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Joined: Thu Mar 26, 2020 4:27 am
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Vehicle: 1974 Suzuki lj50

Post Posted: Thu Mar 26, 2020 4:32 am 
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Hey everyone just wondering if anyone has successfully tuned a Suzuki lj50. I currently have fibre glass reeds in mine and I am looking for a bigger carby for performance and also expansion chambers for it. Are there any expansion chambers that fit on it or do I have to get them made up? Also is their any bigger carby that will fit on it easy? Thanks all

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Joined: Wed Aug 19, 2009 11:30 pm
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Vehicle: LJ50V, SJ70

Post Posted: Thu Mar 26, 2020 6:34 pm 
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"Sucessfully Tuned". Explain what you want that to mean..

Factory is well balanced for a great off-road 4wd, but if you want it to be something different........... well, you are going to lose some aspect of drivability.

Can you do any fabrication and modification, or are you seeking straight bolt-on parts?

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Vehicle: 1974 Suzuki lj50

Post Posted: Thu Mar 26, 2020 10:00 pm 
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Was thinking bolt on

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Joined: Mon Apr 19, 2010 11:30 pm
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Location: Georgetown, Guyana
Vehicle: 98 5 dr SQ420, 05 5dr JB420

Post Posted: Fri Mar 27, 2020 4:14 am 
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Thinking back to my youth, tuned two stroke motors tend to have a very narrow power band, especially when expansion chambers are involved, I don't think that's the best approach with a 4WD vehicle - I will admit - it was a heck of a lot of fun with a two wheeler - and if I could find something like a street legal YZ125, I'd be all over it.

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Location: Melbourne

Post Posted: Fri Mar 27, 2020 6:55 am 
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That's also my understanding of expansion chambers - they are tuned to produce maximum scavenge in a narrow RPM band. Like turbo petrols and big cams, they're the opposite of what you're looking for in a 4WD.

I always understood that the first "muffler" in the engine pipe of the LJ50 was effectively the expansion chamber.

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Joined: Wed Mar 05, 2008 10:30 pm
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Location: Waikerie

Post Posted: Fri Mar 27, 2020 9:30 am 
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Jaydentedesco wrote:
Was thinking bolt on
Probably not gunna happen in Oz. There has been some in the US in years gone by, but would be a struggle to find now.


try here ...

http://www.lj10.com/forums/index.php



Gwagensteve wrote:

I always understood that the first "muffler" in the engine pipe of the LJ50 was effectively the expansion chamber.
Krect.

There is a way to "tune" the LJ50 motor, but 'tis a big PITA. Involves three expansion chambers tuned to different rev ranges, and works quite well. I did this on one of mine (thirty plus years ago) along with triple mikuni carbies, also differently tuned. One from a 175 zook and two from 200 kwakas jetted differently. Actual jetting and settings have long since vanished from my memory banks.

I think I could dig up the specs of the chamber from my last Elljay, which according to other owners, went really well.

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Post Posted: Fri Mar 27, 2020 9:43 am 
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Golly.

I've seen some underside shots of JDM SJ30's (550cc 2 stroke Sierras) with three expansion chambers on them, and now I think about it, they were probably all different to achieve what you're describing.

Interesting.

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Vehicle: LJ50V, SJ70

Post Posted: Fri Mar 27, 2020 7:39 pm 
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Jaydentedesco wrote:
Was thinking bolt on

For bolt-on, there are a few manifolds available ex Japan that raise the engine's rev range, but these are detrimental to low speed driving (ie poor off road crawling, poor take-off from lights or hill starts, etc). These will bolt up to the original exhaust, or can be used with a full free-flowing system.


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Vehicle: LJ50V, SJ70

Post Posted: Fri Mar 27, 2020 7:52 pm 
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Next step is a bit more involved than bolt-on.

A Mikuni BN carby (34-28, the smallest model) is ideal for a free-revving LJ50. These carbs were designed for two stroke Jet-Skis, and feature a self-contained vacuum fuel pump and a floatless fuel bowl, so they will work at any angle without flooding or running lean (imagine a jet ski "getting air" over waves to imagine the conditions this carb was designed for.

https://www.ebay.com.au/itm/Mikuni-BN34 ... SwXi1dguk-

But this carb does not bolt up directly to an LJ50 engine. You will need to machine an adaptor to the inlet manifold, you will need to machine an adaptor to the air cleaner, and source a cable pulley wheel to work the oil pump. (https://www.ebay.com/itm/ADA-Mikuni-10- ... Swqvxd-HXv)

If you are installing this on a stock engine, you will need to fit smaller jets to avoid the engine running rich. Once you have done this, the only advantage you have for all your hard work is the benefit of the floatless fuel bowl. in other respects it will be like the standard carb. This carb is really only suited to a worked engine.


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Post Posted: Fri Mar 27, 2020 8:34 pm 
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A worked engine?

The cylinders can be bored out to as much as 68mm. A two stroke engine does not have a camshaft that controls the opening and closing of the exhaust and inlet valves. Instead, it relies on the piston rising and falling in the bore to expose ports in the cylinder wall for inlet and exhaust gases. The position (and size and shape) of these ports provide the same sort of changes that different camshafts do in a four stroke engine. When you increase the bore in the LJ50 engine, because of the angle of the inlet and exhaust passages in the block, you change the size, shape and position of the ports.

Below is an exaggerated diagram showing the changes. When you increase the bore to 64mm, you lower the ports about 1.2mm. When the bore is increased to 68mm, you lower the ports 3.1mm. This causes dramatic changes to the port timing and results in extremely poor running.

To remedy this, you need to add a spacer between the cylinder block and crankcase to raise the ports relative to the pistons. You also need to shave the cylinder head surface of the cylinder block to maintain compression by the same amount.


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Post Posted: Fri Mar 27, 2020 9:11 pm 
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Extra pics I should have attached:


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