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My 421 RZ-Bike


RGL

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Hello at All,

 

my name is Raphael. I'am from Germany and I already spent a lot of time reading this great forum. I hope that somebody could help me with some questions.

 

Last winter I bought some 421cub-cylinders (68mm wiseco piston) with a plus 4mm Crank and built a nice motor for my RZ350. My further setup is Jolly-Moto-Pipes, Boyesen Reeds with stock carbs (26mm) and air-box. On the Dyno the motor produced 73hp (crank) at 8800 rpm. For me it was not really enough because other RZ with stock RZ-Cylinders produced more than 80hp at the same time (but at higher rpm). So what I want to know is the best carb size to get more power without losing too much torque at lower rpm. This is important because I ride this bike on the street. I'am thinking about 30mm or 35mm carbs. And do you prefer Mikunis or Keihins? In Germany most people know Mikuni but we have less experiences with Keihin-Carbs.

And my importants question is about the exhaust. As I already told I use a Jolly-Moto Pipe. But this pipe was built for 350ccm-motors with another porting. Banshee-pipes wont fit into my RZ-frame. So I cant buy a propper one. It would be great if somebody could give me the measures of good pipes. Maximum Revs should be around 10.000 rpm with good midrange-power. My aim ist to get 85hp at the crank.Is this real? I heard the 421 cheetahs produces around 100hp with 35mm carbs. Is this difference normal (because "only" the intakes are bigger)?

 

Thanks for reading this and sorry for my non-perfect English!

 

Cheers

Raphael

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yes your carbs are really holding you back.

 

for the type of power you want, i would reccomend a set of 33mm Keihin PWK carbs, some V force 3 reeds, and a nice intake such as Boss racing or similar. if you can, ditch the airbox and run K&N pod filters. tons of people on here will be able to help you with the jetting then.

 

also you have not mentioned what ignition mods you have, if any. there is alot power to be found in the ignition timing.

 

if you currently have no ignition mods, advancing the timing and changing the carbs will easily get you another 10hp, maybe more...

 

also your jolly moto pipes should be pretty close. if you had the larger bore cub (72/73mm) then you would say that they are definitely holding you back.

 

what size domes do you have in the head? what fuel are you using?

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your carbs and pipes are really holding the potential of that motor back. id say snag you some keihin 35mm pwk and try to get a different pipe.. might even have to have something custom made.

 

that motor will make into the 90s.. you just gotta get the setup right on it.

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this motor is in the actual rz350 bike right?? if so, specs from our banshee pipes probably arent going to work that well for you considering those pipes will have to be made totally different to get them to fit the bike.. im not sure who you could contact about this.

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you need small bore banshee drag pipes(hand rolled not stamped ones!). left and right side exit. You will need to modify the pipes a bit to fit the frame. You will loose big power with the pipes made for the rz350 engine....and the small carbs. You will need to cnahe the stinger outlet size a bit larger as well...

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Put some 39PWKs on there. That motor at the RPMs you'll be using it at will pull them no problem.

 

What you need to look for is some Shearer hand coned pipes used. You can cut the pipes on the welds and swap the cones around to get them to fit the bike. A guy in France bought my old hand rolled pipes last year for exactly that...he cut them up and rewelded them for his bike...turned out ok.

 

The ideal man to go to for that is Kenny Roberts. I have no idea on how to get a hold of him though...he is the man for that street bike stuff....

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Hi,

 

yes this is an good idea to look for some banshee pipes. Don't kill me for this question but what are really good pipes for the 421cub? I think you have a big market in USA but in Germany we have none!!!

 

Kenny Roberts? Do you mean this Kenny Roberts...our Twostrokeyamaha-god? Does he building pipes for cubs in bikes?

 

And yes, this cube works really fine into my RZ350-bike. And I also know this mentioned France-Guy from the RZ-Forum. The problem is that nobody - also him - tells anything about the measurements of their pipes...no chance! But I think it's a waste to drive this motor with standard-pipes any longer.

 

39mm Keihin...this is really big :cool: . I think I choose something between 35mm and 39mm. Next summer I want to disrupt the dyno-station :evil: .

 

Cheers

Raphael

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shearer really makes the best pipes for the cub. you could probably pick up a set and have them cut and fitted to fit your setup..

 

and i would really go with the 39mm pwk. youre going to be running a lot of fuel through that thing and the bigger carbs will help. you may also need to look into bigger bowls so you dont run the carbs dry.

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Sorry...but I have to disagree on that Tyler...

 

Kenny Roberts was racing bikes and tuning for Yamaha before Matt was old enough to get a hard on, that's who taught Matt about pipes....

 

Kenny's been making pipes lately....or at least R&D work on pipes.

 

Don't get me wrong, Matt Shearer makes a fine pipe (I use them) but if you could get Kenny Roberts to build you a set for your street bike...that would be like playing golf with Tiger Woods....

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Sorry...but I have to disagree on that Tyler...

 

Kenny Roberts was racing bikes and tuning for Yamaha before Matt was old enough to get a hard on, that's who taught Matt about pipes....

 

Kenny's been making pipes lately....or at least R&D work on pipes.

 

Don't get me wrong, Matt Shearer makes a fine pipe (I use them) but if you could get Kenny Roberts to build you a set for your street bike...that would be like playing golf with Tiger Woods....

just a thought but that motor would dyno even less in a quad with the added weight of the wheels and such so it is not even near making what it could.

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Check out this link.....................He builds some badass pipes and is a site sponser!!!!!! You will not be dissapointed. I have seen his 358 cub RZ at the drag strip and it is quite impressive!!! He has also built some RZ pipes for a few road racers. The site is http://www.twocycletech.com/ Make the phone call...you will love them!!!!!!!

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Sorry...but I have to disagree on that Tyler...

 

Kenny Roberts was racing bikes and tuning for Yamaha before Matt was old enough to get a hard on, that's who taught Matt about pipes....

 

Kenny's been making pipes lately....or at least R&D work on pipes.

 

Don't get me wrong, Matt Shearer makes a fine pipe (I use them) but if you could get Kenny Roberts to build you a set for your street bike...that would be like playing golf with Tiger Woods....

 

ah shit, youre prolly right. i was thinking in terms of the atv world. i dont think matt is prolly making them for the RZ's.

 

does kenny do mainly the RZ shit?

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spec 2 pipes are OK at best, Toomeys are a little better...never heared of pipe factory. My dad has Jim Loma's pipes on his rz and those things are sick as fuck

 

Note: this isnt his rz, just found the pic online with Jim Loma's pipes

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post-27716-1226122295.jpg

Edited by bansheejoel
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