Stinger Posted January 13, 2006 Report Share Posted January 13, 2006 (edited) I know there is no exact amount of power at which the stock carbs won't work but I'm looking for at what point it's generally a good idea to upgrade to a larger set of carbs or you will be leaving a noticeable amount of power on the table. Since they are so expensive, I'd rather not upgrade unless it's costing me alot of power. I've got all the normal mods: Boyesen Dual Stage CF Reeds Milled Head (155psi) FMF Fatties Airbox Delete Dual K&N's and I ported it with the Race Logic Stage III kit and also raised the tranfer ports. I'm also having Jeff at F.A.S.T raise my transfer ports and such for me to gain a little over the standard porting I did. I'm thinking I'm probably "borderline" on whether I need new carbs or not. What do you think? [Edit] Porting Pics added below Edited January 14, 2006 by Stinger Quote Link to comment Share on other sites More sharing options...
BigRed350x Posted January 14, 2006 Report Share Posted January 14, 2006 Pretty much any time you get more than just a cleanup port you will benefit from some bigger carbs. I have been running stock carbs on my gorr port for a while now and it's ok, but i know there is a lot more in there if I put some bigger carbs on. If I weren't going to cubs this summer I would put some on there. Quote Link to comment Share on other sites More sharing options...
itsaripper Posted January 14, 2006 Report Share Posted January 14, 2006 The rule of thumb is use as small a carb as you can get away with. You wiil get a wider spread of power cause it will work down to a lower rpm. That will make it easyer to tune Haveing said that, the more you port the more air you will move through the cylinder. Because of that you will kiss lower end goodby and hello mid and top end. This is where the larger carbs will work better. My 2cents here Go with PWK28 or PWK28s bored to 30 34mm and 35s are going to be way to big. Quote Link to comment Share on other sites More sharing options...
locogato11283 Posted January 14, 2006 Report Share Posted January 14, 2006 id run 33mm pwk. but more than likely for what you are doing stock carbs will be fine. if ur gonna upgrade go with 33mm pwk. that way if you end up building a stroker motor youll have a good carb for it. Quote Link to comment Share on other sites More sharing options...
BigRed350x Posted January 14, 2006 Report Share Posted January 14, 2006 id run 33mm pwk. but more than likely for what you are doing stock carbs will be fine. if ur gonna upgrade go with 33mm pwk. that way if you end up building a stroker motor youll have a good carb for it. 459261[/snapback] I just bought a set of 33pwk's for my buildup! I can't wait. I'm not putting anything on, just making a huge pile of parts that are all going on, once I get the cub cylinders. Quote Link to comment Share on other sites More sharing options...
rocketboy Posted January 14, 2006 Report Share Posted January 14, 2006 (edited) and I ported it with the Race Logic Stage III kit and also raised the tranfer ports. I'm also having Jeff at F.A.S.T raise my transfer ports and such for me to gain a little over the standard porting I did. I'm thinking I'm probably "borderline" on whether I need new carbs or not. What do you think? 459123[/snapback] i could help yo u decide alot easier if yo u knew your actual exhaust and transfer timing numbers after its done being ported ,but youd probably be ahead to run dual 33 pwk s or the bored out 30mm kehein pwk's ,the stock carb limit is probably around the high 70's RWHP on gas ,but i nall actuallity you wont be any where near that limit so dont be too concerned . Edited January 14, 2006 by rocketboy Quote Link to comment Share on other sites More sharing options...
Stinger Posted January 14, 2006 Author Report Share Posted January 14, 2006 (edited) i could help yo u decide alot easier if yo u knew your actual exhaust and transfer timing numbers after its done being ported ,but youd probably be ahead to run dual 33 pwk s or the bored out 30mm kehein pwk's ,the stock carb limit is probably around the high 70's RWHP on gas ,but i nall actuallity you wont be any where near that limit so dont be too concerned . 459414[/snapback] Looking at what's been said so far I don't think the stockers will be hurting me too much just yet. RaceLogic doesn't publish the timing #'s and I don't have a degree wheel to check them (Maybe I can get Jeff to do it?) but here are some pics of the port work. The exhaust port was raised about .010-.012" and the transfers will get the same unless Jeff thinks something else will work better. These two show the amount of material to be removed: These two are the semi-finished ports...I still have to bevel and smooth a bit more after it gets bored/honed. First set is a before and after comparo: Edited January 14, 2006 by Stinger Quote Link to comment Share on other sites More sharing options...
fastbanshee4u Posted January 14, 2006 Report Share Posted January 14, 2006 So many people buy carbs who dont really need them.But once your done with your bike you will need big main jets.I have ported many bikes,and you can make a banshee very fast with stock carbs.Dont spend to much time polishing where the reeds sit,just get everything evenly sized. Shape your transfer bridge sharply,try a small round file for this also.Give me the distance from the top of the exhaust port to the cylinder top,in millimeters 30-26. If you want a good tip for more top end than most $300 port jobs let me know? Congrtats on doing it your self,your going to love the extra power. Quote Link to comment Share on other sites More sharing options...
Stinger Posted January 14, 2006 Author Report Share Posted January 14, 2006 (edited) So many people buy carbs who dont really need them.But once your done with your bike you will need big main jets.I have ported many bikes,and you can make a banshee very fast with stock carbs.Dont spend to much time polishing where the reeds sit,just get everything evenly sized. Shape your transfer bridge sharply,try a small round file for this also.Give me the distance from the top of the exhaust port to the cylinder top,in millimeters 30-26. If you want a good tip for more top end than most $300 port jobs let me know? Congrtats on doing it your self,your going to love the extra power. 459493[/snapback] Exhaust Port Height: I got 1.127" or 28.6mm to the top of the exhaust port. I plan to raise the transfers 2.5-3mm from stock as well. Main Jets: The biggest mains I have on hand are 380's. Think I'll need to go bigger than that? I assume I'll also need to change the pilots correct? Tranfer Tunnels: I've done some porting in the tranfer tunnels but my porting bits are too large to get it all. I just bought a smaller bit though. I will get the bridge cut more sharply than stock with a file as mentioned. Is making the tranfer tunnels larger a good idea or should I just make them smooth and be done with it? Case Porting: Also, I plan to port the case while I have it apart but I'm not sure what I should or shouldn't cut. I noticed there seems to be about a 2mm overlab where the case is smaller than the transfer tunnels. I plan to port the case so it matches up with the tranfer tunnels. Is there any other areas on the case I should modify or smooth out? Modifying Pistons: Should I modify the Wiseco Pro-Lites in any way (cut the ports larger, remove some material from the bottom of the piston, etc. to match my port job or is that not benificial? Does it compromise the structural integrity of the pistons? Power Goals/How I Use the Shee: I use my Shee for just about everything. I race MX, jump, ride trails, hillclimb, and hit the dunes. Because of this I want a good all around power, not some peaky engine that does nothing but spin or bog. A smooth powerband (not 4 stroke smooth ) would be perfect. I'm up for any/all the tips you've got. What's your tip for more top end than most $300 port jobs? Thanks everybody for the insite... Edited January 14, 2006 by Stinger Quote Link to comment Share on other sites More sharing options...
dawarriorman Posted January 15, 2006 Report Share Posted January 15, 2006 Modifying Pistons:Should I modify the Wiseco Pro-Lites in any way (cut the ports larger, remove some material from the bottom of the piston, etc. to match my port job or is that not benificial? Does it compromise the structural integrity of the pistons? Leave the pistons alone. Messing with them will weaken them and make you more likely to break a skirt. Quote Link to comment Share on other sites More sharing options...
rocketboy Posted January 15, 2006 Report Share Posted January 15, 2006 (edited) my honest 2 cents is your intake looks decent, the exhaust is all wrong IMO ,its is too wide and low ,the shape isnt ideal at all . the height is pretty wimpy even for FMF pipes ,the intake accounts for very lil power making propertys ,the transfers and exhasut wil l m make the bulk of your added performance gains . Edited January 15, 2006 by rocketboy Quote Link to comment Share on other sites More sharing options...
Stinger Posted January 15, 2006 Author Report Share Posted January 15, 2006 my honest 2 cents is your intake looks decent, the exhaust is all wrong IMO ,its is too wide and low ,the shape isnt ideal at all . the height is pretty wimpy even for FMF pipes ,the intake accounts for very lil power making propertys ,the transfers and exhasut wil l m make the bulk of your added performance gains . 459606[/snapback] The exhaust gets wider as it gets to the top, even though in my pics it looks like the widest part is centered on the port (because I can't take a pic straight at the port). Here is a pic of the actual exhaust shape: Quote Link to comment Share on other sites More sharing options...
fastbanshee4u Posted January 16, 2006 Report Share Posted January 16, 2006 I would raise exhaust to 27.5 t0 28 mm, change domes to 19 or 20s to get back some compression.Keep the top of the exhaust port arched nice to keep ring and piston wear down. Mic the diameter of the inside of your head pipes and try to get the cylinders close to that. Use a drum sander in a diegrinder,then blend that to the cylinder edge with paper wraped around a dowel rod or dremel flex shaft..Get your exhaust real smooth.Dremel makes sanding/buffing wheels that work great,brown first then the grey one. Yes, on your cases just taper to match the the cylinders. Match the gaskets also or buy from Twister racing. Get used to spinning or buy a 4 stroke,also Fattys hit hard and spin easy. Good luck Quote Link to comment Share on other sites More sharing options...
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