Problems after bench sync of carbs

[watty51]

This is a good one...

After bench synching my carbs on a cb350f yesterday using this method I found on this post :

LOOK INTO INLET SIDE AND YOU SHOULD SEE THAT EACH SLIDE HAS A GAP OF ABOUT 1/8"
WIND THE IDLE SCREW IN ( RAISES ALL FOUR SLIDES) UNTIL THE DRILL SHANK 1/8" JUST SLIDES UNDER THE LOWEST CARB THEN ADJUST ALL TO SAME HEIGHT.

ONCE FIRED UP ADJUST THE IDLE SCREW TO GET TICKOVER.

So did all that, put carbs back on with standard air box with new soft rubbers and now the bike wont idle at all, in fact whats happened is the choke in the upright, on, position (butterflys closed) wont start the bike and doesnt rev to 3000 - 4000 but if you put choke lever in lower position (butterflys open) it revs up to 4000-5000 revs. As soon as you move the lever to slow the revs down it just stalls. It seems the wrong way round.

Only took off carbs originally to check float levels as one was leaking but they are all fine now. Bike was running ok before this. One step forward and 2 two step back.

[PatM]

If I recall, i didn't follow that guide/procedure and settles all 4 slides so they were FULLY closed- that way the idle-circuit (which i believe is independent of throttles) operates. Then once started- adjust throttle-stop screw to achieve a reasonable idle and warm up/sync carbs off the gauges.
Ive certainly had the carbs causing the bike to rev-up to an unhealthy rpm, but dont remember the cure- in fact, i think my  re-jetted 'spare' bank do that.
ill be interested to see the replies as Ill try (if it accords with my knowledge) whats suggested.

Ive always had an issue starting my bike form cold- and never once its been started or warm.
On start up, it runs on 3 then the 4th comes in...pop, pop in the silencer- No 3 (which is the problem carb or cylinder) exhaust is cold until fires..Ive tried everything i know.

[K2-K6]

It's usually the one fixed carb that catches out setup routines I think,  often number two which you have to match the others to.

[Bryanj]

Sounds like you have adjusted the slide openings so that they do not close fully. you need to unadjust all the slides so that they touch the bottom on the flat side with the tickover screw wound all the way out so it nearly falls out. then screw in the adjuster till one slide starts to open and use a drill shank as a feeler to set the others to that point 1/8 is WAY to big use a 1mm or even smaller. When all set unscrew the tickover screw again to make sure all slides touch bottom

[watty51]

Thanks for all the replies. I will give all above mentioned a try next week and give you some updates.

[watty51]

Update as promised.

Many thanks to Bryanj. I followed your advice and I am pleased to say the bike is now running perfect with choke on and off. Took a bit of fiddling adjusting the slides to touch the bottom of the flatsides but all sorted now.

Tickover  is very stable at 1200rpm and when on choke revs at 3500...

Cheers

[Bryanj]

As my wife reminds me regularly there is a dance to go with the I told you so, but don't worry you are not the first and will not be the last to make that mistake

[billywingnut]

I'm still trying to cure what I believe is a carb problem having rebuilt the bike this year. Its been off the road since 1998.The bike starts OK, after a minute or so I close the choke until the bike runs ok at around 1200 rpm. I get this misfire from carbs ( difficult to tell if it's just one carb) it sounds  like it's spitting. This seems to stop as I take the revs up. Would faulty coils cause this kind of issue or have I not set them up correctly. I have fitted new carb kits as part of my rebuild and did a thorough job of cleaning them. Had new plugs, points and plug tops. Double checked timing, tappets etc. Set slow running screws to two and a half turns out set sliders to 1mm from bottom. Any ideas? 

Merry Christmas all

[K2-K6]

One of the good things about following Bryan's method to carb sync is that it's independent of other possible problems,  so whatever you do,  leave that setup alone.

Don't know if you have a strobe to verify the timing while it's running. It could be slightly advanced which can lead to spitting.

[K2-K6]

Just a thought,  we've seen on her before, I think,  the vent tubes to the float chambers blocked.

What this appears to do is the fuel dropping from there tank can't normalise at the float level in the chamber. It may alter the chamber into slightly pressurised from the tank head and push out too much fuel via the idle jetting route making it too rich at tickover with some cylinders stalling then coughing.

[TheOlderGentleman]

Don't know if you have a strobe to verify the timing while it's running. It could be slightly advanced which can lead to spitting.

You really need to have the ignition timing (and valve clearances) perfectly set before doing proper carb balancing, with the carbs on the bike and the engine running, obviously.