850-T3 stumbling idle

My 1980 T3 Cali starts first touch of the button when the choke lever is operated. After about 10 seconds it sounds like it is running on only one cylinder. If I flip the choke lever off it cleans up but I need to keep it going using some throttle until it is good and warm.
Even when hot it will not slow run nicely but gradually fades away until the engine stalls.
I have had the timing checked and the small mixture screws adjusted by Corsa. I have fiddled around with the slow running speed needles and have balanced the carbs and set the “pull” on the throttle cables as evenly as I can using a ball-bearing vacuum gadget.
The bike has a Dyna Tec electronic ignition system.
Anyone got any ideas? What slow running speed should it actually have? I see old “barn-find” state Guzzis on YouTube wheezing away at slow running speed that mine could not do.
All the best,

My Spada ticks over just below the thousand mark once it has warmed up, but for the first 15 mins or so I need to hold the throttle open just a tad to keep it running at lights etcWinding in the larger screws on the outside of the carbs should just lift the tickover speed enough to keep it running.

What are “slow running speed needles” ? Firstly, the motor’s not properly warmed up until about 10 miles of riding. Until then idling will be on the slow side, IF it idles at all. Secondly choke is only for cold starting, usually you then need to slack it off immediately, and yet motor may not take full air, this is the problem with the ‘on/off switch’ type choke levers, and is why I modded mine to a continuously variable handlebar lever control. Otherwise it’s going too rich and not running right if choke is still on full is not unusual. Thirdly check how many turns out (from fully screwed in) are the idle mixture screws, in my experience 2 - 2.5 turns is about it, not the 1.5 turns as it says in Haynes manual, this is a starting point only, you’re supposed to then tweak them more it until it idles. HTH

By slow running speed needles I meant the needles that act on a tapered track on each throttle slide to set its height above the “floor” of the cavity that the slides operate inside.
Thanks for the ideas. I had not realised you need 10 miles of warming up. I need to check my mixture screws perhaps although I have left them alone since Paul at Corsa set them.
All the best,

Those needles actually dictate the mid range (between coming off idle jets to wound fully open). Your problem appears to be below this point

“act on taper track on the throttle slides” sounds more like Throttle Stop Screws to me, rather than the Mixture Screw.

Remember to open the throttle slightly when adjusting these as the screws can bite into the slides.
All the best

Good advice Steve , took me a few goes before i realised why the screw wasn’t increasing the speed when i tried screwing it in , Dohh! .

Yes he means throttle stop screws.           It is very easy to make the slides too far up on the throttle stop screws when attempting to make it idle, if the (other) mixture adjustment screws aren't out far enough (too lean).    This means poor or no engine braking when you close the twistgrip, maybe even it keeps pulling for a second or so!     Guess how I know.         Curse you Haynes .. 1.5 turns, my ar5se ..... took me years to work out that that isn't the actual final setting ....          

Mike H2014-09-15 14:45:51

 Are the bottom of the slides actually chewed tho?

[QUOTE=Mike H]

 Are the bottom of the slides actually chewed tho? [/QUOTE]

Worth a look,

Thanks everyone. How do I find out the correct setting point for the mixture screws please? Is it as Mike says and I should have them about 2.25 turns open? Is there a knack to setting the idle speed by operating on these instead of the throttle stop screws?
All the best,

And check one or both of yer chokes isnt actually hanging up…

Haynes says (and it's basically right, just a question of interpretation), set the screws at 1.5 turns (out from fully screwed in), then start the engine, and then try to get it warmed up enough to idle on its own. (The problem with that is getting it warm enough while just standing on the stand.)    This usually means upping the throttle stops so that it will keep going.    Then screw out the idle screws equally a bit at a time. Revs should increase. So then reduce the throttle stops to achieve previous idle speed.    Repeat, until screwing out the idle screws doesn't increase speed.    Do a final trim of the idle speed with the throttle stop screws.    One at a time, screw in each idle screw until the speed drops, then out again only just enough so that idle speed is back to what it was.    That's it. In my experience the final setting tends to to be in the order of 2.25 - 2.5 turns.    Then when you take it out for a proper ride, after a few miles you will most likely find that the idle is now too fast, in which case lower it to what you want by screwing out the throttle stop screws by equal amounts (to keep the slides in balance), but leave the idle screws alone.    Then that should be it, job's a good 'un.    Note that this assumes that the slide heights have already been matched both on the throttle stops and hanging on the cables. I.e. do this first, or during the early stages of sorting the mixture screws.    HTH (?)       

Mike H2014-09-15 21:24:21

Many thanks Mike. I can see my weekend’s work ahead of me!
All the best,

Guilty of talking bollox It seems that 2.5 turns or whatever only applied to my carbs while the jets were half blocked with the dreaded green lergy. Just checked them again, and they are currently around 1.5 - 1.75 turns, and have been ever since new jets were put in last year. So Haynes is right.

Here’s another old favourite to check, where the mixture screws bed in there is a teensy weensy “O” ring at the bottom of the 'ole, often found in the carb refurb pack and discarded, without these the correct mixture setting will be nigh on impossible, wind out the mixture screws and have a poke with a large needle or similar, if it’s not there, get someCheers, Gerry…

Yes that is true! Often omitted, even on new carbs. (Guess how I know.) But I was told that while new, the screw threads are not worn out yet, so should be little likelihood of air leaking past. But after some years of use, O-rings are at least prudent, if not actually necessary to cure an air leak type fault. There’s also O-rings for the throttle stop screws too.