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Another carb trouble thread...

  • Thread starter Thread starter Nightcrawler
  • Start date Start date
N

Nightcrawler

Guest
78 GS550 carbs fully cleaned and rebuilt using whole new kits. I am obviously trying to get these things tuned. I can get an ok idle however when I do anything in med-higher rpm it lags like it is very lean.

Build thread here:
http://www.thegsresources.com/_forum/showthread.php?t=191184


I have smaller air filters on it instead of the stock box, and a 4-1 exhaust system. I am guessing the stock main jets are to small? If so what size should I take them to #95?

I also have the vacuum line just plugged from carb #3 I installed a new universal petcock as the old stock one was pretty trashed.

I read the guides on basscliffs site, I have a dyna S electronic ignition and have the timing pretty much set on it as it states in its manual.

I am new to all this so any help would be most appreciated. Thanks for your time!

http://www.thegsresources.com/_forum/showthread.php?t=191184
 
With pods and 4-1, you will need to raise the needle a notch and go up a few sizes on the mains. Which pods are you using?
 
Actually, I meant which brand of pods. Generic pods like those listed are frequently a headache for jetting as their airflow is wonky. K&N pods are spendy, but much less of a nightmare (though jetting is still tricky).

In any event, stock jetting for your bike is 80 mains, and 15 pilots. With all that extra air, you will need to add fuel to the mix at every circuit. Get ready for a lot of trial and error. Jets are pretty cheap, so you should pick up a range of sizes for mains.

I'd start with adjusting the needle clip by 1 or 2 notches to put it in the 4th slot down. You might need to increase the pilot to a 17.5. I have gone back and forth on the pilot size between stock 15s and 17.5s, so YMMV.

For mains, you will need to bump up 2-3 steps in size. Maybe pick up 3 sets of mains in 97.5, 100 and 102.5 and try from there. Start with the 100s while you dial in the pilot and needle jetting. That will take a while to get right, and you won't be able to really check the main jetting with a WOT chop until the pilot circuit and the needle clip settings are right.

For the pilot setting, try the 17.5 with your mixture screws at the typical baseline (fuel 1 turn out and air 1.5-2 turns out). You might also try using the 15 pilot with richer screw settings (1.25 fuel and 1.5 air). No matter how you slice it, getting the pilot set properly is kind of a bitch.

Once you have a good pilot setting, then do a mid-range throttle chop to see how the needle is doing. If it leans out at 1/3-1/2 throttle, you might need to shim the needle a bit higher. If it bogs down, go the other way. Changing the needle setting is fun, as you get to rebuild and re-synch the carbs each time.

With the pilot and needle sorted, you can then do a WOT chop to see if the mains are good. No matter what, you will need to increase the main jet size, so don't postpone that change by using 80s in there for the other circuits. Lean at WOT is bad business.

With 100s in place, check the full throttle chop. Use those results to move up or down a size.

HTH
 
MisterCinders said:
Actually, I meant which brand of pods. Generic pods like those listed are frequently a headache for jetting as their airflow is wonky. K&N pods are spendy, but much less of a nightmare (though jetting is still tricky).

In any event, stock jetting for your bike is 80 mains, and 15 pilots. With all that extra air, you will need to add fuel to the mix at every circuit. Get ready for a lot of trial and error. Jets are pretty cheap, so you should pick up a range of sizes for mains.

I'd start with adjusting the needle clip by 1 or 2 notches to put it in the 4th slot down. You might need to increase the pilot to a 17.5. I have gone back and forth on the pilot size between stock 15s and 17.5s, so YMMV.

For mains, you will need to bump up 2-3 steps in size. Maybe pick up 3 sets of mains in 97.5, 100 and 102.5 and try from there. Start with the 100s while you dial in the pilot and needle jetting. That will take a while to get right, and you won't be able to really check the main jetting with a WOT chop until the pilot circuit and the needle clip settings are right.

For the pilot setting, try the 17.5 with your mixture screws at the typical baseline (fuel 1 turn out and air 1.5-2 turns out). You might also try using the 15 pilot with richer screw settings (1.25 fuel and 1.5 air). No matter how you slice it, getting the pilot set properly is kind of a bitch.

Once you have a good pilot setting, then do a mid-range throttle chop to see how the needle is doing. If it leans out at 1/3-1/2 throttle, you might need to shim the needle a bit higher. If it bogs down, go the other way. Changing the needle setting is fun, as you get to rebuild and re-synch the carbs each time.

With the pilot and needle sorted, you can then do a WOT chop to see if the mains are good. No matter what, you will need to increase the main jet size, so don't postpone that change by using 80s in there for the other circuits. Lean at WOT is bad business.

With 100s in place, check the full throttle chop. Use those results to move up or down a size.

HTH
Click to expand...

Great info man! This is exactly what I was looking for. I will get on this soon as possible. I have 95, 100, 102.5, 105 and 110 mains. Where is the best place to pick up a set of 17.5 needles? The more I take this carb apart the better I will get at it no? Thanks again, if this works out I owe you a drink or two for sure!
 
Steve said:
Certainly don't want to deprive you of any wrenching time, but if you still had the stock airbox and exhaust, you could be riding, instead of wrenching. :p

.
Click to expand...


I still have them, they just are trashed, air box has some holes, and exhaust is covered in rust and has some holes as well. The beat up look doesn't really fit into my bikes theme. Plus its raining and 52 Degrees here in Chicago, so I can wait another week.
 
Nightcrawler said:
I still have them, they just are trashed, air box has some holes, and exhaust is covered in rust and has some holes as well. The beat up look doesn't really fit into my bikes theme. Plus its raining and 52 Degrees here in Chicago, so I can wait another week.
Click to expand...

Where are you in Chicago? If you need help with synching those carbs, etc., I am in the city and have a carbtune.
 
Nightcrawler said:
Great info man! This is exactly what I was looking for. I will get on this soon as possible. I have 95, 100, 102.5, 105 and 110 mains. Where is the best place to pick up a set of 17.5 needles? The more I take this carb apart the better I will get at it no? Thanks again, if this works out I owe you a drink or two for sure!
Click to expand...

You can get new pilots from Z1. If they don't turn up on the web site, just call them. A lot of times the jet selection doesn't appear on the site for some reason.
 
MisterCinders said:
Where are you in Chicago? If you need help with synching those carbs, etc., I am in the city and have a carbtune.
Click to expand...

I am in Oak Lawn but for sure if you got some free time in the upcoming weeks I sure could use someone with solid knowledge of these GS's giving the once over to this bike. I pretty much have done everything myself and never worked on a bike before. With the carbs the way they are now shes not even drive-able, soon as I get the new mains in there and tune a bit she probably will be so I could head downtown with her then. I will pick up those 17.5's and probably the K&N RC-2314's asap.
 
Nightcrawler said:
I am in Oak Lawn but for sure if you got some free time in the upcoming weeks I sure could use someone with solid knowledge of these GS's giving the once over to this bike. I pretty much have done everything myself and never worked on a bike before. With the carbs the way they are now shes not even drive-able, soon as I get the new mains in there and tune a bit she probably will be so I could head downtown with her then. I will pick up those 17.5's and probably the K&N RC-2314's asap.
Click to expand...

Cool. If you get the jetting in shape, you can bench synch the carbs and bring her into town for a vacuum synch.
 
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