carburetor woes -- GT550

Coyote · Post by **Coyote** » Sat Mar 07, 2009 12:34 pm

Let me start out by saying this is my GT550 cafe bike 'RedZone'. The bike starts instantly, idles very well and accelerates like a rocket. I am running pods and chambers.
Even thouh the bike runs great, it refuses to return to idle when you come to a stop. It will drop to about 2,000 and then just sit at that mark for about 15 seconds before dropping back to 1,200. I can pull the R's down by slipping the clutch while in gear and they stay down - right at idle (1,200). Really the entire deceleration is poor. From 6K to 2K is about 5 seconds and then another 15 seconds before it drops from 2K to idle. There are no air leaks. I have triple checked it.
Everything I read says this is caused by a lean condition. My question is can this also be caused by a too rich condition? I am currently 2 over on the pilots already and too lean can't really be the issue. I'm thinking the pilots are too large.
To lean the condition do I turn the air screws in or out? Some say these are really fuel screws and screwing them out adds more fuel to the mixture. Others (including Clymer) say that the mixture screw controls air. So screwing them out would add more air. Which way is it? I was going to see if I could tweek some of this problem out with the mixture screws. What else might be the problem??
The bike is a 75 with the pully controled carbs.

Suzukidave · Post by **Suzukidave** » Sat Mar 07, 2009 2:41 pm

I read that if you have to adjust the pilot screw more than 1/2 a turn ether way you need to correct the pilot jet . A " M" needs 1 1/2 turns out , whats yours set at now ? http://www.3cyl.com/~tripleed/suzigtcarb/23.jpg

tz375 · Post by **tz375** » Sat Mar 07, 2009 11:54 pm

Chris the easy way to remember this is that if the screw is on the air filter side of the carb, it controls air flow. So out means more air = leaner.

If the screw is on the motor side of the carb it controls the mixed air and fuel and open = more fuel = richer.

It's that simple and it doesn't matter what make or design of carb.

The problem is more likely to be a tiny air leak between the carbs and the cylinders than anywhere else - assuming that the slides are returning properly and not hanging up. Rod controlled (push pull) carbs often have slop in the linkages so that if they open together they don't close together.

One might be slow to return.

I'd pull the filters off and watch the slides as you run the motor. Try blipping the throttle and the slides will probably move together. Try to close them more slowly and see if one or more hang up slightly.

With the motor stopped, open the throttle part way and use a finger to see if each slide will lift a little. Chances are that one will have some slop and will hang up on teh way back down.

Triplerocky · Post by **Triplerocky** » Sun Mar 08, 2009 10:08 am

Had the very same problem 3 times; on the GT380 the LH carb jet needle developed a step, hitting the needle jet and stopping there; on the TT600 there was a (unsuspected) tiny mesh filter BEHIND the needle valve that was dirty enough to prevent a correct fuel flow; now I have the problem on the TS400, after some kilometers at steady throttle, if you abruptly close it, the motor tends to do strange things, coughing, backfiring, staying "happy" on RPM, while is a kitty after some time at idle.
I think the problem is once again of mechanichal nature, an incorrect fuel flow, due either to the needle valve or dirty in the carb duct.
All in all, the problem is an incorrect fuel level in the bowl due to an insufficient fuel flow (starvation?) from the needle valve, pipe fuel, petcock.
P.S. Even after I consumed both of my hands in disassembling/reassembling the carb, changing jet needle, needle jet, main and pilot jet, bought cases of carb cleaner, importuned Lane in a transoceanic parts sending, altough different because the notorious P.O. BORED THE NEEDLE JET

, the problem still persists.
Next trial will be the removing of the small wire that limit the movement of the needle trough the valve seat.

Coyote · Post by **Coyote** » Sun Mar 08, 2009 8:58 pm

Sorry I have been dragging my feet on this issue, but the slave driver has had me working the yard for the past 2 days. I did get a chance to check the air screws and all are 1 1/2 turns out per book. Checked throttle cable slack to make sure that wasn't the issue. I am not using a return cable - but am relying on the slide springs for return. I could add another cable but I don't think that's the cause of the problem as the pulley is against the throttle stop as all this takes place.
Didn't get a Chane to run it again today so I don't know if tweaking the air screws will make any difference. I WILL have a chance tomorrow and will update then.

Coyote · Post by **Coyote** » Mon Mar 09, 2009 4:56 pm

Well I messed with it quite a while today. The only way I can get it to return to idle in its own is by opening the air screws 2 1/2 full turns out. Still slow but the hanging at 2K is gone. This indicates that the 2 over pilot jets are too large right?
I don't know whether to go back to the stock jets or procure a set of 1 overs. I would need to order the 1 overs as I never did get a set. I went from stock to 2 over in one shot.
Am I on the right track??

H2RICK · Post by **H2RICK** » Tue Mar 10, 2009 10:36 am

Sounds like you are, Chris. Of course you remember that you can get half-sizes in pilot jets e.g. 17.5, 22.5, etc etc.......should make your tuning a lot easier.

advant63 · Post by **advant63** » Tue Mar 10, 2009 2:03 pm

would the wrong air jet give the same effect?

tz375 · Post by **tz375** » Tue Mar 10, 2009 2:24 pm

Typically a lean condition leads to high idle speed and too rich makes it blubber and stall.

I'd double/triple check that the slides are really closing all the way and that nothing is causing even one of them to hang up slightly. With the motor off, does the throttle click closed with a nice click from all three cabs together and is there at least a small amount of slack in the throttle wire.

Looking down each throttle body, can you see all three click closed. A small mirror on a stick is useful here. I got one from Sears for a couple of bucks.

Then try closing them slowly and see if one tends to lag or hang.

When you are 100% sure that nothing is hanging up, I'd start looking for small leak in the intake stubs. The rich pilot jets may be masking this slightly when accelerating.

H2RICK · Post by **H2RICK** » Tue Mar 10, 2009 8:35 pm

Advant, I don't believe those later style 550 carbs use a jet of any kind for the pilot air passage....but it's been awhile since I've looked at one to be absolutely sure.....

Arne · Post by **Arne** » Tue Mar 10, 2009 9:47 pm

It really sounds like your idle jet is a bit too large. I wouldn't sweat it if you had to turn the screw out between 1 and 3 turns from seated, but you could certainly get different idle jets.

You could also change air jets, but your just playing with the other side of the equation.

Good luck. Arne

Coyote · Post by **Coyote** » Thu Mar 12, 2009 10:40 am

In the first place, the way these carbs are made and their associated linkage, every thing is locked solid together. If one slide hangs, the others hang with it. There is no way for the others to drop and leave one hanging as they are all coupled together.
Anyway, hanging is not an issue. Comes back to the throttle stop / idle adjuster hard every time. If a slide were to hang, the pulley would not return to the stop.
I have a set of 1 over (27.5) pilot jets on order. My gut feeling is the 2 overs that are in them are just too fat.
Speaking of jets, I can get them at a really good price. $8.95 plus tax = $9.72 for a packet of 4. Should be in tomorrow.
It's snowing right now and it's supposed to be cold for the next few days so I may not get to it right away.

tz375 · Post by **tz375** » Thu Mar 12, 2009 5:19 pm

Chris, that's good to hear. Hope those jets do the Biz.

On my H models there was always some slack in the linkages. I know a guy on a different forum that had problems with his 550 carb linkages- something about a woodruff key being loose in its slot on the shaft or something.

Coyote · Post by **Coyote** » Sun Mar 15, 2009 7:39 pm

Well guys, I got the new one over pilots yesterday. Today I pulled the seat, the tank, the throttle cable and finally the carbs. Laid the carbs on a towel (workin in the driveway) and pulled all the bowls. I removed all the 2 over pilots and replaced them with the new one overs. Put the bowls back on and was ready to re install the carbs and thought this is a good time to check the slide movement. I couldn't believe my eyes. The outer 2 slides were lifting a 1/4 inch before the center began to rise. So much for my carb syncro guy. Took the carbs to my shop and re synced to the instructions below. I put all back together and it's a totally different bike now. Will wheelie if you have a mind to. Returns to idle just fine now. I let the bike idle for 15 minutes and it never faltered or changed RPM.
I have all this accurate and valuable info on CD if anybody wants it. Just 2 bucks to cover the media, the mailer and the postage. It's just a 50 page PDF but it's packed with everything you ever needed or wanted to know. It has become my rule book.

Suzukidave · Post by **Suzukidave** » Sun Mar 15, 2009 8:03 pm

Thats great to read Chris .. another happy ending . I guess you now have some extra pilot jets .