changing my 421 cub from c12 race fuel to gas...need help!

[epyc421cc]

Hey guys I just got a 421cc stroker banshee that runs on c12 race fuel...now I wanna put it back to gas so I am wondering what size head I need for it...will a stock head work or should I get the 421 head?..and what dome cc sizes as well...my compression seems fairly low for race fuel bike at 150psi...iv heard they should be any where from 160-200...bike runs great...but I am a little lost in what to do for the swap...I am not sure what the dome size in it right now is...

[Deadbeat]

what head is on it now, a modded stocker?

[dirtydownunder]

If you're at sea level 22-24cc domes will be good for pump gas. A stock head will have to get modded to run 68mm bore and chamber work.

Check the ignition timing see if it's not over advanced for race gas.

[epyc421cc]

Do the jets need to be replac3d and timing and what not?..

[dirtydownunder]

if it has a timing plate, id put it at 0 and start fresh. check it has a stock cdi, to make sure it doesnt have an aftermarket adjustable cdi.

 

what  jets are in it now ?, what carbs ?

 

 

the bike is gonna lose  a considerable  amount of power, switching to gas.   why buy it, to switch to pump ?

[epyc421cc]

Always wanted a banshee never had one or any two stroke for that matter...it was a trade off for my 05 crf450r...I know ill lose about 8-10hp swapping over...im in for a big learning curve lol

[dirtydownunder]

gotchya, youll switch it all back

id shoot for some custom domes, instead of off shelf ones.   hit up wildcard racing, a sponsor on here. they did my pump gas 421 domes.

[epyc421cc]

Nice...I had thought about selling motor complete but it was the 421 stroker that I wanted...will still put out alot more power than just the stock 350...

[dirtydownunder]

it will, but all the power will be in the top end, it wont be too awesome to trail ride with.

what pipes are  on it ?

[epyc421cc]

T5's or somethin..I was thinkin about puttin a 2 in a carb on it and diff pipes for more bottom end when I swap...

[dirtydownunder]

2n1 are pretty poo,  nothing beats 2 carbs.

 

theres not much you can do, to that cylinder to give it more bottom end, besides leaving it on race gas with decent amount of compression and timing.

 

t5's arnt optimal for that cylinder either.

 

 

what size carbs are on it ?

throw some pix up.

[epyc421cc]

Not sure what size the carbs are and im away from it right now...race gas is too expensive lol...19L (5gallons) is 145$...c12 110 octane...I was told I could run a couple bottles of octane boost to get supreme gas to 105 or something but not sure...

[dirtydownunder]

nah you cant do that either haha.  

 

speak to a builder (one of the sponsors) and see what you can get away with on pump fuel.  421 cub, a pretty much  a drag/race cylinder, not intended for down low powers.

[trickedcarbine]

Mat shearer has a 2/1 pipe design for guys with cub remorse. It helps get you a bit more low end back with out totally choking off the air flow. I would personally try some CPI pipes or maybe rockets over shearers if you want bottom end, maybe even stick with your current pipes.

 

As far as what you need to do with the head, what kind of head is it? Shell with inserts? If so just get new domes cut from a reputable builder. They will get it set up the way it should be.

 

Jetting should be easy. In fact you will probably drop a size or two in the main and maybe lean the needle out one clip.

 

Timing, just stick it at 4 degrees and leave it be. You could speak with whomever is doing your domes and they will have good insight as to what kind of timing you will be able to get away with on premium and their dome set up.

[epyc421cc]

Awesome thanks for the info...I had intendedit use more on open back roads pitsand hill climbs...not so much theracing..