Carb size help.

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mike91
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Carb size help.

#1 Post by mike91 » Mon Aug 21, 2017 6:47 pm

I am setting up a 1984 US version for road racing and am looking for some help with carb size. I have a set of round slide 32's and flat slide 34's as well as the boots to mount them. The top end is one over size with DG pipes. Thanks for the help guys.

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T.RexRacing
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Re: Carb size help.

#2 Post by T.RexRacing » Mon Aug 21, 2017 7:01 pm

Still have the stock ones? use 'em unless you've ported the engine and need the air. My opinion and nothing more. The money would be better spent on a better set of pipes. See here for great pipes.
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seahorse
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Re: Carb size help.

#3 Post by seahorse » Mon Aug 21, 2017 8:23 pm

Agree whole heartedly with Trex
The VM26ss carbs properly jetted on the mains and needle will suit bikes up to 421 with the added bonus of retaining good bottom end.
If your in the US get a set of TRUSA pipes, if in the UK buy nothing but the best Kenny Gibbons TSA pipes.
81 RD 250 LC Hybrid .Widened frame with Aprilia RS250 Back end & Front end, strokd RZ 421, Kennys TSA's, 31KVM26SS Carbs M-360 P-25 ALBA Ndl Pos 3, Air 1.3/4
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JonW
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Re: Carb size help.

#4 Post by JonW » Mon Aug 21, 2017 10:07 pm

There are some new pipes on the scene in the uk now as well: http://rdlccrazy.proboards.com/thread/4 ... ypvs-bikes" onclick="window.open(this.href);return false;

...and in time Tyga will probably adapt their new LC pipes (soon to be released) to RZ fit as well.

personally id fit larger carbs to make use of engines over 400cc, but the 26s will do what you need, certainly your flatslides seem very big for a 1st over 350 on DGs.
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mboddy
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Re: Carb size help.

#5 Post by mboddy » Tue Aug 22, 2017 10:42 am

What flat slides are they?
I ran 32mm Lectron flat slides on my RD350LC race bike for years (with RZ reed blocks) and they worked well with mild porting and Suzuki RG250 MK1 pipes.
Bike was very fast and I won lots. It was even faster when I changed them to 34mm Lectrons.
My TZR250 race bike also runs 34mm Lectrons. Very fast with the pipes designed for big carbs.
When I tried it with Jolly Motos it was hugely down on power. Seems that the Jollys are designed for use with stock carbs.

The original 26mm round slides are crap. Good bottom end is useless. You are setting up a race bike. You want good top end to be at the pointy end of the field.
DG pipes don't have a good reputation as race pipes.
We race RDs, RDLCs, RZs, TZRs, TDRs and TZs at PCRA

mike91
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Re: Carb size help.

#6 Post by mike91 » Tue Aug 22, 2017 1:17 pm

As always thanks for the help. The 34's are Lectrons so I will give them a try this weekend. I'm not really sure of the brand of the chambers but from what I hear if you can find them Toomys are the way to go. Does anyone have a set they would part with? Thanks again and I'll let everybody know how they work.

mike91
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Re: Carb size help.

#7 Post by mike91 » Tue Aug 22, 2017 1:21 pm

Just looked at the pictures of the TSA pipes and mine "look" the same???

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JonW
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Re: Carb size help.

#8 Post by JonW » Wed Aug 23, 2017 12:14 am

look the same isnt always 'the same'.

IMHO you should take mboddys advice, he knows lectrons and race bikes very very well.
80 XT500 Supermoto!
81 RD350LC Resto
82 RD421LC Hybrid
82 RD350LC decapitation project
82 RD250LC JDM '251LC' YPVS
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Re: Carb size help.

#9 Post by T.RexRacing » Wed Aug 23, 2017 8:26 am

You will gain little adding big carbs to DG pipes and stock porting.
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mike91
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Re: Carb size help.

#10 Post by mike91 » Tue Aug 29, 2017 12:12 am

Ran the 34's this weekend and after a little jetting the bike ran very good. Pulled cleanly all the way through so now that that's done we just have to get the forks and brakes to work! Trying Race Tech springs and emulator's on the forks and EBC floating rotors on the brakes.

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Re: Carb size help.

#11 Post by Questo vecchio rz » Tue Aug 29, 2017 3:42 am

You need to clarify are you experienced at racing, is engine ported , head milled for squish, crank condition and is it stock 4mm?
What class , organization & region do you intend to race and what will your competition be.

Suspension/Chassis setup is priority...not the motor! Make sure the motors fresh...but don't worry about power ...yet, 60+ h.p. is easy as $1500.00-$2000.00 on these bikes if you wrench & spend wisely.

Others here provided good advice above.

1.) You will not gain performance from 32-34 mm carbs without some port work.
2.) 26 mn will be just fine... For stock unported cylinders, even mild portwork. Low end performance is not worth much considering on a race bike unless your on a kart track etc...

If this your average racebike, just buy some used Toomeys. Toomeys will deliver all you'll likley ever need..great 10,000rpm top end and good midrange power A real good designed pipe for a low buck or higher spec race/track bike, basically there cost effective and crash well, nice mild steel .Custom spec built pipes from various builders will be costly $800-$1200.00 and not quickly or cheaply replaceable. You can always add Custom built pipes that are ( built around your port specs) later if you decide to do a complete race motor w programmable ign/PVL etc... .(If your crank is new low hrs)Don't worry too much about crank life @ high RPM as you'll put a new one in anyways likley each season. These motors are strong little F#@kers and take alot of abuse

IMO Your better off setting & sorting your suspension.
Suggestions but not limited to...
0.) Your Race Tech front end or other allowable internal/external modifications.
1.) Tapered head race bearings.
2.) Buy a fully adj rear (race)shock that's specifically built for a RZ & sprung for your weight!...DO NOT use a swapped retrofit shock!!
3.)Buy some Conti attack rubber.
4.), Brake calipers!/rotors in "perfect" working order,good compound pads .
5.)Consider a steering dampner.
6.) All new wheel/linkage bearings,
7.) Race non O ring chain.
8.) Several rear sprockets up & down tooth count.
9.) Clean fresh motor (Mod as you see fit) Basic start would be at a minimum... Fresh crank & topend, milled head,new perf. reeds,new intake boots..DO A LEAK DOWN?
10.) Fresh clutch..
11.) All new cables,brake & oil inj lines..clutch,throttle,YPVS,injector.
12.) Your preference to (riding position )stock bars,clipons,rearsets. You don't need clip ons at all, if you prefer a upright riding style

Your stock frame is perfectly fine as long as its straight. Your linkage,bearings etc..are all in perfect condition.
A solid RZ, that's reliable & fun you might be able to assemble for around 3.5-5k ( not including your bike). If you spend thrifty.

Realize.. what the RZ is usually a 45-55 h.p. bike with basic suspension. There's fun..then there's winning $$$ + ability. To you can PM 50Joe (Joe Pomeroy) here or search him out on 2 stroke world/Aprila RS250 or WERA forums, he's a great help in setting up a RZ.
His bikes beat most everything when he was racing. #1plates don't lie. Tony Doukas here if TDR (reed fame)AKA banshee superstore was fielding a couple RZs a year ago, but he never to my knowledge posted his results if his racing endevor.

If it's just a "track day" bike...most of the above still applies. Just have fun
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Re: Carb size help.

#12 Post by seahorse » Sun Sep 10, 2017 6:33 pm

mboddy wrote:What flat slides are they?

The original 26mm round slides are crap. Good bottom end is useless. You are setting up a race bike. You want good top end to be at the pointy end of the field.
DG pipes don't have a good reputation as race pipes.
You have probably never experienced tuning a 421 engine, if you have bottom end why not take advantage of it. The Main Jet top end wont vary much weather they are 28' 32 or 34. What's particularly interesting is that not many can post up their jetting specs on the bigger carbs, cause they still are yet to tune the fucking things. Let alone put any KM's on them.
81 RD 250 LC Hybrid .Widened frame with Aprilia RS250 Back end & Front end, strokd RZ 421, Kennys TSA's, 31KVM26SS Carbs M-360 P-25 ALBA Ndl Pos 3, Air 1.3/4
81Rd350lc resto 2016
81 Rd250lc resto 2017
1999 ZRX 1100

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