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GS1000 jetting?

Sandy

Sandy

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Just came back from my first ride after putting my '79 GS1000N back to stock because it is now eligable for collector plate status. It had a 4 into 1 and K&N pods on it before. If I remove the air cleaner element and leave the air box cover off it runs really strong up to about 7,500 rpm and will pull about 125MPH before it runs out of steam. Put the air box cover and filter back on and it starts misfiring like crazy at anything over 1/2 to 2/3 throttle at almost any RPM. Checked timing, its bang on. I have the stock specs for the carbs so I'm going rebuild them and put them back to stock also. That should cure this problem. I hope! Anyway, I was wondering if anyone out there can recommend a jetting other than stock. The bike will have a K&N replacement element and will be run mostly at an elevation over 3,000 feet. My previous GS1000 was in this configuration an ran like gang busters. It would run strong right up to 8,500 RPM and pull 135-140 MPH with stock gearing, so I know the stock jetting will work. Just wondering if somebody has better idea.
 
When my 78 GS1000 was stock I ran the standard jetting. I also had a K&N filter in the standard airbox.
 
If I understand correctly, you want the bike to be completely stock (other than the K&N filter) and you want to run it with the air box lid on. The jetting is obviously rich right now.
I would think the slightly better breathing K&N filter would MAYBE require one step up on the mains (2.5 increase), however, the 3,000 elevation will make the bike run a bit richer which could cancel out the need for the larger main. The stock needle position should be fine. You may have to adjust the pilot and air screws a bit for lower speeds.
 
It also depends on how good the 4-1 was. I borrowed one once, and it was worse than the old standard pipes! Peaky and less power. The only stock feature you may want to tweak is the pilot circuit as it was adjusted to get past test, not to be the most driveable. It can be tricky tho as it has the pilot and air screws.
 
Thanks for the answers folks. Anyway I pulled the carbs this morning and found some interesting jetting. Main Jets 117.5 (BIG!!)should be 95, Pilot Jet 20 should be 15, Needle Jet 258-04 should be A0-2, Needle 5DL36 I think is stock, the book shows it should be 5DL36-3. I'll order one anyway just to be safe. I think I'll probably go with the 97.5 main, everything else stock except I'll probably start by raising the needles a notch. None of the adjusting screws have ever been touched. They all still have the dab of yellow paint on them. Who ever did the original pipe/air pods conversion just threw the jets in it and forgot about. It never did run as good as a stock bike but it sounded neat. If that's what counts, ....I guess. This is so typical of most conversions I see out there. Too many obnoxiously loud pipes out there that don't make horsepower. Come guys, if you're going to pipe it, at least tune it. I'll let you know how it runs when I'm done. Again, thanks for the info.
 
I don't know what 4-1 pipe was on it, but my '79 1000 with V&H 4-1 and K&N pods runs strong with 138 Dynojet mains which are the same as #130 Mikuni mains, so the 117.5 mains are not really that big. In fact, they may have been too lean.
If you're running stock except for the K&N filter, why do you plan to raise the stock needles a notch? I just think that's too rich. The filter does'nt increase flow that much. I might try adjusting the pilots out a 1/8 turn or so to allow for the filter at lower speeds, but that's it. Just my experience. :)
 
Thought I'd raise the needles to pickup the mid range a bit but I guess that would probably be over kill. My previous 1000 ran fine with the stock configuration so just going one size on the main should be all I need. As for running lean with pipe on it, it did. You could feel lean surge while cruising 70 - 80MPH at half throttle and throughout the top of mid range and it didn't make much power over 7,000 RPM at full throttle. Bike would only top out just over 120MPH with stock gearing. It really wasn't set up correctly. Also got better gas mileage than it should have. Plugs didn't look that white however. Even after full throttle plug checks. Go figure? Thanks again for the advice.
 
Just a reminder, cam timing will have an effect on the top end.
Some bikes are set with the timing around 104 or so and they have more torque but less top end. If the timing is around 110, the top end is better but the low/midrange power decreases. So it's not always jetting. :)
 
Keith you're scaring me! Keep talking like this and you're going to have me tweaking this thing for every last ounce of horsepower. Just when thought I was trying to get away from that madness. This is supposed to be a nice sedate daily driver. Anyway, is there a trick or easy procedure on the GS1000's to indexing the cams short of buying or having custom made different cam sprockets? I don't believe I asked that!!! It's been 15 years since my last GS1000, which if I didn't roll it up into a ball I would probably still have. So I'm kind of out of loop as far GS's are concerned. After that I got into racing 750 Super Bike on a strictly amateur level so I'm well aware of this horsepower madness. Hell, I'm going to be a grandfather in two weeks, ...guess it's in the blood.
 
Well, it's just a fact the main reason two "identical" bikes differ in top speed is because of cam timing.
I have'nt timed cams myself, I just know about the effect it has on the powerband. I had V&H time mine at 106 degrees each. Nice wide powerband. I realize I'm sacrificing a little top end, but I don't really feel it. It does'nt matter much if I can go 128 or 134 mph, it's still flying.
The timing set at 106 is just a good compromise. The bike is just more enjoyable to ride because the power just always seems to be there.
I bought slotted cam sprockets but you can rat-tail file or ? to slot the existing sprocket holes. I'll try to leave you alone in peace now. :lol:
 
Thanks for the help Keith. Got it back together today with the 97.5 jets, everything else new and stock. Runs pretty good now. Didn't get a chance to try any high rpm stuff but it pulls great up to 6,500 rpm in all gears and has good throttle response pretty well anywhere. Pulls good. Idled a little rough. The pilot air screws I found set at only one turn so I back them out to 1 1/2 and it smoothened out the idle quite a bit. I kind of guessed at 1 1/2 though, the manual I have doesn't list any specs. What should they be? I'll have to borrow some carb sticks and do a proper sync when I get a chance. Runs great for now though and I'm back on road. Again thanks for your help.
 
The PILOT screws (underneath) are generally 1 1/4 turns out from the factory. They are for fine tuning the pilot circuit and because of differences in each cylinder, they are commonly set at different points. It's not unusual to find them set for example: 1 1/2, 1 1/8, 1, 1 1/4.
You just have to take plug reads and make fine adjustments of 1/8 turn or ?
The side AIR screws, are to be set to achieve the highest rpm possible, and then you re-set the idle to 1,100 with the idle screwknob. Put the bike on the centerstand and warm it up first. Adjust two screws at a time in 1/4 to 1/2 turn increments to more easily hear the rpm's . Fine tune those two and then do the other two. Then re-set the idle with the idle screwknob.
A good carb synch is very important to avoid mixture problems.
 
Sandy,

The needle # is 5DL36, the -3 is the groove number that it is set on from the factory. Those needle jet numbers are probably the same parts too, one a Mikuni listing and one a Suzuki listing. I was running my 79 GS 1000 (Yosh header, stock airbox/filter) in Denver with 97.5 mains. A K&N will probably need a little more fuel, so I would try 100s or 102.5s. Let us know how it works and SEND PICTURES.
 
Don, thanks for clearing up the numbering system for the needles. Anyway pictures of my GS are in the gallery under 1979 GS1000, Sandy Oates. Thanks for the interest and enjoy all the pictures in the gallery. I think it's a great way to show off our GS's.
 
Interesting thread I have a 78 GS1000 with 1080 kit, ported head, pipe, K&N oval filters, 9.8mm lift street stage 3 cams, 28mm Kawa carbs etc.

I run Mikuni 120 mains, slightly bigger pilots and needles lowered right down. With the extra suck of the modifications it can run rich. Make sure you don't confuse the Dynojet and mikuni jets. I also had my mains drilled out at a carb place, so don't assume that what is stamped on the jet is what it actually flows. The ones in my bike are stamped 95, so that would confuse anyone else! If I had bigger carbs on the bike I would have to increase the mains a little.

Glad to see another decent bike here :)
 
Good info on jetting. When I saved my 80gs1000e, not only did I discover one of the carbs was totally mashed up and not functioning, I discovered that I had all kinds of different settings across the 4 carbs. Bought 4 carb kits and returned them all to stock and picked up a used set of carbs on Ebay to replace the bad #3 carb. Now the bike runs excellent!

Only wish I had a set of spokes on my 1000 like yours has. Checked out your bike in the gallery, looks very sharp and especially nice with those rims. Hey, at least my 77gs550 has the spokes! I want some for my 1000 now! 8)
 
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