Jetting my 78 GS1000

[KEITH KRAUSE]

Back from my vacation. Not sure what's happening Billy.
Is that photo AFTER the needle jet swaps? Also, I assume these reads are after "general" riding around town? Throttle position matters in trying to narrow it down. Also, are you still having "richness" trouble with 1 and 4, or just 4? If both 1 and 4, and considering all four carbs are set up identically(?) I'd still have to wonder about the spark quality. I know you said you tried another coil but that doesn't prove anything, especially if it was just another used coil. Was it tested?
Have you tried swapping the 1 and 4 plug leads (and the coil terminals) to the coil for 2 and 3? That would prove any weak coil issue.
Also, the pilot fuel screws are not always set at the same point for best performance. They're the fine tuning of the pilot circuit and are commonly set at different points to allow for small differences in each cylinder. It's common to end up with a final setting of: Cyl 1: 1 turn out, Cyl 2: 1 1/4 turns out, Cy: 3: 3/4 turns out, Cyl 4: 1 turn out, or similar. Larger differences may show something's wrong though. I really don't think this is your main problem but wanted to mention it may be contributing to a problem. You don't just set all four of them uniformly. You'll find this out but you have to reach the fine tuning stage first.
Try the coil swap and let us know what specific throttle position these reads are at and if it's 1 and 4, or just 4. Also, the needle jet swap question.
If you still have a problem, it may help to come up with a list of things that can cause richness in one cylinder and we can eliminate things and find the problem.

[BadBillyB]

Back from my vacation. Not sure what's happening Billy.
Is that photo AFTER the needle jet swaps? Also, I assume these reads are after "general" riding around town? Throttle position matters in trying to narrow it down. Also, are you still having "richness" trouble with 1 and 4, or just 4? If both 1 and 4, and considering all four carbs are set up identically(?) I'd still have to wonder about the spark quality. I know you said you tried another coil but that doesn't prove anything, especially if it was just another used coil. Was it tested?
Have you tried swapping the 1 and 4 plug leads (and the coil terminals) to the coil for 2 and 3? That would prove any weak coil issue.
Also, the pilot fuel screws are not always set at the same point for best performance. They're the fine tuning of the pilot circuit and are commonly set at different points to allow for small differences in each cylinder. It's common to end up with a final setting of: Cyl 1: 1 turn out, Cyl 2: 1 1/4 turns out, Cy: 3: 3/4 turns out, Cyl 4: 1 turn out, or similar. Larger differences may show something's wrong though. I really don't think this is your main problem but wanted to mention it may be contributing to a problem. You don't just set all four of them uniformly. You'll find this out but you have to reach the fine tuning stage first.
Try the coil swap and let us know what specific throttle position these reads are at and if it's 1 and 4, or just 4. Also, the needle jet swap question.
If you still have a problem, it may help to come up with a list of things that can cause richness in one cylinder and we can eliminate things and find the problem.

Hey Keith, welcome back and thanks for sticking with me. Photo is before needle jet swap. Cyl 2 looks like cyl 3 (slightly rich). Cyl 1 is almost as black as cyl 4 but not quite.....I didn't use a test coil, I just swapped the plug wires and coil terminals from 1&4 and 2&3.....This rules out the coils and wires....I have already swapped out the jets and re-installed the carbs but unfortunately it got cold again here in North Fla and have not yet done the test ride/plug read. Tomorrow night I will ride it home from work and then back again the following morning. The verdict on the needle jets will be in on wed night. The sputtering/stuttering is at less than 1/8 throttle opening, so the sources of extra fuel are limited, in my mind, to the float level, pilot jet, choke circuit, jet needle, needle setting or the needle jet itself. Looking into the bore of my needle jets, they look like crap, all pitted looking and rough. There does not seem to be an obvious "ovaling" of the holes though. So, I guess we will see what the jet swap tells us before shelling out $70 bucks for 4 new ones.......BadBillyB

[KEITH KRAUSE]

OK. Sounds like those needle jets aren't helping things. Should be smooth.
Because it's easier to ask instead of searching back: these needle jets, besides being in poor condition, are the wrong size also, correct? Also, did you go through ALL the electrical connections? Dirty coil conections and plug caps can cause poor spark and a false rich burn. Just trying to be sure all the basics are done.

[BadBillyB]

OK. Sounds like those needle jets aren't helping things. Should be smooth.
Because it's easier to ask instead of searching back: these needle jets, besides being in poor condition, are the wrong size also, correct? Also, did you go through ALL the electrical connections? Dirty coil conections and plug caps can cause poor spark and a false rich burn. Just trying to be sure all the basics are done.

Well crapola, nothing I have tried has made any difference. The needle jets are the correct ones Keith, they are series 258 0-2 and swapping 3 and 4 made no difference. All 4 plugs are black after hours of mixed driving, mostly cruising.....I tried different set of stock size pilot jets in it just in case PO had drilled on them. No dice.....Maybe the carbs are fine and I am just missing something.. I rechecked ignition timing and verified that the advance mechanism is working correctly and giving the correct amount of advance....I do know that my timing chain is badly stretched as I locked down the side bolt on the tensioner and then removed it. I then marked how far the plunger was sticking out before releasing it. It was just about at the limit of the tensioners ability to remove slack from the chain. I am wondering if my valve timing is so retarded that it's messing with the bottom end. Especially the intake cam timing as it is a long run to the crank......What do you think ???.....BadBillyB

[KEITH KRAUSE]

Just saw your reply Billy. Late for work. Sorry. Will try to help later tonight if I can.

[KEITH KRAUSE]

If you think the cam chain needs to be replaced soon, you should do it, especially if you think it's giving you problems. Putting it off is asking for trouble if you try to squeeze every mile out of it. But if the tensioner is still doing its job and there's no significant chain slack noise, I doubt it causing any richness issues.
As for the performance, you said the bike's running fairly well, but the black plugs are an obvious sign it's rich. OK.
I've followed your progress and what you say you've done to fix the problem and it would be easy to say you've missed something or done something wrong, but to move ahead I have to assume you've done things right and haven't cut corners on any of the basics to tuning/jetting. That puts us at a point that doesn't make sense.
You've installed a freer flowing pipe and removed the air box lid. Both of these mod's would lean the stock jetting. You said the plugs were black from general riding around, which would be mostly the jet needle circuit. You said the jet needle e-clips are in the 3rd (factory) position. As far as you know, all the other jetting components are stock, correct float levels, "ballpark" pilot fuel/air screw adjustments, clean carbs, carbs synched, fresh o-rings/manifold o-rings, good spark/timing, compression was checked, etc. But you still have black plugs.
Just wondering. Didn't you have black plugs at only 1 and 4 earlier? But now it's all four? No adjustments since, just more miles of testing?
I see you're on line. Please bring me up to speed and I'll try to think of something to try.

[BadBillyB]

Well theres finally light at the end of the tunnel....I got my new needle jets (258 series 0-2) from motorcyclecarbs.com the other day and decided to just install them without making any other changes. I was hoping the bike would run great and it did not. It would not hardly run past idle. It was running OK before the change, but had a "burble" or flat spot at around 3K and the plugs were always black.....Then remembering what Keith said about the jet needle clip needing to be in at least the 4th groove from the top with my particular mods, I decided to try his advise. The bike runs better now than ever before. It is very close to being perfect and I am finally getting good results. The old needle jets were so bad that the bike ran better with the needle clip in the 2nd groove.....I think now that I will try 17.5 pilot jets and go down to a 100 main jet (from a 110) as I can feel it lay down a bit when it gets on the mains.....Seems to run the best with the fuel mix screws at around 1 1/4 turns out, but still experimenting with these....Thanks Keith, you were right, but it only works if you have good parts (jets).......BadBillyB

[Hoomgar]

How did I not see this thread until now?!?!? :shock: :?

Looks like the experts got you covered so I wont muddy the water but if you need any additional thought and trouble shooting angles don't hesitate to let me know.

[BadBillyB]

How did I not see this thread until now?!?!? :shock: :?

Looks like the experts got you covered so I wont muddy the water but if you need any additional thought and trouble shooting angles don't hesitate to let me know.

Thanks Hoomie.....I thinks its all downhill from here. Tuning carbs with bad parts in them is like tuning a motor with a weak cylinder. Lots of effort and little results....I'm not going nowhere, I dig this forum, so many great minds.......and great bikes......BadBillyB

[KEITH KRAUSE]

You say the bike is running very close to perfect but still needs some work.
If the "fuel mix screws" (actually pilot fuel screws) are at 1 1/4 and I assume your pilot circuit reads are lean (?), I'd try richening them a little (about 1/4 to 1/2 turn more ) and stick with the 15 pilot jet. Then re-set the side air screws for best idle at 1,000 rpm. Test, get plug reads at minimal throttle.
I don't know why the bike is "laying down" as you say at open throttle? With the air box lid off and that pipe, it should be able to handle a 110 to 115 main jet. All bikes can be different but going to a 100 main jet is not enough in my experience. I think something's wrong or missed but there's not much I can do from here.
Without reading back, what have you done to the carbs? If you list what you've done, I can try to list things that you may have missed.
I assume the carbs were vacuum synched well?
The inner o-rings are all replaced, especially the o-ring on the needle jet/bleed pipe?
The floats are set at .94 and the float needle valves HAVE GOOD SPRINGS? Not sagged?
The factory jet needle plastic spacers were re-installed in correct order? Thicker one above the e-clip/thinner under the clip?
Floatbowl vent lines removed so the bowls can breath easy?
No possible intake leaks?
Ignition timing, etc, all good?
Valve clearances set?
Compression was good?

[renobruce]

Billy, what ever came of your carb struggles? I just read this whole thread.... I need a conclusion!

[BadBillyB]

Sorry Bruce, I dont get on the forum as much as I used to as I now have an affliction with RC air planes and have been hanging out elsewhere. The bike runs so good now that I have been just riding it. It could stand having 17.5 pilots put in it and the main jet is probably a little large. I said before that it lays down a bit at WOT and Keith took this as maybe being a problem, but what I meant is it probably could pull a little harder on the top end with the ideal main jet. A 110 main jet is like 5 steps richer than stock. It really does run GOOD now with the new needle jets and the needles set as Keith suggested......Being a perfectionist, sometimes I just have to cut myself off and move on to more important issues.......BadBillyB

[Tom MLC]

Bill, I was studying this thread, too. As I struggled with my own carb challenges. I owe a lot to Keith Krause, and his wealth of knowledge.

Glad you're running well.

Me too.

[KEITH KRAUSE]

Good to hear the news. Makes my day.

[80GS750]

hey keith! im definately gonna need your help with my 1000.

i have stock vm carbs.... what appears to be an older aftermarket exhaust, and im gonna have pods on the carbs....

whats a good starting point? i know nothing about these vm carbs, but do have some good experience with the cv carbs on my 750.

im gonna get the o ring kit from here and rebuild the carbs, but i will need a starting point with the jets... you seem to have a lot of knowledge so i figured i would ask you about it!!!

thanks in advance

nate