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Post subject: Misfire
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sonic242  Sunday Rider Joined: 26 Jul 2007 Total posts: 35 |
Ok here we go I have rd250lc which has undergone a full restoration. The engine has been fitted with 350 barrels new bearing, seals and rings. The carbs have been changed to 31K with 220 mains and 22.5 pilots the reads valves are still 250. It tick over fine and seems to rev ok how ever when under load it runs fine to 4000 rpms then starts misfire cough and splutters quite a bit then goes ok but no mental power band but does seam to pull a bit. The carbs have been cleaned float heights checked vac for fuel taps has been blocked off.
Any help would be much appreciated
Cheers Davie
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Posted: Sun May 11, 2008 7:38 pm
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Vindaloobeast Rear-wheel Steering! Joined: 25 Aug 2005 Total posts: 2623 Location: Gloucester |
Bedtime reading..
http://www.yamaha-rd.com/forum/topic-50367.html
Took me 3 years..!
Beast.
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Posted: Sun May 11, 2008 7:40 pm
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sonic242Sunday Rider Joined: 26 Jul 2007 Total posts: 35 |
Ok so the up shot is I should change the needle what about the emulation tubes? My bike total standard do you think this would help. Where did you get the needle valve from?
Cheers Davie
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Posted: Sun May 11, 2008 8:19 pm
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VindaloobeastRear-wheel Steering! Joined: 25 Aug 2005 Total posts: 2623 Location: Gloucester |
If I was in your shoes Id go back to standard and by the book and then recheck it. I had a kit needlevalve in a faulty set of carbs. Is your oil pump a 350 one..?
Beast.
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Posted: Sun May 11, 2008 8:22 pm
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sonic242Sunday Rider Joined: 26 Jul 2007 Total posts: 35 |
I don’t have standard carbs as the standard ones are 250 other than that the 350 (31K) are standard I was advised on here that 220 main were the way to go for this setup. The oil pump was changed for a 350 one the bike is smoky could it be getting to much oil. I did check the pump setup and seamed ok.
Cheers Davie
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Posted: Sun May 11, 2008 8:40 pm
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VindaloobeastRear-wheel Steering! Joined: 25 Aug 2005 Total posts: 2623 Location: Gloucester |
The engines on these bikes go rich at the transition naturally. They all do and you will find many posts on here just like yours of people complaining of similar symptoms but most people cant be bothered to iron it out.
The stumble is because its over rich and the engine is starting to 4 stroke. A simple way to test it is to whip off the airbox lid and filter out. It takes 5 minutes. Dont go mad. Just bring the throttle on gently from idle and you should notice an improvement. At least you have proved the rich theory. Then I would suggest you replace the airbox lid and filter and drop the needles in the carbs by 2 notches. I say 2 but on mine I went top to bottom and it made no difference. If the 2 notches makes it better check drive and if reqd change it to just one notch. Ensure the plate in the carb slide has the hole visible with plate in situ. Yesterday my bike was smoking like mad with the faulty needle valves.
If the needle adjustment fails to make any significant difference then you need to be looking at the needle valve and also ensure the carb and emulsion tube is cleaned properly. A standard engine should run fine with airbox and filter. A tuned one needs air.
Hope this helps.
Beast
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Posted: Sun May 11, 2008 8:50 pm
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sonic242Sunday Rider Joined: 26 Jul 2007 Total posts: 35 |
Thanks beast will give that a try tomorrow I read you post and there are definitely similarity to the problems you were having and the problems I am having The bike will not rev past about 8.5 Rpm and but feels flat.
Thanks for the help
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Posted: Sun May 11, 2008 9:01 pm
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Post subject: Misfire now sorted I hope
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sonic242Sunday Rider Joined: 26 Jul 2007 Total posts: 35 |
Cheers Beast
II think I have now got the bike sorted. Strip and the cleaned the carbs again reset the floats bowls, set the idle screw with a dial gauge, reset oil pump, reset the carbs with the lolly sticks method, reset the airscrews took it for a quick up and down the street and it was running great that for your help. I will try and get a longer run but it’s wee bit to load for this time of night around here.
Cheers David 
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Posted: Tue May 13, 2008 8:21 pm
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