Carb mechanic wanted

[hjfisk]

Thats what is known as a bench sync..i know how to do that as well. Thanks. I dont get the feeling the ends are broke oof any screws but hey maybe it wouldnt hurt to check. or if anything got sucked in there too..just a thought.

My thoughts are that you said in a earlier post that you had turned the screw in and out and got no change , that either there is blockage in the screw jets or the tips are broken and causing blockage, also those only control the idle speed to a certain amount about 2000 I believe

[chuck hahn]

I justooked at Bikecliffs 8 valve 750 service amnual and i reread it a few times and didnt see the clip setting listed, but i did howver read about bending the tabs to set the float height. The thing i havent ever heard anyone mention is this little tid bit..Start the engine and check the float heights with the engine running.. shows a guage that has lines on it to properly read the float theights while the engine is running..

[tatu]

And to Tatu..since others have posted and cleared up my confusion about JETTTINGS and SETTINGS and explained the range of thottle that the pi,ot effect i offer my apology..

It's ok, don't worry about it. If I might offer up a bit of experience about plugs, I have known even brand new ngk plugs to fail and not work again when engines have been flooded, so I would not use fluid to clean them just a gentle wire brush or leave them.

[waterman]

Chuck, after a little checking in the carb spec sticky above, it seems there may be a little controversy over the stock carb settings for your 77B. Maybe someone can shed some light on this. I think TCK has a 750B. I hope this doesn't add to your confusion.

BTW, according to both references the needle should be clipped in the third position.

Im finding all this sooo strange because the Suzuki service manual that originally came with my GS750B 1977 say, and the actual settings on the bike were:

VM26SS
Main Jet: 105
Air Jet: 1.1
Needle Jet: P-1
Jet Needle: 5F21-3
Pilot Jet:22.5
Pilot air jet: 1.6
Cutaway: 2.5
air screw: 1-1/4 turns back


but with that information and my engine number (which my dealer verified is original to my bike frame) it would be

VM26SS
Main Jet: 100
Air Jet: .7
Needle Jet: O-6
Jet Needle: 5F21-3
Pilot Jet:15
Pilot air jet: 1.6
Cutaway: 1.6
air screw: 1 turn back

My Clymer manual doesnt give any details at all, I guess they decided not to because of so many variables.....

So what should I believe???

http://motorbikearchives.com/Bike-Te...50EN-1979.html

Just found this which had the following excerpt:

The GS750B came with a # 100 main jet, 0-6 needle, 5F21-3 jet needle, and # 15 pilot jet. The GS750C (1978) and GS750N (1979) carburetors were changed to a #102.5 main jet, 0-4 needle, 5DL36-2 jet needle and #15 pilot jet.

What that all means is that the GS750N is leaner at the small throttle openings usually encountered in EPA emissions test modes. The dual-taper 5DL36-2 jet needle is initially leaner, secondarily richer to smooth the transition from idle to off idle, (or from small, steady-state carb openings at low speeds to gentle acceleration, as encountered in traffic). The float level was also lowered between the GS750B and GS750N, from 26mm to 24mm.

[chuck hahn]

The whole process i was gonna use was to scrub them with some kind of solvent to get the soot and coolrs off the center ceramic. Then use my compressor to really be sure they are dry and anything in the bottoms gets flushed out.. I have several little toothbrushes and even some brass and stainless steel toothbrushes..

[chuck hahn]

I had seen that chart in the stickys..and even at these specs mine arent at either one!! dont figure why this thing falls on its face. The ones that are in RIGHT NOW are 110 mains and 17.5 pilots.The only thing thats the same is the needle jet..

[chuck hahn]

After much misreading and misunderstanding terms and functions i think i am finaly getting a grip on this.. Its just so awefully frustrting though!!!!

[rustybronco]

Example....

Jet Needle: 5F21-3

what this means in the above referenced carb, the carb uses a needle identified by the number 5f21 stamped on it. the -3 after the 5F21, means the clip goes on the third notch down from the top. if it had been a -2 on it, you guessed it... second clip position down from the top.

[chuck hahn]

OK>>that i didnt know either..the needel jet is telling you where it likes to be..Now these are the kinda things i need to know! Thats cool! I like the way you explain things Dale.

[Octain]

New plugs should be used... Or at least I would use new ones.

And, ahh.. Rebuild the carbs.
(sorry, had to say it)

[chuck hahn]

No parts today. Maybe tomorrow. You all get a break from me today..thats a jab at myself threre!! I do feel m och more confident that I can get these things back on track very shortly though.

[Spyderman]

hi chuck how about some info for you on the carbs and how they work
the three circuits of the carbs

1 the pilot circuit from 0 to 1/4 throttle
stock pilot jet size 15
this is controlled by the pilot jet the fuel mixture screw on the bottom of the carb and the air mixture screw on the side of the carb
settings for the 77 750 i had
5/8 to 7/8 of a turn (fuel screws) bottom of the carb
1 1/2 to 1 3/4 for the (air screws) side of the carb

the needle and needle jet circuit from 1/4 to 3/4 throttle
this is controlled by the movement of the needle up and down in the needle jet the fuel is metered by the taper of the needle
the clip position and the size of the needle jet
5F21-3 is the stock needle with a position of 3rd from the top for the clip
O-6 this is the stock needle jet O-6 is the size for diameter
( the jet needle is the tube that unscrews from the carb with a 8mm wrench and the main jet screws into to it on one end)
this circuit can be affected by the size of the main jet if the main jet is too big then it will be rich on this circuit as well
if it is too small then this circuit will be lean as well
and the clip position will affect how fast or slow the fuel flows into the carb on this circuit (closer to the taper of the needle will richen the mixture closer to the top of the needle will lean the mixture)

the main jet circuit from 3/4 to wide open throttle
stock main jet size is 100
this circuit is controlled my the main jet only so size is important to get correct

now in order to know what to change you need to know how to read your plugs
the end of the plug will tell you what your pilot circuit is doing
looking down the center electrode from the top down to the bottom of the plug
from the top to about 1/2 way down will tell you what your needle circuit is doing
from 1/2 down to the bottom will tell you what your main jet is doing

you want the plugs to be a nice tan color all the way down the center electrode when the jetting is right

when you rejet your carbs you start with the main jet then once this is right you move onto the needle and once you have that right you do the pilot
plug chops
you need to go out and ride it pull a plug read it and make one change then ride it and read the plug again do this until you have it right
in order to get a good reading on each circuit you must ride it at the specified throttle setting for about 3/4 of a mile and then hit the kill switch then release the throttle then stop the bike and pull a plug and read it
i'm sure you are familiar with doing plug chops

i hope i have helped to to better understand your carbs

[chuck hahn]

I followed all that except the start on the main..then the needle and then the pilot..you mean doing the plug chops..right> So if i run it and pull a plug and the first section of the electrode like you said is tannish that means the MAIN JET is the proper jet . Then the second part will read what the NEEDLE JET is doing..right so its basically like looking at a layer cake as far as the plugs are concerned.

[chuck hahn]

What are you saying is the TOP of the plug..the end near the square the wrench grabs or am i looking at the top as in from the spot where the spark jumps across?

[Spyderman]

I followed all that except the start on the main..then the needle and then the pi,lot..you mean doing the plug chops..right> So if i run it and pull a plug and the first section of the lectrode like you said is tannish that means the MAIN JET is the proper jet . Then the second part will read what the NEEDLE JET is doing..right so its basically like looking at a leyer cake as far as the plugs are concerned.

ok so doing plug chops you start with the main jet and your looking at the bottom 1/2 of the center electrode if it is a nice tan color then your fine if it's white then your too lean and if it's black then your too rich
when the main jet is right (good tan color)
then move onto the needle circuit this is mostly done by moving the clip position once this is right then move on an do the pilot circuit

and yes it's like a layer cake the top is the pilot circuit
the middle is the needle circuit and the bottom is the main circuit