How much carburator cfm necessary?

[Bill Hilly]

I am intending to leave my TBR7's motor internally stock, but do plan on replacing the exhaust, and either modifying the air box, or running a pod filter. I have a variety of main jets, and I also have a variety of the pilot jets that I ordered from AliExpress when I had my Brozz 250. I have what it would take to properly jet the stock PZ30 clone carb, but I have been on some Chinese dual sport Facebook sights, and most seem to think that the Nibbi PE28 FL (version with a flange) will create more power. I personally don't see how bolting a larger carb to the stock intake on an untouched head can flow better, but I may be wrong. Would I actually gain power in the internally stock motor? I know that if the intake, and head were ported, and polished it could flow more, but I don't intend to do that stuff yet Thanks

[Megadan]

Some people might disagree with me, but here is my take, and this is as somebody with a Nibbi carburetor lol.

Don't bother with the PE28FL if all you have is just an exhaust. The PZ30/VM26 carbs are more than enough to support the kind of power the CG engine makes, especially with no head work.

Now, that said, if you went and ported the head, you would then notice a difference in the mid and upper RPM ranges when really getting on the throttle with a PE28. That is one thing I noticed when I swapped back and forth between the carburetors after doing head work. Especially so after putting a cam in. It's not a huge difference, but you do notice it.

Without any engine work, there may be an improvement in throttle response, and maybe a teeny bit up top, but that would be more attributed to less turbulent airflow and better velocity than anything else.

If anybody needs evidence of the PZ30/VM26 being more than adequate. My First Hawk was pretty standard other than the ebay exhaust and a pod filter. 17/43 sprockets with Shinko 705's. Carburetor was a VM26 "30mm" clone with a 27.5 pilot and a 115 main jet. That bike got around in traffic without feeling slow and could easily top 68mph on a consistent basis, and hit 70 more than a few times, with my 6'4 nearly 300lb butt at the time in the seat.

Unfortunately, everybody in the facebook group does mods because somebody else did mods. Monkey see, monkey do, with no thought. Hell, I originated the PE30 on the Hawk, and when I try to argue against them using it they tell me I am dumb lol. Take my word for it, most of the guys on that Facebook group have egos. They want to look and sound important in the community, but know absolutely nothing about what they are doing and give horrible advice to other newbies who have absolutely no idea what they are doing.

[Thumper]

Completely agree with Megadan. And you have jets for the the original carb.

For now, just go through the standard rejet and shim. This will really improve the performance anyway. I still have the original carb on my storm, just rejet for cat delete and exhaust mod. It is fantastic, and it cost me about $15 bucks for jets (with lots of spares!).

At some point after you have lots of miles on the bike, if you start making major performance changes, maybe it will be worth getting a new carb.

[Bill Hilly]

Originally Posted by Thumper

Completely agree with Megadan. And you have jets for the the original carb.

For now, just go through the standard rejet and shim. This will really improve the performance anyway. I still have the original carb on my storm, just rejet for cat delete and exhaust mod. It is fantastic, and it cost me about $15 bucks for jets (with lots of spares!).

At some point after you have lots of miles on the bike, if you start making major performance changes, maybe it will be worth getting a new carb.

Yes, That's what I plan to do. I got the bike with nearly no miles on it, but the guy had already re-jetted the carb with a 110, but I don't know if he shimmed the needle. It runs very good though . He also had 39/17 sprockets on it, but I now have the 46/17 on it. I did put the actual genuine Honda studs on it. I had the stock airbox on my Brozz, and a pretty decently modded stock exhaust, and I was running a 115 main, and if I remember right a 38 pilot, and had the needle shimmed. It was enough for me. I personally don't see having a nearly new bike, and tearing into the motor yet. I also can't personally justify having a cheap bike, and constantly spending 5-10% of it's value on mods that the motor can't benefit from in stock configuration.

[Deckard_Cain]

When all I had was an exhaust, a knock off Amazon vm26 was perfect. It was fine when I had more engine mods too.

In fact, of all the carbs I've tried (only about 1 or 2 fewer than Dan), the vm26 was the most reliable, stable, and compliant carburetor. For your uses, something like that would be just fine.

At 600ft, I ended up using a 22.5 pilot (Mikuni scale) and a 115 to 117.5 main.

[Megadan]

Originally Posted by Deckard_Cain

In fact, of all the carbs I've tried (only about 1 or 2 fewer than Dan), the vm26 was the most reliable, stable, and compliant carburetor. For your uses, something like that would be just fine.

Same for me. Even when compared to a PZ30 the VM26 clone was actually better in all regards. People scoff at that statement claiming it really doesn't matter because "it's the same" but there was definitely something just slightly different in how they ran

[Bill Hilly]

Originally Posted by Megadan

Same for me. Even when compared to a PZ30 the VM26 clone was actually better in all regards. People scoff at that statement claiming it really doesn't matter because "it's the same" but there was definitely something just slightly different in how they ran

Do the VM26 clones have an easy to access idle air/fuel mix screw ? That was my biggest disappointment with the PZ30 on my Brozz.

[Bill Hilly]

I was looking at exhaust last night, contemplating whether to gut the cat out like I did my Brozz. There was one on eBay for around $77.50, with the make an offer option. I offered $72.50, and this morning ebay said they accepted, with tax it was around $76.50, so I think I done alright. I had already made up my mind that I would withdrawal the offer if they hadn't accepted by this morning. I think that doing a neat job of gutting the cat, and a not so neat job of opening the rear of the Brozz's exhaust gave me as much, or nearly as much as an aftermarket exhaust would have because I was running a 115 / 38 jet set in the factory carb,and stock air box, if memory serves me. Do any of y'all know why all the aftermarket exhaust seem to have an enlarged oblong bulge in the pipe about were a catalytic converter would be ? I didn't order the exact exhaust (JFG, or something), that seems popular on the Facebook, but did order one for a Honda CRF 150/230F, so I assume it should be alright. I hope so. I am posting the link to what I bought. https://www.ebay.com/itm/27472535351...mis&media=COPY

[Brasky]

Looks the same as my exhaust but different color. Mine I had to enlarge the bolt holes like normal. The middle bracket didn’t even come close to lining up so I had to cut it off and make a new one. But now that it’s finished it has great clearance around the motor, frame, and air box with no rubbing and it sounds deep and throaty

[TominMO]

Originally Posted by Bill Hilly

Do any of y'all know why all the aftermarket exhaust seem to have an enlarged oblong bulge in the pipe about were a catalytic converter would be?

The bulge without the cat is a resonator chamber, to make the exhaust note sound better.

[Bill Hilly]

Originally Posted by Brasky

Looks the same as my exhaust but different color. Mine I had to enlarge the bolt holes like normal. The middle bracket didn’t even come close to lining up so I had to cut it off and make a new one. But now that it’s finished it has great clearance around the motor, frame, and air box with no rubbing and it sounds deep and throaty

I was thinking that the middle bracket and clamp was all one piece. I'm just going by memory of how I think it was on my Brozz though. How far off was it ? I just looked at my bike, and I was wrong. The clamp, and bracket are separate. Sorry