Try it in a 29
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VM29 specs, manual, tuning tips for GS750/1000???
- Thread starter Chuck78
- Start date
Jet sizing???
Jet sizing???
So I have the VM29 A7 for Kawasaki's, with the 1.5 slide vs the 2.0 that comes with the VM29-A12 GS750/1000 version. On stock GS's, the earliest GS750B's up to engine #11,787 came with 2.5 slide cutaways, but the rest of the 750/850/1000 VM26's came with 1.5's stock. I wonder if this will have any ill effect on low throttle openings, and I wonder why the difference between Kawasaki & GS versions? Maybe the stock parts on the smoothies were intended for stock bike tune, where the Suzuki's had drastically more radical cams than stock kz's & CB's????
Jet sizing???
So I have the VM29 A7 for Kawasaki's, with the 1.5 slide vs the 2.0 that comes with the VM29-A12 GS750/1000 version. On stock GS's, the earliest GS750B's up to engine #11,787 came with 2.5 slide cutaways, but the rest of the 750/850/1000 VM26's came with 1.5's stock. I wonder if this will have any ill effect on low throttle openings, and I wonder why the difference between Kawasaki & GS versions? Maybe the stock parts on the smoothies were intended for stock bike tune, where the Suzuki's had drastically more radical cams than stock kz's & CB's????
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Also the main air jets are smaller (.8 or .9) than the gs1000 carbs (1.5). The 750 vm26 carbs run .8 to 1.1. The 750 carbs needed a 112.5 main on my 920cc 10:1 w/750 cams. The 1000 carbs with larger main air jets needed a 117.5 main to achieve identical AFR O2 readings.
The larger venturi is going to require larger mains than a 26, however, due to lower velocity using the same slightly worked head & gs750 cams. I'm expecting that I may need a 115-120 main. Any ideas?
Hoping the standard pilot of 25 on all models will do the trick, if that is what is in them still! It was tuned for an 860cc 750 with stock cams, large ovalnk&n pods, and a kerker or similar 4:1
I read
The larger venturi is going to require larger mains than a 26, however, due to lower velocity using the same slightly worked head & gs750 cams. I'm expecting that I may need a 115-120 main. Any ideas?
Hoping the standard pilot of 25 on all models will do the trick, if that is what is in them still! It was tuned for an 860cc 750 with stock cams, large ovalnk&n pods, and a kerker or similar 4:1
I read
It's on eBay that I found a spare smoothbore drain plug, listed for a vm33 smoothbore. Hard to try it on mine without purchasing! There's an entire vm29 bowl&drain listed for $65... Trying not to spend that much though.
Interesting... A 1979 CycleWorld article said that a stock GS engine'd race bike went from 12.72 @103.8mph 1/4 mile to 12.19@108.95mph with Yoshi hand bent unmuffled race pipe and VM29's (I assume with velocity stacks), but vm26's jetted for the yoshi race pipe, the best time they could turn was 12.88@104.4mph... So you definitely have solid evidence to upgrade to smoothbores if running a free flow performance exhaust, or else you forgo big performance gains and actually lose performance at the benefit of the open exhaust sound... Interesting. Likely due to drastic loss in mid torque, where the smoothbore 29's definitely are helping build high end HP.
Point of this was that a stock gs750 engine ran 117.5 mains on this race bike with yoshi pipe. This 860 was running nylon 110 mains, so I am guessing the 920 might need somewhere in that mid 1-teens range. Any better opinions?
Point of this was that a stock gs750 engine ran 117.5 mains on this race bike with yoshi pipe. This 860 was running nylon 110 mains, so I am guessing the 920 might need somewhere in that mid 1-teens range. Any better opinions?
S
Spyderman
Guest
as for your question about the 1.5 VS 2.0 cut away what it does is the 2 increases the amount of air so the it will make mixture leaner on the 1/8 to 1/4 throttle setting
the 1.5 will make the 1/8 to 1/4 throttle position a little richer
The slide valve affects carburetion between 1/8 thru 1/2 throttle. It especially affects it between 1/8 and 1/4 and has a lesser affect up to 1/2. The slides come in various sizes and the size is determined by how much is cutaway from the backside of it, The larger the cutaway, the leaner the mixture (since more air is allowed through it) and the smaller the cutaway, the richer the mixture will be. Throttle valves have numbers on them that explains how much the cutaway is. If there is a 3 stamped into the slide, it has a 3.0mm cutaway, while a 1 will have a 1.0mm cutaway will be richer than a 3mm cutaway.
so i wouldn't really worry about the cutaway too much because it's affected by the pilot circuit's air mixture screw as well and can usually be compensated for with small adjustments to the needle circuit and the pilot circuit
hope that helps
the 1.5 will make the 1/8 to 1/4 throttle position a little richer
The slide valve affects carburetion between 1/8 thru 1/2 throttle. It especially affects it between 1/8 and 1/4 and has a lesser affect up to 1/2. The slides come in various sizes and the size is determined by how much is cutaway from the backside of it, The larger the cutaway, the leaner the mixture (since more air is allowed through it) and the smaller the cutaway, the richer the mixture will be. Throttle valves have numbers on them that explains how much the cutaway is. If there is a 3 stamped into the slide, it has a 3.0mm cutaway, while a 1 will have a 1.0mm cutaway will be richer than a 3mm cutaway.
so i wouldn't really worry about the cutaway too much because it's affected by the pilot circuit's air mixture screw as well and can usually be compensated for with small adjustments to the needle circuit and the pilot circuit
hope that helps
Well... I guess I don't have to worry about tuning my smoothbores anymore. some very very cruel person that knows a whole lot about 1970's Kawasaki & Suzuki big 4 cyl superbikes spotted my GS in the back of my truck loaded, parked right next to my house where it has been since I returned from vacation, broke my wrist and didn't have any help to unload it!
this morning I went out to my truck and noticed my carbs and air filters were gone! Geez, of all the luck, someone was able to distinguish that I did not have stock VM26 carbs on my bike even though they look nearly identical, the thieves saw the big hex quick change main jet drain plugs and knew they could use those very sought after & rare carbs on their Z1/KZ1000 most likely, lots of those in this part of town, or at least knew they were very valuable carbs worth the 3 minutes of removal to steal.
needless to say, I am heartbroken over the loss of a crucial part of my bike that was almost completely set up exactly how I have wanted it for years.I was going to put CR 31 smooth bores on the big bore GS 425 project, then I thought if I get this Rickman frame, maybe I would not hassle around with refurbishing an old worn set of VM 29's again, & just go with a pricey new set of Keihin CR Specials... well now it looks like I may need two sets of 4 cylinder CR's, and one set for the twin. better start doing lots of side jobs. majorly bummed out here in Columbus Ohio.
this morning I went out to my truck and noticed my carbs and air filters were gone! Geez, of all the luck, someone was able to distinguish that I did not have stock VM26 carbs on my bike even though they look nearly identical, the thieves saw the big hex quick change main jet drain plugs and knew they could use those very sought after & rare carbs on their Z1/KZ1000 most likely, lots of those in this part of town, or at least knew they were very valuable carbs worth the 3 minutes of removal to steal.
needless to say, I am heartbroken over the loss of a crucial part of my bike that was almost completely set up exactly how I have wanted it for years.I was going to put CR 31 smooth bores on the big bore GS 425 project, then I thought if I get this Rickman frame, maybe I would not hassle around with refurbishing an old worn set of VM 29's again, & just go with a pricey new set of Keihin CR Specials... well now it looks like I may need two sets of 4 cylinder CR's, and one set for the twin. better start doing lots of side jobs. majorly bummed out here in Columbus Ohio.
Wow Chuck, I'm sorry to hear about your carburetors that just sucks! I bet they turn up somewhere, I'll keep my eyes open for them. I bet someone local took them. Someone that saw your motorcycle before and knew what you had. Them Bastards! Next time you need a hand unloading your motorcycle or anything like that let me know. My brother doesn't live to far from you, I know he'd help you out. You take it easy my friend.
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That stinks, Chuck.
Half the people here don't recognize smoothbores so for a thief to recognize them is surprising.
Like Storm mentioned they may turn up locally at a trackday or Vintage night.
Half the people here don't recognize smoothbores so for a thief to recognize them is surprising.
Like Storm mentioned they may turn up locally at a trackday or Vintage night.
S
Spyderman
Guest
wow sorry to hear about the theft chuck i also think that it's a local and a fellow GS or KZ enthusiast that knew exactly what they were keep your eyes peeled on the local machines that are around you, you might just see them
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Seeing them and being able to prove they were his are different worlds.
S
Spyderman
Guest
i don't think there will be too much trouble really #1 and #4 have some unique marks and he has the photos right on page 1 of this thread so it might be easier than you think no harm in trying if he does see them
Yeah if he has some certain marks and pics thats cool. Damned shame that it comes down to that though. Now whats everyone have to do...start etching their initials in the carbs from now on?? Just ridiculous.
Wouldnt it be cool to see them at bike night, call the cops and have him arrested on the spot..and remove the carbs there on the curb in front of all his people!!
Wouldnt it be cool to see them at bike night, call the cops and have him arrested on the spot..and remove the carbs there on the curb in front of all his people!!
thanks for the encouragement guys! There are a lot of guys building KZ dragbike types around this part of town, but I think it's someone a bit closer to home that took them, or his good friend. Sad. We have a lot of mutual friends, or rather they are acquaintances with a lot of my friends and I am acquaintances with some of their good friends. makes it tougher when spreading the word because will get back to them from their good friends that wouldn't think they would do such a thing, and then they will keep quiet about it or just stash them for a while and then sell them off or eventually leak them out on one of their bike builds.
the really awesome local vintage Japanese bike salvage place here have one set of vm29's left, they just sold one for $650 the day before mine got stolen, ultrasonic cleaned even. They have one set left, but I need to use every penny I have to snatch up this Rickman CR frame (additional braces and mounts welded on it for a GS1100E engine) while it's still available to me, & I have a fracture in my wrist and I'm not supposed to do anything much with it anyhow, although it feels pretty fine to me now since the day after I cracked it. prescription ibuprofen does wonders! no more riding this season for me though, so I can wait on the carbs.
I noticed that the VM 29 smoothbores were very similar to the Keihin CR 29's (or at least the CR31's my bud has on his kz1000), which are still available brand new for basically the same price as a good used rack of Mikuni VM29 smoothbores, but the CR's are very popular and always sell out as soon as they get in stock at pretty much any vendor. A special order will always result in a back order period.
also, I'd have an even bigger problem with liability because the CR's are very recognizable by the giant red CR logo on the side, and everyone that's into the cafe racer trend knows that those are the best carbs & very $$$! it was surprising that my Mikuni Smoothbores got stolen, because the only telltale sign of what they are as installed on the bike is the big hex drain plug for quick main jet changes on the majority of them except a few early models. The Mikuni 29mm smoothbores look so similar to stock that most people would not have a clue, which I kind of like for my primary bike. Although with the Fox piggyback shocks on it and it getting more modified and updated every year, it looks like quite the flashy vintage racer bike and attracts attention no matter what. at least I don't have to worry about someone stealing my CBR rotors or MTC pistons, the shocks and carbs I was really worried about, but the shocks are so identifiable no one has them around here and they have a couple scrapes that are unique to them as well
At $749 brand new, the CR specials are quite lofty in price, but they are brand new and just need tuned and jetted properly. I will have to do some side job furnace installs or something to afford those!
I do have all the rebuild parts for VM29's still, so I will try and keep my eyes out for a deal and hope that they are usable. If anyone sees anything on ebay or elsewhere, pass it along to me please.
on the other hand, I was planning on getting a set of gs500 or CB 360 Keihin CR Specials for the big bore GS425 project, and contemplate maybe even getting a set if I build up that Rickman frame that I want as a second big bike, instead of swapping all of my parts on to it. that long long stretch tank might not be ideal for long-haul rides! That's where the GS tank & double seat comes in handy, & I can put saddlebags on it
I noticed that the VM 29 smoothbores were very similar to the Keihin CR 29's (or at least the CR31's my bud has on his kz1000), which are still available brand new for basically the same price as a good used rack of Mikuni VM29 smoothbores, but the CR's are very popular and always sell out as soon as they get in stock at pretty much any vendor. A special order will always result in a back order period.
also, I'd have an even bigger problem with liability because the CR's are very recognizable by the giant red CR logo on the side, and everyone that's into the cafe racer trend knows that those are the best carbs & very $$$! it was surprising that my Mikuni Smoothbores got stolen, because the only telltale sign of what they are as installed on the bike is the big hex drain plug for quick main jet changes on the majority of them except a few early models. The Mikuni 29mm smoothbores look so similar to stock that most people would not have a clue, which I kind of like for my primary bike. Although with the Fox piggyback shocks on it and it getting more modified and updated every year, it looks like quite the flashy vintage racer bike and attracts attention no matter what. at least I don't have to worry about someone stealing my CBR rotors or MTC pistons, the shocks and carbs I was really worried about, but the shocks are so identifiable no one has them around here and they have a couple scrapes that are unique to them as well
At $749 brand new, the CR specials are quite lofty in price, but they are brand new and just need tuned and jetted properly. I will have to do some side job furnace installs or something to afford those!
I do have all the rebuild parts for VM29's still, so I will try and keep my eyes out for a deal and hope that they are usable. If anyone sees anything on ebay or elsewhere, pass it along to me please.
on the other hand, I was planning on getting a set of gs500 or CB 360 Keihin CR Specials for the big bore GS425 project, and contemplate maybe even getting a set if I build up that Rickman frame that I want as a second big bike, instead of swapping all of my parts on to it. that long long stretch tank might not be ideal for long-haul rides! That's where the GS tank & double seat comes in handy, & I can put saddlebags on it
Agemax
Forum Guru
Smoothbores are easily identified not just by the hex drain plug but by the small square casting on the side of the bodies. I fabricated a small bracket that bolts to the carb tops and then to the frame, hidden under the tank. Prevents them from getting stolen, and offers some support to hold them in, especially with no filter box, they rely on just the inlet manifolds to keep them in place.
Darnit!!! I just had mine supported with zip ties for the time being!!! Meant to make a bracket. I now realize that that would make it much more complicated to steal them, you would have to remove the tank which would require my key to pop the seat lock open unless the thief was able to jam a screwdriver in there! A thief would not take the time to do all that, tank removal & all... Darn it darn it darn it.
