Brozz Performance?

Spins · 04-23-2020, 09:15 PM

I broke my Brozz in with the OEM oil and changed it around 100 miles and adjusted my valves. The bike starts and idles better now. It was my first time adjusting valves and took more than a few attempts to get it right.
While I was breaking in the bike I did run it out a little and was able to hit 73mph . It felt like it might have a little more left. Now after changing the oil and adjusting the valves the bike appears to have lost top end. It’ll only hit 68. My bike now has just over 300 miles and nothing has changed I did a top end run and hit 68mph. GPS shows actual 62. I haven’t rejetted the carb yet. I’m running 89 octane non ethanol fuel. Im not sure why the bike has dropped 5 mph.
I don’t beat on it and usually buzz around at 45 to 50 mph or less and don’t rev it out past 6000 rpm usually. The bike runs fine I just assumed it would wake up a little after a few more miles on the odometer. Then I planned on rejetting. Perhaps the warmer weather has something to do with it?

Baskt_Case · 04-24-2020, 01:08 AM

Quote:

Originally Posted by Spins

Now after changing the oil and adjusting the valves the bike appears to have lost top end.

You adjusted the valves. Definitely a mechanical change.

Do not trust the factory speedometer. Only GPS.

Most properly tuned 250 Chinabikes will average around 63 mph top cruising speed.

Megadan · 04-24-2020, 02:25 AM

I agree, the valve adjustment will have affected it a little bit. The changing weather will have a bit more to do with it. The one drawback to mechanical slide carburetors like these bikes use is that they do not self correct at all for any change in air density, humidity, etc.

That means as it gets warmer outside, your AFR is richer. Colder, it gets leaner. More humid? Richer. Increase in Elevation? richer. etc.

That basically means that there is a set of parameters that your carburetor is perfectly tuned for, and when you meet those parameters the Angels sing and the afterburners kick in. The rest of the time your bike will run pretty decently unless one of those parameters changes drastically enough that it requires jet changes. On my last Hawk (street oriented gearing, tires, exhaust, pod filter and a VM26 carb) I had a couple of those perfect moments where my bike managed to walk past 70, even hit 74 once (accurate speedo and phone GPS confirmed). No wind and the right conditions The rest of the time, getting to 68-70 was about all it had.

If I may ask, what specs did you set the valve lash to?

As far as top speed, 68-70mph is pretty average top speed for the TBR7 with mods from what I have seen. I wouldn't be too upset about it. Also keep in mind that even the slightest head wind on these low powered machines can kill quite a lot of the top end. Ride into a 10+mph head wind and laugh at how hard you struggle to get past 60mph lol.

Spins · 04-24-2020, 01:55 PM

I set the valve lash to .005” on both the intake and exhaust. I turned the engine around a full cycle and rechecked before tightening everything back up.

I know the stock Speedo is wildly optimistic. Mine is 5 mph off.

Megadan · 04-24-2020, 02:03 PM

Quote:

Originally Posted by Spins

I set the valve lash to .005” on both the intake and exhaust. I turned the engine around a full cycle and rechecked before tightening everything back up.

I know the stock Speedo is wildly optimistic. Mine is 5 mph off.

Ok, just to verify this. You set the lash to .005 inches, aka 5 thousandths.

That might be part of the problem. While not drastically on the big side, it is technically still out of spec.

Valve lash on most of these CG engines falls within .003in, plus or minus .001in. (aka .002in to .004in).

In metric that is .05mm to .10mm.

I personally set my bike to .06mm intake and .08mm exhaust. In SAE that roughly works out to .0025in intake and .003in exhaust

Spins · 04-24-2020, 02:36 PM

I know the bike is running a Little lean. I’m in Central Florida. I can feel it surge a little while going a steady lower speed.

Spins · 04-24-2020, 04:17 PM

My bad it was .05mm. I picked up the correct feeler gauge from Amazon. I always get this confused. I used the setting from the bikes manual .

So should I crank then down a bit ?

Megadan · 04-24-2020, 04:25 PM

Quote:

Originally Posted by Spins

My bad it was .05mm. I picked up the correct feeler gauge from Amazon. I always get this confused. I used the setting from the bikes manual .

So should I crank then down a bit ?

No, if you have them at .05mm then the gap is fine.

04-23-2020, 09:15 PM	#1
Spins Join Date: Jan 2020 Posts: 287	Brozz Performance? I broke my Brozz in with the OEM oil and changed it around 100 miles and adjusted my valves. The bike starts and idles better now. It was my first time adjusting valves and took more than a few attempts to get it right. While I was breaking in the bike I did run it out a little and was able to hit 73mph . It felt like it might have a little more left. Now after changing the oil and adjusting the valves the bike appears to have lost top end. It’ll only hit 68. My bike now has just over 300 miles and nothing has changed I did a top end run and hit 68mph. GPS shows actual 62. I haven’t rejetted the carb yet. I’m running 89 octane non ethanol fuel. Im not sure why the bike has dropped 5 mph. I don’t beat on it and usually buzz around at 45 to 50 mph or less and don’t rev it out past 6000 rpm usually. The bike runs fine I just assumed it would wake up a little after a few more miles on the odometer. Then I planned on rejetting. Perhaps the warmer weather has something to do with it?
	0

04-24-2020, 02:25 AM	#3
Megadan Join Date: Apr 2017 Location: Omaha, NE Posts: 8,016	I agree, the valve adjustment will have affected it a little bit. The changing weather will have a bit more to do with it. The one drawback to mechanical slide carburetors like these bikes use is that they do not self correct at all for any change in air density, humidity, etc. That means as it gets warmer outside, your AFR is richer. Colder, it gets leaner. More humid? Richer. Increase in Elevation? richer. etc. That basically means that there is a set of parameters that your carburetor is perfectly tuned for, and when you meet those parameters the Angels sing and the afterburners kick in. The rest of the time your bike will run pretty decently unless one of those parameters changes drastically enough that it requires jet changes. On my last Hawk (street oriented gearing, tires, exhaust, pod filter and a VM26 carb) I had a couple of those perfect moments where my bike managed to walk past 70, even hit 74 once (accurate speedo and phone GPS confirmed). No wind and the right conditions The rest of the time, getting to 68-70 was about all it had. If I may ask, what specs did you set the valve lash to? As far as top speed, 68-70mph is pretty average top speed for the TBR7 with mods from what I have seen. I wouldn't be too upset about it. Also keep in mind that even the slightest head wind on these low powered machines can kill quite a lot of the top end. Ride into a 10+mph head wind and laugh at how hard you struggle to get past 60mph 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
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04-24-2020, 01:55 PM	#4
Spins Join Date: Jan 2020 Posts: 287	I set the valve lash to .005” on both the intake and exhaust. I turned the engine around a full cycle and rechecked before tightening everything back up. I know the stock Speedo is wildly optimistic. Mine is 5 mph off.
	0

04-24-2020, 02:36 PM	#6
Spins Join Date: Jan 2020 Posts: 287	I know the bike is running a Little lean. I’m in Central Florida. I can feel it surge a little while going a steady lower speed.
	0

04-24-2020, 04:17 PM	#7
Spins Join Date: Jan 2020 Posts: 287	My bad it was .05mm. I picked up the correct feeler gauge from Amazon. I always get this confused. I used the setting from the bikes manual . So should I crank then down a bit ?
	1