Thanks man ! Yep, I run the OE dual carbs on bikes normally, but I’ve always wondered why some folks have good success with single carbs, while others struggle with them so my curiosity finally got the better of me, lol ! When I tried the different designs, it then got me wondering why the front cylinder was always leaner and why singles work on a Harley (or car motors). Turns out that the firing order and delay between the cylinders firing is a big reason why. Now it all makes sense so I can finally move on to the next project, ha,ha. Thanks again and all the best !

@@StevesDIYs Still unanswered is why Yamaha did what they did, right? Or were racks of carbs just the way?

@@mestep511 The engine is a stressed member, rigidly mounted into the frame. That gives you low center of gravity and good ground clearance. Balancing and vibration is important in a case like this. 90 degree V-twins are well balanced but that makes the engine long. A 75 degree cylinder angle is a good compromise: narrow enough to fit in a compact frame but a lot less "vibey" than narrower V-twins. Big KTM adventure bikes have a 75 degree V-twin for the same reason. The engine rotates backwards and the firing order is like this: rear cylinder fires, crank turns 285 degrees, front cylinder fires, crank turns 435 degrees - the cycle starts again. Harleys are similar, but the engines turn the other way. Front fires, crank turns 315 degrees, rear fires, crank turns 405 degrees, cycle starts again. But since the HD engines have different valve timing (overlap, duration) and the intake tracts are shaped differently the AFR deviation is much less pronounced. They aren't balanced perfectly, either. Yamaha had to squeeze 55 BHP out of a compact 750 engine which was almost on par with the stock 80 cu in big twins' output back then. They had to use two carbs, intake runners close to straight in shape to achieve that - the twin carb setup took care of the AFR issues, too. Had they used carburetors with better design/support, eg. Mikuni BSTs on 1988-on big bore Viragos or the BSR37s used on V-star 1100s (that's what I adapted to mine) life would be much easier for the average Virago owner.

Thanks man ! I was thinking to swap the timing over on the ‘82 750 Bobber (it has the OE dual carbs on it still), just to see the performance difference (and how low I can set the idle to hear the loping sound without getting too low on oil pressure). If it performed the same, it would definitely have a much different sounding idle. Probably would vibrate like a Harley when running though, but that’s what padded grips are for 🤣🤣🤣

Thanks man ! Yep, I do have fun playing with these for sure. I was thinking to contact them to see if they would send me one so I could do a comparison on the test motor rig, just haven’t had time to yet. I’ll probably hit them up in the fall so I can play with them in the winter. Thanks again and all the best ! Steve

Hey man, there’s actually nothing inside the frame but a hollow area where the air flows from the hole that the filter mounts to the frame all the way up to the neck where the triple tree is. The two holes where each carb elbow connects to the frame just have another smaller rubber elbow inside the frame to help keep oil from the motor’s vent valve from getting sucked into the carbs.

Hey man ! Yep, as long as the cam doesn’t move when rotating the crank (or cam gear) it would be easier that way vs. having to hold the gear up with a finger. The gear still needs to be removed from the chain to put it so the gear hole lines up to the pinhole though (which is always the fun part to get the teeth back into the right link on the chain, lol)

By the way, Many thanks Steve for your fine videos. I just finished rebuilding my 1981 750 Virago and I utilized many of your tips and techniques. It's a runner now and I couldn't have done it without you. All the best! @@StevesDIYs

Thanks man ! Yep, I do tend to dive off into the deep end when something aggravates me on why it doesn’t make sense lol. One day I may get tired of messing with these old bikes, but seems like there’s always something new to learn about them. I’ll have to look up the 1900cc bike as I didn’t realize Yamaha made one that big back in the day…sounds like they went all out on that one 👍. Finally, with this long standing question figured out on why the single carb won’t balance, can now get back to working on the final design to make the right side kick starter for one of these…that’s been on my bucket list for a very very long time so I’m hoping this is the year I can make it happen 🤞🤞. Thanks again and all the best ! Steve

@@StevesDIYs I want a r/s-kicker ! I don't know why they didn't make it that-way . If anyone can do it properly Steve , you are definitely the man ! Dave

@@kdsowen2882 thanks for the vote of confidence 👍👍. I’ve always thought it would be so sweet to be able to kick start one of these like old school lol ! When I first mentioned wanting to make a kicker for them, some folks were like…”why, the electric start is so much easier”. I’m definitely leaving the electric start on it for those grumpy not wanting to start days, but I miss the old days when I was a kid and kick start bikes were all we had. If I get a nice reliable design figured out, I’ll definitely make a video showing it so folks can see how it ends up.

Thanks 👍. Yep, I’d like to get my hands on one of the KJS ones to compare as well just to see…maybe they will see the videos and send me one to test lol ! It does seem that the cylinder timing for the combustion stroke makes the front stay leaner as everyone has done that so far with the standard timing procedure. I’ve heard the pumper carb does a bit better on it going lean for a second when throttled up and down (as seen on gages) so it would probably be a bit smoother than the 40mm Hitachi I had on it. Thanks again and all the best !

KJS has done extensive testing to develop their manifold and chose the Mikuni 40mm pumper to include in their kit.Yes I would love to see it on your test engine to compare both timing setups.

Thanks ! It wouldn’t hurt the motor to run it with the front cylinder leading since it is just changing the firing offset between the two cylinders, but I’d say it would affect how smooth the idle is since the two cylinders fire so much closer together. It is probably going to run more like a single cylinder motor (like a larger cc Thumper) with more low rpm power, but less smoothness at higher rpms.

Thanks and glad the video helped a bit 👍. Yep, I still have the manifold on the test motor and if I can get my hands on one from KJS or Mikunioz I’ll do another comparison video of them with the load test like I did for the equal and unequal runner ones. I think the carburetor plays into how well they do as well, but using the same carb for the testing gives a better apples to apples comparison. Thanks again and all the best ! Steve

Hey ! No, I didn’t swap out to the others ones as I’m not sure where the black one I had came from and the equal runner one I made was totally out of balance. If I can get my hands on a Mikunoz or another one still being made, I’ll probably set those up on the rig and see how they do with both the timing as normal and then also swapped 👍

Hey man ! It might be that this would only work for a 1st Gen since it only has one pickup pad on the flywheel vs. the 2nd Gens having two..not sure about that though, but seems like it should work the same way since the plugs fire on each rotation for both generations

@@StevesDIYswere I put a 98 model motor on a 85 frame I had to change flywheel when i did that I had to make it like a 85 with old flywheel pick up coils stater is off the 85 into the 98 model motor were the flywheel ain't as wide as the 98 I had to take half inch spacers on the stater and pick up coils it's set up just like the one you did it on on the test rig I'll try it again later and let you know

👍. Finally, I was able to understand why it’s so hard to balance a single carb and can move on and stop thinking about this 🤣🤣🤣

Hello again, I never said that this manifold was made correctly or incorrectly…it might be the best design or other designs may work even better than this one…who knows. It did do better than the other ones I tested though, but that doesn’t mean that there aren’t more balanced designs (KJS, Mikunioz…even the one you apparently make it seems (by looking up your info). Also not sure why you mention that the rear cylinder would have a richer AFR reading on the test rig due to higher temperatures…when riding the bike, the rear cylinder does get less air flow so it runs hotter, but on the test rig, no air is flowing over the motor. The video shows that the richer cylinder switches from the rear to the front when the timing is swapped…that is really the main purpose of this video and has nothing to do with if the manifold was designed properly or not. Since is seems you make a single carb manifold, if you would like me to put one of yours on the test rig and see if it balances the cylinders with the normal timing setup, you are welcome to send me one and I can put it in the test rig the next time I bring it to the shop again and make a video of the results. Or maybe you have already tested the Physics of your design and can provide a link to the data…I’d be happy to post a link to it in the comments. All the best, Steve