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Post by tunneruk on Mar 19, 2012 16:18:06 GMT 1
Guys, guys, guys
I need some advice
I've just finished my 250LC, she flew through her MOT last week so I've finally been able to put a few miles on her.
My problem is this -
The bike has got absolutely no bottom end power, I mean NONE, such is the extent of the problem that I struggle to pull away from a standstill. However as soon as the little fun needle reaches 7k RPM she absolutely rockets off up the road!
The bike does about 5500rpm at 70 MPH so won't pull top gear regardless of how much throttle is applied, I have to be one or two cogs down before it feels comfortable, it will however pull right through 100MPH once wound up.
It's a completely standard bike, standard carbs, standard pipes, standard airbox and filter complete with inlet trumpet.
I'm under no illusion that the bike should be torquey but I honestly don't think it's running right.
Any help would be greatly appreciated!
CT
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Post by ducatidave on Mar 19, 2012 16:29:08 GMT 1
Is it german mines same : (
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Post by bigal1 on Mar 19, 2012 16:48:02 GMT 1
try messing about with the sprokets
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Post by arrow on Mar 19, 2012 17:28:32 GMT 1
The pipes you put on it, could they be 350 ones ?
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Post by tunneruk on Mar 19, 2012 18:21:11 GMT 1
Ok ......
It's a UK bike........
The pipes are without doubt 250 specific
It's definitely an engine running issue, I appreciate the comment regarding sprockets but it's really bogging down below 6500RPM no matter what gear it's in, there's just a whole bunch of induction roar
Keep the ideas coming!
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Post by midlifecrisisrd on Mar 19, 2012 19:12:02 GMT 1
Think it's time to strip the carbs and clean them.
Might be worth checking the reeds as well.
Steve
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Post by tunneruk on Mar 19, 2012 19:16:58 GMT 1
Think it's time to strip the carbs and clean them. Might be worth checking the reeds as well. Steve Ok, the carbs are no problem, I can whip them off and clean the life out of them, The reeds looked fine when I put them back in, what checks should I make? |
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Post by arrow on Mar 19, 2012 20:45:07 GMT 1
Do you have the trumpet thingy on the air box ?
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Post by midlifecrisisrd on Mar 19, 2012 21:22:59 GMT 1
Think it's time to strip the carbs and clean them. Might be worth checking the reeds as well. Steve Ok, the carbs are no problem, I can whip them off and clean the life out of them, The reeds looked fine when I put them back in, what checks should I make? Just need to check they close properly and none have broke. Remember to remove and clean the emulsion tubes in the carbs. Steve |
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Post by lckid on Mar 19, 2012 21:33:26 GMT 1
Ok ...... It's a UK bike........ The pipes are without doubt 250 specific It's definitely an engine running issue, I appreciate the comment regarding sprockets but it's really bogging down below 6500RPM no matter what gear it's in, there's just a whole bunch of induction roar Keep the ideas coming! Check jet sizes? and needles, could be head/base gaskets leaking? are the cylinders std and not tuned??? |
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Post by tunneruk on Mar 19, 2012 21:37:04 GMT 1
Ok, the carbs are no problem, I can whip them off and clean the life out of them, The reeds looked fine when I put them back in, what checks should I make? Just need to check they close properly and none have broke. Well the reeds close but I've not had the emulsion tubes out for an ultrasonic clean. Are they easy to remove? Remember to remove and clean the emulsion tubes in the carbs. Steve |
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Post by gazilla on Mar 19, 2012 21:40:26 GMT 1
In the tech section there is a great one regarding setting up carbs.It sounds to me that there is some sort of idle/mid range setup problem.If you sort it out can i borrow as mine wont pull above 4,000 revs and think its the carbs.
Gaz
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Post by ianboom on Mar 19, 2012 21:58:36 GMT 1
I built a 250LC for the wife that was very similar to yours, turned out it was the reeds, they were fibre ones and looked fine apart from a tiny gap you could see daylight through if you held them up to the light. Fitted some old standard steel ones and the bike was transformed.
Wouldn't have thought it'd have made that much difference, but it did!
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Post by tunneruk on Mar 19, 2012 22:07:36 GMT 1
I built a 250LC for the wife that was very similar to yours, turned out it was the reeds, they were fibre ones and looked fine apart from a tiny gap you could see daylight through if you held them up to the light. Fitted some old standard steel ones and the bike was transformed. Wouldn't have thought it'd have made that much difference, but it did! My bike has yellow fibre reeds which from memory look to close up well but it's certainly worth a look. Steel reeds ................. Really? |
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Post by oldelsieboy on Mar 19, 2012 22:15:12 GMT 1
I built a 250LC for the wife that was very similar to yours, turned out it was the reeds, they were fibre ones and looked fine apart from a tiny gap you could see daylight through if you held them up to the light. Fitted some old standard steel ones and the bike was transformed. Wouldn't have thought it'd have made that much difference, but it did! My bike has yellow fibre reeds which from memory look to close up well but it's certainly worth a look. Steel reeds ................. Really? Hi Chris Think I have a spare set of standard reeds if you want to give em a try. OEB |
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Post by tunneruk on Mar 19, 2012 22:28:41 GMT 1
My bike has yellow fibre reeds which from memory look to close up well but it's certainly worth a look. Steel reeds ................. Really? Hi Chris Think I have a spare set of standard reeds if you want to give em a try. OEB 5 Star that man! I've got fibre reeds in mine, I take it that these aren't standard then? |
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Post by oldelsieboy on Mar 19, 2012 22:55:03 GMT 1
Hi Chris Think I have a spare set of standard reeds if you want to give em a try. OEB 5 Star that man! I've got fibre reeds in mine, I take it that these aren't standard then? Steel reeds are standard. Suppose I'll have to find em now  OEB |
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Post by arrow on Mar 20, 2012 7:42:47 GMT 1
Do you have the trumpet thingy on the air box ? |
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Post by tunneruk on Mar 20, 2012 7:55:20 GMT 1
Yeah the inlet trumpet is in place and did make a bit of a difference.
I'll investigate the reeds situation as I'd not considered that. It's too much of a gaping hole in the rev range to be carb adjustment, it's not a bit fluffy, it's fundamentally wrong!
Will going back to standard reeds affect the top end power? I assume that's why they were upgraded in the first place?
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Post by arrow on Mar 20, 2012 13:49:35 GMT 1
Yeah the inlet trumpet is in place and did make a bit of a difference. I'll investigate the reeds situation as I'd not considered that. It's too much of a gaping hole in the rev range to be carb adjustment, it's not a bit fluffy, it's fundamentally wrong! Will going back to standard reeds affect the top end power? I assume that's why they were upgraded in the first place?IMO no mate. I have found the best overall performance with a standard set up is with the standard reeds. By the way I asked about the trumpet thingy as I tried mine without it and the motor ran as flat as a snakes fxxny ! |
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Post by arrow on Mar 20, 2012 13:54:34 GMT 1
Have you got the slides the correct way round in the carbs ??
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Post by tunneruk on Mar 20, 2012 20:05:12 GMT 1
Have you got the slides the correct way round in the carbs ?? AFAIK the slides only go down into the carbs one way? |
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Post by arrow on Mar 20, 2012 20:26:21 GMT 1
The left slide will go in the right carb the wrong way round, ie with the cutaway facing the motor not the air filter.
And vice versa, right in left, but the wrong way round. Catches loads of people out that one..................
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Post by arrow on Mar 21, 2012 20:28:40 GMT 1
Any luck with that ?
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Post by tunneruk on Mar 25, 2012 18:56:35 GMT 1
Hi Fella,
Cheers for the suggestion but it's one of the first things I checked.
The carbs are clean as a whistle and tip top
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Post by pepsisteve on Mar 25, 2012 21:02:29 GMT 1
when mine was a 250 you could let the revs drop right down to 3k in top gear and then throttle stop it and it would pull no problem at all right until its top speed, so all i can say is you have a problem. yamaha would not have been able to sell a bike that didnt run below 7k
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Post by tunneruk on Mar 25, 2012 21:18:05 GMT 1
It goes really well past about 6.5k, pulls clean and strong through to 9.5k
70MPH is about 5.5k in top so just doesn't work, it's all induction noise and not a lot else. I've taken to keeping the revs above 6.5k at all times.
It's quite to happy to buzz along at 80-90mph in 5th at 7-8k rpm.
I'll get the standard reeds fitted and take from there.
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Post by tunneruk on Mar 29, 2012 19:46:58 GMT 1
So.......
My standard reeds arrived today (cheers Andy)
They've made the problem about 50% better, there's more bottom end but she still struggles to pull away and still wont pull top.
I hate being beaten!!!
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Deleted
Deleted Member
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Post by Deleted on Mar 29, 2012 23:17:35 GMT 1
keep at it, you will get there in the end,
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Post by midlifecrisisrd on Mar 30, 2012 8:22:31 GMT 1
If you are sure the pilot/airscrew circuits are perfect then I'd suggest a compression test to check the piston/bores are fine.
Will also need to check the timing with a strobe light in case the pick up or cdi is playing havoc.
As has been said it could be base gaskets drawing air or a crank seal. If either of these it seems unlikely both sides would have the same problem so would be a difference in the plug colours. How are they?
Might be worth getting a loan of another set of carbs to rule out as it has been known for carbs to be clean but still won't work, a lot of little internal passages.
Steve
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