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Author Topic: Main jet diameter  (Read 387 times)

Madcoop

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Main jet diameter
« on: April 30, 2019, 03:46:49 PM »

Can anyone tell me what size replacement main jets I need for the carb. I ordered a set of 90/92.5 jets for the bike but they look too small. I believe there are two diameters available for these carbs. A 6mm and an 8mm. I have the 6mm ones here. Hoping someone can give me an answer, before I have to strip the carbs down again to find out. Thanks.
« Last Edit: May 01, 2019, 08:28:28 PM by Madcoop »
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umop-ǝpisdn

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Re: Main jet diameter
« Reply #1 on: April 30, 2019, 09:42:29 PM »

I'm not a carb guy, but I can parrot what I have heard in the past..

The jet size depends largely on any modifications that have been made to the inlet air flow. +2.5 for each of the following:
de-snorkelling the airbox
enlarging the hole in the air filter inlet <-- this is known to reduce bottom end torque somewhat, but improve the top end.
fitting a free-flowing exhaust

In reality, it would seem that 95 for the front and 97.5 for the rear (or is it the other way around?) is a good rule of thumb, with room for adjustment either way.

The pilot jet will also need some love to help with idle.

There is also talk of fitting shims and third notches on needles and float adjustment which blew my feeble mind a little and that I won't even pretend to understand. I would imagine that Joss will at some stage throw in his 2c worth and that it'll be worth far more than my babbling.

In the meantime, lets talk electrical upgrades. Grab a 20cm bit of 30A wire, maybe 4mm2 or 10ga and crimp/solder a ring terminal to each end.

One ring terminal goes to the -'ve terminal on the battery, the other, to the chassis, literally anywhere where you can find a bolt. The relay holder is a handy spot, but quite visible and ugly, so feel free to improvise.

The earth/ground on these bikes is terrible. If you are feeling comfortable with the idea, replace the ground wire from the headlight to also earth to the chassis. This offloads about half the draw that would otherwise pass through the feeble earth wire in the wiring loom.

Next up, we should talk about the charging system. Let me know about comfort levels here. I don't want you to think that I am talking down to you, neither do I want to blow your mind with babble.
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I used to be a sensitive, new age guy, but times have changed and now I am more of a caring, understanding, ninties type.

Joss

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Re: Main jet diameter
« Reply #2 on: May 01, 2019, 10:14:46 AM »

Are you looking for replacement standard jets or are you upjetting because of a modification? If you want totally standard you should be using 87.5/90.

I've never heard of different diameter jets for the BDS26. I could probably dig some out and measure with calipers for you tonight.
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Madcoop

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Re: Main jet diameter
« Reply #3 on: May 01, 2019, 08:27:54 PM »

Hey guys. Thanks for your replies. I have spoken with my supplier now and it seems that the diameter doesn't matter both will fit and have the same flow rate. I did in fact wonder what difference it would make. I would still be interested to know the actual size though if you are able to dig one out Joss. Don't put yourself out though! I have a new engine on its way now, so things have not exactly been going to plan... ::) I am however having a lot of fun and learning loads along the way. When I get a minute to pull this engine I will be able to check the sizes for myself anyway.

Some good information in there too about the electrics. Thankfully the loom on this bike looks really good apart from one piece of insulation tape on a wire round the neck of the frame. I will get to the rectifier and ignition coils when I am able, but for now the engine is my top priority. Good advice about the earths though, I would never have thought about the headlight.

Charging systems, I could perhaps keep up a little, but I am completely new to bikes with a self taught background in car mechanics. I like to read and learn and then try it for myself if I can. The magneto system is one I haven't dabbled with, however I understand the principals involved with an alternator. I did take the covers off for a look though...lol  When the engine is out the bike and on my workbench I intend to just dive right in! Nothing ventured, nothing gained, right.

Here is one for you though, what about capacitors. I have heard of people fitting them in tandem with and in fact replacing batteries on bikes. Although I don't really fancy sitting on a power cap that would kill you in an instant, I am interested to know if adding a smaller cap to the power system may help provide a more reliable power source and in turn a happier ignition system.
« Last Edit: May 01, 2019, 08:31:30 PM by Madcoop »
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umop-ǝpisdn

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Re: Main jet diameter
« Reply #4 on: May 01, 2019, 09:52:18 PM »

Yep, very similar concepts to an alternator.

The magneto is comprised of two parts. The stator and the flywheel. Yes, the flywheel. The flywheel on these engines is actually a powerful, cup-like magnet. It spins around the stator, a circular collection of copper windings. This generates AC current that varies wildly in voltage as the RPMs increase/reduce. Obviously AC voltage is of little use to a DC system.

That's where the reg/rec comes into the picture. It rectifies (converts to DC) and regulates the output to a steady 14.5VDC.

The regulator part is the problem. It senses it's voltage on the output side and judges accordingly how much excess current to shunt to the chassis. The issue is that the reg/rec is not directly connected to the battery, it is routed via a complex loom that increases in resistance wildly, therefore what the reg/rec sees as 14.5V, the battery sees as 12.5V or even less, below the ideal charging voltage for a lead-acid battery. Long story short, your battery dies and kills the reg/rec along with it.

Short story slightly longer, it's a good idea to wire the outputs (+'ve and -'ve) from your reg/rec directly to the battery and then from the battery back to the wiring loom. Brown is +'ve and black with white trace is ground. The +'ve wire should be fused between the reg/rec and battery, but it's not necessary to fuse between the battery and loom, as there is a fuse directly after the connector.

The connectors used throughout the bike are standard 2.8mm auto-electrical:

https://www.banggood.com/buy/2.8mm-connector.html

On the battery side though, you would use a ring terminal. Wire gauge to suit max of 30A draw and an appropriate fuse, or an auto-resetting circuit breaker, for extra style points.

As for the reg/rec, MOSFET type are good. The Shindengen brand is amazing. The FH020AA being my preferred one:

http://www.roadstercycle.com/ <-- he sells a Hyosung loom. Do not use it, as it doesn't directly connect the power to the battery.
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I used to be a sensitive, new age guy, but times have changed and now I am more of a caring, understanding, ninties type.

Joss

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Re: Main jet diameter
« Reply #5 on: May 02, 2019, 08:37:58 AM »

Hey guys. Thanks for your replies. I have spoken with my supplier now and it seems that the diameter doesn't matter both will fit and have the same flow rate. I did in fact wonder what difference it would make. I would still be interested to know the actual size though if you are able to dig one out Joss. Don't put yourself out though! I have a new engine on its way now, so things have not exactly been going to plan... ::) I am however having a lot of fun and learning loads along the way. When I get a minute to pull this engine I will be able to check the sizes for myself anyway.


Not a problem, I'll get back to you with them. Once installed they should look like the pic in my thread: http://korider.com/index.php?topic=25231.msg250204#msg250204 (at the bottom). Out of curiosity, are you UK based?
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Madcoop

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Re: Main jet diameter
« Reply #6 on: May 03, 2019, 08:26:05 AM »

Morning fellas, and thanks for your continued input. Again some good info, and an excellent description of the rectifier fix. I pretty much have that straight in my head, but it would be great if you had a photograph of this mod installed so i can verify my thinking on how to do it. Fairly straight forward i think and an auto resetting circuit breaker sounds right up my street...lol Perhaps I would be best to concentrate on actually getting this bike roadworthy again, before I start to pretty it up, so to speak. will definately be looking at the wiring mods already suggested whilst i have the bike apart though. My to do list is however still fairly extensive, and I haven't even been near an MOT....To someone who only really knows cars, it is actually quite difficult to know what is considered good and what isn't with bikes.
I didn't for one moment think I would be swapping an engine in order to do this. It has been suggested that I may well be able to move forward with the current engine, but i have too many question marks over its history now, and would hate to be travelling at speed when it decides to blow itself up and lock the back wheel on me.
Joss, yes I am UK based, up here in Scotland. There are some amazing roads up here which I am really looking forward to experiencing on two wheels and in a few years time will be even better with my son in tow.
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