'82 GS 650 glz - Carburation issue (probly)

[upb4dawn]

OK, this is my first post, your patience is requested. I've read the Newbie Mistakes etc.
Just brought a fairly low mileage bike back from the near dead. I will describe the behavior, and then I'll list what's been done:
The bike starts quickly, idles, and runs smoothly and fine at low and medium speeds, has good low end pull. At 4500-5000 rpm it starts to flatten out, and it won't rev much past 6K. When idling, it smells rich to me, and doesn't require much choke to start (summer temps tho). The plugs are on the sooty side.
Fuel tank's been cleaned. A new petcock. Valves have been adjusted. New plugs, rectifier. It's got new intake tubes and o-rings, cleaned carbs and new o-rings, 6-Sigma jet kit as prescribed for the K&N dual pod air filters, and drilled exhaust. Floats have been adjusted, but I'm not terribly confident here about my accuracy and will check them when I pull the carbs again. Needles have been raised somewhat by changing the little washers.

Is it likely that it's fuel starvation at higher speed due to improper float settings? Maybe a combination of too rich jets and too low float level?

I'm thinking it's a carburation problem, but would also wonder about the coils, in my experience weak coils can peter out at the higher revs.

Any guidance on what to check next? What is the spec resistance for the coils?
Thank you in advance.

 

[Guest]

The bike starts quickly, idles, and runs smoothly and fine at low and medium speeds, has good low end pull. At 4500-5000 rpm it starts to flatten out, and it won't rev much past 6K.

Without knowing what throttle opening you are running it is impossible to know what circuit your carbs are using. Pilot covers idle to 1/8 or so, then the needle controls 1/8 to ~3/8, then main jets above that. There is overlap between these, but that is the basic setup. To test the various circuits put a piece of tape on your throttle housing and mark 0 to full throttle in increments of 1/8 throttle. Then go for a ride and see where it is giving you trouble. When you get into the area that is giving trouble try pulling the choke/enrichener knob. If it runs better and pulls harder then you are lean, if it bogs just a bit you are pretty close and if it bogs badly then you are rich.


Mark

 

[Steve]

When you adjusted the needles "by changing the little washers", exactly what did you do?

On the needle, from top to bottom:
Thick nylon spacer
Circlip
Thin metal washer
Spring

What did you change, what did you adjust, please list for each item.

.

 

[upb4dawn]

Without knowing what throttle opening you are running it is impossible to know what circuit your carbs are using. Pilot covers idle to 1/8 or so, then the needle controls 1/8 to ~3/8, then main jets above that. There is overlap between these, but that is the basic setup. To test the various circuits put a piece of tape on your throttle housing and mark 0 to full throttle in increments of 1/8 throttle. Then go for a ride and see where it is giving you trouble. When you get into the area that is giving trouble try pulling the choke/enrichener knob. If it runs better and pulls harder then you are lean, if it bogs just a bit you are pretty close and if it bogs badly then you are rich.


Mark

I'll mark as you suggested and make note, but I can't get it past 5500-6 no matter what the throttle opening is. At about 1/2+ throttle, nothing. The only thing that changes is the intake sound.....

Thanks,
Doug

 

[upb4dawn]

When you adjusted the needles "by changing the little washers", exactly what did you do?

On the needle, from top to bottom:
Thick nylon spacer
Circlip
Thin metal washer
Spring

What did you change, what did you adjust, please list for each item.

.

Thanks.
The stock layout is the one you described.
With the Jet Kit, the instructions were to put the spacers below the clip. So, in my case now it's: clip, small white nylon spacer that came w/ the clip, a thin washer, and then the spring. The intention is to raise the needle.
Thoughts?
Doug

 

[loud et]

Sounds like something that just happened to me. I installed a dynojet stage 3 kit and I was constantly rich. Turns out I over oiled my pods.
Do you think you possibly did that t?
Quick test: remove the pods and see if you get full throttle response all the way to redline.
Here is my story from this week:

http://www.thegsresources.com/_foru...17-Help-tuning-Stage-3-Dynojet-on-BS-32-carbs

 

[upb4dawn]

Thanks.

I didn't oil the pods at all. I've read both "oil them" and "don't oil them". I figured it would always be easier to ad oil than wash it out.

Doug

 

[Steve]

With the Jet Kit, the instructions were to put the spacers below the clip. So, in my case now it's: clip, small white nylon spacer that came w/ the clip, a thin washer, and then the spring. The intention is to raise the needle.
Thoughts?
Doug

Anything added below the clip only increases the spring pressure. What really matters is the difference in what is ABOVE the clip.

With nothing above the clip, you have raised it the maximum possible. I don't see that preventing operation above 5k, but it will make it run a bit rich above 1/2 throttle.

.

 

[upb4dawn]

Thanks. The nylon spacer that came with the kit (white) is slightly thinner than the stock spacer (brownish). So, perhaps I'll try moving them above the clip, thus raising the needle only a small amount. I'll go down one size on the main jets (now 142.5 center two and 145 outer two carbs...will go to 140 center and 142.5 outer), and re-check the float level, too.

Doug

 

[dantodd]

Thanks. The nylon spacer that came with the kit (white) is slightly thinner than the stock spacer (brownish). So, perhaps I'll try moving them above the clip, thus raising the needle only a small amount. I'll go down one size on the main jets (now 142.5 center two and 145 outer two carbs...will go to 140 center and 142.5 outer), and re-check the float level, too.

Doug

Is it running rich at WOT and the middle? Unless you have a lot of experience I'd make ONE change at a time. You'd hate to over lean and not know which adjustment did it.

 

[Steve]

Thanks. The nylon spacer that came with the kit (white) is slightly thinner than the stock spacer (brownish). So, perhaps I'll try moving them above the clip, thus raising the needle only a small amount. I'll go down one size on the main jets (now 142.5 center two and 145 outer two carbs...will go to 140 center and 142.5 outer), and re-check the float level, too.

Doug

OK, now I have a BUNCH of new questions. :-k

The stock '82 650 uses 110 main jets. With K&N filters, I might expect 117.5 or 120. Your "drilled" exhaust probably did nothing to enhance any airflow, so no jetting change required, unless you drilled out the entire baffle. The Mikuni 120 is the same as a Dynojet 128 or a Kehin 138. I have no idea what numbering system 6 Sigma uses, so I don't know if your 142.5 and 145 are simply "too large" or "WAY too large". Plug checks will have to be done. (Have you done any yet?)

Another thing: why are you using two different-sized main jets? The only bikes that came that way stock were the '83 and up 550 and the 1150.

Before you make any changes, try reading the plugs to see what is really happening when you have the problem. Find a stretch of road where you can run the bike to its problem point of 6000 RPM. Hold the throttle there for at least half a minute, if you can. Pull the clutch, hit the kill switch, coast to a safe spot where you can pull the plugs to check their color. Let us know what you find.

One last question about your "drilled" exhaust. Did you drill the small holes around the perimeter of the main hole? Or something a bit more drastic? The L exhaust sounds funny enough. Drilling the holes around the main hole just add some crappy noise, not really pleasant at all. And they don't do much to enhance airflow, which is where any performance gains are realized.

.

 

[upb4dawn]

OK, more questions are good.
When I ordered the jet kit, they (6-Sigma) ask questions regarding intake and exhaust mods, and most common riding elevation (in my case: sea level to 1500').
The jets provided by them are supposedly matched to the modifications and riding locale. In my case K & N dual pods (two carbs per filter) and drilled mufflers (center and small holes around -- came that way, not my favorite choice, but ... my budget doesn't support $350 for 4/1 and I'm hesitant to cut the system mufflers off for clamp on's).
They sent 4 new pilot jets (all the same @ 47.5), and 6 main jets in 3 pair, recommending the richer one go in the center pair of cylinders (I wrote the combo wrong on a previous post), giving you two choices. IE: 140/142.5, and 142.5/145. The jump up in sizes did seem big to me from 110 (stock). They also sent nylon spacers, several sets of thin washers (aka needle shims), and some reasonably good (seemingly so) instructions. I've read on-line other folk's satisfaction w/ this vendor's products ("it has to be true, I read it on the internet..").

FYI- I've had 7 bikes, and I've worked on them all. The last two are fuel injected, and I made changes with them as well, all successfully ('99 BMW and '97 Moto Guzzi). This bike is for my daughter, who picked it up cheap, and wanted a cafe racer style bike on a budget. This one's a great bike, just the right size for this project, and so far has been a pleasure to work on. This last part's a mite frustrating, I must say.

 

[Guest]

Is it running rich at WOT and the middle? Unless you have a lot of experience is make ONE change at a time. You'd hate to over lean and not know which adjustment did it.

Even having a lot of experience it is far, far easier to sort carburation when you make one change at a time. Most of the people on this site who complain about how it is impossible to get a bike to run well with pods try to make wholesale changes and never manage to sort it out. Jetting isn't that hard, it is just tedious and slow. You have to start at one end (I recommend the pilot circuit) and work your way through to the other end one change at a time, keeping lots of notes and details along the way.


Mark

 

[upb4dawn]

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?

 

[Steve]

Personally, I would make a few changes, mostly getting back toward stock.

First, get some "steel putty", plug up the perimeter holes. The only thing they are doing is adding to an already questionable sound. When the putty sets, you can paint the patches black, they will be rather inconspicuous.

Second, put the stock pilot jets in. Jetting needs are based on air flow. Even the most radical race-prepped bike will not flow much more air AT IDLE, so there is no need to increase the pilot jets, and certainly not two sizes.

Third, examine the thickness of the nylon spacer they provided for the needle. If it is a bit thinner than the stock one, great. Put it ABOVE the clip. The usual practice is to substitute a stack of washers for the stock nylon spacer, shooting for about 1/2 to 2/3 the original thickness. If you have enough washers that they supplied, you can explore that option, too.

Fourth, since we don't know how 6 Sigma sizes their jets, go with the smallest jets you have available that are larger than stock. Something around 120 would be good, if you have them.

Finally, what are the settings on your mixture screws? Their main affect is on the pilot circuit, but they do contribute to the overall mixture all the time. Because you are using pilot jets that are two sizes larger than stock, if your mixture screws are also turned out a bit farther than stock, you might simply be adding more fuel when it's not needed, espcially since your needles are too high and your main jets are too large.

By the way, have you had a chance to check plug color yet?

.

 

[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).

 

[Guest]

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.

 

[Guest]

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