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Author Topic: Carburettor Information  (Read 8868 times)

Offline lariviere

  • Posts: 25
Re: Carburettor Information
« Reply #40 on: Mar 25, 2015, 10:28:39 »
can someone explaine me how and where to fit the pilote jet?
thank you

Offline waketrip

  • Posts: 34
Re: Carburettor Information
« Reply #41 on: Mar 25, 2015, 11:10:00 »
Red Ace, keep in mind that 30mm carburettors are what's being mounted Stock on 250cc engines,  so it'll definitely be too big for a 125 engine.

An all around improvement (quicker pickup, smoothness, throttle response) could possibly be achieved by mounting a keihin or mikuni, good quality 26mm carburettor if they make them in this size.

A 28mm will probably give you better top end gains, but at low and mid range RPM's it might lose a little.

You have to realize that the size of the carburettor is not what increases performance and/or hp, but carefully choosing the correct size for the cc's and intended application, and the quality of the carb itself.

Generally speaking, a smaller diameter carb will provide more air flow speed, and will perform well at low and mid rpms, buy may not provide enough airflow at very high rpms, thus hurting top end power.

A bigger diameter carb, will enhance high rpm operation, giving you more hp at the top end, but the engine may run worse low and mid rpms.

And even more important than these two, is a properly jetted carb, with the adequate pilot, main and needle jets for the intended use.

Normally the stock (typical) carbs as specified by manufacturers for single cylinder engines  are:

125cc --- 24/26mm
150cc --- 28mm
250cc --- 30/32 mm

but these vary wildly, as does jetting, because manufacturers may prefer to have an engine consume less fuel than to have it perform its best, or enhance low rpms, or high rpms,  so that's why there is no ''ideal'' carb size for any given engine.
« Last Edit: Mar 25, 2015, 11:12:10 by waketrip »

Offline orrible-64

  • Posts: 711
Re: Carburettor Information
« Reply #42 on: Mar 27, 2015, 08:42:39 »
On advice from other guys In the pits this week, 28 mm should work ok. I run a 26mm


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Offline orrible-64

  • Posts: 711
Re: Carburettor Information
« Reply #43 on: Mar 27, 2015, 08:43:57 »
Ran bike today open pipe what a lovely noise it made.


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Offline orrible-64

  • Posts: 711
Re: Carburettor Information
« Reply #44 on: Mar 27, 2015, 08:44:41 »
Ran 73.6 mph


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Offline Racing Ruben

  • Posts: 56
Re: Carburettor Information
« Reply #45 on: Feb 22, 2016, 15:00:33 »
Hey guys,

Wasn't quite sure where to post this. It's about carburettors so I put it here.
I'm in the process of changing to a genuine Keihin PE28.
 I'm running the 150cc big bore kit with the 125 head, open exhaust,... (you can look at my setup on the database spreadsheet)
It feels like I'm not getting the maximum out of my 150cc.  Especially in fifth gear there's no real power.  I can get to arround 115kph on a flat stretch of road but it takes a while to go from 100kph to 115kph.  I tried different jets but that didn't make a real difference.

So I'm trying a bigger carb. I was hoping it would be an easy fit but that wasn't the case. 
First problem: the holes on the rubber adaptor to connect the carb with the manifold didn't match.  I tried to reposition the holes but it looked like it would never fit perfectly.
So I eventually found a manifold from a Yamaha XT 550 that would connect the carb directly to the cylinder.  It has al the right holes in all the right places.
Second problem: the angle on that manifold is somewhat different so the carb gets really close to the upper engine mount and to a piece of the frame.  So I can't use a velocity stack anymore because there's no room for it.  I did find a foam air filter (UNI) that does fit.
Third problem:  the carb fits nicely but it's tilted at an angle.  So here's my question:  What is the maximum angle you can tilt a carburettor?  How would you notice it's tilted too much?  Can this be compensated by adjusting the float height (no idea how that works)
I didn't get to starting the bike because I'm still waiting on the O-ring for the new manifold. 
Does anybody else use this carburettor or a different 28mm carb?

Any thoughts on this?
« Last Edit: Feb 22, 2016, 15:03:46 by Racing Ruben »

Offline LOLitsPOOP

  • Posts: 22
Re: Carburettor Information
« Reply #46 on: Feb 22, 2016, 17:07:46 »
Yeah, you have the wrong manifold.  You need an angled one.

You can get one from ebay: http://www.ebay.com.au/itm/Upgrade-30mm-Carburetor-Intake-Manifold-For-200cc-250cc-Dirt-Bike-ATV-Quad-Buggy-/262217103643?hash=item3d0d5b791b:g:qE8AAOSwJkJWhJTY

This is my setup.  OKO 26mm Flatslide



Offline Racing Ruben

  • Posts: 56
Re: Carburettor Information
« Reply #47 on: Feb 22, 2016, 18:38:29 »
Thanks man, I've ordered the manifold.  I hope it gets delivered quickly.

Greetings from Belgium

Offline 2b

  • Posts: 335
Re: Carburettor Information
« Reply #48 on: Mar 06, 2016, 05:37:17 »
Hey Lolitspoop

Not sure if I have asked before, but I am going to change the Carb when I do my 150 upgrade over winter and like the idea of your set up.

Can you post links to the Carb and Trumpet that you have pictured above.

Cheers.
He's obsessed with order and clarity. He doesn't like mess.
Harold Pinter

Build thread: http://www.dotheton.com/forum/index.php?topic=61167.msg694438#msg694438

Offline LOLitsPOOP

  • Posts: 22
Re: Carburettor Information
« Reply #49 on: Mar 06, 2016, 07:56:19 »
About the carb;
http://www.oko-australia.com.au/

Good site for more info including tuning;
http://www.mid-atlantictrials.com/OKO.html

I bought my gear from DHZmoto in Sydney.