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Post by richclare on Jun 6, 2017 17:37:12 GMT 1
Evenin' all, I think I read somewhere the 4l0-00 carbs could have been modified by Yamaha to try and sort the midrange problems. Can anyone tell me if mine have been done? Did the mod solve the issues? Also before I spend time & money cleaning my carbs is it just better to change them for 31k's? Cheers Rich     |
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Post by Hybrid500 on Jun 7, 2017 11:42:32 GMT 1
Hi, from my understanding no they havent been modded.
You should have a drilling into the Air jet, and then its blanked off, I'll forward diagram makes more sense.
I was sent this by another member on Saturday as I have same carbs. If you try the mod yourself be careful drilling, I had drill bit break ......
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Post by Hybrid500 on Jun 7, 2017 11:49:43 GMT 1
Drop me a text and I'll forward diagram, struggling to add photos!
07792824941
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Post by oldelsieboy on Jun 7, 2017 12:08:11 GMT 1
Here you go.  |
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Post by richclare on Jun 7, 2017 12:16:51 GMT 1
Hi guys,
Thank you very much for your replies. I will see if the mod has been done tonight. Can you tell me if the mod sorts out the midrange problems? Many thanks again.
Rich
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Post by muttsnuts on Jun 7, 2017 16:03:09 GMT 1
yours have not been modded, so need doing, yes it will solve the problem so long as everything else is correct, but you do need to up jet as per the technical bulletin and some carbs prefer 165 mains and others prefer 170's
be sure not to get the drilling out of alignment otherwise your carbs will be scrap
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Post by richclare on Jun 7, 2017 17:32:00 GMT 1
yours have not been modded, so need doing, yes it will solve the problem so long as everything else is correct, but you do need to up jet as per the technical bulletin and some carbs prefer 165 mains and others prefer 170's be sure not to get the drilling out of alignment otherwise your carbs will be scrap That's great. Thanks very much for your reply muttsnuts. Is that 3mm diameter drill (can't see the figure clearly on the tech sheet). How is the hole blocked - grub screw with loctite? Cheers Rich |
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Post by richclare on Jun 7, 2017 20:06:43 GMT 1
Hi, from my understanding no they havent been modded. You should have a drilling into the Air jet, and then its blanked off, I'll forward diagram makes more sense. I was sent this by another member on Saturday as I have same carbs. If you try the mod yourself be careful drilling, I had drill bit break ...... Hi whiteblue (best colours IMO), Could you send me any photos of your modified carbs, with any tips😉 Did you use a pillar drill and did you drill in one hit or gradually increase the size? Many thanks, Rich |
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Post by Hybrid500 on Jun 7, 2017 21:12:10 GMT 1
I'll be honest, I've just bought some 31k carbs , I tried some 4LO 01 carbs that were so much better than mine.
What jets have you got in currently?
As the drill bit broke off it's not possible to mod mine now, they need doing in a pillar drill, clamping is an issue as well, as it's only a 3mm drill it might be difficult to drill out gradually as 3mm is so small anyway.
Depending on your jets you might be able to get it better than it is
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Post by muttsnuts on Jun 8, 2017 9:20:45 GMT 1
yours have not been modded, so need doing, yes it will solve the problem so long as everything else is correct, but you do need to up jet as per the technical bulletin and some carbs prefer 165 mains and others prefer 170's be sure not to get the drilling out of alignment otherwise your carbs will be scrap That's great. Thanks very much for your reply muttsnuts. Is that 3mm diameter drill (can't see the figure clearly on the tech sheet). How is the hole blocked - grub screw with loctite? Cheers Rich you leave the 3mm hole open to the air, it feeds the air correction circuit, then the hole on in th eimnlet side of the carb is blocked up, it says use araldite or the likes, but I have the correct brass balls and block them off with that when I do the mods for people |
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Post by richclare on Jun 8, 2017 10:55:06 GMT 1
That's great. Thanks very much for your reply muttsnuts. Is that 3mm diameter drill (can't see the figure clearly on the tech sheet). How is the hole blocked - grub screw with loctite? Cheers Rich you leave the 3mm hole open to the air, it feeds the air correction circuit, then the hole on in th eimnlet side of the carb is blocked up, it says use araldite or the likes, but I have the correct brass balls and block them off with that when I do the mods for people Thanks mutts. I might be coming to you soon for some ball therapy! 😉 The knowledge on here is brilliant and good people too. Have a good day. Rich |
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Post by Hybrid500 on Jun 9, 2017 13:58:01 GMT 1
I'd be tempted to let mutts do them ....
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Post by mwiseman58 on Jul 9, 2017 1:22:50 GMT 1
I had this mod done back in 1980 when I bought the bike. To be honest it only made a small difference and eventually I blocked up the new hole and drilled out the original again as there were reports of the air bleed becoming blocked due to the unfiltered air feeding them. I have lived with the flat spot ever since and still have the same bike. Has anyone else found this mod made a big difference? Is there a better way to remove this annoying flat spot? When I was young it wasn't a problem as I just kept the revs up. Now that I am approaching 60 and more sedate in my riding I find the flat spot annoying. Are the 31k carbs the best way to go?
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Post by Hybrid500 on Jul 13, 2017 23:26:12 GMT 1
I had this mod done back in 1980 when I bought the bike. To be honest it only made a small difference and eventually I blocked up the new hole and drilled out the original again as there were reports of the air bleed becoming blocked due to the unfiltered air feeding them. I have lived with the flat spot ever since and still have the same bike. Has anyone else found this mod made a big difference? Is there a better way to remove this annoying flat spot? When I was young it wasn't a problem as I just kept the revs up. Now that I am approaching 60 and more sedate in my riding I find the flat spot annoying. Are the 31k carbs the best way to go? I'm using 31k carbs now on mine made a huge difference, jetted as per standard 31k, with standard unmodded airbox and Allspeeds |
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Post by richclare on Jul 14, 2017 6:25:28 GMT 1
Hi WB350,
That's good to know there is a fall back if everything else fails or if I can't be ar**d😉
I'm going to try the standard 4l0-00 carbs for the moment.
Cheers Rich
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Post by mwiseman58 on Jul 29, 2017 20:47:53 GMT 1
I have just got myself a set of 31k carbs so when I get back on the road I will let you all know how they compare to the un-modded original 4l0 O0 carbs. Unfortunately mine were modded back in 1980 but I accidently broke a tap in one of the 3mm holes whilst trying to temporarily block it with a grub screw. So I just blocked off both 3mm holes and reverted to original. I can't wait to try the 31k's.
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Post by richclare on Jul 29, 2017 23:40:22 GMT 1
I have just got myself a set of 31k carbs so when I get back on the road I will let you all know how they compare to the un-modded original 4l0 O0 carbs. Unfortunately mine were modded back in 1980 but I accidently broke a tap in one of the 3mm holes whilst trying to temporarily block it with a grub screw. So I just blocked off both 3mm holes and reverted to original. I can't wait to try the 31k's. I would be very interested in your results. Let me know how it goes as it will help me and others, I'm sure. My rebuild is coming to an end so should be riding soon. Today the new battery went in and things were alight - very exciting times ;-) Cheers Rich |
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Post by mwiseman58 on Jul 30, 2017 3:26:37 GMT 1
Will let u all know but it will be a few weeks. Cheers
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Post by rasteirinho on Aug 23, 2017 13:31:18 GMT 1
Hello, I have drilled my carbs and the hole apears in the front of the air jet. Should the air jet be drilled also? If not the only difference is that the air instead of coming from the air filter side, comes from the side of the carburettor. Will this make a huge difference? I am thinking of blanking the filter side hole with a screw, so I can revert it if necessary. Thanks
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Post by mwiseman58 on Aug 26, 2017 23:54:54 GMT 1
No don't drill the airjet itself but yes do blank off the hole on the airfilter side. I assume u have done this on early 4l0_00 carbs as the later ones don't need this mod.
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Post by mwiseman58 on Nov 8, 2017 22:35:50 GMT 1
Well I have finally got my bike on the road again fitted with the 31k carbs. I have also fitted a 5mm reed block spacer on the cylinder side. I can report this combo has completely removed the flat spot that the 1980 models are plagued with. It pulls smoothly all the way through that dreaded 4-5000 rev range and has made the bike much better to ride in traffic and around town. My advice for anyone trying to improve the 4lo-00 carbs is to ditch them and fit 31k ones. You will be pleased you did.
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Post by richclare on Nov 8, 2017 22:54:12 GMT 1
Well I have finally got my bike on the road again fitted with the 31k carbs. I have also fitted a 5mm reed block spacer on the cylinder side. I can report this combo has completely removed the flat spot that the 1980 models are plagued with. It pulls smoothly all the way through that dreaded 4-5000 rev range and has made the bike much better to ride in traffic and around town. My advice for anyone trying to improve the 4lo-00 carbs is to ditch them and fit 31k ones. You will be pleased you did. That's good to hear...... and thanks for reporting back. I'm still running my motor in and no obvious carb issues at the moment. I'm sure they will come! Enjoy your bike. Cheers Rich |
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Post by richclare on Jul 7, 2018 17:44:13 GMT 1
Hi, It's been a while since I have posted anything as I had a few teething issues! After running the engine in, the dreaded mid-range flat spot became very evident. I decided to try drilling the extra feed for the air circuit, as discussed earlier. I was rather nervous to say the least. I clamped each carb and checked the vertical alignment with a set square, several times😉. Drilling was pretty easy as the alloy is soft. The only real problem was the metal melting around the drill bit, but taking it in little bits eliminated this. I then checked for burrs etc. and gave them a good clean. The old feed hole was blocked with a stainless grub screw and thread lock. I had read before of the difference it makes but riding the bike after was just incredible. It now pulls, smoothly, all the way through. Rich  |
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Post by earthman on Jul 7, 2018 19:04:20 GMT 1
Great to hear that things worked out good for you in the end.
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Post by richclare on Jul 7, 2018 23:38:00 GMT 1
Just a question - the air circuit is now breathing air from outside the air box. Should I take any precautions regarding dirt/dust entering the new hole (nurse)? Or is this just something I have to accept.
Cheers
Rich
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Post by muttsnuts on Jul 8, 2018 12:18:36 GMT 1
if you want to restrict/stop the ingress of dirt, you can fit an elbow and a small clear tube to the 3mm drilling in the body you did, the later carbs have the breather drilled into the float bowl breather and has the clear tube attched to that
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Post by richclare on Jul 8, 2018 16:07:26 GMT 1
if you want to restrict/stop the ingress of dirt, you can fit an elbow and a small clear tube to the 3mm drilling in the body you did, the later carbs have the breather drilled into the float bowl breather and has the clear tube attched to that Hi Muttsnuts, Many thanks for the info. Can you give me an idea where I would find an elbow to fit. Rich |
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Post by pdxjim on Feb 6, 2019 7:34:10 GMT 1
While were on the subject ... I've got an early 4U0 JDM bike here. Carbs are stamped 4U0 00. Frame #4U0-005761. No tie bars below the engine. Carbs are different to the 4L0 00 ones, as the boss that gets drilled down to the air jet has a brass ball fitted where the hole is to be drilled. I'm still in the process of getting this thing running, so I don't know if the midrange flatspot is there or not. Muttsnuts, what can you tell me about the 4L0 00 carbs?  |
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Post by midlifecrisisrd on Feb 6, 2019 8:55:40 GMT 1
While were on the subject ... I've got an early 4U0 JDM bike here. Carbs are stamped 4U0 00. Frame #4U0-005761. No tie bars below the engine. Carbs are different to the 4L0 00 ones, as the boss that gets drilled down to the air jet has a brass ball fitted where the hole is to be drilled. I'm still in the process of getting this thing running, so I don't know if the midrange flatspot is there or not. Muttsnuts, what can you tell me about the 4L0 00 carbs? By the looks of where the balls and castings are I'd say there is already a passage from the air jet up to the breather for the float bowl Steve |
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