RZ/RD 350 & Misc. 2-Stroke Tech BBS

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 Post subject: Carb Sync questions
PostPosted: Tue Nov 14, 2017 10:14 am 
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Joined: Mon Dec 07, 2015 10:15 am
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Location: Milton, Ontario
I have replaced the throttle cable now and have a question about syncing the carbs. Should the carb slides be flush with the top of the intake port at WOT or how do I set them. They both bottom out but the right one moves before the left one. That part is easy to correct but I seem to recall from the racing days that you open the throttle all the way and the bottom of the slides should be flush with the top of the intake ports. Thanks very much.


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 Post subject: Re: Carb Sync questions
PostPosted: Wed Nov 15, 2017 2:15 pm 
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Joined: Sat Nov 26, 2005 11:44 am
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Location: Wolfenb├╝ttel, Germany
As nobody feels obliged to share their method:
The important area is certainly a low position where the needle position is important.

I though flush the upper position close to WOT (unscrew upper airbox and use a lamp & mirror to check visually)
For cable actuation that's ok, as they move pretty parallel (i.e. flush at WOT means also flush at low position)

The RD500 has a link coupling that doesn't move the lower/upper carb slides parallel.
It has a mark at the middle position that you ought to synchronize, but in my experience that's crap.
The important area is the very low range, so I put something like an 10mm allen key under the slide and actuate the throttle until it just gets free. Then keep the throttle constant and check the other side. Then do the same for left/right carbys.
Also saw a variant of that method with popsicles under the slide, that should start moving at the same time when slowly increasing throttle positions.

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 Post subject: Re: Carb Sync questions
PostPosted: Wed Nov 15, 2017 3:15 pm 
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Joined: Mon Dec 07, 2015 10:15 am
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Location: Milton, Ontario
Thanks Martin. I appreciate it.


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 Post subject: Re: Carb Sync questions
PostPosted: Wed Nov 15, 2017 9:15 pm 
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Joined: Mon Mar 03, 2014 8:44 pm
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Location: Calgary, Alberta, Canada
I'd look in to buying a carb Uni syn. It will be way more accurate as it deals with the vacuum associated with each carb and matches them while your engine is running.

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 Post subject: Re: Carb Sync questions
PostPosted: Thu Nov 16, 2017 1:06 pm 
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Joined: Mon Dec 07, 2015 10:15 am
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Location: Milton, Ontario
Thanks Rory. It looks like you would need two of them to do both carbs correct? Do they just go in the intake side of the carbs when you pull the airbox off?


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 Post subject: Re: Carb Sync questions
PostPosted: Fri Nov 17, 2017 5:21 am 
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Location: Calgary, Alberta, Canada
One is enough. Yes on the intake. Read the first carb, and then the second. Make adjustments to even them up.

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 Post subject: Re: Carb Sync questions
PostPosted: Fri Nov 17, 2017 9:31 am 
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Joined: Fri Nov 01, 2013 8:34 pm
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Location: back in the hills
I machined a set of fittings that fit into the crossover spigots that allow use of a mercury or dial gauges. I find it much easier and accurate.

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 Post subject: Re: Carb Sync questions
PostPosted: Fri Nov 17, 2017 10:21 am 
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Joined: Mon Dec 07, 2015 10:15 am
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Location: Milton, Ontario
Hi Rory. Do you use the 4025 or the 4027 Uni Syn. There seems to be bad reviews about the 4027 motorcycle version. Seems it is pretty cheaply made in China and breaks easily.


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 Post subject: Re: Carb Sync questions
PostPosted: Fri Nov 17, 2017 3:08 pm 
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Location: Houston texas
T.RexRacing wrote:
I machined a set of fittings that fit into the crossover spigots that allow use of a mercury or dial gauges. I find it much easier and accurate.


^^^^ and you can sync without disturbing the filter assembly.
can you post a pic of your set up .
thanks mark

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 Post subject: Re: Carb Sync questions
PostPosted: Fri Nov 17, 2017 9:00 pm 
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I can't tell you that right now, as I'm 900 kms north of home.

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 Post subject: Re: Carb Sync questions
PostPosted: Fri Nov 17, 2017 10:39 pm 
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Joined: Fri Nov 01, 2013 8:34 pm
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Location: back in the hills
two-stroke-brit wrote:
T.RexRacing wrote:
I machined a set of fittings that fit into the crossover spigots that allow use of a mercury or dial gauges. I find it much easier and accurate.


^^^^ and you can sync without disturbing the filter assembly.
can you post a pic of your set up .
thanks mark


Gimme a day or two. Kinda occupied and this site doesn't like me posting photos for some reason.

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