Summary - Carburetor Tuning

[Tino]

Hello all.
I have been reading about carburetor tuning for few good days now and I get more and more confused by the minute. Everyone uses an almost different name for all the screws/jets that are used in the carburetor.
To clarify my confusion I will be showing you some pictures with what I see to be the air screw, pilot jet, main jet ... etc.

Here is an image of the Air Screw

Another image of the Air Screw

Image of the Air Jet

Image of the Pilot Jet and Main Jet

From all the reading I have done, what I understand is that the Main Jet and Pilot Jet, when put back, after a carburetor clean-up, will be screwed in such that they will be seated all the way in, hand tight.

Now for the Air Screw and Air Jet, which one of them will have to be turned out (counter clockwise) 2.5-3.5 turns from seated?
Also in which order will these 2 have to be adjusted for a carburetor tuneup? Once the carburetor is connected back it will be very hard to re-adjust the Air Jet.
Will someone be willing to write a tuneup sequence, using the screw/jet naming I used above? It will be greatly appreciated.

Thanks.

 

[Skyboy8950]

The air screw is the one that is adjusted. You can't get to anything else when the bike is all together. Everything else but the air screw is simply screwed in all the way and seated.

 

[BassCliff]

Hi Mr. Tino,

From the Carb Cleanup Series page:

Note #2: Bill Kingston has brought it to our attention that the references to a Pilot Air Screw may be incorrect. He states that on these carbs use a Fuel Flow Screw instead. This means that you are controlling fuel running through the passages with this adjustment, not air. So when turning the screw counterclockwise you are increasing fuel flow and when you turn it clockwise you decrease fuel flow.

A more accurate term, I think, is mixture screw. The screw (noted in the first two pictures) is usually set, initially, for approx. 2.5 turns out from lightly seated, depending on the bike. You may have to remove the caps covering these screws.

Thank you for your indulgence,

BassCliff

 

[hampshirehog]

You screw in the airjet until tight(ish) - you don't adjust it by turning it in other words. You tune in with the airscrew by screwing it in and out.

 

[SqDancerLynn1]

Turn the air screw in until LIGHTLY seated turn out 2.5 turns gets you in the ballpark
Air jet -- hand tight
Main jet --- hand tight
Pilot jet plug -- held in by float bowl

 

[jetta90]

Tino - if you have CV carbs, which by the pictures you appear to have, then what you are referring to as the " air screw " is really your mixture screw. It controls your fuel and air mixture at idle.
I've been piddling around with mine for quite some time trying to get them set as well.
I am still trying different adjustments but I have found, at least for my bike, 2 to 3 turns out is way too rich. I have the screws turned out 1/2 turn now and plan on a good test run tomorrow. Be aware that the pilot jet size will have an effect on how many turns out you need to be.
Going by your pics and you lables you will need to adjust the "air screw" out on your 4 carbs.

 

[Tino]

Guys.
thank you very much. Now I can start the carburetor rebuild process.

 

[Skyboy8950]

I'm glad we all said the same thing!

 

[650BrownDeer]

Keep screws set

Keep screws set

So, If the screws are set at an amount out from seated, how does one keep them there. I asked a parts guys at my local 'used bike parts' shop about loc-tite and he said nothing in a carb should get loc-tite.

I just had the experience of finding my main jets had fallen off - and I had screwed them in what I thought was tight.. its hard for a bike to run that way. They were just sitting in the bowls...mocking me...

 

[Guest]

people call em wrong names all the time

people call em wrong names all the time

as mr basscliff pointed out the only adjustable screw at the front of the
cv carbs is a "pilot mixture screw", it is NOT an air screw

the pilot air jet is at the back of the carbs and draws air from there (at idle)
the pilot fuel jet takes care of the fuel (at idle)

the "pilot mixture screw" controls the quantity of the air/fuel mixture

 

[Guest]

So, If the screws are set at an amount out from seated, how does one keep them there. I asked a parts guys at my local 'used bike parts' shop about loc-tite and he said nothing in a carb should get loc-tite.

I just had the experience of finding my main jets had fallen off - and I had screwed them in what I thought was tight.. its hard for a bike to run that way. They were just sitting in the bowls...mocking me...

only hand tight for all jets
the pilot mixture screw has a spring on it that keeps it in place
if hand-tight doesnt keep your jets in place i'd suspect worn or cross-threaded threads in the carb body or on the jets

 

[jetta90]

I just reread all of the above comments and I just wanted to add some claryfication to "hand tight"................... when folks are referring to hand tight they mean snugged well down with a flat screw driver................."hand tight" does not mean "finger tight".
There needs to be a flat head screw driver and a bit of muscle involved, just don't ask King Kong to do it. Be sensible about it and the'll hold.
Again, only for the jets found inside the carbs.
The fuel/air mixture control screws found on the top front portion of CV carbs are adjusted in and out as needed, and are tensioned in place by a spring.

 

[KnightRider]

Ok Here goes, 1982 GS650L, weak fire , found its the coils,electronic ignition not points, air fuel mixture 1/2 out , still didnt work . Checked Air filter and only had the foam. took a car air filter , the flat one , cut the rubber off and then folded out till i got it around the plastic holder,folded in on the induction in , and out on the cover end,strap tank to body with seat off , adjust the screws at 3and a half to 5 rpm.
Because of my coils,I havent the mony for yet , It doesnt Idle very smooth but I got em firing smooth under load full Range. <<Said This to let YOU Know that Air Fuel Mix is SOOOO Important With The GS Series It Isnt Funny . With New coils Ill Set at 1 hal turn out and get a Stock Filter and it will run like New. Also Is YOU Have Changed or modified the exhaust , then YOU will have to rejet out, Its all about Flow. Hope This Helps to see How The Air , Fuel ,Fire ,all can be at diff adjust on diff bikes or Same bike By the Exhaust, Settings , and Fire>Hot plugs -cold plugs < !
Its Been a Hum dinger figgurin out mine lol
Your friend KnightRider

 

[lurch12_2000]

I just reread all of the above comments and I just wanted to add some claryfication to "hand tight"................... when folks are referring to hand tight they mean snugged well down with a flat screw driver................."hand tight" does not mean "finger tight".
There needs to be a flat head screw driver and a bit of muscle involved, just don't ask King Kong to do it. Be sensible about it and the'll hold.
Again, only for the jets found inside the carbs.
The fuel/air mixture control screws found on the top front portion of CV carbs are adjusted in and out as needed, and are tensioned in place by a spring.

Hand tight to me means using no tools, so I would define what you want to do with the pilot mixture screw since you can't get get your hand down there because it's recessed, is using the proper sized flat head only use one finger and your thumb to turn in until you feel it seat and then count your counter-clockwise turns out (2 for my bike) for richening and hopefully running better. So you have a starting point if you screw up, count how many turns clockwise to seat first and write that down. It may be different for each carb depending on what the previous owner might have done or still at their setting from the factory if the plug covers were still on.

 

[gaillarry]

Note #2: Bill Kingston has brought it to our attention that the references to a Pilot Air Screw may be incorrect. He states that on these carbs use a Fuel Flow Screw instead. This means that you are controlling fuel running through the passages with this adjustment, not air. So when turning the screw counterclockwise you are increasing fuel flow and when you turn it clockwise you decrease fuel flow.

From this I presume if the spark plugs are burning rich you would decrease (CW) the mixture screw?

 

[jetta90]

lurch12_2000...............what you want to do for your "fuel air mixture" (this screw is found on the front and top portion of each CV carb) is screw it in gently until it seats. Then you back it out however many turns you need to, so your bike idles. Some people back it out as much as 3 turns others much less.

The jets you need to tighten down firmly, without inviting King Kong, are found inside the carburator..............for example, the main jet and pilot jet. You don't want to find your main jets sitting at the bottom of your float bowls like 650BrownDeer just talked about.

 

[jetta90]

gaillarry, yes you would screw each little screw in equal amounts to decrease the amount of fuel and air mixture on the CV carburator. Go maybe half turn at a time on all 4 carbs and go from there. As you get closer to where you need to be you may have to turn each screw in 1/4 turn or maybe even less.