tuning stock carbs/best after market carb

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TN-592
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tuning stock carbs/best after market carb

#1 Post by TN-592 » Thu Mar 02, 2017 9:02 am

I am having trouble with a stock carbs,very hard to start and after it gets hot then it starts without problem so I tune it to work at the idle 1200rpm,after some time when it get cold it is almost impossible to start it.Now i have air screw at 2 turns float hight at 21mm.What are the factory seetings?And what is the best aftermarket carb for the stock motor?

JackB
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Re: tuning stock carbs/best after market carb

#2 Post by JackB » Thu Mar 02, 2017 9:30 am

I cant say what may be wrong but you have some kind of problem. The stock carbs work fine. My bike always starts 1-3 kicks hot or cold. Many times 1-2. I think for aftermarket carbs the Kehin PWK 28 carbs are the most popular for a mostly stock bike. You can buy them new from yamaha,kawi dealers,maybe others too. They used them on some motocross bikes. You just have to change out the jetting that comes in them. Search this site,there is a lot of posts that will tell you everything you need to know.
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75RD350rider
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Re: tuning stock carbs/best after market carb

#3 Post by 75RD350rider » Thu Mar 02, 2017 11:34 am

I love my Spec II prepped VM 30 round-slides on my RZ. I pulled the infernal EPA carbs twice and after spending 30 minutes to change a needle clip setting decided I had enough of that. My bike starts 1st kick if ridden daily, maybe 2 or 3 kicks if it sets a month and runs clean from idle to 10.5K
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RuZty
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Re: tuning stock carbs/best after market carb

#4 Post by RuZty » Thu Mar 02, 2017 11:57 am

I went to PWK28 a few years ago and the bike runs better across the board. The only thing that was slightly better with the stock (non EPA) Mikunis was cold starting.

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Questo vecchio rz
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Re: tuning stock carbs/best after market carb

#5 Post by Questo vecchio rz » Thu Mar 02, 2017 1:45 pm

There are a lot of variables in your question how many miles are on your carbs what is your location altitude and the honest assessment of the condition of your machine


Assuming your bike is completley stock and equipped with the stock airbox.

There is nothing with the stock carbs that cuase it from running correctly, unless there is something wrong , usually it is just dirty or has been altered from factory specs horn simply worn parts you will have to rebuild it

Recommend a complete teardown & cleaning,perhaps do a ulrasonic cleaning or service.

Jet it all to stock factory specs.

Inspect your floats and set them perfectly.

Inspect your floatbowls, ensure there on the correct carb.

There is no "best replacement" carb. Honestly they all work well. Mikuni round or flatslides, and Kehien PWKs. Be forewarned PWKs are NOT a simple bolt on. Theres alot of little details involved in doing it the right way. But once done they are a great option.
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evan_calgary
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Re: tuning stock carbs/best after market carb

#6 Post by evan_calgary » Thu Mar 02, 2017 3:16 pm

That sounds a lot more like bad compression than a carb issue. Difficulty cold starting was always a dead giveaway on a dirt bike the rings were toast.

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Re: tuning stock carbs/best after market carb

#7 Post by JonW » Thu Mar 02, 2017 8:07 pm

I agree with Evan, poor starting is usually a clue to low compression on an older motor.
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Re: tuning stock carbs/best after market carb

#8 Post by hondaror » Fri Mar 03, 2017 2:19 am

Like Questo said, where is the bike from? US has a different carb from most other locations. ...and yes, hard start could mean other issues. Could be a combination of both, due to age.
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Re: tuning stock carbs/best after market carb

#9 Post by Bare » Fri Mar 03, 2017 4:24 pm

RuZty wrote:I went to PWK28 a few years ago and the bike runs better across the board. The only thing that was slightly better with the stock (non EPA) Mikunis was cold starting.
Jettings are too lean. PWKs typically start first kick

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Re: tuning stock carbs/best after market carb

#10 Post by RuZty » Fri Mar 03, 2017 8:54 pm

Bare wrote:
RuZty wrote:I went to PWK28 a few years ago and the bike runs better across the board. The only thing that was slightly better with the stock (non EPA) Mikunis was cold starting.
Jettings are too lean. PWKs typically start first kick
Starts fine most of the time, only struggles when the temps get into single digit cold. Conveniently I seem to have lost interest in riding in those conditions in the last year or so.

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pushstartrearset
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Re: tuning stock carbs/best after market carb

#11 Post by pushstartrearset » Fri Mar 03, 2017 11:07 pm

JonW wrote:I agree with Evan, poor starting is usually a clue to low compression on an older motor.
3rd.

Both our RZs have close to 30k miles. One would take about 50 kicks to start. The other about 15. Cold starting. When warm about 3 kicks. Very tired motors that need complete rebuilds.

What is the mileage? Running pipes? what pipes? Airbox? Is it modded? If no airbox, what are you running? Single filters? Y-boot? Aftermarket or stock ignition? What is set @ or are you running the default tunings?

I think if i had to pick a PWK, it would be over 28mm (simply not as great a needle selection for PWK28s as i have spent time fiddling w/ them w/ the daytona). Like a PWK 32 (much larger selection of needles to really fine tune). More likely, i would want to stick w/ Mikuni TM28~32? carbs and do the Dave Freist (R.I.P.) treatment to them.
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Re: tuning stock carbs/best after market carb

#12 Post by vmxwinn » Sat Mar 04, 2017 1:38 am

I highly recommend PWK 28 for a stock to mildly modded motor. There is a build process to install them but it is not difficult. Follow this thread and you will end up eith a really sweet running RZ.

viewtopic.php?f=1&t=9667&hilit=PWK&start=0" onclick="window.open(this.href);return false;
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Re: tuning stock carbs/best after market carb

#13 Post by MK » Sat Mar 04, 2017 1:36 pm

Im my world poor cold starting is usually a result from jerks throwing all the parts in one box and then swap left/right float bowl on reassembly.
By this mod you successfully disabled the cold start enrichment as the choke jet is only in the right float bowl.
Bye
Martin

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Re: tuning stock carbs/best after market carb

#14 Post by Bare » Sat Mar 04, 2017 3:26 pm

PWKS feature Individual choke assemblies.. parts mixup /bungle unlikely to be relevant here.

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wolfman
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Re: tuning stock carbs/best after market carb

#15 Post by wolfman » Sat Mar 04, 2017 4:06 pm

Starts / runs fine after warm ?
Gotta be rings.
If it were carbs, heat wouldn't affect much.
Rings though ? Definitely!!!
Compression test first, then leak down test. Then carbs.
I run the pwk's and they're great. The mic's were good too though.
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