Stock Carb Size

[GleasmJA]

Just wondering what the stock carb size is? Wondering what size to go to for aftermarket carbs!!

 

What i have is T-5's, .030 bore, Open top airbox, K&N, Toomey alum radiator.

 

Looking at getting port job and cool head. What would be a rough MM size to look for with this. Thanks for the help.

 

Jon

[sandman]

stock=26mm

reccommend=28 pwk's

[bigboybanshee]

Just wondering what the stock carb size is?  Wondering what size to go to for aftermarket carbs!!

 

What i have is T-5's, .030 bore, Open top airbox, K&N, Toomey alum radiator.

 

Looking at getting port job and cool head.  What would be a rough MM size to look for with this.  Thanks for the help.

 

Jon

443033[/snapback]

 

Best thing to do is ask the person who's porting your cylinders as to which carb size would be best for your application. I was about to go out and purchase a set of 34mm carbs for my banshee before I talked to my builder, then he recommended I should get some 39's to get the full potential. What I thought was adequate would have been, but wouldn't have achieved the most power out of the portwork.

 

It's a wise idea to talk to them and it could potentially save you some money in the long run

[wayfst]

39's holy crap! you run'n a snowmobile motor!

[bigboybanshee]

39's holy crap! you run'n a snowmobile motor!

443199[/snapback]

 

LOL! You would think it!!! I thought that they might be too much fuel but figured I'd wait and see...sure enough, they were right on the money I'm really glad I asked my builder, he knew exactly what would work best with his portwork, no doubt!

[Malott 1]

LOL! You would think it!!! I thought that they might be too much fuel but figured I'd wait and see...sure enough, they were right on the money   I'm really glad I asked my builder, he knew exactly what would work best with his portwork, no doubt!

443215[/snapback]

I wondered about the 39's. I asked a few builders about 39's and they told me if I was running a cub I would be fine but on stock cylinders they didn't recommend going over 36's.

[Banchetta]

Just wondering what the stock carb size is?  Wondering what size to go to for aftermarket carbs!!

 

What i have is T-5's, .030 bore, Open top airbox, K&N, Toomey alum radiator.

 

Looking at getting port job and cool head.  What would be a rough MM size to look for with this.  Thanks for the help.

 

Jon

443033[/snapback]

Don't waste your money on carbs unless you have no other mods left to do. Carbs give minimal gains per dollar. W/o porting, you will lose hp w/ larger carbs.

[wayfst]

I just wonder about air velocity. You want good speed through the carbs to pull the fuel. the slower the air, the higher you have to jet. When we build a bike for low end power we look for the smallest useable carb. The air velocity is good on the bottom but the size is restrictive for top end use ( this is why single carbs are good for trails). so common understanding is the larger you go the more top end you'll have but the less bottom end, to a point, past that and you lose it all. now don't get me wrong, I'm not saying your builder is wrong, it's just------those are really big carbs!

[Banchetta]

Agree, I've dyno tested a lot on this. I've seen ported stock carbs lose hp from bottom to top on a non ported shee. I also tested a set of 34mm carbs on a stock port and lost 8hp from bottom to top. W/ all the testing I've done, I've never seen a gain on one end and lose on the other. My stroker actually gained more on the bottom than on top going from stock to 35's.....go figure.

[Shee-Male]

I think with stock size jugs/reeds a 39 is a little big the power band will only be 200rpm long @ 9000 rpm

not to mention poor throttle response and no bottom end

[GleasmJA]

thanks guys.... very helpfull information. I'll have to take all that into consideration before i go jumping the gun.

[bigboybanshee]

I wondered about the 39's. I asked a few builders about 39's and they told me if I was running a cub I would be fine but on stock cylinders they didn't recommend going over 36's.

443340[/snapback]

 

That's interesting. I probably would have been OK with 36's, but the way I was told that with the port I received with the pipes I'm running, the more gas I can feed it the better. Granted, that doesn't mean I need to find the biggest carb and slap it on there, I'm pretty sure when I was told to get 39's, he was suggesting those would be the biggest I could run without having too much gas (I did ask him what would be ideal for the most power). I didn't get into any technical details with him...I took his word, it worked, I'm happier than a pig in shit.

 

I think with stock size jugs/reeds a 39 is a little big the power band will only be 200rpm long @ 9000 rpm

not to mention poor throttle response and no bottom end

443413[/snapback]

 

I don't quite understand what you mean about the powerband only being 200 rpm long @ 9000 rpms...doesn't make any sense to me, not sure what you are trying to point out. My cylinders are not stock port and I do not have stock reeds

 

I don't need bottom end being that my banshee is setup strictly for drag racing, it's wide open from the starting line to finish. I want as much top end as possible...

 

Now, if someone wants to donate a set of smaller carbs (35's /36's, etc.) to do some testing on this, I'll be happy to do so and will return them when I'm done...but my whole reason for giving my scenario in this is not because I'm having any problems with my setup, it was merely to backup what I was suggesting about contacting your engine builder for the best recommendation, especially when porting is involved. I love my setup, it flat out rips and pulls really hard. I have no complaints, whatsoever.

[Banchetta]

That's interesting. I probably would have been OK with 36's, but the way I was told that with the port I received with the pipes I'm running, the more gas I can feed it the better. Granted, that doesn't mean I need to find the biggest carb and slap it on there, I'm pretty sure when I was told to get 39's, he was suggesting those would be the biggest I could run without having too much gas (I did ask him what would be ideal for the most power). I didn't get into any technical details with him...I took his word, it worked, I'm happier than a pig in shit.

I don't quite understand what you mean about the powerband only being 200 rpm long @ 9000 rpms...doesn't make any sense to me, not sure what you are trying to point out. My cylinders are not stock port and I do not have stock reeds

 

I don't need bottom end being that my banshee is setup strictly for drag racing, it's wide open from the starting line to finish. I want as much top end as possible...

 

Now, if someone wants to donate a set of smaller carbs (35's /36's, etc.) to do some testing on this, I'll be happy to do so and will return them when I'm done...but my whole reason for giving my scenario in this is not because I'm having any problems with my setup, it was merely to backup what I was suggesting about contacting your engine builder for the best recommendation, especially when porting is involved. I love my setup, it flat out rips and pulls really hard. I have no complaints, whatsoever.

443686[/snapback]

What he was saying is that your peak power will only be for 200rpms. So say you make your peak hp at 10,000rpms. He was saying that you probably only have peak hp from 9800-10000rpms. where if you have a broader powerband, then your peak hp will go from 7000-10000rpms...In your case, you want peak hp and torque between the rpms you shift in, so if you shift at 10000rpms and it drops to 9600rpms after a shift, then you'll want a motor to be at its peak between those rpms.....Where as other racers speed up and slow down, so they need peak torque at a broader power (5000-9000rpms) so they don't have to constantly shift to find the peak hp...Dragracers look for peak hp and torque, where xc racers will give up the most hp for a broader power curve...

[bigboybanshee]

What he was saying is that your peak power will only be for 200rpms. So say you make your peak hp at 10,000rpms. He was saying that you probably only have peak hp from 9800-10000rpms. where if you have a broader powerband, then your peak hp will go from 7000-10000rpms...In your case, you want peak hp and torque between the rpms you shift in, so if you shift at 10000rpms and it drops to 9600rpms after a shift, then you'll want a motor to be at its peak between those rpms.....Where as other racers speed up and slow down, so they need peak torque at a broader power (5000-9000rpms) so they don't have to constantly shift to find the peak hp...Dragracers look for peak hp and torque, where xc racers will give up the most hp for a broader power curve...

444289[/snapback]

 

 

Thanks for explaining that, makes complete sense now.