Thanks !!! I do enjoy working on these old bikes so I figure folks might like seeing some of the reasons why they get grumpy or won’t cooperate after a build or restore. It’s always frustrating to feel like you’ve done everything right, but they still just won’t run correctly. After 40 years or so, there’s no telling what these old girls have been through for maintenance and some of the little things can really make a big difference sometimes. Thanks again and all the best !

Thanks and glad the videos are helping some 👍. All the best ! Steve

Hey man ! Thanks and Happy 2023 to you and yours as well ! Yep, cross sectioning one makes it very easy to see what happens when the needle is repeatedly over tightened. I too had wondered just how much damage is done so it worked out good to cut these broken carbs up to see. Thanks again and all the best !

Thanks man and Happy New Year to you as well ! Yep, it’s easy to see the result of cranking down on the needle when the carb is sectioned for sure. The only bike I’ve had with the plugs still in it was my Stock ‘81 750 and it dials in sooooo easy compared to the other ones for sure. Now that I know the hole size and what it looks like inside, I can go back and clean up the other bikes so they should adjust better again as well. Maybe one day I’ll justify getting a precision grinder for the lathe and can make a cool little tool that can resurface the seat and reset the hole diameter…bet the bikes would adjust like brand new again. Thanks again and all the best !

Thanks man and Happy 2023 to you as well !

Thanks ! Glad the video helped some 👍. All the best ! Steve

Thanks man and glad the video helped some with what can happen with the mix needle. All the best ! Steve

Thanks man and glad the videos help some 👍. All the best ! Steve

Thanks man ! Yep, sometimes being able to see what’s going on with an adjustment helps to make more sense of it for sure. Thanks again and all the best !

Thanks man and glad the video helped some with how the mix needle adjustment works 👍. These are actually the Hitachi HSC40 carbs that were in the 1st Gens (‘81 to about ‘85 or so). For the Mikuni’s, they probably do have a different holes size in the carb body since the mix needle is designed with different dimensions. I’m not sure of the hole size for them, but if you grab a set of the Acetylene torch tip cleaners and can bend them so they will reach up into the throat of the carb to the other size of the hole, you should be able to check on that side for which just fits into the hole since that side wouldn’t be damaged. Thanks again and all the best ! Steve

Hey ! In the past I probably would have said that the vm38 or vm40 would be a better match, but I recently picked up a “front yard find” Suzuki Intruder 1400 I got along with 5 Viragos and it actually has 34 mm carbs on it an is a powerhouse, lol. So now I’d say, if jetted properly, a vm34 would work as I’ve actually seen them running on on a twin cylinder 1400 cc. Seems like most have gone with the vm38’s though when swapping them out if I’m not mistaken. For the “soft seat”, it is when the mix needle bottoms out in the port and you lightly touch the surfaces together vs. tightening it in like you would a normal screw. The spring is compressed quite a bit when you are at the soft seat and for the 1st Gen Hitachis, the little end of the needle should be sticking up into the carb throat some. These Hitachis are pretty sensitive to debris since the idle jet and one of the jets up top for the air are pretty small. I always install little inline fuel filters just before the carbs to catch anything that might be in the 40 year old gas tank which helps a ton on keeping the carbs clean and running. Also, since I’ve had several petcocks go bad and stop sealing off, I also put inline shutoffs in the lines so I can insure the fuel doesn’t keep coming into the bowls when parked and then getting into my oil. Hope this helps a bit and all the best ! Steve

Hey man ! Yep, I went really slow towards the end of the machining with the fly cutter on the mill (like “0.002 per pass) just to try to get to the exact center of the mix needle port so the edges were very clean due to taking very light passes. It’s probably impossible to see in the video, but the damaged seat burr goes all the way around the diameter of the seat surface. These were actually unusable carbs that someone had damaged trying to get the mix needles out of…probably because they had seated them so hard that it locked the needles in and they wouldn’t back up again (thus the very damaged needle seat.)

have you checked the intake boots for leaks?

Hey man ! If the pilot adjustment has to be way in, a lot of times either the enricher (choke) cable or lever is not letting the plunger go all the way down, or the rubber ends of plungers got dissolved if the carbs were soaked and they weren’t removed. It could also be that the floats are set too high so it’s getting extra fuel when it shouldn’t be from the regular fuel circuit. Normally the rpms will go up a bit when the needles are adjusted in as it leans the mix out, but in just a few seconds it will start to miss and fall. I always tend to stay on the rich side (more turns out) vs. lean as I’d rather foul a plug or two till I get it dialed in vs. turning the chrome pipes gold or purple, lol. For finicky carbs, I turn them in, then turn the needles out until the rpms start lowering, then turn them in about 1/8 turn and blip the throttle to see if it accelerates quick or has a flat spot. If it will accelerate quick like normal, I go in another 1/8 turn and blip it again repeating until it has a flat spot on the acceleration. Then I know the range of too far out and too far in so I’ll pick the middle to start then ride it around a bit and check the plugs for fouling. It’s hard to tell the condition of the carbs since they are many years old now, so there is no “spec” setting for them unless they are fully rebuilt (all the way down to the seals in the butterfly shaft ends for example) since little bits of air get in and change things. Hope this helps a little and all the best ! Steve

Hey ! That’s an odd one as usually the carbs don’t like extra air coming through the boot ports if the vacuum lines are open. Was anything changed on the carbs like little filters added to the larger hoses that go up to the top of the carbs over the diaphragms? If so, restricting the air up top can make the slides slap up and down as the air is no longer free to move in and out…makes it sound like it’s gasping for breath. Other than that, I’m not sure why they would run better by opening the vacuum line as I can’t think of another area in the carb that is restricting air that, by allowing air in to the vacuum port, would level them out.

I put on aftermarket exhaust and had to reject the carbs to dynojet stage 1 and drilling the diaphragms as they mentioned in the instructions also 2 and half turns out. After installing them the bike starts ok with a little bit of bobbing from the exhaust the spark plugs got white/tan color . Do you think it needs more turns out if it’s running lean?

Hey ! If I can get a good repeatable process to make them I’d say I’ll probably make some extras while setup on them to see how folks like them 👍. These first ones I’ll be doing on my manual lathe, but I bought a mini lathe last year that I’m planning to convert to a little cnc lathe and these would be just the right size for it. The brass stock should be here this week so I’m hoping to make the first ones this weekend 🤞🤞🤞

@@StevesDIYs kool

Hey ! Yes, if you screw the mix needle in all the way until it is seated, it should actually block off the port even if the hole has gotten too big. Sounds more like there is an issue with the float heights being off and the fuel too high in the carb bowl or there’s an issue with the choke circuit not closing all of the fuel off (it’s actually an enricher circuit vs. being an actual choke circuit). They will actually increase in rpms for a short time when the needle is all the way in as it leans out the mix, but if you try to throttle the bike up, it will pop real bad when the throttle is released since it’s running lean.

@@StevesDIYs Ok so I think I've found this issue. I checked the float height per your video and it was spot on. But so this is pretty funny. When rebuilding the carb I was so scared of damaging the body that as soon as I felt resistance I would stop turning. So it wasn't actually screwed in at all. Your video showed that when its all the way in the tip should be above the surface, so I took out the carb and turned in the screw and felt some resistance but kept turning and then saw the little tip come up. This should be it. Would have never found this out without your video, so thanks a bunch Steve!! Your videos are really helpful!

@@MegaDwaas hey again ! Sounds like you got it figured out 👍. Don’t feel too bad though as that has gotten me as well in the past with thinking they were seated, but really weren’t all the way in (thus the video as I decided it might be important to show, lol !). I found that some of the aftermarket needles being made don’t have the correct root dimension in the threads so they “feel” like they are seated, but are really several turns out. Now, I always check to be sure I can see the needle tip (for the 1st Gen Hitachis) inside the carb throat so I know it will fully seat. Glad the videos helped some and all the best ! Steve

Hey man, yep, if the needle seat has been damaged in the carb, you can use a set of acetylene torch tip cleaners (that come in a pack of various diameter tiny round files) to open the hole back up in the carb 👍

@@StevesDIYs Sounds good thanks! The problem I’m having is that the needle on right side carb doesn’t want to seat period, I keep turning and turning and it never bottoms out, the other side bottoms out fine. I can’t even get it out to check if the screw is stripped or if the threads in the hole is stripped

@WowItzAkina ah ! That’s not good. Hopefully the needle threads are the ones that stripped out…if it’s the ones in the carb body, then it s probably not salvageable and that carb body will need to be replaced. Question…When you are trying to back it out, is the needle pretty close to the top of the port or is it way down in there? If it’s near the top (but below the surface) that’s about how far they thread out before running out of threads normally. They usually have to be thumped or grabbed with small tweezers to pull them on out. If it’s way down in the port still, then you might be able to blow compressed air up into where the idle jet goes while turning to see if it will help to back it out…maybe it will catch a bit of the threads and come on out.

@@StevesDIYs So the needle is actually sticking out, like you can see it sticking out when you look where the butterfly flap is, if you need a better description, I could probably take some pictures and send them to you by email or over Facebook. Problem is I can’t back the screw off to get it flush

@WowItzAkina ah…yep, if you can see the small tip of the needle sticking out through the tiny hole in the throat of the carb, then it’s definitely all the way down into the port. So, when you are rotating the needle to back it out, can you see the tip of the needle rotating as well? If not, then the tip may have broken off as well.

I always knew they could be damaged if tightened too hard, but never knew exactly what the damage looked like…all makes sense now on why some carbs have to be out more than the standard 1.5 or so turns.