Jetting my 78 GS1000

[80GS750]

thats right....

with different tolerances, each cylinder will pull different vacuum than another

 

[KEITH KRAUSE]

hey keith you mean the 4th position down the needle right?

the way i understand it, they count positions down the needle..

You should always count e-clip positions from the top-down.

 

[KEITH KRAUSE]

I have a 1979 GS 1000 with a Two Brothers 4-1 with a D&D can, and K&N pods. The bike came to me running rich, according to the PO, fouling the plug in cyl #3. He had installed a Dyna S, and told me that that he had installed a Dynojet Stage 3 kit. The pipes have dents on the #2 and #3 cylinders from hitting. I pulled the carbs apart, and they all have 112.5 Mikuni mains (have a little box-within -a box marked on them), 15 pilots. It appears that he never installed the Dynojet kit. I believe the needles are still the Mikuni; they are a sort-of light brass color, but they do have 5 grooves for adjustment, and are marked 5DL36, IIRC. The needles in the box with the other Dynojet stuff are a silver color, and also have the adjustment grooves, but seem slimmer than the current ones.
The mains in the box are 138s and 142s (DJ).
I'm planning on keeping the pipes, and running a K&N replacement with the airbox, and either using the stock filterbox with the lid off, or just the K&N attached to the airbox., as I'm planning on using the bike as a sport-tourer, and I think the airbox with the crankcase vent dumping into it will help mitigate the effects of temp, humidity, etc. I know that the stock mains were 95s, so the mains were changed out. I talked to the support folks at Dyno, and they recommended using the 138s and installing their needles with the clip in groove#2. Does this sound like a likely starting point for the setup?

You mention 3 possible airbox mods, all of which will require different jetting. You need to decide what you want for sure.
Your cyl 3 fouling could be from a leaking petcock by the way.
The DJ jet needles are tapered more than the stockers and have 6 positions instead of the stockers 5. The 5 position needle you describe (5DL6-3) is the stock needle.
The dented exhaust may cause trouble. Using parts for other than what they were designed for causes trouble too.
The stage 3 DJ kit isn't designed for running with a stock airbox/lid off, etc. I've never experimented with mis-matched parts as you suggest so jetting suggestions would be pure guessing.
Seems to me the bike was running pretty lean with the 112.5 mains, not rich as the PO said, unless there's other things causing it. I'm guessing the jet needle was positioned lean too but that's just assuming. The stock 15 pilot would be lean too.
The DJ folks are just guessing. They're giving you the "base settings" they suggest for a 1000 with a quality pipe and K&N pod filters. Even with the lid off, the 138 DJ main (approx' the same as a 130 Mikuni main) will be too much and your bike will bog under full throttle, especially typical full throttle passing speeds. Not what you want for sport touring or any other riding for that matter.
Let me know what exact airbox set up you'll choose and I'll try to suggest a good starting point, if not spot on the first try.

 

[KEITH KRAUSE]

As for synching carbs on a test bike and then expecting that adjustment to be accurate and correct when installed on another bike...only fool I've heard of that claims he does that is wiredgeorge. The last few posts explained why you can't.
Actually, I personally doubt he does it as he says. It's just a part of his "total package" that he offers. He wants you to believe your carbs will come back 1000% bolt-on-and-go. So he assumes your ignorance and tells you he'll synch 'em on a test bike, which of course just shows his ignorance, and/or poor salesmanship.
He figures if you know you have to learn to synch anyway, heck, maybe you'll just learn to synch AND rebuild your own carbs yourself.

 

[jknappsax]

Keith, I think I've decided to take the path of least resistance, and install the DJ Stage 3 kit, and put the pods back on. I just want to get this thing on the road for the summer, then I can rethink what I want to do next winter. Dynojet tells me that I don't need to change from the 15 pilot jets, just the mains and the needles, then finetune with the grooves and washers. Locally, I can't find anyone with Mikuni jets, and ordering and waiting is driving me crazy; I just went through the same thing with valve shims, and the process went from about an hour to weeks, and I HAVE the DJ kit, so I think this wil get me on the road much sooner. My rationale for going back to the stock airbox was that the breather gases would keep conditions at the carbs more consistent, but I know a lot of folks run pods with no problems, so maybe I'm just being paranoid about constantly having to mess with tuning due to the pods.

 

[KEITH KRAUSE]

I'm not sure what you're meaning is about the breather, but if this bike is READY to jet, and by reading any of my past posts you know what I mean by being ready, then you shouldn't have any major problems. Worst thing I read in your posts is that you have a Two Brothers exhaust that I assume isn't specifically designed for your bike and it's also dented. Using questionable parts, you can't get upset if it has problems.
I can give you jetting suggestions that work very often with a quality/correctly flowing exhaust and properly oiled K&N pods.
138 main.
DJ jet needle, jet needle e-clip in the 4th position from the top. Be sure the jet needle factory plastic spacers are replaced in correct order on the DJ needles...thicker spacer directly on top the e-clip and thinner spacer goes under the clip.
Stock 15 pilot jet is fine, but you'll need richer than factory adjustment at the pilot fuel screws underneath. Try 1 1/2 turns out from lightly seated initially.
Adjust side air screws using the highest rpm method. They'll end up about 1 1/2 to 1 3/4 turns out usually.
REMOVE the 2 floatbowl vent lines and leave the ports open to breath.
Bench synch the carbs well.
After start up and fully warm, vacuum tool synch.
Test the main, needles, and pilot circuit at full, 1/3 and minimal throttle positions respectively.
There are several posts around to help you with making a crankcase breather catch if interested.

 

[jknappsax]

I appreciate the advice. I believe it is ready; the valves are set, I have the carbs apart and soaking, they go back together today, keeping your advice in mind. They go back on the bike, check ignition timing (the previous owner wasn't sure if he had installed and set the Dyna S correctly), then the carb tuning. The bike already was set up with a K&N crankcase breather as well as the pods. I think this will be the quickest way to get this beast on the road. I personally doubt that it IS a Two Brothers exhaust; I don't think they made exhausts for these bikes, but I will work with whatever I have. Thanks again.

 

[80GS750]

keith:

i really need your help here...

i have the air and fuel screw set exactly like you said.... where do i set the slides (you know the bolts in the top middle of the carbs that move the pistons up and down)

she wants to start up... when i choke it just a little it sounds like she wants to pop a couple times but just wont start up...

with the slides set all the way down, i get nothing. i can put my hand over the carbs and it doesnt draw in any vacuum at all....

with them set up a little bit, i can hear them sucking air and its like she wants to start, but i get nothing....

with them set up quite a ways, she still wont start at all... and i can feel (which is weird) when i put my hands over the carbs it feels like they are pushing air OUT with every revolution... not sucking it in.....

why in the heck would it do that?

i am lost.... i didnt have near this many problems with my 750 and i put the dj stage 3 in it and she ran great.... help!

thanks in advance

 

[80GS750]

for the record, i checked all the valve clearances and a few seemed like they might be a little tight, but all the others were within spec, so i just left her alone... im a cheapass....

 

[80GS750]

one other thing.....

i have emgo pods.... and im running the not so stock exhaust that i got with the bike...

the exhaust has 4-2 with turnouts... im assuming it flows better than stock, but not as well as a good 4-1

 

[80GS750]

keith? are you there???

lol

 

[KEITH KRAUSE]

keith? are you there???

lol

I don't visit as much as I used to. Don't have the time.
Sounds like you're just having trouble with the bench synch??
You don't "pre-set" the screws you mentioned on top of the arms that control the slides. At least that's what I interpreted from your post. You DO adjust them while you're bench synching of course. Then, after start up/fully warm, you'll hook up a vacuum tool and tune them better. The bench synch, to me, is only done so the bike will initially start up and run well enough to do the vacuum tool synch.
I made a very detailed post some time ago about bench synching VM carbs but I never learned how to save it as a link. Try a search. I remember the thread title is something like: "GS1K, re-jet, bad fuel economy, attn Keith Krause". The author is "Hoomgar". It's a long thread and I believe it's at reply #36.
Basically, you set the slides to their lowest point, uniformly. You need to watch them carefully and it's easy to adjust them incorrectly. Once set correctly, you need to adjust the idle adjuster knob so the bike will start up and hold an idle. If the idle adjuster knob isn't adjusted high enough, the bike won't start. Don't worry about adjusting them a bit high initially because once the bike starts up and the choke is off, you can easily set the idle to the base idle of 1,000 rpm's which is where you want it to be when you set the side air screws and then set them using the highest rpm method. Then you're ready to vacuum synch.

 

[80GS750]

oh ok,

what i did at first was set them at the lowest point, and all at the same height,
then i ended up having to choke the crap out of it to get her to start....

after playing with it quite a bit i see exactly what you mean....

i also found that someone had put a plug, i mean taken a caulking gun and filled the hole in my 1-2 muffler completely up with sylicone...

i took a screwdriver and knocked it all out of there and its definately caulk.

who would do such a thing!!!

could have been why 1-2 werent firing off right away...

 

[80GS750]

i found that post....

great info! thanks a ton.

i will post here soon with my progress.... hopefully shes running soon!!!

 

[KEITH KRAUSE]

OK. Good luck with it.
Bench synching the carbs incorrectly and not adjusting the idle adjuster up enough is a common problem if you're not careful. I've seen/heard of guys doing it wrong and they'll drain a good battery trying to make it start.
I decided to look up that old synch info too and I had a little trouble. Found it under "78 GS1K, carb rejet, attn KEITH KRAUSE", on page 4.

 

[80GS750]

ive got my smart charger connected to it the whole time, that way she stays good while i try to get her going.....

 

[80GS750]

ok keith,

i have the engine back together now... but cant get her to start...

with all the slides all the way down, very close to the same height in relation to each other.... i can move the idle screw from bottomed out to all the way up and still i get nothing out of her....

unless i choke it... then it runs for maybe 3-4 seconds and dies....

i was messing with some adjustments and was able to get it to run for maybe 20 seconds, then i killed it, and i cant get anything out of it now....

it was running like crap. so i think my timing is off. the manual really sucks in this department and i cant get it set where it should be....

what i need is either someone to help me out, or a step by step with pics too.....

thanks in advance keith.

 

[KEITH KRAUSE]

The timing should be verified correct before start up. You can't vacuum synch without the timing correct first.
Do you have stock ignition or a Dyna S or ? Make sure the timing marks line up as your manual states. You can statically check (key on only/plugs removed and watch for spark at #3 and then check #4 spark) by turning the crank with a 19mm wrench. You can check advance by doing the same thing but holding the advance mechanism at full advance with your thumb/index finger. Crank slowly as the correct mark comes around and when the marks line up nicely you should see the spark snap. Good enough for start up purposes. Once running/warmed up, you can fine tune the timing and then synch.
If that's not your problem, are you using the gas tank with extended fuel/vacuum lines for fuel and vacuum/venting? If using a temporary reservoir or the tank are you sure it's vented properly so fuel will flow? Is the vacuum port at #3 plugged as it must be if using a reservoir?

 

[80GS750]

i will check the timing like you said too... never thought of it that way.

im using a reservoir, thats vented so the fuel will flow.... and i have a plug in the vacuum line so that it cant draw in air through it...

 

[80GS750]

what im thinking is this:

it starts when i choke it, so the mixture must be too lean the way i have it right now...

so i may try to adjust the air screws a tiny bit at a time, then try moving the slides up from the bottom as i crank it and see if i get better results with different mixtures....

both the air screw on the side and the fuel screw in the bottom are for idle purposes correct? that makes it tricky to get it stoich without having it running first....