuel (for the drag-bike). They filled the 50cc pit bike up,..started it up,...and had a huge loss of power...it wouldn't even pull the weight of a rider around the pits, without someone pushing......started and idled fine....upon arriving back home, drained out the 105,..filled back up with 87,...and full power (well, for a 50 cc) was back. He said that was the best way he could explain the slower burning,..no power gained,...when using higher octane than needed (going from 87-to-105 octane) and (most importantly) the motor was not designed to be able to benefit from it.....

01-04-2021, 06:15 AM	#18
Megadan Join Date: Apr 2017 Location: Omaha, NE Posts: 8,110	People are putting too much thought into octane with these bikes. A standard CG250 engine from any of these machines found on this site would likely run on horse piss if it was flammable. These engines are fairly low compression with extremely modest ignition timing. Heck, my Hawk has run on 87 WITH the compression increased (pre CDI or ignition advance flywheel key). I was in a pinch and I didn't like it, but I never experienced any knock/ping of any kind. In fact, the equivalent US octane these engines are actually rated to run on would be 85 octane, something not really found here unless you start to get into the higher altitudes. The only thing I do recommend is to try your best to avoid the E10 fuels. You can't avoid ethanol in modern fuel though. Even "No Ethanol" gasoline can have up to 9% ethanol in it and they don't have to tell you about it (more common than you think). One thing I always recommend with these bikes is to add either a couple ounces of MMO to a full tank, or the same with marine grade fuel stabilizer. Doing this has the benefits of lubricating the moving parts of the carburetor as well as putting a film of oil inside the steel of the tank to help stop corrosion from forming. Some would also claim it can reduce wear on the intake valve face, but if it does it would be minimal. Plus, MMO mixed gas just smells so good when burned lol. __________________ 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
	2

01-06-2021, 11:08 AM	#21
grumpyunk Join Date: Jul 2018 Location: nw of atlanta Posts: 169	If you want ethanol-free fuel, you can buy it that way, or make your E10 free by adding water. The ethanol mixed with gasoline can be forced to precipitate out of the mixture by adding water. You can watch it being done on youtube if you want. The fuel in a video was placed into a glass(?) jug, and a measured amount of water added. Within a short while, the ethanol started to fall out of solution, and gather at the bottom. This example waited some time, an hour or more, and then decanted the ethanol-free fuel into his gas can. I do not remember the proportion or amount of water needed for each gallon. You can also calculate the Exx ratio in your fuel using calibrated glassware. I don't remeber the name, but you add specific amount of water to a specific amount of fuel and then wait. The level(amount) at the bottom of the tube tells the percentage ethanol in the fuel. Premium, high-octane, fuel just prevents or slows the combustion of fuel due to higher compression pressure. The flame front starts as the spark plug rather than than having more than one ignition point inside the combustion chamber. The single flame will burn smoothly while two flame fronts colliding will cause ping/knock/pre-ignition. Premium fuel actually burns slower than regular. From what I understand. Using premium fuel provides no performance advantage unless the engine is designed to use it. These engines should tolerate ethanol fuel, they may not, as it has been on the market for quite some time and they don't like to pay for repairs caused by its use. Keep the fuel fresh, drain as needed, and adding some MMO or 2T lube to a tank of gas won't hurt anything, and may prevent rust on the inside of the tank and corrosion of the float bowl & associated parts. IMO tom __________________ vertical and above ground - my daily goal
	0

01-06-2021, 02:02 PM	#22
cycleway4 Join Date: Feb 2007 Location: Virginia Posts: 269	Probably 20 years ago,..I attended a Turbo Motorcycle Owners Group Rally. As in many rallys of this type, there were seminars that were able to be attended. I went to one such seminar on tuning the Kawasaki 750 Turbo, led by at the time, the #1 Kawasaki 750 Turbo drag racing guru in the country. The subject of using high octane premium fuel/its advantages on stock bikes came up (not necessarily turbo bikes, just stock)....our instructor explained that there was no advantage at all using a higher octane than a motor was designed for,..or needed...that higher octane fuel actually burned slower, was less prone to pre-ignition/spark knock, etc. The higher octane in fact offered no power gain when not needed,..in fact the opposite. As an example, he offered the following story to prove a point: at a recent drag race event, the bike his team used as a pit-bike (a 50cc Honda) ran out of fuel...all they had with them, was 105 octane fuel (for the drag-bike). They filled the 50cc pit bike up,..started it up,...and had a huge loss of power...it wouldn't even pull the weight of a rider around the pits, without someone pushing......started and idled fine....upon arriving back home, drained out the 105,..filled back up with 87,...and full power (well, for a 50 cc) was back. He said that was the best way he could explain the slower burning,..no power gained,...when using higher octane than needed (going from 87-to-105 octane) and (most importantly) the motor was not designed to be able to benefit from it..... __________________ <div>Steve 2006 Roketa DB-07A/RSX-200E 2008 Roketa 250 Scooter 2019 Brozz 250
	1

01-03-2021, 12:52 PM	#16
JohnC Join Date: Oct 2020 Location: Southeast Michigan Posts: 100	Hi, I live in Southeast Michigan, about 600 feet elevation. I have my 2020 Brozz 250 currently with a 120 main jet, one washer on the needle and always 87 octane, no ethanol fuel. I started with a 105 main, and moved to a 115 for a few hundred miles, and it seemed it was still a little on the lean side, looking at the plug. I am currently finishing up a port and polish, so I got a real good look a the head, ports and piston. It is running a little rich. I guess I'll wait until I see any impact from the head work. I would rather a little rich, than lean. I would think 115 would be in the ball park for 1000 feet. Thanks, John
	0

01-04-2021, 10:46 AM	#19
putterputter Join Date: Jan 2021 Location: Ohio Posts: 21	The gas station is Marathon, which is supposed to be top tier and also has some STP in it , so i could drop to a low octane rating, and i use the Star Tron to combat this ethanol in the gas and also stablize it , maybe the Marvel Myestery oil would do the same thing. Is the Keihin stock carb just as good as the Minuki VM 26 and are both just as easy to work on and rejet? I want to get a second as a backup , just not sure whether to get another KeiHin or Mikuli ? What do you guys think?
	0

01-04-2021, 11:22 AM	#20
TheChairman Join Date: May 2020 Location: Philadelphia Posts: 115	I have experience with both. They are both excellent carburetors. They rejet almost exactly the same way, with the exception of them taking different jets. As you progress, you'll notice that basically all small engine carburetors are the same.
	0