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Broke Down Today!

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Sibon73
Two Stroke Sniffer



Joined: 24 Jun 2011
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PostPosted: 14:26 - 28 Jul 2011    Post subject: Broke Down Today! Reply with quote
Hi all

I broke down this morning on my way in to work (at least it's a nice day for it).

The Bike: RS125 2000 (1,000 miles after a full rebuild)

The Symptoms:
Was running fine, warmed it up as normal, always take it steady for the 1st mile or so mainly due to the area / roads. Came to the point where I normally open it up a bit and it flat spotted around 10k but kept running. Came to a junction and it just died.

Started it up again, and it seemed to run OK but then just died as though out of petrol.

My quick checks at road side:
Spark plug, sooty black in colour so gave it a clean
Air filter was OK
Plenty of fuel

Unfortunately thats the limit of my knowledge.

Set off again and it got me to work, 2 to 3 miles away without cutting out. It flat spotted around 10k, was almost like hitting a limiter though.

Just checked the plug at dinner and it's a tan colour - but thats after just 2/3miles.

What would cause it just to drop revs and cut out?

Thanks
Simon
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at106
Brolly Dolly



Joined: 16 Jul 2011
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PostPosted: 17:03 - 28 Jul 2011    Post subject: Reply with quote
It sounds to me asthough it's not getting enough fuel. I would clean the carburettor, and make sure the jets are not blocked.

Also is the fuel tap a vacumn one or a gravity fed one?
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Sibon73
Two Stroke Sniffer



Joined: 24 Jun 2011
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PostPosted: 17:26 - 28 Jul 2011    Post subject: Reply with quote
I think it is a vacuum one, will have a look at the carb tonight.

Sorry newbie question.....will I have to take the full carb off or just remove the top for the jets? It's a 28mm Carb

Cheers
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at106
Brolly Dolly



Joined: 16 Jul 2011
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PostPosted: 17:43 - 28 Jul 2011    Post subject: Reply with quote
Sibon73 wrote:
I think it is a vacuum one, will have a look at the carb tonight.

Sorry newbie question.....will I have to take the full carb off or just remove the top for the jets? It's a 28mm Carb

Cheers


I would completely remove the carb as then you can strip it down and make sure it's all clean inside.

If your fuel tap is a vacumn one there should be two pipes coming from it, one will go to the carb to supply fuel, the other will go to the engine and start at the bottom of the fuel tap, when suction is applied to this a diaphram opens allowing fuel to flow. You need to test that this is working by applying suction to the pipe and fuel should flow out of the one going to the carb.
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Sibon73
Two Stroke Sniffer



Joined: 24 Jun 2011
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PostPosted: 20:08 - 28 Jul 2011    Post subject: Reply with quote
Cheers at106
Stripped the carb, everything seemed ok. There is just one pipe down from the tap, checked that and fuel is flowing ok. Everything seemed ok on the ride home apart from high rev point, checked the plug and slightly darker around the edge but the centre was a tan colour still. Just a bit spluttery at the 9-10k mark

Cheers
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temeluchus
World Chat Champion



Joined: 01 Oct 2008
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PostPosted: 20:37 - 28 Jul 2011    Post subject: Reply with quote
As a rule, black sooty plug means too much fuel.

Two usual culprits are a stuck or faulty choke-check the cable if there is one and the mech on the carb itself for free movement- and a problem with the float and needle-check the float needle and its seat are clean and that the float floats and is correctly adjusted.
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Sibon73
Two Stroke Sniffer



Joined: 24 Jun 2011
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PostPosted: 10:01 - 29 Jul 2011    Post subject: Reply with quote
Got to work fine this morning, seemed to run a bit better than normal through the low-mid rev range, just flat spot around 10k.

This was the plug seconds after pulling up at work.

https://i1118.photobucket.com/albums/k608/s1bon/Picture012.jpg

Didn't check the needle last night but will have another look this evening along with the choke.

Cheers
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at106
Brolly Dolly



Joined: 16 Jul 2011
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PostPosted: 10:22 - 29 Jul 2011    Post subject: Reply with quote
The plug looks fine to me Thumbs Up When you say the air filter is ok is the filter clean?
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Wafer_Thin_Ham
Super Spammer



Joined: 18 Nov 2005
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PostPosted: 10:25 - 29 Jul 2011    Post subject: Reply with quote
desrestricted?

Isn't the powervalve meant to open around 10k?
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Sibon73
Two Stroke Sniffer



Joined: 24 Jun 2011
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PostPosted: 10:35 - 29 Jul 2011    Post subject: Reply with quote
at106 wrote:
The plug looks fine to me Thumbs Up When you say the air filter is ok is the filter clean?


Yes took the filter out, looked clean to me, air would easily pass through it. The chap I bought it off said it might need the needle moving a notch in the carb. Need to read up on that though before I start messing with adjustments.
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Sibon73
Two Stroke Sniffer



Joined: 24 Jun 2011
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PostPosted: 10:44 - 29 Jul 2011    Post subject: Reply with quote
Big_Ham wrote:
desrestricted?

Isn't the powervalve meant to open around 10k?


It is, after I run it in someone told me to take the blade out and give it a clean as crap can build up while only using 3/4 throttle. It did have a build up, gave it a clean and l checked this just the other week and it looked clean, a little build up but that may have been from before.

The first kick I get is around 8-9k, it powers on and revs up then just after 10k, seems to want me to change gear like there is nothing left in that gear.
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P.addy
Red Rocket



Joined: 14 Feb 2008
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PostPosted: 11:01 - 29 Jul 2011    Post subject: Reply with quote
Should be fairly flat until around 8k, and then shoot up like a train.

Plug looks nigh on perfect.

Are you/have you run low on reserve? Could just get the carb off and give it a nice clean blow out, check your vacuum pipe.

Just a quick one, when was it rebuilt, you say 1000 miles ago, but I mean time wise.
My old RS has a full rebuild ~1000 miles before I bought it, 60 miles later it shat its main bearing and randomly turned off now and then at lights after riding properly. In the end it seized and cost me £250 Laughing
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Sibon73
Two Stroke Sniffer



Joined: 24 Jun 2011
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PostPosted: 11:23 - 29 Jul 2011    Post subject: Reply with quote
##Paddy## wrote:
Should be fairly flat until around 8k, and then shoot up like a train.

Plug looks nigh on perfect.

Are you/have you run low on reserve? Could just get the carb off and give it a nice clean blow out, check your vacuum pipe.

Just a quick one, when was it rebuilt, you say 1000 miles ago, but I mean time wise.
My old RS has a full rebuild ~1000 miles before I bought it, 60 miles later it shat its main bearing and randomly turned off now and then at lights after riding properly. In the end it seized and cost me £250 Laughing


Hi Paddy - Rebuild was about 2 months ago, I went to see it in pieces and put a deposit on it then, it's only done the miles I've put on it. Chap I bought it off buys / rebuilds bikes as a part time paying hobby, had about 8 bikes on the go, mine was just the next to be completed. It does as you say, steady build up to 8k then goes. Is 10k the max or should it go beyond that?
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P.addy
Red Rocket



Joined: 14 Feb 2008
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PostPosted: 13:33 - 29 Jul 2011    Post subject: Reply with quote
Sibon73 wrote:
Is 10k the max or should it go beyond that?


Glad to know it came from someone who rebuilds.

Erm, what does the top the redline say on the rev counter, I cant recall.
Mine revved to there Laughing
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Sibon73
Two Stroke Sniffer



Joined: 24 Jun 2011
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PostPosted: 14:03 - 29 Jul 2011    Post subject: Reply with quote
##Paddy## wrote:
Sibon73 wrote:
Is 10k the max or should it go beyond that?


Glad to know it came from someone who rebuilds.

Erm, what does the top the redline say on the rev counter, I cant recall.
Mine revved to there Laughing


14k Shocked lol, I'm starting to wonder if the flat spot is the rev counter, it does jump sometimes when idleing as though the rev needle isn't attached, will be on about 1.5k then the needle just drops like engines cut out but idle speed doesn't change - a little tap and it kicks back in.

I realise this was nothing to do with the breakdown, but that (touch wood) is in the past.

Maybe the real revs are hitting the top end but the needle is telling me otherwise. I'm bidding on a couple at the minute anyway as it's on my tidy up / fix list (Show and Tell Forum)

Will check needle and choke tonight and see how it runs
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P.addy
Red Rocket



Joined: 14 Feb 2008
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PostPosted: 14:06 - 29 Jul 2011    Post subject: Reply with quote
Definitely check the choke...although the plug would say its not stuck open.

Do you have an air leak near your carb??get the bike running and spray wd40 around the place where the carb connects to engine/airbox... if the revs change you may have a leak somewhere...that may be holding it back at 10k.
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Sibon73
Two Stroke Sniffer



Joined: 24 Jun 2011
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PostPosted: 14:49 - 29 Jul 2011    Post subject: Reply with quote
##Paddy## wrote:
Definitely check the choke...although the plug would say its not stuck open.

Do you have an air leak near your carb??get the bike running and spray wd40 around the place where the carb connects to engine/airbox... if the revs change you may have a leak somewhere...that may be holding it back at 10k.


I did notice last night when looking at the carb that the actual airbox was loose to the vent that comes out of it (that attatches to the carb) , it could be moved about, the connection to the carb was solid enough. Could that be it? Is too much air getting in there?
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