Jump to content

409 big bore kit slower than stock...carb problem?


Recommended Posts

I just had the LA Sleeve 409 big bore kit installed on the banshee.The quad runs fine, its just slow. Its alot slower than when it was stock. It doesn't smoke, stutter, blue my pipes, or anything like that. I contacted LA Sleeve and they told me I needed to install a 35mm 2-into-1 carb kit. Would the bigger carbs make that big of a difference. Would changing my Jetting help or will the stock carbs just not flow enough no matter what the jetting is set at? I have 2 carbs off of a 750 cc 2 stroke water buffalo street bike that I was told would work with very minor modifications. Anyone know anything about those carbs? Any ideas???!!?

Link to comment
Share on other sites

No experience with big bore banshees or a single carb on a twin. ... But with reference to jetting, moving to a bigger carb reduces air velocity and requires jetting up, and over-boring the cylinders increases air velocity through the original carbs and therefore requires jetting down. ... If that theory holds true, then you're running rich.

 

By going to the 409, so many parameters have changed and it's a new ball game as far as jetting the original carbs goes. ... port timing, port time area, compression, CR, MSV, etc., etc.

 

Get your mains dialled in with plug chops, and go from there on the other circuits.

 

OR ... listen to loco, he's got the hands on experience. ;) ... You'd certainly be better going bigger on the carbs, but dual 35s loco? :shrugani:

 

Rare.

Link to comment
Share on other sites

OR ... listen to loco, he's got the hands on experience.  ;)  ... You'd certainly be better going bigger on the carbs, but dual 35s loco?  :shrugani:

 

Rare.

398349[/snapback]

there are tons of people running 35s on 350 motors. i dont see why you couldnt run them on a 409. an engine that big will require more fuel and air to make it run to its full potential. i def wouldnt go with a 2 into 1. need more info on the cylinders. they ported or what? compression? personally id get rid of the 409 stuff...

Link to comment
Share on other sites

I had a 404 sleeve that hauled ass.

the ports need cleaned up. especially the transfers,the sleeve restricts them more than stock so they need fixed, same withthe intake and exhaust.

Single 35mm will be enough carb for the motor. Depending on what your gonna do with it either got dual 33's, dual 35's or single 35.

 

When you get it ported your going to need to change the domes if you have an aftermarket head, larger bore your going to need the large bore version domes.

See DLNOSS he'll hook you up. if you can run race fuel get that compression to the 170-180 area after porting. Than come back and tell us how much it hauls.

Link to comment
Share on other sites

going big bore never repalces good high quality porting o n a 2 stroke(especially one with archaic port work) thats why some of the fastest bikes are 350's or small 4mills, smaller the smaller the displacement,the faster you ca n get those pistons pumpin high-ass rpms. the 409 needs porting and plenty of it t obe quick ,i would run 34 tm flatslides or 33-35 pwks if it were me . your likely down on topend power due to the stock carbs restricting flow to each 204cc cylinder IMO :cheers:power is all in the porting! :bolt:

Edited by rocketboy
Link to comment
Share on other sites

the ports need cleaned up.  especially the transfers,the sleeve restricts them more than stock so they need fixed, same withthe intake and exhaust.

398625[/snapback]

 

going big bore never repalces good high quality porting o n a 2 stroke(especially one with archaic port work) thats why some of the fastest bikes are 350's or small 4mills

 

youve got the same size flow parts (carbs, transfers, ex port, etc.) with a motor needing a ton more air. like running stock heads on yur sb 383, make'm no sense chief.

Link to comment
Share on other sites

What happens when you put the larger sleeve in is that the OD of the sleeve now chokes down your transfers.Thus you now have a bigger bore with smaller tansfer ports.Now your trying to fill a bigger hole by way of a smaller passage.

Thats what I determined after going to the larger sleeves.Be ready for some serious grind time!

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
×
×
  • Create New...