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Post by 4l04ever on Nov 18, 2023 18:07:41 GMT 1
Has anyone used 4L1-00 carbs on a standard 350? If so, what jetting did you use?
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Post by bezzer on Nov 18, 2023 20:50:12 GMT 1
Out of interest Rob, are 4L0 and 4L1 carb bodies the same dimensionally?, meaning either could be used given the correct jetting/settings?.
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Post by midlifecrisisrd on Nov 18, 2023 21:12:30 GMT 1
Air correction jet is different between the 4l1 and 4l0
Steve
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Post by midlifecrisisrd on Nov 18, 2023 21:14:27 GMT 1
Dare say with 5k1 needles and the matching nozzles jetting wouldn't be a mile out
Steve
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Post by tony2stroke on Nov 18, 2023 22:14:17 GMT 1
0.8 air jet 350 4L0 01, 250 1mm air jet 4L1 00
0.5 for 4L0 00
All the same basic carb bodies.
0.7 for 31k and 31w
You could always fit a 0.8 air jet to correct the air jet difference
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Post by 4l04ever on Nov 18, 2023 22:44:40 GMT 1
Forgot to say....using all 350 (4L0-01) internals in the 4L1-00 bodies, due to the air jet difference....what mains/pilots/other settings are people using, or are they not a good option?
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Post by jon on Nov 19, 2023 9:34:17 GMT 1
Not that it helps you directly (but may give some faith) but my brother in law only found out after selling his LC back in the day it had 250 carbs. It did have small can microns, it it ran fine.
Odd that the 250LC is smaller. I have some 250 aircooled carbs. Once again the pilot jet is different to the 400. But, from memory the 250 is bigger?
In your situation, can’t you remove the brass balls and get a machine shop to drill the jet out to 1mm. May be good practice to remove the balls anyway?
Jon
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Post by 4l04ever on Nov 19, 2023 10:09:43 GMT 1
The issue is that the 250 carbs already have a 1mm air jet drilling whereas a 350 should be 0.8mm
I guess you could drill it out and tap it and fit a pilot jet of the required size...
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Post by Tobyjugs on Nov 19, 2023 13:53:52 GMT 1
When i first joined this forum i was using a pair of 250 carbs on my 400cc engine and i jetted them to suit the engine. I did not know there were different types carbs for the models. It had the classic small stumble but was still making just over 70 PK. Then after reading about the different types of carbs on this forum i thought i needed to get a set of 31K carbs. The end result was a lot more jetting changes and again similar performance.
It did make me think why do lots of people say use the 31K carbs.
I have had problems where the carbs have not worked properly and i have changed them because basically they have been too small for the state of tune.
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Post by chrisg on Nov 19, 2023 18:53:04 GMT 1
The issue is that the 250 carbs already have a 1mm air jet drilling whereas a 350 should be 0.8mm I guess you could drill it out and tap it and fit a pilot jet of the required size... I would have thought that the 350 would be 1mm and 250 0.8mm. 🤔 |
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Post by reedpete on Nov 19, 2023 23:16:46 GMT 1
The air jet size is initially counter intuitive but is actually logical..
Essentially the size of the air jet affects the foaming in the emulsion tube, more foaming equals less fuel… and there a sweet spot in terms of how ‘foamy’ the fuel emulsion ends up.
Ultimately it’s more fuel you need in the engine on a 350… the 350 creates a stronger induction pulse in the carb, so needs a limit to how much air is added via the mix.
The carbs are non linear enough already so the air jet is just another example of where the foaming isn’t proportional and The tendency is that the stronger the induction pulse , proportional more air is sucked into the emulsion tube. Consequently the air jet is smaller to restrict the excess air.
The only thing that puzzles me is why these carbs is designed with a fixed jet…could just have easily been removable …I guess it’s because it must have been cheaper… but that is at the expense of build flexibility.
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Post by dougw on Nov 20, 2023 16:50:30 GMT 1
I`m running 4L0-00 carbs, modified to Yams recall, on my 350 but it is not quite stock. Genuine Yam air filter and snorkel still in place (cowardice due to historical lean running on other LC`s) YPVS Reed blocks and some porting work. New original needles and needle jets from Allens Performance as listed in Haynes Manual for 4LO-00. 27.5 Pilots Originally ran 170 up from 160 mains as recommended by Yam for continual high speed use , went to 180`s (pattern) and now up at 190 genuine Mikuni mains. Some very slight signs of rich running now at the 6000 RPM mark that was not evident with 180`s but not enough to worry me into changing anything. Having said that I`ve got some NOS Ledar Nozzles to try next when I can shake off the dark cold night lethargy . This bike is supposed to be my daily run-around so not looking for peak horsepower and want it reliable and user friendly. Forgot to say....using all 350 (4L0-01) internals in the 4L1-00 bodies, due to the air jet difference....what mains/pilots/other settings are people using, or are they not a good option? |
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sev
Newbe
Posts: 4
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Post by sev on Nov 20, 2023 23:02:34 GMT 1
Try googling Dave Freist/Dale Alexander carb mod. It gives details of how to drill out the air jet and tap for adjustable air jets. I have done it on an aircooled rd. I got my jets from motocarb I think.
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Post by jessy03 on Nov 21, 2023 18:21:09 GMT 1
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Post by abar121 on Nov 22, 2023 11:38:25 GMT 1
Looks well worth a try. What 4mm thread air jets would be used? Pilot jets? |
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Post by tony2stroke on Nov 22, 2023 12:15:32 GMT 1
Mikuni 30/97 air jet the size you want ie 0.8
So Mikuni 30/97 0.8 air jet to change from 4L1 00 250 to 350 4L0 01 spec
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Post by tony2stroke on Nov 22, 2023 13:14:20 GMT 1
Mikuni 30/97 air jet the size you want ie 0.8 So Mikuni 30/97 0.8 air jet to change from 4L1 00 250 to 350 4L0 01 spec Forgot the BS Mikuni BS30/97 |
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Post by jessy03 on Nov 22, 2023 15:29:32 GMT 1
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trv2t
L plate rider.
Posts: 18
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Post by trv2t on Nov 25, 2023 17:13:39 GMT 1
Where are the carbs marked up ? I recently looked at a 250 to 350LC but couldnt see any 4L1 or 4L0 marking on the carbs?
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Post by tony2stroke on Nov 25, 2023 17:25:42 GMT 1
Where are the carbs marked up ? I recently looked at a 250 to 350LC but couldnt see any 4L1 or 4L0 marking on the carbs? Where the carb joins to the rubber inlet manifold, there is a little square with the numbers stamped, as you look at the carb side on, ie look at the carb on right side side just above the oil line spigot on the carb, HTH |
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trv2t
L plate rider.
Posts: 18
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Post by trv2t on Nov 25, 2023 17:31:20 GMT 1
Where are the carbs marked up ? I recently looked at a 250 to 350LC but couldnt see any 4L1 or 4L0 marking on the carbs? Where the carb joins to the rubber inlet manifold, there is a little square with the numbers stamped, as you look at the carb side on, ie look at the carb on right side side just above the oil line spigot on the carb, HTH |
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