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carb update 1980 gs550

  • Thread starter Thread starter Outlander
  • Start date Start date
O

Outlander

Guest
After getting some much needed help here from you fine folk, and after doing some reading, also here, I tore down carbs 1 and 2 and was cleaning them.

Here is what I found. After pulling the aluminum plug out of the carbs to gain access to the idle mixture screws, I was confused. Carb 1 idle mixture screw was set by factory? 1 1/8 turn. Carb 2 was set at 1/8th turn? This is no where near what I have been reading here. So, my next question is this. Since my number 1 and 2 carbs were running rich, would turning out the screws lean them out?

I also found that the idle mixture jets were filthy. Both had to be extracted using an extractor, as they were so tight in their seats. Both have been replaced.

I also found that my pilot air jet is 155, and not the 150 that is factory specs. Could this be why the idle mixture screws were turned in so far?

Any ideas?
 
Is the bike stock to the best of your knowledge? If someone installed an exhaust/pods, it wouldn’t be surprising to find jetting modifications. Larger air jets are sometimes installed if larger pilots are also installed. Check everything closely to see what’s going on. Taking by itself, larger air jets will lean the mixture so it seems very strange to find the pilot screws so botched up. On stock bikes, 3 turns is a good starting point on the 550; my old 550T required 3.5 turns to achieve the highest idle speed and run best.

Good luck.
 
another update

another update

I drilled out the other caps on carbs 3 and 4. Both idle mixture screws were right around 2 turns. In the beginning, carbs 1 and 2 were running really rich. Carbs 3 and 4 were perfect.

After checking the rest of the jets, they all have the same numbers as specs, except the pilot air jet, which all 4 have 155 instead of 150. I am awaiting the o-rings and fasteners that I have ordered from here to rebuild my carbs, and then I will set all idle mixture screws at 2 turns and see where she is.

A couple other questions, on the petcock, it has pri res and full up and down position. What is pri, and what is it for? I always thought it was primary, but now I see it is "prime"? What does it do?

Last question, what is "po" mean? Other than police officer and ****ed off. I see it in reference to people buying parts.....
 
The difference could just be the air box... ON & reserve only flow fuel when vacuum is applied to the petcock. Prime, flows fuel all the time until the tank is empty. I would start with the screws out 1 to 1.5 turns. They were set very lean due to new EPA regulations
 
Last edited:
For CV carbs, more turns out means more fuel. As stated before, 3 turns out is a good starting point for a stock 550; I learned this from personal experience from fiddling with my '81 550T - at 2 turns the idle hunted just like a bike with leaking intake boot O-rings. Of course, this is with the fish brine they call gasoline here in So. Cal. It might be different in other places in the country.

Good luck.
 
Outlander said:
A couple other questions, on the petcock, it has pri res and full up and down position. What is pri, and what is it for? I always thought it was primary, but now I see it is "prime"? What does it do?

Last question, what is "po" mean? Other than police officer and ****ed off. I see it in reference to people buying parts.....
Click to expand...

PO = Previous owner, usually punctuated with an expletive or two.

PRI = Prime. Petcock will allow fuel to flow without any vacuum from the engine. Used to start a bike with empty carb bowls. If you run out of fuel, for example, this setting will fill the bowls after you refuel, so you don't have to run the starter excessively.
 
SqDancerLynn1 said:
The difference could just be the air box... ON & reserve only flow fuel when vacuum is applied to the petcock. Prime, flows fuel all the time until the tank is empty. I would start with the screws out 1 to 1.5 turns. They were set very lean due to new EPA regulations
Click to expand...

As Dancer said the RES and ON positions only operate when the motor is runninf and there is vacuum applied to the petcock from the inlet manifold tube. Prime is used when the carbs are empty (after rebuild or maintenance) so they can be filled up ready to start. Do not leave it on prime permanently, otherwise there is a good chance the carbs will flood and gas will get into your engine oil.
PO is previous owner and is a derogatory tem usually.
Cheers. Don
 
The '80 petcock is an oddball of sorts, no RES position. It's either ON or PRI (petcock with a slot).
 
XenoMorph said:
My 1980 GS550E Has On, PRI, and Res...
Click to expand...

Sorry, I stand corrected. Many 1980 model bikes (including the 550L) have the petcock with a slot, not a lever. You are the lucky one.:-D
 
nessism i have a question for you. i finally have everything ready to go back together on the 80 550L i live in IL do u think i should put the airscrews at 3 turns out?everything is stock on my bike as well but if i remember correctly it has a 79 550L exhaust on it and i don't know if that is a good thing or a bad thing.
 
Three turns out was the sweet spot of my 550T with BS/CV carbs. I think it's a good starting point, you can tweak from there as necessary.
 
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