Jetting GS750E with pods..help!!!

[mugwampbro]

Hello everybody !!!

'82 gs750E
K&N pods/ (didn't have stock airbox)
Stock 4/2 exaust
Mikuni BS 32 (CV's)
current jets: 112.5 main, 42.5 primary, 170 air
New aftermarket stator/regulator/rectifier
Complete "Dyna 2000" ignition system

Need jetting recommendation...I am a master carb re-builder (auto's only up to now) and have cleaned/rebuilt these carbs. Have gotten out most bugs in carbs up to now thru the use of searching (countless hours) this forum. After re-build had many issues..wouldn't start/idle, bogging, etc. One by one, I solved most of the problems. I think I'm at the re-jetting stage. According to technical forums these carbs (with pods) is the hardest combo to dial in. No jet kits available for this combo..but don't mind buying jets by the piece. I realize that until WOT that the carbs are pulling off the pilot circuit... so the place to start jetting is with the pilot and air jets. The bike starts and idles perfect at 900 RPM's !!!(no vacumn leaks !!!) and will set to 1100 when done tuning..... but requires choke to be left on (enrichening) to get'er down the road. It bogs at about 4500 rpm to 6000 rpm at WOT which I believe is the 'transition' from pilot circuit to main circuit, but after that it pulls stong up to +9500. Plug check confirms LEAN condition.
I realize that compression and such are going to play a part in final, perfect tuning, but somebody out there has had to have had the same problem and could provide an initial or even final jetting recommendation. I've been on-line on the GSresources forums for hours this morning alone and I can find nothing. I'm getting burnt out man...(wanh,wanh,wanh). Can anybody help??? Also..are there any pics of how to do the needle jet, adjust position, thing?

1)Floats set to knats-ass
2)removed hoses from bowl vents (turbulence issue/ thank you Keith)
3)primary circuit screws = OUT/ 4 turns (suggests compensating for lean condition) for highest/smoothest idle at 1500 RPM
4)5/16 fuel line
5)replaced vacumn petcock with simple on/off version and plugged vac. line at carb
6) carbs bench synched to knats-ass

mugwampbro@hotmail.com...I will post final tuning when done and maybe it help someone else..Thanx..JOE

 

[80GS1000]

FWIW, there IS a Dynojet stage 3 kit for your bike: http://www.dynojet.com/jetkits/motorcycle/suzuki.aspx

I just installed a DJ stage 3 kit on my GS1000 along with pods and a 4 into 1, seems to work well (fast revving, no flat spots) but I have yet to ride the bike. Takes a lot of the guesswork out of rejetting.

 

[Guest]

Sounds like you need to raise the needle. If you don't have a jet needle with notches you can shim it with washers. I got a mini variety pack from Radio Shack and it had the right sizes. Two washers = one notch. I would start raising it two notches.
Personally I would get a Dynojet kit.

Looks like your running stock jets with K&N pods. That won't work. I would start with 117.5 mains. If you don't notice a difference in you idle backing out your idle mixture screws go up to 45 on the pilot jet. Plus do raise the jet needle two notches.

 

[mugwampbro]

That's the kind of info I'm looking for and thanx. The dynajet kits start with a 122.5 main and do not include any pilot jets and also say they are for pods and aftermarket exaust, which would explain the big jump in main jet size. Stage 1 and 3. Thats why I said they don't make a kit for my application.
I think I'm going to wait for more responses before I tear into the carbs again..and thank you for the recommendation....everybody, Keep 'em coming !!!!

 

[80GS1000]

Use the Dynojet DJ124 main jets for pods with the stock exhaust. Check step 3 in the stage 3 directions here: http://www.dynojet.com/pdf/3315.pdf which says "If you are running the stock exhaust (with pods) use the DJ124 main jets".

Keep in mind that the Dynojet jet size numbers do not seem equivalent to the Mikuni numbers - different scale apparently. Can anyone confirm or deny this? I used a DJ170 main on the GS1000 with pipe/pods which sounded HUGE, but the bike seems to run well.

 

[Guest]

Mikuni jets are sized by volume of gas flow. The Dynojets use the actual size. I run 138 dynojet mains which are close to 127.5 in Mikuni land. If the Dynojet suggestion is 124 that is close to 115 Mikuni. I would still start with the 117.5. I like to start big and work my way down. Less holes in the pistons this way.

 

[mugwampbro]

OH..those 'PESKY" holes in pistons !!! Thanx for the imput !! After countless hours of research on this exellent forum though, I believe that this bike runs off the pilot (primary) jets until WOT. I am running lean and according to my research.. the 4 or more turns out on pilot screw that I have to make to make it somewhat rideable, confirms this. It seems the logical place to start is with the pilot circuit. Since the DJ kits don't address this issue and are quite expensive.. I am hesitant to purchase. Keep the feedback coming!!

 

[80GS1000]

I thought this diagram explains the relationship between the pilot, needle, and main pretty well.

 

[mugwampbro]

Also, remember... the stumbling and bogging occur from takeoff to about 6000 RPM... (at all throttle positions)...after that it pulls like a MACK truck all the way to redline. Plug check still comfirms 'lean condition' though.... so I know I'll have to increase main jet size..I just don't think that is the place to start. But correct me if I'm wrong

 

[80GS750]

spend the money and get the dynojet stage 3, it comes with the jets you will need and lots of other goodies so you can tune it correctly, i would not try to jet it out without the kit, buying the stuff a bit at a time and you will find yourself tearing those carbs apart over and over again trying to tune it just right.

i put in the stage 3 and have had to make no adjustments so far, just follow the directions and you should be good... the stage 3 can be had for right at 100 bucks if you search around!

 

[mugwampbro]

TO GS750: Do you have just the pods change? what size pilot jet are you using? you did only a main jet change to fix???

 

[80GS750]

i have pods and the v&h 4-1, i installed the complete stage 3 kit, they come with 2 sizes of jets, i used the largest ones they had i think it said 130 but i cant remember.. it comes with new adjustable needles, you have to drill out the air hole in the pistons ( comes with bit) and there is a restrictor for the air inlet hole in the front of the carb.....

it runs great so far... i have a tiny bit of tuning to do but thats just getting the air/fuel screws just right, and setting the needle hights (if they need it)

im waiting on a new front tire before i can really open her up
my old one is dangerous!

 

[80GS750]

the stage 3 comes with 2 sizes of jets, and you would need the smaller ones, but the adjustable needles and restrictors are well worth it,

it also comes with a complete instruction guide to help you tune it too...


the idle circuit DOES NOT CHANGE. it really makes no difference at that low of rpm as long as your air/fuel screws are right!

 

[KEITH KRAUSE]

First of all, K&N pods and stock exhaust are a poor flow match. Neither a stage 1 or 3 kit is designed for that combo. So trying to buy separate jets and getting it right the first try is difficult. I personally would find a good pipe or go back to the stock air box.
When testing the various jetting circuits, remember that approx' 3/4 to full is the main jet, 1/4 to 3/4 is the jet needle, and closed throttle to 1/4 is the pilot circuit. Charts/others opinions vary a bit, but allowing for some overlap between the three circuits, those are the basics. It's about throttle position, not rpm's.
Pods will effect the main and jet needle circuits the most. Simple richer mixture screw adjustment should be enough for the pilot circuit.

What I'm not sure about is your factory/stock main jet size. Is it 112.5??
If so, I don't understand the info at that link showing the DJ stage 3 kit recommending a size 124? That's approx' the same size as a 115 to 117.5 Mikuni jet AND that's an increase allowing for a pipe too? What would they recommend without the pipe, a DJ118 or ? That would actually be a smaller than stock main. Makes no sense, if indeed the stock main here is a 112.5 or very close.
Pending what the correct main jet is, I'll take a guess based on past experience, though I don't have a whole lot of actual test experience with pods and stock exhaust combo. I do have some. I can only suggest what makes sense to me. The trick is understanding that pipe doesn't flow as well as the filters. The pipe compromises the pods, but how much?
For K&N pods, oiled correctly, I'd try a minimum of 3 full sizes up (15) and a maximum of 5 full sizes up (25), for the main jets. So I'd go in the middle and get 132.5 mains if the stock jets are 112.5.
For the jet needles, a minimum of 1 position richer and a maximum of 2 positions richer when using the stock needles. Again, I'd try the middle, 1 1/2 positions. If US model, your needles are non-adjustable so you have to shim them. A typical jetting spacer (used for 1/2 position changes) is approx' .022" thick. So I'd shim the needles approx' .065/.070" and test.
For the pilot circuit, I'd try an additional 1 full turn richer than where the screws were from the factory. Generally, you set these screws using the highest rpm method. If you have problems, then the pilot jet is the wrong size to begin with. In your case, the screw would usually be 2 to 3 full turns out.
If you notice throttle response issues, then you will have to drill out the orifice to each diaphragm/piston chamber.
Remember it's easy to over-oil the pods. 1 quick pass from about 5" to shoot 2 or 3 pleats at a time as I rotate the filter is my method. Shooting each pleat as per K&N instructions seems a bit much and after some trial and error, I don't follow that anymore.
As for the order of circuit testing, the majority jet the main first, the needle second, the pilot last.
I've jetted that way, and I've many times found jetting the needle first, the main second, and the pilot last, to work and even be easier sometimes. Many times I've jetted the mains to what I thought was right, only to find that I now had a bog at high speed roll on after my jet needles were dialed in. Though the bikes seemed to handle the main jet at full throttle when accelerating through the gears, opening it up (such as to pass) from cruising in top gear resulted in bogging/hesitation. In this case, I always get the jet needle perfect and if I'm slightly compromising the main jet, oh well. Real world passing/accelerating power is more important than straight through drag racing. You spend the most time riding on the jet needles and they should be right.
So it depends on your bike and the mods as to what sequence is quicker or easier/more accurate.
I'd get the jet needles mixing right at a solid 1/3 throttle according to the plug reads first. Then I'd simply run the largest main that gives you the best top end WITHOUT creating a bog/hesitation during a roll on from top gear at approx' 55/65 mph. Then I'd get the pilot circuit set so the bike warms up correctly with a "normal" amount of choke, and cruises around town without any surging/hesitation at steady speeds and the plug colors look good. Keep in mind that a little decel' pop is normal with pods. If too much popping, then try richer screw adjustments. In my opinion, 4 turns out is the maximum range the screws have and after that you need larger pilot jets. If it "spits" out the pods, same procedure.

 

[Guest]

dear master carb-rebuilder;
If you are more than 3 1/2 turns out on the pilot screws you need to go up a jet size, Its going to take a while to dial that thing in, the main jet is in the mix as soon as the needle hits the taper, if not a little before.
raise the needles-go up a jet size-raise the needles- go up a jet size-repeat as required, or as someone else suggested start rich and work down, but it may be harder to read plugs that way. If the local shop is friendly you should be able to trade jets.
good idea using the choke to confirm whether you are rich or lean, you can't do that if you start out rich.

 

[sbbloom69]

Jet Needle Shimming

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

 

[jlgace]

I will agree with Krause re: your pods/stock pipe combination. Before you take on the task of rejetting, you should make absolutely sure you never intend to go to an aftermarket pipe. Once you get it right, you probably won't want to change it later (the jetting).

My $0.02 regarding the jetting: start with the main first. The needle is dependent on the main due to the larger quantity of fuel that can flow past the needle on a larger main than a smaller one, given the same needle position. As mentioned by others, when you're testing a main you are only testing at WOT when the needle is out of the way. Everything less than WOT will be influenced by your needle. Always start rich with the main and work down, because as you say, fouled plugs are cheaper to replace than pistons. You probably won't need to change the pilot with this setup as I believe someone already mentioned, so I'd concentrate on setting the needle once you get the main dialed in. If your idle/just off idle is still bad after playing with the needle and fuel mixture screws, then consider an upsize on the pilot. Still think you should do yourself a favour and get a pipe though.

TO sbbloom69: Fwiw you should be able to purchase different size needles for your carb if they cannot be moved.