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Post by biffa on Feb 3, 2020 21:49:07 GMT 1
Just checked the main jets on my 4L0 and they're 160. I've been reading through a lot of old posts on here and it seems everyone is running over 200s.
My bike has Swarbricks, a skimmed head and has been ported but I ran it for two years before I stripped it and the plug colour was fine.
Could this have anything to do with having the earlier carbs? If not I can't understand why it didn't blow up...
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Jetting
Feb 3, 2020 22:28:16 GMT 1
via mobile
Post by Delbert on Feb 3, 2020 22:28:16 GMT 1
Or 250 carbs maybe , I had 250 carbs on my old 350 and I think I was having to run something like 160s or it just bogged out ,
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Post by biffa on Feb 3, 2020 22:35:13 GMT 1
Would never have thought of that, but it's a matching numbers UK bike.
Strange thing to change but I'll certainly have a look.
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Post by biffa on Feb 3, 2020 22:37:43 GMT 1
Just been and had a look, both carbs stamped 4L0 00
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Jetting
Feb 3, 2020 22:57:22 GMT 1
via mobile
Post by shaunthe2nd on Feb 3, 2020 22:57:22 GMT 1
4L0 00's were fitted with 160's as standard. There was a drilling mod for these carbs to to open up the air circuit to the atmosphere. Search on here I put some pics up somewhere.
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Jetting
Feb 3, 2020 22:59:01 GMT 1
via mobile
Post by shaunthe2nd on Feb 3, 2020 22:59:01 GMT 1
4L0 01 were later carbs fitted with 220's.
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Post by biffa on Feb 3, 2020 22:59:59 GMT 1
OK, thanks.
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Post by biffa on Feb 3, 2020 23:10:19 GMT 1
Found your thread, checked and mine have been modded. Thanks for your help.
Still would have thought that it would have been up-jetted after the mods but it was running fine so I'll just do a plug chop once it's finished.
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Post by jon on Feb 3, 2020 23:46:48 GMT 1
If you’re carbs have been modded, and your running Swarbrick’s I would definitely upjet.
Jon
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Post by biffa on Feb 4, 2020 0:00:19 GMT 1
Just found this www.rd350lc.net/YAMAHAtechServInfo4L0carbs.jpgLike I said, ran the bike for two years without any trouble but was looking to see how it was set-up. After reading this might go to a 170 for a bit of leeway. Not that I'm going to be at continuous high speed these days
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Post by biffa on Feb 4, 2020 0:10:28 GMT 1
It looks like the engine's had some work done, hopefully by someone who knew what they were doing.
I just had the crankcases vapour blasted and the bloke doing it who's an ex-racer pointed out some hand-etched numbers on the magneto side of the cases.
The crank pins have been welded but there's no drilled sump plugs or other general racing damage and the internals were mint.
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Post by oldbritguy on Feb 4, 2020 1:42:17 GMT 1
Hand etched numbers on crankcases behind rotor/stator were done at factory upon machining/line boring for crank and gearbox shaft bearings.
Numbers on top and bottom cases should be the same to show they are a machined matched pair.
Have a look at Dusty's engine build threads (LC and YPVS), they are shown quite clearly in those.
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Post by biffa on Feb 4, 2020 10:11:15 GMT 1
That's that cleared up! Numbers match so all good.
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Post by 4l04ever on Feb 4, 2020 23:56:54 GMT 1
Are you running with a standard airbox with the snorkel and filter fitted?
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Post by biffa on Feb 5, 2020 8:08:17 GMT 1
I'm planning to use the standard airbox and filter when it goes back together, not sure about the snorkel but assume there was one on when it came apart.
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