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carbs? why what size when? OPEN DEBATE


camatv

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Going to run 28s but not sure if it’s best for open road. In fact I’m sure 35s will be better but I got the 28s now and don’t ha e money for other carbs.

fluked out and picked up a HJR dune ported serval with two sets of domes for a great price local. 

So building another engine on the side it seems.

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Going to run 28s but not sure if it’s best for open road. In fact I’m sure 35s will be better but I got the 28s now and don’t ha e money for other carbs.

fluked out and picked up a HJR dune ported serval with two sets of domes for a great price local. 

So building another engine on the side it seems.

Run em i would, u can always upgrade u know there will be powder to be had

 

Sent from my LGMS210 using Tapatalk

 

 

 

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  • 1 year later...
On 1/27/2010 at 7:22 PM, BigRed350x said:

First off I will say that I don't care about dyno results. I ride big dunes and drag race with friends out on the dunes. All of my testing is real-world testing in real life. Not sitting on some dyno in a shop.

 

On my 4mil Duner (4mil gorr ported stock cylinders, vforce3, cool head, 19cc domes noss cut to my spec, reed spacers(just to get the carb bowls off the clutch arm), upp intakes, shearer pipes) I've run 33pwk's, 34PJ's, 35PWK's, 35PWK AirStrykers, 38mm PWK Airstrykers, 39mm PWK's, 34mm TM Flatslides and 35.5 TM Flatslides. Every single carb setup was run on methanol, so my results might be different than you gasser guys.

 

The 38's provided the best power and best top-end speed. The 33's made great throttle response and good low end, but you could feel them holding the bike back on the big end. The 34PJ's were the carbs I ran the most and liked the most for dune riding and play racing on this particular setup. They felt like they gave the best of both worlds - throttle response and top end power. When I'd go somewhere just to drag race and do WOT straight runs I'd swap out to the 38's. The 39's were pretty similar to the 38's, I just prefer the airstryker design with methanol.

 

Its a mix and match between providing your engine with the most CFM you can/it wants and getting your intake velocity high enough to efficiently pull the air and fuel into the engine. The velocity is affected by porting though, so it will vary bike to bike. The bigger carbs are going to have lower velocity through the carb and less of a venturi effect on the jets in the carbs. The smaller carbs will be just the opposite, but will also restrict the CFM available to the engine at your target rpm.

 

If 33's worked on any engine setup out there, you'd see 33's on everyone's bikes, including the big drag bike setups.

 

I run stock carbs on my stock stroke duner, 34PJ's on my 4mil duner, and 41's on my drag bike. I think my drag bike would cave in a set of 33's and suck them into the engine. LOL

Well put... 

 

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holy 9 year old thread revival, lol..... but dont forget about roll-on throttle.   stock carbs have too tight of a venturri to handle moisture well, which is the main reason they tend to runaway.  stock pipes were restrictive enough to not really need much more, but swap those to certain pipes, and the problem gets much worse.    ideally, you want to stick to carbs that match the cfm (pulsed) of the engine, but lower rpm can loose suction on the jets  at wot, which is why you can train yourself for roll-on throttle, instead of wot stabs, and pick up a good running bottom end.   on that point, technically, you could pick up some 44-48mm carbs made for the 6-800cc range and set them to open half at wot, but then there is the problem of the shape of the opening and both sides of the opening that will mess with things, and probably an issue with the size of the emulsion tube and orifices, making it different than the equivalent area carb full open.

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