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I am a newbie to the GS world with a 1979GS1000l. Having known nothing about them, this website has been incredible to say the least. anyway it runs great, but i have fournd a set of mikuni 33mm smoothbores for 250 bucks, is that a good deal, will they even work on my bike.if so what kind of jetting would i need at 5000 feet elevation where i live? also i would like K&N individuales on it, is there a certain one that works better that others,and can you get a yoshimura exhaust sytem for this bike, is a vance&Hines system just as good? a lot of questions i know, but any help or other suggestions are greatly appreciated. thanks
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The 33mm roundslide Keihin carbs were a decent aftermarket upgrade, but they did have their problems. They use a main jet that is unique (and expensive) and they have a reputation for being difficult to tune for a number of reasons: 1) They have a synchronization adjuster on each carb that is stupidly (#!@) difficult to use, 2) They have weak throttle return springs that makes the idle/RPMs stay high (you have to have perfectly adjusted/lubed push/pull cables to safely run them), 3) The needle jet / emulsion tube wears rather quickly (due to the large/heavy needle), resulting in fouled plugs and frustration for inexperienced tuners, and 4) the idle/low end/midrange circuits of these carbs don't seem as responsive as stock carbs, and this often gives the impression that these carbs are like on/off switches. This last point has several contributing reasons, such as an air/fuel screw that barely needs opened (most guys assume it's at least 1 turn open), the above mentioned high idle, often poor synchronization, and the basic fact that larger carb throats have slower airspeed, thus making fuel & air mixing less efficient. For the GS1000, Degreeing your cams to 106 will help immensely with the midrange carburation of these carbs (or any others, for that matter).
You will need different carb boots to mount these to your motor, but you may get them with the carbs (check for cracks since the aftermarket boots will rip fairly easily from the weight of the carbs - solution: zip tie the carbs up to the frame to take the weight off the boots). There is a specific K&N size to fit these carbs (stock airbox has to be removed) - make sure the dealer that orders the filters measures the back of the carbs (!), cost should be about $120 for the set of 4.
$250 isn't too bad of a price AS LONG AS they are clean and ready to run. If you have to put another $100-150 in them to have them cleaned, then it's not a good price. Tell him that you are aware of potential problems and see if you can talk him down. See if you can testride them on his bike before purchasing and check the sparkplugs after the ride. You probably will have to have them jetted to your bike, and that will cost too. Are you getting extra jets with them? I would recommend trying 112 or 115 mains in them first with the needle in a middle position and the air/fuel screw 1/4 turn out.
I don't think that you can get a Yosh pipe for your bike anymore. Vance & Hines is an excellent all-round pipe. Stay away from Mac pipes. -
great info
Thanks for the info Don, I have also been looking into a stage3 dynojet kit. do you think this would be a better option for my bike?Comment
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degreeing
how would i degree my cam to 106 degrees, i am not a trained mechanic, but i do a fair bit of my own maintenance, i have normal tools, nothing special, is this somthing i can do?Comment
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I personally consider Dynojet kits for your bike (26mm carbs, right?) a waste of money (Dynojet kits for CV carbs make more sense because they come with softer springs and adjustable needles). You can rejet your bike just the way it is with a little help from us and the K&N filters. But first you should get the cams degreed and see if you are happy enough with the performance. Degreeing the cams is a little tricky. It involves removing the cams, replacing each stock sprocket with a slotted sprocket (or having your stock sprockets machined/slotted), replacing the cams, setting up a degree wheel, setting up dial indicators, taking the readings and running them through a mathematical formula, adjusting the cams in the slots, and repeating the readings/formula/adjustment until the number is right for BOTH cams. Are you comfortable with cam replacement? (It can result in bent valves). You should check the valve clearances too while you are in there.Comment
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Don Your knowledge, and my lack thereof, of my machine is amazing. since the 33mm smoothbores seem to be a mechanical nightmare and since jet kits are not the way to go, (and yes they are 26mm carbs) what do you personally think is the best option for a good performance gain all across the rpm range, if possible. Where would i get the aftermarket cam sprockets, and would degreeing to 106 have negative affects in higher rpm opperation? I am not opposed to changing cams, someday i fully intend to, but not in the near futur. I AM sure i will post many questions dealin with that later; a couple of ?'s (sorry if my ignorenc of this subject is annoying) when you say CV carbs are you reffering to the 33mm smothbores? and in another forum i have been told that smoothbores of a smaller diameter would be superior to stock. any thoughts?Comment
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Your stock carbs are very good carbs and proper tuning should provide improved performance. Their limitation is the maximum airflow that they can allow, but that won't really be a problem unless the motor flows more air than stock (bigger pistons, cams, header and porting).
The 29mm smoothbores that look just like your stock carbs would be a big improvement in topend airflow, but it is difficult to find a good set of these and many people claim that they have these carbs when in fact they DON'T!
The 33mm smoothbores are good carbs IF they are setup properly.
I feel that the best performance gain at all RPM comes from degreeing the cams. This is because of the performance you feel when you crack the throttle: it doesn't stutter or balk - it pulls cleanly (as long as your carbs and ignition are not interfering with the process). Degreeing your cams gets them to the ideal balance of low and top end power. Dragracers would use this same cam spec too (I checked it out with Kerry at Schnitz racing). Schnitz racing has the slotted sprockets, $45 a pair, I think.
CV carbs are the stock vacuum controlled carbs found on all bikes after 1980. They are made in sizes very similar to the smoothbores (32mm, 34mm, etc) but they are fundamentally different and not as performance oriented (although they can be tuned for high performance).Comment
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Your stock carbs are very good carbs and proper tuning should provide improved performance. Their limitation is the maximum airflow that they can allow, but that won't really be a problem unless the motor flows more air than stock (bigger pistons, cams, header and porting).
The 29mm smoothbores that look just like your stock carbs would be a big improvement in topend airflow, but it is difficult to find a good set of these and many people claim that they have these carbs when in fact they DON'T!
The 33mm smoothbores are good carbs IF they are setup properly.
I feel that the best performance gain at all RPM comes from degreeing the cams. This is because of the performance you feel when you crack the throttle: it doesn't stutter or balk - it pulls cleanly (as long as your carbs and ignition are not interfering with the process). Degreeing your cams gets them to the ideal balance of low and top end power. Dragracers would use this same cam spec too (I checked it out with Kerry at Schnitz racing). Schnitz racing has the slotted sprockets, $45 a pair, I think.
CV carbs are the stock vacuum controlled carbs found on all bikes after 1980. They are made in sizes very similar to the smoothbores (32mm, 34mm, etc) but they are fundamentally different and not as performance oriented (although they can be tuned for high performance).Comment
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Thank you Don, the information you have provided is very appreciated.Comment
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This may sound like a dumb question, but what is the difference (apart from the diameter) between the 29 mm smoothbores that Don refers to and the stock VM28SS carbs?Comment
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These are the carbs that I have on my 1000S? right? been wondering that myself since I read this topic.Originally posted by jlangforComment
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The 1000S didn't have 29mm smoothbores as standard. Has someone fitted them to your bike Robinjo?Comment
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No I was talking about the VM28SS carbs that I think are the type on my bike, they are 28mm but I don't see a type on the carbs.Originally posted by brit7.11Comment
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The 29 smoothbores most distinct feature is an insert in the carb throat that "smooths the bore", thus reducing internal turbulence. They also have a removable cap on the bowl for changing mains without removing the carbs/bowls, they have different air bleed holes, and they seem to be lighter (aluminum bodies?). There used to be a company named "Maxi-bore" that would bore out 26 or 28mm carbs to 29mm, so bore size alone is not definitive.Comment
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Well Don i did it. i am know the pround owner of some mikuni 33mm smoothbores. the man i bought them from used them on a gsxr 1127 motor i believe. you said the 33's were good carbs IF they were set up right. so know i am need of serious help. he threw in the k@N individuals and velocity stacks which i assume are for racing only also he gave me 4 sets of main jets. from what i have been reading they all seem to big, like the 150 range. i will soon be getting the vance and hines maegaphone system but right now i have a stock exhaust. so any help in setting these up for my stock exhaust and eventually the aftermarket exhaust would be just great! thanks.Comment
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