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Yamaha RXS100 Wasting Huge Amounts of Fuel on Idle (with Video)


Antony
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Hi everyone,

I bought a Yamaha RXS100. It was a wreck. I've had to buy several new parts for it and blah blah blah. It's getting there.

When I put it all together, it wouldn't start, fuel would be peeing out of the overflow.

The problem seemed to be that the float was not set correctly. I bent the float a tiny amount, and that fixed the overflowing problem.

So, it starts on choke, as expected, push the choke in after 10 seconds and it idles ok ish - I've tried to set the air screw correctly.

It consumes huge amounts of fuel though! Roughly 2 minutes of idling consumes 20ml.

Sometimes it dumps fuel rapidly, sometimes it seems to keep hold of it for a bit?!? 

I thought I understood how carbs work, but obviously not.

I was trying to unscrew the air screw to introduce more air and less fuel, but then it doesn't sound right and it won't tick over nicely.

The main jet seems ok, the pilot jet seems ok. They don't appear to be blocked or anything.

Here's a video: Here

If you look at 16-18sec, you can see how quickly it takes that fuel. Look at the little part of pipe on the filter!

What could the problem be?

Thanks!

Also, I looked for where it's dumping the fuel, and it doesn't seem to be going anywhere!

It's not leaking out. It's not in the airbox either! There is no black/gray smoke!

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Hi Mate, check the main jet size 120 i think and make sure its the right length as i think these are the long hex type, check your reeds are sealing and the inlet rubber isn't leaking, check the rings aren't partly stuck and also the crank seals arent leaking as all that fuel is going somewhere.

Did you fit a new carb kit (keyster) as these kits can be a bit hit and miss, they don't get great reviews on the RD forums but i fitted one the the DT175MX and it works ok (mostly).

Mark 

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2 hours ago, MarkRD250LC said:

Hi Mate, check the main jet size 120 i think and make sure its the right length as i think these are the long hex type, check your reeds are sealing and the inlet rubber isn't leaking, check the rings aren't partly stuck and also the crank seals arent leaking as all that fuel is going somewhere.

Did you fit a new carb kit (keyster) as these kits can be a bit hit and miss, they don't get great reviews on the RD forums but i fitted one the the DT175MX and it works ok (mostly).

Mark 

Thanks Mark... It just occurred to me that ofcourse, petrol has to go somewhere.. maybe it's in the gearbox...

I've just dropped the gearbox oil. It's green and stinks of petrol. 😬😬😬

That oil hasn't even done 1 mile.

 

What the?!

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Sounds like an engine split job to me, but start with the basics as you split it (check reeds/rings etc) and personally i would use genuine crank seals and gaskets.

is it a keeper for the road or just a bit of fun?

i do like the RXS i just sold mine to fund the RS100 project, very quick bike.

Mark 

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34 minutes ago, MarkRD250LC said:

Sounds like an engine split job to me, but start with the basics as you split it (check reeds/rings etc) and personally i would use genuine crank seals and gaskets.

is it a keeper for the road or just a bit of fun?

i do like the RXS i just sold mine to fund the RS100 project, very quick bike.

Mark 

Ok, thanks. The rings are new. I don't know anything about reeds yet. I didn't replace the seals when I rebuilt it. The gaskets are cheap replacements.

Ive never had a motorbike in the UK and I don't even have CBT. It was a project just to mess with, although I'm growing to love this little machine. 🤣

Ok, I'll get the seal kit and all that and rebuild it.

 

Edited by Antony
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