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Post by airbraker on May 11, 2012 12:57:27 GMT 1
Just put a new top end on my RD250LC. (Standard bore barells new rings small ends ect)
Had problems with idle before and while rebuilding I stripped carbs and cleaned them with spray thourally including idle jets. I set the air screws correctly 1 and an 8th turn.
Before starting I checked slides sat down together and put two match sticks in back of carbs to check sync. Anyway now I am running in the revs don't come down sharply they will hover at around 2k and then slowly sit down to the idle speed. Also get bogging as I pull away from idle. Occasionally it cuts out when I pull away from the idle position.
I then have to use the choke briefly for a first time start again. This causes me to constantly rev slightly due to lack of faith and this reving will some times iniciate a bog/cut out.
The rev from idle is a warp warp rather than a rip rip sound. Over 2k the bike revs crisply and there doesn’t appear to be any problems. I am at the limit of my ability now any body got any thoughts ?
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Post by arrow on May 11, 2012 14:46:46 GMT 1
That sounds like the pilot jets all day long mate. Take them out and check them. I would replace them myself during a build as they are only cheap.
Deffo pilot circuit.
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Post by Tone on May 11, 2012 16:29:10 GMT 1
Sounds like it could also be an air leak somehere. Have you got the choke balance tube fitted between the carbs ?
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Post by airbraker on May 11, 2012 20:27:35 GMT 1
I will replace pilot jets. They looked ok had a hole in and all sorts. Balance pipe fitted and tube fitted between carbs. Cant hear or see air leak anywhere. Spoke to the God that is Norbo and he suggested looking at needles. I replaced one with a spare that I have and it seems to have improved things some what. Wont know for definate until tomorrow. I think I will order new needles and pilot jets anyway.
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Post by Tone on May 11, 2012 20:44:22 GMT 1
What clip position on the needles are you using? Assuming you got standard airbox and pipes.
When you stripped carbs did you remove needle jets to make sure the tiny holes are clear?
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Post by crash on May 11, 2012 21:00:00 GMT 1
did you push out emulsion tubes and clean them mate?
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Post by arrow on May 11, 2012 21:29:47 GMT 1
Emulsion tubes/needle jets (same thing) not the issue here. The bike runs well after 2000 rpm and reqiires use of the choke sometimes to keep it going. Both would suggest the holes in the above mentioned jets are clear.
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Post by Tone on May 12, 2012 5:56:21 GMT 1
I would still remove the needle jets to make sure everything is clear. When I first got my LC2 it had similar symptoms of bogging down when pulling away which was cured by droppiing the needle clip one notch from standard. On stripping the carbs found that it had the aftermarket Ledar needle jets fitted. Replaced these with standard Yamaha ones, put clip back to standard and it sorted it.
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Post by airbraker on May 12, 2012 9:04:31 GMT 1
Cheers men I will contact Mr Norbo Monday about new needles and pilot jets, will let you know how it turns out.
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Post by airbraker on May 12, 2012 16:56:38 GMT 1
Yea I'm coming round to that way of thinking. Did some more tests this afternoon and found that the bike sits down to idle after a run nice at around 1300 revs. If you just sit and leave it the revs oh so slowly drop to around 1100 after about 2/3 minutes. Then when you throttle it bogs and needs encouragement to come up. A quick twist will initiate a complete stall which then requires a touch of choke to get it going again. So it idles and it revs its just this little twilight zone or transition zone ? Bent needles maybe ? They have been in and out more times than a fiddlers elbow would not be at all surprised !
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Post by arrow on May 12, 2012 17:47:21 GMT 1
Stick 2 small bits of bluetac on the ends of the air correction screws to seal them, and let us know if it makes any differance.
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paulo
Thrash Merchant
Posts: 406
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Post by paulo on May 12, 2012 21:01:08 GMT 1
Sounds like a pilot circuit problem. If you screw the air screws back home from the 1 1/8TH setting that they are at now, does it improve ?. If so next size pilot jets required. If not double check original pilots or carb passageways are not blocked.
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Post by pepsisteve on May 12, 2012 21:17:04 GMT 1
i would wind the air screws in 1/4-1/2 turn see what that does.
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Post by flames on May 13, 2012 10:01:04 GMT 1
never had my airscrews all the way out but on other bikes ive had they have a rubber o ring on them.has yours got them? and if not does anyone know if they should have them? the other thing,when you screwed it in to measure your 1 1/8 turn out,you didnt screw them in tight did you? coz this can damage the seat.
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Post by airbraker on May 13, 2012 12:37:19 GMT 1
Did'nt drive them in just wound in till they touched and then out again. Will try the air screw adjustment in and see what happens. Incidently its a complete b*****d to start !
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Post by arrow on May 13, 2012 13:23:56 GMT 1
Do you have the carb slides in the wrong carb and hence the wrong way round ? Carb bowls the wrong way round also ?
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