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Cool
07-08-2016, 07:26 PM
Hi Everyone,

Just curious - does Anyone have this carby on their rs125 and is the bike running OK?

I bought the bike a month ago - 2012 model which runs well enough until you back off the throttle at about 100km hour, then it jerks and stutters and is definately Not Happy.

My bike is Stock standard - std filter etc. Main jet 185, pilot jet u36. With an arrow pipe.
It is an Australian model.

Can anyone explain the workings of this carby VHST 28CD Carby with Throttle position sensor compared to a stock Old school carburretor with no extra bits? (like the carby from an rd350 yamaha.)

i.e. Throttle position sensor ? What effect does it have?
Extra pipe next to fuel pipe. is blocked off on my bike by a cable tie.
Extra pipe with hose - opposite this one on other side of carby.

Thanks in advance.

bigpt
07-15-2016, 09:23 PM
sling the carb and either buy the 34 or 28 phbh the carb can not be jet properly it runs lean or mid-range,very bad carb I spent nearly two hundred pounds on slides needles and idle jet trust me your wasting your time it either runs lean or rich the cable tie will be to block air off you can try if you want but your best off getting another carb,I have three vhst carbs sat in my garage,have a look at my old threads I tried everything,and seen loads of top end seizures cause of these carbs they are alright if you have the bike fully standard no powervalve and exhaust with a cat in it,but its not going to be much fun to ride,check my old threads out Paul uk.

Cool
07-24-2016, 06:00 AM
sling the carb and either buy the 34 or 28 phbh the carb can not be jet properly it runs lean or mid-range,very bad carb I spent nearly two hundred pounds on slides needles and idle jet trust me your wasting your time it either runs lean or rich the cable tie will be to block air off you can try if you want but your best off getting another carb,I have three vhst carbs sat in my garage,have a look at my old threads I tried everything,and seen loads of top end seizures cause of these carbs they are alright if you have the bike fully standard no powervalve and exhaust with a cat in it,but its not going to be much fun to ride,check my old threads out Paul uk.

Thanks for the info Paul.
Everyone seems to be saying the same thing - carby is a bit of a dud.
I already paid for a few pilot jets and main jets.
Will experiment a little bit but the 34mm carby sounds like the answer. It is very expensive ship the 34mm carb and manifold to Australia.

cheers

Jim

2T Institute
07-25-2016, 07:10 AM
nothing wrong with the vhst you just have to know how to set it up and jet it. For starters the tps is really nothing to do the the carby, it is a input for the ignition. A 185 and a U36 sound way to rich. What atomiser is used?

Cool
07-26-2016, 08:40 PM
nothing wrong with the vhst you just have to know how to set it up and jet it. For starters the tps is really nothing to do the the carby, it is a input for the ignition. A 185 and a U36 sound way to rich. What atomiser is used?

Atomiser - 268HN
Needle - D49 on position 2
Slide - 45
Main jet - 185
Pilot jet - 36U

All settings are STANDARD as per arrow expansion chamber. What settings would you suggest?
I thought the 36U pilot jet was a bit small?? as the full power spec is S45. I just tried a S45 and the problem on throttling off is MUCH better. However it does seem to be too rich now.
I am going to try a 170 main jet (with care not to seize it).
I welcome any constructive feedback.
I am surprised you have to fiddle with the "as delivered" setup to get the bike to run properly.

2T Institute
07-27-2016, 08:21 AM
AQ 269 Atomiser
U36 pilot
45 slide
135 Main
D56 needle position 3.5
9.5g floats
float height 7mm from horizontal
That is the race kit set up with the air corrector removed and pilot air corrector hole is 1.0mm
The 7mm needle shroud as well
I think the needle shroud would be the first thing to try

Remember these are sold to L platers and it's their first real bike usually and keep it pinned everywhere :)

Cool
07-27-2016, 09:25 PM
AQ 269 Atomiser
U36 pilot
45 slide
135 Main
D56 needle position 3.5
9.5g floats
float height 7mm from horizontal
That is the race kit set up with the air corrector removed and pilot air corrector hole is 1.0mm
The 7mm needle shroud as well
I think the needle shroud would be the first thing to try

Remember these are sold to L platers and it's their first real bike usually and keep it pinned everywhere :)

Thanks for the feedback.
Are you running the std airbox or a Pod filter.?

2T Institute
07-29-2016, 07:29 AM
found just by removing snorkel from the airbox lost 1.5hp

bigpt
08-05-2016, 06:27 PM
135 is for stock standard restricted carb pipe no power valve listen we used 178 main jet and was still slightly lean take my advice just bhy,the 28 phbh only cheap the 34 is too big without porting and look at all the wrecked top end cause of these carb,their a four stroke carb.

Cool
08-06-2016, 12:24 AM
Thanks for the feedback.
I will only make small changes.

Motolorax
08-06-2016, 04:49 AM
I've messed about with the TPS since fitting the 34mm on my 2012. Disconnected, taped wide open or left closed seems to make on obvious difference to performance. If it was modifying the ignition timing I would have expected to see some difference in running wide open. I'm still struggling to get better wide-open performance from the 34mm than I can coax from the 28, although midrange (7-9krpm) is much stronger on the 34mm. I'm interested to see where you get to fiddling with this carbie.

bigpt
08-07-2016, 06:50 AM
can't believe lads like you saying use a 135 main jet on a full power rs ,135 it will seize with a small jet like that will power valve and unrestricted pipe on it,you both have lots of experience with these bikes off other forums and have never said use 135,

Cool
08-09-2016, 05:35 PM
can't believe lads like you saying use a 135 main jet on a full power rs ,135 it will seize with a small jet like that will power valve and unrestricted pipe on it,you both have lots of experience with these bikes off other forums and have never said use 135,

Thanks mate. Sound advice.

Motolorax
08-11-2016, 11:02 PM
For what it's worth I lean seized whilst wide open with a VHST28 using 160 main with a Giannelli pipe. I'm still not sure if it was the jetting or a leak in the manifold. I'm now using a 162 in a 34mm Dellorto and it's too still rich..