'82 GS 650 glz - Carburation issue (probly)

[upb4dawn]

Thanks again, Steve. Just to make sure, I'm assuming there's no point in chasing the notion of weak ignition coils until I sort this stuff out.

First of all, the plugs are black and sooty, but that's just from a regular check and not a throttle chop as you've suggested.
Second, the mixture screws are likely screwed out way too far. They are at 2.5+, I think I remember reading stock was about 1.5.
As for 'how 6-Sigma sizes their jets' .. I have no clue, and am surprised there's more than one sizing convention, but .. then I looked at the DynaJet website and their kit for this bike is a set of 155's and 160' (4 each)... that's even 'huger'.
I'm considering ordering a set of 120's, But I might do what you've suggested first (I'm getting pretty handy at pulling the carbs and disassembling them..but still would rather avoid it) and see if there's improvement. That would be: changing the spacer locations, going to the leaner set of jets, reinstalling the stock pilot jets, and screwing in the mixture screws.
FYI- I won't get at it for a few days to a week, but I'll report back when I do.
Appreciate you sticking w/ me on this. I really like this bike, and see that it has tons of potential. I've got it looking pretty cool, too (was in pretty horrible cosmetic shape). This is the primary thing in the way of it being awesome.
PS... as for exhaust options.. what are your thoughts on a pair of reverse cone megaphones? Probly free-er flowing than stock, and way cheaper than a set of 4/1's.

[upb4dawn]

I didn't oil the K& N's at all.
What size were the DynoJet kit's jets? On their website, they say 155's and 160's. Seems awfully large (just based on what little I'm learning).

[smilinbrad]

I'm with Steve here. This is a stock engine with pods. If a K&N filter in a stock airbox is good for two sizes (+10) then pods must need about four (+20) since the sizes run in multiples of 5. Put everything else back to stock and start from there. Put in new plugs, run it a little and check your color.

[mmattockx]

Thanks. Recommendation duly noted.
As for 'starting with the pilot circuit', would you recommend putting everything back to stock, then change just the pilot jets?

I wouldn't go back to stock, since you know that will be too lean. I agree with Steve that two sizes on the pilot jet is too much. Since you have a stock exhaust (ie - minimal flow increase on that side) I would go back to the stock pilot jet, mixture screws out 2.5 or 3 turns, set the needle in the middle groove, take a guess on your mains (stay on the rich side, that is safe) and start from there. Know that every circuit affects the ones above it, but not the other way around, which is why I say start at the bottom and work up. That way you don't have to go back and reset things as you tweak the other circuits. Use the mixture screws to get the pilot to where it will start well, idle smoothly and let you cruise at less than 1/8 throttle without surging. Try the choke test on it to ensure you are in the ballpark. Once you have the pilot circuit set start working on the needles. Test ride and choke test for them. Raise the needle to richen the mixture, lower it for leaner. Rinse and repeat for the main jet.

Note that for these tests I try to test at a steady throttle position. I go out on a back road and get into 3rd or 4th gear, let it slow down to below 3000rpm, then roll open to whatever throttle opening I am checking and let it pull for a while to get stable airflow through the carbs, then try the choke test. Once you have everything working well then start working on roll ons and other transient throttle behavior. You may find that you need to compromise one of the settings a bit to get good roll on behavior or whatever is important to you.


Mark

[upb4dawn]

OK, thanks guys.
I've ordered some jets from JetsRUs. I'll not be able to do work on this for a while anyway. I'll put things back to stock (keeping the K&N dual pods - the DPO binned the stock airbox & used cheapo pods), except for the thinner needle spacers & the jets I ordered. I'll post back w/ results.
Doug

[Steve]

Second, the mixture screws are likely screwed out way too far. They are at 2.5+, I think I remember reading stock was about 1.5.
As for 'how 6-Sigma sizes their jets' .. I have no clue, and am surprised there's more than one sizing convention, but .. then I looked at the DynaJet website and their kit for this bike is a set of 155's and 160' (4 each)... that's even 'huger'.

Yes, the stock setting was rather lean, but they were also set for pure, 100% gasoline, and the bikes ran terrible and took FOREVER to warm up. Simply turning them out about half a turn farther made the bike MUCH more friendly.

As for sizing, look back in post #11, where I mention Mikuni, Dynojet and Kehin, giving their respective numbers for the same size jet. No idea what Sigma uses, as very few people have reported using Sigma.

.

[upb4dawn]

update

I wouldn't go back to stock, since you know that will be too lean. I agree with Steve that two sizes on the pilot jet is too much. Since you have a stock exhaust (ie - minimal flow increase on that side) I would go back to the stock pilot jet, mixture screws out 2.5 or 3 turns, set the needle in the middle groove, take a guess on your mains (stay on the rich side, that is safe) and start from there. Know that every circuit affects the ones above it, but not the other way around, which is why I say start at the bottom and work up. That way you don't have to go back and reset things as you tweak the other circuits. Use the mixture screws to get the pilot to where it will start well, idle smoothly and let you cruise at less than 1/8 throttle without surging. Try the choke test on it to ensure you are in the ballpark. Once you have the pilot circuit set start working on the needles. Test ride and choke test for them. Raise the needle to richen the mixture, lower it for leaner. Rinse and repeat for the main jet.

Note that for these tests I try to test at a steady throttle position. I go out on a back road and get into 3rd or 4th gear, let it slow down to below 3000rpm, then roll open to whatever throttle opening I am checking and let it pull for a while to get stable airflow through the carbs, then try the choke test. Once you have everything working well then start working on roll ons and other transient throttle behavior. You may find that you need to compromise one of the settings a bit to get good roll on behavior or whatever is important to you.


Mark

OK, I put the stock pilot jets (42.5) back in. I checked the float levels, & they seemed spot on. I put in 120 main jets (stock being 110, and the ones I'd used last were 140/142.5's), and I set the needle with the small white spacer (the one sent by 6 Sigma) above the clip. This is about 1/2+ the thickness of the stock spacer. Mixture screw out 2.5 turns.
The result:.. starts a bit more reluctantly (more 'cold natured'), sounds good on the stand & rev's willingly, but then no power at all in any range; it barely pulls out up the street. No throttle response, or even loss of power when rolling on the throttle. @1/4 throttle to Mid range runs somewhat better (limped home) with the choke pulled. So, too lean across the board, seems to me. The plugs are dark and sooty, but then I had to use the choke to limp back home.
I'm getting to be pretty good at pulling the carbs and tearing them down. But, the fun is wearing a bit thin. I'm in for the long haul, but thought I'd post this and see what's said before I see about getting more jets. Thinking of going up one size on the pilots (45), and maybe up some on the mains.
I'm once again going to have to wait several days before attending to any of this.
Thoughts and recommendations appreciated.
Doug

[tom203]

This sigma kit- does it involve any modification of vacuum slide hole?

[upb4dawn]

This sigma kit- does it involve any modification of vacuum slide hole?

Yes, there's a small drill included to slightly enlarge the hole.

[mmattockx]

OK, I put the stock pilot jets (42.5) back in. I checked the float levels, & they seemed spot on. I put in 120 main jets (stock being 110, and the ones I'd used last were 140/142.5's), and I set the needle with the small white spacer (the one sent by 6 Sigma) above the clip. This is about 1/2+ the thickness of the stock spacer. Mixture screw out 2.5 turns.
The result:.. starts a bit more reluctantly (more 'cold natured'), sounds good on the stand & rev's willingly, but then no power at all in any range; it barely pulls out up the street. No throttle response, or even loss of power when rolling on the throttle. @1/4 throttle to Mid range runs somewhat better (limped home) with the choke pulled. So, too lean across the board, seems to me. The plugs are dark and sooty, but then I had to use the choke to limp back home.
I'm getting to be pretty good at pulling the carbs and tearing them down. But, the fun is wearing a bit thin. I'm in for the long haul, but thought I'd post this and see what's said before I see about getting more jets. Thinking of going up one size on the pilots (45), and maybe up some on the mains.
I'm once again going to have to wait several days before attending to any of this.
Thoughts and recommendations appreciated.
Doug

First off, welcome to carb tuning. It is slow and tedious, which is why so many people never get pods running correctly. They get impatient and lazy and try to change everything at once hoping for a magic answer and it just doesn't work that way. Go slow and methodical and keep notes on EVERYTHING you change and you will get it sorted in the end.

1) Go to 3.0 turns on the mixture screws and test ride again at small throttle openings. Don't bother farting around with the needle or mains until you have it running properly on the pilots.

2) Are these needles grooved? What groove is the clip in? I would start with it in the middle position if there are choices. It sounds like you have the needles lower than stock at the moment, is that correct?


Mark

[upb4dawn]

Thanks. I'm good with the slow and patient approach, I just can only work on the bike about one day a week for a while. So, progress is slow.
Yes, I keep notes, it's imperative.

These needles are not grooved. Stock, there's a tan/brown plastic washer above the clip, and a washer and spring below the clip. The white spacer is about 1/2 the thickness of the stock spacer; it's now in the spot formerly held by the stock spacer, effectively raising the needle.
FYI- It ran pretty damned good with the (seemingly way too large) 47.5 pilots sent in the kit, (and the big mains, and the needle as high as it would go- no spacer) up to 5000 rpm, then nothing.

[boris.h]

Hi!
I'm exactly in the same case with you:
GS 650 (673cc) on a gs 550 base
velocity stacks
bandit 600 header (33mm inside diameter tubes) and a danmoto exhaust (no restriction)

I started with mikuni #112.5 mains --> no power anywhere
- then I tried #130 mains yesterday --> much better but still lot of hesitation anywhere (idle ok 1000 rpm)
- then I will try tonight #142.5 mains, drilling my actual jets to 1.65mm (corresponding to mikuni #142.5), I think I'll be close to a good result to start trying the bike on the road and doing some plug chops to make a better tunning...

2) I trust in the fact that the #2 and #3 rd cylinders are hotter that the two other because they are in the center oif the engine... So they have to be a little (one size) richer than the two on the sides to help colding..
3) You can note that, for my personnal configuration, the mixture screws are setted between 3 turns and 3.75 turns to get a nice brown color on the spark plugs, with a %42.5 idle jet.

I'll keep you informed in using %142.5 mains in my case.

[upb4dawn]

Interesting. My engine is basically stock except for K & N dual pods, and stock exhaust that's been drilled out (I'm told this does nothing/little in the breathing department).
The jet kit I purchased came with 3 pairs of mains. 140, 142.5, & 145. Thus, you can do two different sets that have a one size larger pair in the middle, for the heat reason you mentioned. It also came with 47.5 pilots. The jet sizes seem much too large when compared to the sizing recommendations for this minor amount of modification.
With this set up it ran pretty well up to 5K or so, then waaaaaah...... nothing. I tried putting things back as stock as possible, w/ 120 mains and the needle raised a bit, and it won't pull the hat off my head from any rpm. So, I have two extremes to work from.
I'll be anxious to hear your progress.

[boris.h]

Yep, the behaviour that you expained is a bit strange. Because it would not push above 5000 rpm because it would be too rich for you. It would be better for you to be between 120 and 130 for me. But, I have to go forward to give you a real feedback.. I have to finish the exhaust and the intake velocity stacks (tonight) and go to 142.5 to ride it....

[upb4dawn]

So, it would seem I'm getting there, slowly but surely.
Right now, the pilots are up one size, to 45. The needle is raised about 1/2 the thickness of the stock spacer above the clip. 125 main jets. Starts and idles fine. Low speed response is just fine, very smooth and pretty strong for 1/4 throttle. The zoom starts to taper off fast around 4000 and really falls away above that. Likes a lot of choke to get past that part. So the first 1/8 & 1/4 throttle are seemingly good. More throttle is starts to fade away, and is pretty much nothing w/o choke, which it likes. Plugs are dark, but not sooty.
Next step would seem to me to raise the needle some more...

Any thoughts out there?
Thanks for any suggestions.