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grantevans713

New 421 banshee build, carb selection question

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So this winter im putting a 421 kit into my banshee. Right now its stock bore with some aggressive porting, wiseco pistons, toomey t5s, custom billet reeds, cool heads, pump gas domes, amd it has been running great with a pairt of the old mikuni t34 02e.

The meat and potatoes of the new engine build will be:

⦁    DriveLine Performance 421cc Big Bore Assassin LP Cylinder Kit with additional intake and transfer porting

⦁    Wiseco 68mm blaster style pistons

⦁    HotRods 4mm 115 Long Rod Stroker Crankshaft

 

There are other modifications going in, and still some on it already like timing, clutch lockup, oversized radiator, etc. What I am curious about is weather or not I can just reuse my carbs? Can I just run bigger jets with these and all the power upgrades? Is there someone I can send them out to and have them bored? I felt like the 34s might have been to big for what was on it, and looking around some people run 35s or 36s, but others recommend 39s. I do plan to continue just running pump gas, I live at 1600 elevation and ride occasionally, but my trips to the dune every year are at 4000 elevation and I ride there probably more than I do locally. With the drastic difference I had considered the Lectron carbs, but all the info on them that I've found here is very old. Riding style generally will be more relaxed, but lets face it there are times you are almost full throttle for an entire tank of gas.

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1 hour ago, Burt Reynolds said:

Your 34’s will work. I have a drag ported 4mil with CPI in frames and run 33’s just fine.     You might get more hp out of larger carbs though.

My buddy says I should get 39s and run 19cc domes for 110, make it a drag bike. Not sure I want to do all that but what kind of HP gains are we talking with bigger carbs? ALso if I were to get them ported is there a reputable person I could send them to?

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It depends on where you want your power,and your type of porting.  Drag ported 421 I would probably run 38mm’s. Trail stock to 34,dune port in the middle.

If your going for high rpm peak drag racing horsepower then I would think 36-38mm

I’ve been out of the game for to long but the best port work I have ever got was from Chris Grissom racing.

Edited by Burt Reynolds

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I asked driveline for more aggressive porting, so it will be on the drag side of things. When I am riding usually its full throttle into a coast, or I keep it wide open and blast around. I might end up going with some 39s as they seem to be more widespread. If I could find someone reliable or recommended I would send these out and get an oval bore done to put them right in the middle.

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On 7/10/2020 at 4:22 PM, grantevans713 said:

My buddy says I should get 39s and run 19cc domes for 110, make it a drag bike. Not sure I want to do all that but what kind of HP gains are we talking with bigger carbs? ALso if I were to get them ported is there a reputable person I could send them to?

What your wanting and what your buddy is telling you are two different things. Your ordering a LP 421, NOT a hp 421. So your already not getting a drag engine. Therefore your 34mm carbs are actually a perfect choice and I would not consider changing them.

if you want to build a drag bike, you need to switch your cylinders and then you can consider bigger carbs, although still not needed.

19cc dimes and vp110 is costly and unless this is a real drag bike (cut, stretched, and lengthened) you absolutely don’t need it.

if your building a general purpose fast dune bike, your current choice is perfect.

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On 7/12/2020 at 11:45 AM, gusto said:

What your wanting and what your buddy is telling you are two different things. Your ordering a LP 421, NOT a hp 421. So your already not getting a drag engine. Therefore your 34mm carbs are actually a perfect choice and I would not consider changing them.

if you want to build a drag bike, you need to switch your cylinders and then you can consider bigger carbs, although still not needed.

19cc dimes and vp110 is costly and unless this is a real drag bike (cut, stretched, and lengthened) you absolutely don’t need it.

if your building a general purpose fast dune bike, your current choice is perfect.

Thanks for the response, I already got everything ordered for 110 just to try it out, carbs, domes etc. I am considering ordering a second set of domes to swap out to run 91. Would need some jets to swap out as well I'm sure.

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