Virago Single Carb Intake Cylinder Imbalance - It's got a lot to do with the cylinder timing

[@mestep511]

This series is incredible. Thanks for all the science and hard work you do. Inquisitive people sure are condemned to tinkering with things even if things seem to be working fine. Single carbs? Switching timing? Sure, gotta know!

[@StevesDIYs]

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 !

[@mestep511]

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

[@hondapapi81]

@@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.

[@paulwoods682]

Great stuff Steve! It would be very interesting to see how the change in timing of firing affects the power, vibration and other characteristics of the motor. Now I know why a Harley has the characteristic exhaust note, different to the 'normal' Virago.

[@StevesDIYs]

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 🤣🤣🤣

[@brianredman9347]

While setting the timing on my Virago I just removed the pin from the cam and then as you move the crank the cam sits still. Then I replaced the pin when I was done. I had my front cylinder 180 degrees out after a topend renuild and I used this method to correct it.

[@StevesDIYs]

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)

[@brianredman9347]

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

[@Rufford72]

I put a KJS manifold and Mikuni 40 pumper carb on my 1985 XV700.I did use a hotter plug.They claimed it was a plug and play set up but I did have to change the needle position to riches it up a little.It responses well now but like you said the rear plug looks a little rich.Looks like your on to something with the timing.Thanks for the informative videos

[@StevesDIYs]

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 !

[@Rufford72]

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.

[@kdsowen2882]

Man you are having some fun with these XV's ! (I still have my two 981 chain-drives, just about to replace my slipping clutch ) As others have said , Nobody else dives as-deeply into these great-bikes as much as you do . Yamaha should definitely fund you for promoting their Brand . My younger-Brother brought the bike that these evolved-into , back from Australia with him : Road Liner 1900 . They were never sold in NZ , USA was their biggest market in a few variations including some completely-assembled there , claiming Made in The USA But without these early-bikes , they wouldn't be here . Check them out, ceramic-bores , 3 x oil-pumps , very-tech for a 'V' Dave

[@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

[@kdsowen2882]

@@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

[@StevesDIYs]

@@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.

[@marting.4505]

I've been looking for something like this for my 1994 Kawasaki VN-15, but all I can find are hackjob intakes in the style of the black one you showed in the beginning, with the very short runner to the front cylinder and the longer one to the rear. Any pointers on a good(-ish) solution? The following model generations all came with a single carb setup from the factory, but they didn't have the problem of unequally opposed intakes on the cylinder heads.

[@StevesDIYs]

Hey ! I’m not sure who might be making one for the Vulcan if anyone. From the studies I did on the Viragos, the manifold design definitely makes a difference so if I found one, I would definitely check with the Vulcan Facebook forums to see how they did. Sorry I could not help any though, Steve

[@ronniebornman4122]

Interesting video! I’ve always been curious what the “airbox” inside the frame looked like. Would you mind sharing some photos of that box frame cut open? Thanks!

[@StevesDIYs]

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.

[@tatul9082]

I love the work that you do for these bikes! I really hope you get your hands on some mikunioz and kjs manifolds since thhey are the only "good" ones left on the aftermarket now that Adam is no longer makinng manifolds. Have you contacted either of them? both of them have been usually really useful when contacted about their products.

[@StevesDIYs]

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

[@DarrenKEMP-us4mo]

Hi steve great videos just wondering with the front leading can it be riden like that or will you have problems cheers 9:46

[@StevesDIYs]

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.

[@alexcalmets9633]

Good day Steve !! I’ve been looking for a full video how to swap the single carb. Do you have something like this Xv1100 full single carb conversion

[@StevesDIYs]

Hey man, I haven’t done a complete swap for one of my bikes yet as I’m hoping to get a couple more manifolds to test out to see which one balances the cylinders the best. I think more modern carbs would work better than these old Hitachi’s I was testing with though based on what comes in the kit from Mikunioz.

[@alexcalmets9633]

@@StevesDIYs my mikuni hsr t42 is put in bout I don’t know how to plug the rest of the hoses

[@zebcamp7781]

Have you thought of testing the other manifolds with the changed firing order?

[@StevesDIYs]

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 👍

[@juanantoniosimon4131]

Hola steves..yo acabo de pedir un colector de mikunioz por eBay Australia y he comprado un carburador dellorto phm40, qué pienso tendré que adaptar y ajustar.. qué opinas?

[@samng3958]

Thanks for the videos. I was considering going with twin vm or tm38's for my XV1100 but this experiment gives me renewed hope for going the single carb route. I'm curious to what the results would have been if you held it at about 2000 rpm for about 10-15 seconds with the p/s pump on for load. Either way thank you for this. i'll be thinking of getting my hands on an A. Smith intake or even a MikuniOz intake

[@StevesDIYs]

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

[@nicolafiorilli7187]

Awesome , what do you thing ? Better stock timing or your set ?

[@StevesDIYs]

Hello, swapping which cylinders is the leading cylinder definitely helps balance the air/fuel ratio for a single carb intake, but since I still run the stock dual carbs on my main motorcycles, I haven’t had a chance to really test out which way runs better overall with the single carb setup. Maybe other owners that have swapped the timing will see the comments and reply on their results.

[@StolenBodyRecords]

Hey Steve, what jets did you end up using after this?

[@StevesDIYs]

Hey ! To get the single carb to run right, I ended up at about a 155 on the main and a 50 on the pilot if I remember right. Since the carb was one of the stock Hitachi’s from the 1st Gens, it’s probably not the best pick for a single carb though.

[@StolenBodyRecords]

@@StevesDIYs amazing thanks. I just switched up the sparks plugs for 5's and it sorted running issues. Im just not 100% sure they wont get fouled again

[@WendellJones-f6d]

I tried it on my 85 700 but it only hit on the front cylinder i got a 98 750 engine i had to change the balancer flywheel for my wire harness to work i got tired of the starter gears grinding but it runs just fine i had to space the stater and pickup coils tho

[@StevesDIYs]

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

[@WendellJones-f6d]

@@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

[@jerrybigrig9475]

😎👍😎

[@StevesDIYs]

👍. 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 🤣🤣🤣

[@vtcmotors]

This manifold is wrongly made, does not match any physics, so you wasting your time! Most VTwin engines run richer on rear cylinder due to higher temperature.

[@StevesDIYs]

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

[@vtcmotors]

Dude, you having no idea what you are up to... Virago runs with single carb as a champ. Just one thing... You must know what to hell are you are doing. Stop confusing people. Thanks a lot and cheers.

[@StevesDIYs]

Hello again, as I showed in the videos, a lot of running one of these with a single carb successfully has to do with the design of the manifold. It’s apparent that you cannot just put any single carb manifold on these and expect it to run right as the AFR gets thrown off between the two cylinders if not designed correctly. As with the replies to the comments you had made on the other video and previously on this video, I’d be happy to put one of the single carb manifolds you make on the test rig and show how it performs on balancing the AFR for the two cylinders if you believe your design is optimized. Or, if you have some data that shows how well yours performs against the stock dual carbs (or even other single manifolds) I’d be happy to see it. All the best ! Steve

[@marting.4505]

@vtcmotors The numbers don't lie, and physics can't be tricked. So either step up and prove him wrong; with the emphasis on the proof part. We want hard facts, and not some backyard-mechanic blah-blah.