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80 gs1000 air screw setting (straight pipes, pods)

  • Thread starter Thread starter jmlcolorado
  • Start date Start date
J

jmlcolorado

Guest
Okay guys, i am in the middle of the complete rebuild on my carbs that have siting dry for ten years. Im following the instructions based off bikecliffs site. Everything has been going much better then expected.

One question, im new to the carb world and now that ive ripped mine all apart, where do i set the air screw when i reinstall? Im running normal 4-2 headers with the megaphones cut off and replaces with 1 1/2" pipe on each side and running Pods.

Ive heard everywhere from 7/8 turn out from lightly seated to 2 1/2 turns (on a stock airbox with stock pipes)

I cant seem to find any starting point for aftermarket mods.

Any help would be great!!! Thanks again. I wouldnt know where i was without the people on this forum!
 
OK, sounds like you have been reading too many posts. :eek:

The suggestions for 7/8 turn are for the pilot fuel screws on the VM series carbs found on '79 and older bikes. Your '80 bike has the BS series carbs that do not have separate fuel and air screws. The pilot mixture is preset by the pilot fuel and pilot air jets. Then, the amount of that mixture can be adjusted by the idle mixture adjustment screw that is found on the top of the carb outlet. With your opened-up pipes and pods, you might want to start with three full turns out from lightly seated.

What main jets are you using? With your pods and pipe, you will need main jets that are probably 4-6 sizes larger than stock. I don't know offhand what your stock sizes are, but you can look that up in the carb 'sticky' which is the first post in this forum. One size is an increase of 2.5 in the jet number. For example, if stock is 115, the next size up is 117.5, then 120, etc., so four sizes up would be 125. Please, this is just an example, I don't know what size jets you should have in there, stock, so I don't know what number to suggest, only that it needs to be 4-6 sizes larger than stock.

One other change that will likely be necessary is to adjust the height of the jet needle. Since there are no adjustable positions on the needle (thanks to the EPA), you will have to remove the nylon spacer on the top of the needle, then find and install some washers that have a total thickness that is less than the nylon spacer. That allows the needle to sit higher in the jet, richening the mixture.

.
 
Excelent information steve! THANK YOU! Ive never worken on carbs before...... EVER, so this is kind of intimidating. Ive never even had the gawls to look inside on as they looked to complicated for my impatient hands to touch!!

Ive done a full strip and dip so far. I had to drill out the a "air screws" on two carbs :( Broke a hardened screw extracter on one and had to dremel out the body to get to the next. :( not the best first experiance!!

But i think its going wel now. I was thinking i was going tho have to get a new #4 carb body cause this last air screw wasnt cooperating at all!

But last last night i got it!

So youve gotten me off a lillte more comfortably for the next step. I do on the other hand have a Pilot jet that has no groove to remove in one carb. Gonna have to extract that one to i guess.

Ill look for some jets to help compensate for the new pipes. Does a "jet kit" come with an array of jets to choose or is it only specific to one change in size for each carb?

I gotta admit, im pretty nervous to trial and error these things. Sounds like unless you know what your looking for, it can be quite a project.

I plan on impllementing as many tests as i can to help me along the way including Highest idle, spark chop and anything else to aid me in tuning these things up.

I honestly have a feeling i might get overwhelmed and send it of to a shop to have it done for me, which is against my rules thus far cause i want as much experiance in this bike and i can have.

Thanks again for your advice steve. :) Have a great one.
 
Well, one last piece of advice ...

Learn to do it all yourself. :eek:

Most bike shops, especially the dealers, will not even look at, let alone work on, a bike that is over 10 years old. They claim that there are too many problems with rusted bolts that break too easily, therefore taking too much time over the book rate to make it worth the effort. When they start charging actual time, the bike owner comes back to a $1000 bill for a tune up because they had to drill out and tap a bunch of bolts. The owner freaks out, says "just keep the bike, I'm not paying that much for the repair" and walks out. You might get lucky and find a small independant shop that will work on the bike if it looks like it's in good condition. Most of those guys have cheaper hourly rates, too.

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You can use an Easy Out on the pilot jet. Make sure you heat it a bit with a torch before unscrewing and it should come right out. I've learned that heat is your friend with these old aluminum carb bodies.
 
So stock main is 115 and pilot is 40.

So with my setup, all ill need to do is raise the main a few (ill start with 125) ??

Where do i go with the pilot?
 
jmlcolorado said:
Where do i go with the pilot?
Click to expand...
I would suggest going all the way to a 40. :D

If you find that you have to turn the mixture screws out more than 3 1/2 turns to get it to run right, go for a 42.5 and back the mixture screws down to 1 1/2 to 2 turns.

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Okay so the more we talk about this, the easier it seems.

Sounds like the main gets changed, keep the pilot unless i really need to change it, and adjust the mixture screw is really all it takes to tune these up.

Thats a weight off my shoulders.

Thanks steve, you've been a great help!
 
Well, there's other stuff you haven't asked about, too. :rolleyes:

You will want to shim the needle. The process has been elaborated many times on the board, so I will let you search for it. :o

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Okay so ive got myself some 125 and 127.5 main jets. (4 and 5 sizes up from stock ) Got new "air screws" installed today and tossed the carbs on the bike. I bench sync ed em before too.

Ive got the mixture screw set to three out from lightly seated. The bike will only fire on whatever cylinder i block the inlet side of the carb off on with my hand for a second. Runs for a sec then dies.

It'll fire with full choke but only run for a few seconds on full choke. Actually runs better when i block off the intake about 90%

I tried setting air screws at 1 turn, then 2 turns now at three and a half and im not noticing a change. BTW i have 125 mains installed. Will the mains even matter to get the bike started?

I still need to shim the needle but im hesitant on this because i dont know how much i need to go.

Im just surprised i got the thing to fire up!!
 
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Im thinking about getting a colortune but doesnt make much since if i cant get it to idle on its own
 
You need to get bigger idle jets as well, and probable raise the needles a few notches. My guess is that once you get the correct size idle jets, you won't nees as big of main jets.

I built a heated O2 sensor that would stick on the back of the muffler for tuning. It's very approximate, but will show you it the bike's lean/rich at various riding conditions. Enden up costing about $50 for the camaro sensor
 
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