Please Help....At wits End!

[ghwrenchit]

A slide or throttle plate adjusted wrong can render the mixture screw or air screw useless. Same thing can happen if you try to tune the screws for best idle at anything outside the factory recommended idle speed.
As for the correct procedure when tuning these carbs, most vacuum gauge makers recommend you adjust the air or mixture screws for best idle first and then vacuum synch. You can then fine tune the screws, after the vacuum synch. My first vacuum gauge back in 77?, a "GT", included this info. That's where I first read about it. My current Motion Pro gauge includes this info. I still read the same info/procedure at various websites.
Remember, these instructions assume the BENCH synch has been done previously and done according to exact instructions. If done correctly, the screws will operate/have an effect as designed/expected. If a poor bench synch was done, the screws may not operate as they should.
The recommended order is, bench synch, adjust screws, vacuum gauge synch, fine tune screws.

Thanks Keith,

Forgot about the "Bench Sync" aspect of things. I did one first but was limited on instructions. Used a small brass wire. I have a used set of "sticks" with no paperwork. I'll do alittle hunting for a manual.

ghwrenchit

[david suzuki]

bloody bikes

Sounds like some problems i had on a honda cbr 600 once. I'd sync the carbs, adjust the pilot mixture and did pretty much everything else you could do without rebiulding the engine. In the end i was adjusting the shims one day, and while i was in the enigne i thought i'd change the cam chain too. This was when i found the cam timing to be out one tooth on the exhaust cam. I checked the manual and found it very misleading when it came to describing which marks to use for timing the cams. It said to use the "t" mark but in the diagrams it referred to a different mark. So i would check that aswell while checking your valve clearances too. It just goes to show you never know who's been playing with your bike before you......
.

[wiredgeorge]

Your float bowls have a check valve that allows fuel to be fed to the brass tube already described that picks up gas for the choke circuit. Take a can of spray carb cleaner with the straw attached and put the straw into each of the bowls; into the holes in the bottom/side of the bowl that connect to the hole up on the edge of the bowl that the choke gas pickup tube fits into. Spray carb cleaner through from the bottom of the bowl and it should come out the bowl edge. If not, use a fine wire to poke into the openings from both sides to clear the passageway and check valve in there and repeat the carb cleaner test until each is free. Next, remove your carburetor choke plungers. If you take your carb cleaner straw and put it in the hole in the center of where the plungers seat and blow carb cleaner, it will come out the end of the brass tube and the two smaller holes on each side. If it doesn't, use a fine wire to clear the holes in each of the brass choke gas pickup tubes. Last, if your mixture screws don't effect the idle significantly, you might want to first clean the pilot circuit. Remove the mixture screw and pilot jet. Blow carb cleaner into the air jet on the intake venturi edge. If gas comes out the MAIN JET, you are blowing into the wrong hole. COVER the holes where the pilot jet and mixture screw were and gas should come out the very small hole on the engine side/bottom of the venturi behind the needle jet (brass thing that sticks out of the bottom of the carb venturi the main jet fits into). If gas doesn't come out in an atomized spray, blow carb cleaner through the pilot jet hole and the float needle hole and poke a wire down into the air jet to ensure this passageway is clear and repeat until you get carb cleaner to spray through the entire pilot system via the air jet and through that small hole on the venturi bottom. If you like, you can also go up ONE size to #40 pilot jets and that will make your bike less cold blooded as well. If you do all these things, I can pretty much guarantee all your cold starting and idle issues will go away... one last point on the idle, replace the orings on your mixture screws regardless of how old they are. These need to seal properly to ensure a good steady idle...

One point on bench sync... it is ONLY for getting a bike running. Don't expect the bike to run smoothly or perform optimally until you sync the carbs with a manometer and if you haven't set the fuel level via the service fuel level measurement technique ALL other carb tuning is very very likely a waste of time.

[Mike_H]

Not to whip a dead horse, but I have new information that may be important here. I was stripping my carbs down for paint, and while doing so, checking the installed jets against the service manual. On my air jets, the manual says they should be 160's, but the carbs have 150's in them. Additionally, 1 out of 4 carbs had a 155 in it! Might this be causing some of my starting woes? I hope its this easy.

[KEITH KRAUSE]

Not to whip a dead horse, but I have new information that may be important here. I was stripping my carbs down for paint, and while doing so, checking the installed jets against the service manual. On my air jets, the manual says they should be 160's, but the carbs have 150's in them. Additionally, 1 out of 4 carbs had a 155 in it! Might this be causing some of my starting woes? I hope its this easy.

If the bike is stock, then replace those air jets with the correct size.
Since this thread is kinda old, I went back and read it again. By your description of the problem, it sure seems like either a pilot circuit problem and/or choke circuit problem. Correct jets, float levels correct and complete cleaning should work.
Only other thing I need to mention is that you said the choke had NO effect on rpm's?? If the choke is indeed working, on a cold motor, the choke HAS to effect the rpm's. A richer mixture given to a cold motor will increase the rpm's. It's what the motor wants at that time. If there really is no effect, or even barely any effect, then your choke circuit is not operating correctly. With a correctly operating choke, a typical bike can "idle" at least 3K and up if you did choke it too much. First thought would be the very tiny starter jet at the end of the brass tube in the choke chamber is clogged.