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Jet Needle Shimming
Hi,
I've looked elsewhere, and rather than start a new thread, I figure I'd tack onto this one. I've been trying to dial in a 78 GS550 I got last year. It was a basket case (literally). The previous owner didn't tell me the engined was from a 80 or 81 engine. 78 should have had kick starter, points, and VM carbs. I have the CV BS32 carbs, NO kick starter, and points (looks like the swapper put the point plate on from the 78 versus getting the ignition module for the 81 triggers). I've had the bike running for about 9 months now (didn't ride it over winter). Last summer, I did a complete carb teardown and super-clean (I've done this many times, both Mikuni's and Keihins). The carbs that WERE on the bike came off of who-knows what. Certainly not a GS550 Suzuki. It had 92.5 mains, but had 5C45 needles, #175 pilot air jet, and #40 pilot jet. That setup had good midrange, ****-poor high speed (had to stuff the airbox to richen enough to run), and I had the pilot mixture screws in to 1/2 turn (anything more open would kill the engine at idle).
I got a "clean" set of carbs, labeled "1981 GS500E" off ebay last fall. I just got to them this past weekend. I pulled them and did the super clean again. All the parts were pretty clean. The rubber parts looked good. All the jets matched the 1981 GS550 specs off this site (92.5 main, 4bel2 needle, #40 pilot jet, #140 pilot air jet). I wanted to put these carbs on the bike.
I'm running stock pipes and stock box (but I have a brand-new 4-1 header I was given that I'd like to install, which SHOULD cause a leaner condition).
I put the bike together and fired it up. The bike idles pretty well, almost DIES 1/4 to 3/4, and SCREAMS at WOT. It sputters very badly in the midrange. I know I have a jet needle problem. The mid throttle appears to be very RICH (plugs are black and sooty when I run in the bad spot and then pull the plugs). If I AM rich in the midrange, I have to get the needles DOWN a little with reference to the slide position.
Now my question. I read and hear all the time "just shim the needle up or down". This is fine with an adjustable Canadian or Dynojet needle. I have US stock. Furthermore, the discussions I read about shimming the needle up or down don't seem to make sense, unless all the discussions have been about the needles on VM carbs.
On my Mikuni CV's, the needle passes through a hole on the slide bottom. At the slide bottom in a recess, a spring pushes down against the slide bottom and pushes UP against a washer and the E-clip in the needle. Thus the spring pushes the needle UP against a little plastic spacer, up into the plastic spider looking deal that is kept locked down into the slide via a circlip. Putting a shim UNDER the E-CLIP does nothing to the needle height with respect to the needle jet. It just putts a little more spring pressure holding the needle UP into the plastic holder. It looks to me like if you wanted to richen a carb with a stock US needle, you would have to REMOVE the little plastic spacer above the E-clip to ALLOW the needle to be pushed up higher by the spring. If you wanted to LEAN the mixture, you would have to add shim washers ABOVE the E-clip so that the spring pushes the needle up LESS with respect to the slide.
Can someone confirm this for me? Were both sets of my carbs assembled wrong or do I have this right? I haven't found a good close-up sequential diagram yet of the slide/needle details. The exploded, scanned drawings I've seen seem to show that my description is right.
I'm very close on this GS-550 that my son and are working on. The engine is sound. It has great potential.
I just looked for a Dynojet Stage 1 kit, and it looks like it was dropped this year for the pre-1985 GS550's. Bike bandit, and Dynojet directly stop at 1985 or so. I Can get 95 or 97.5 mains (a friend of my son's works at a bike shop) to richen the mixture when I put the header on. Can I get the Canadian needles easily?
BTW, I just found the absolutely BEST lube for getting the carbs back into the boots. It is affectionately known as "female personal lubricant". Not K-Y jelly, this is the stuff that comes in a squeeze bottle (Astra-Glide is one brand). This stuff is glycerin based. I was able the get the carbs in with finger pressure.
Stu
78/81 GS550
79 CBX
73 CB350F
Hi,
I've looked elsewhere, and rather than start a new thread, I figure I'd tack onto this one. I've been trying to dial in a 78 GS550 I got last year. It was a basket case (literally). The previous owner didn't tell me the engined was from a 80 or 81 engine. 78 should have had kick starter, points, and VM carbs. I have the CV BS32 carbs, NO kick starter, and points (looks like the swapper put the point plate on from the 78 versus getting the ignition module for the 81 triggers). I've had the bike running for about 9 months now (didn't ride it over winter). Last summer, I did a complete carb teardown and super-clean (I've done this many times, both Mikuni's and Keihins). The carbs that WERE on the bike came off of who-knows what. Certainly not a GS550 Suzuki. It had 92.5 mains, but had 5C45 needles, #175 pilot air jet, and #40 pilot jet. That setup had good midrange, ****-poor high speed (had to stuff the airbox to richen enough to run), and I had the pilot mixture screws in to 1/2 turn (anything more open would kill the engine at idle).
I got a "clean" set of carbs, labeled "1981 GS500E" off ebay last fall. I just got to them this past weekend. I pulled them and did the super clean again. All the parts were pretty clean. The rubber parts looked good. All the jets matched the 1981 GS550 specs off this site (92.5 main, 4bel2 needle, #40 pilot jet, #140 pilot air jet). I wanted to put these carbs on the bike.
I'm running stock pipes and stock box (but I have a brand-new 4-1 header I was given that I'd like to install, which SHOULD cause a leaner condition).
I put the bike together and fired it up. The bike idles pretty well, almost DIES 1/4 to 3/4, and SCREAMS at WOT. It sputters very badly in the midrange. I know I have a jet needle problem. The mid throttle appears to be very RICH (plugs are black and sooty when I run in the bad spot and then pull the plugs). If I AM rich in the midrange, I have to get the needles DOWN a little with reference to the slide position.
Now my question. I read and hear all the time "just shim the needle up or down". This is fine with an adjustable Canadian or Dynojet needle. I have US stock. Furthermore, the discussions I read about shimming the needle up or down don't seem to make sense, unless all the discussions have been about the needles on VM carbs.
On my Mikuni CV's, the needle passes through a hole on the slide bottom. At the slide bottom in a recess, a spring pushes down against the slide bottom and pushes UP against a washer and the E-clip in the needle. Thus the spring pushes the needle UP against a little plastic spacer, up into the plastic spider looking deal that is kept locked down into the slide via a circlip. Putting a shim UNDER the E-CLIP does nothing to the needle height with respect to the needle jet. It just putts a little more spring pressure holding the needle UP into the plastic holder. It looks to me like if you wanted to richen a carb with a stock US needle, you would have to REMOVE the little plastic spacer above the E-clip to ALLOW the needle to be pushed up higher by the spring. If you wanted to LEAN the mixture, you would have to add shim washers ABOVE the E-clip so that the spring pushes the needle up LESS with respect to the slide.
Can someone confirm this for me? Were both sets of my carbs assembled wrong or do I have this right? I haven't found a good close-up sequential diagram yet of the slide/needle details. The exploded, scanned drawings I've seen seem to show that my description is right.
I'm very close on this GS-550 that my son and are working on. The engine is sound. It has great potential.
I just looked for a Dynojet Stage 1 kit, and it looks like it was dropped this year for the pre-1985 GS550's. Bike bandit, and Dynojet directly stop at 1985 or so. I Can get 95 or 97.5 mains (a friend of my son's works at a bike shop) to richen the mixture when I put the header on. Can I get the Canadian needles easily?
BTW, I just found the absolutely BEST lube for getting the carbs back into the boots. It is affectionately known as "female personal lubricant". Not K-Y jelly, this is the stuff that comes in a squeeze bottle (Astra-Glide is one brand). This stuff is glycerin based. I was able the get the carbs in with finger pressure.
Stu
78/81 GS550
79 CBX
73 CB350F
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