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Rieju RS3 125 flat spot.

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Riejufixing
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Joined: 24 Jun 2018
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PostPosted: 12:43 - 28 Jul 2019    Post subject: Rieju RS3 125 flat spot. Reply with quote
Identical engine to Yamaha YZF-R125 (etc) but carburetted.

Possible carburation problem or other thing?

As far as I know the carburettor has not been touched since it came out of the factory. Bike has done 15,000+ miles.

Carburettor parts diagramme: https://www.riejuparts.co.uk/collections/rs3-125-engine-2011-15/products/rs3-125-engine-2011-15-t12

Annoying flat spot between ~7,000 RPM and 8,000 RPM. Most noticeable in top 3 gears.

Any pointers?
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jaffa90
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Joined: 06 Apr 2016
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PostPosted: 13:20 - 28 Jul 2019    Post subject: Reply with quote
My shout is part number 2.
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Riejufixing
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PostPosted: 13:29 - 28 Jul 2019    Post subject: Reply with quote
jaffa90 wrote:
My shout is part number 2.

Sticking, presumably?
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jaffa90
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PostPosted: 13:37 - 28 Jul 2019    Post subject: Reply with quote
Riejufixing wrote:
jaffa90 wrote:
My shout is part number 2.

Sticking, presumably?

Yes, i would check the rubber diaphragm condition.
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Robby
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Joined: 16 May 2002
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PostPosted: 15:50 - 28 Jul 2019    Post subject: Reply with quote
If it in regular use or has it been standing?

If it used regularly, I wouldn't go looking for carb trouble. Petrol is very good at keeping them clean and working. It isn't old enough to expect diaphragm trouble, and I would only expect the slide to be sticking if it has been overfilled with oil and the whole thing is covered in oil gunk from the crankcase breather.

Is it up to date on its other servicing, inc valve clearances? I expect they're a fairly frequent service item.
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Riejufixing
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PostPosted: 16:20 - 28 Jul 2019    Post subject: Reply with quote
Robby wrote:
If it in regular use or has it been standing?

If it used regularly, I wouldn't go looking for carb trouble. Petrol is very good at keeping them clean and working. It isn't old enough to expect diaphragm trouble, and I would only expect the slide to be sticking if it has been overfilled with oil and the whole thing is covered in oil gunk from the crankcase breather.

Is it up to date on its other servicing, inc valve clearances? I expect they're a fairly frequent service item.

Used regularly (since April) after a couple of years standing.

2014 reg. Carburettor is Keihin 39s according to the owner's manual. No workshop/service manual is available from Rieju. I guess a YZF-R125 or similar one might be avaiilable.

Didn't know anything about oiling (dashpot?).

No idea about valve clearances, has been used in current ownership for about 800 miles. I suspect it

There don't seem to be any other issues at the moment. It will whizz up to 80 (after the flat spot...).
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Robby
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PostPosted: 18:21 - 28 Jul 2019    Post subject: Reply with quote
Oil as in engine oil. If that is overfilled, it will get spat into the airbox from the crankcase breather. From there it goes through the carb, into the engine.

Get it up to date on its servicing before you go looking for problems, and then bear in mind that if the problem is happening at exactly the same rpm every time it may be a programmed-in flat spot in the CDI to get past some manner of emissions regs.

I expect 8-9k rpm on a 125 would correspond with peak torque and require wide-open throttle to accelerate from there, so it would be maximum emissions land as well.
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Easy-X
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Joined: 08 Mar 2019
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PostPosted: 22:41 - 28 Jul 2019    Post subject: Reply with quote
They are about the most basic of scooter carbs... so cheap you might want to grab a spare just to see what happens Smile
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Riejufixing
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PostPosted: 23:09 - 28 Jul 2019    Post subject: Reply with quote
HardlyDavidson wrote:
They are about the most basic of scooter carbs... so cheap you might want to grab a spare just to see what happens Smile

I've got a spare one; however, I can't find any, even decent used, online for less than £115, nor a new one for less than about £250. Where can I find very cheap ones?
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jaffa90
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PostPosted: 23:31 - 28 Jul 2019    Post subject: Re: Rieju RS3 125 flat spot. Reply with quote
Riejufixing wrote:
Identical engine to Yamaha YZF-R125 (etc) but carburetted.

Possible carburation problem or other thing?

As far as I know the carburettor has not been touched since it came out of the factory. Bike has done 15,000+ miles.

Carburettor parts diagramme: https://www.riejuparts.co.uk/collections/rs3-125-engine-2011-15/products/rs3-125-engine-2011-15-t12

Annoying flat spot between ~7,000 RPM and 8,000 RPM. Most noticeable in top 3 gears.

Any pointers?


I have read the post thinking the problem has just occurred so ignore my replies. Embarassed

If it`s ok above 8,000rpm then rule out valve clearances and go for what Robby said.

Last edited by jaffa90 on 23:38 - 28 Jul 2019; edited 2 times in total
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Riejufixing
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Joined: 24 Jun 2018
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PostPosted: 23:34 - 28 Jul 2019    Post subject: Re: Rieju RS3 125 flat spot. Reply with quote
jaffa90 wrote:
I have read the post thinking the problem has just occurred so ignore my replies.

I think there is merit in your reply! I will have a look at that general area in due course.
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stevo as b4
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PostPosted: 16:42 - 29 Jul 2019    Post subject: Reply with quote
Get it on a dyno IMO. If it was a carburation/ fuel-air ratio problem you'd see it, and it would be possible to jet out assuming the carb was working properly and everything inside was unworn and spotless.

But alarm bells ring that it's only an issue in the top 3gears. Does this bike have a catalytic converter? Carbs and cats don't work that well really. Indeed any petrol engine with emissions controls will never run 100% optimally everywhere.

I also assume that the bike doesn't have a gear position sensor fitted?
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Riejufixing
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PostPosted: 17:27 - 29 Jul 2019    Post subject: Reply with quote
stevo as b4 wrote:
Get it on a dyno IMO. If it was a carburation/ fuel-air ratio problem you'd see it, and it would be possible to jet out assuming the carb was working properly and everything inside was unworn and spotless.

But alarm bells ring that it's only an issue in the top 3gears. Does this bike have a catalytic converter? Carbs and cats don't work that well really. Indeed any petrol engine with emissions controls will never run 100% optimally everywhere.

I also assume that the bike doesn't have a gear position sensor fitted?


Dynos are expensive to use. I think the problem's only actually obvious in the top 3 gears, not that it doesn't generally happen, however I am going by a second-hand description (I have carefully talked it through, even vocalising engine sounds, etc, so I'm confident of what I'm being told). It hasn't as far as I know got a cat., but it has EGR. It's entirely standard.
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Old Thread Alert!

The last post was made 6 years, 175 days ago. Instead of replying here, would creating a new thread be more useful?
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