Mixture screw setting.

RCGBOB44

RCGBOB44

Hero member
Location
Coulsdon,Surrey, sometimes Germany
Ok here's a very simple question, when setting up the mixture screw I understand the principle of setting the engine to run at about 2.5k reves and adjusting the mixture screws to get max revs. Out to richen in to weaken!  But at what point do you start with the screw settings, some say start at one turn out from fully in but is this correct.

Any tips or advice would be really welcome.
 
I thought it was 1 1/2 turns out but not at 2.5k revs! Just do it at idling. If it won't idle wind the idle screw up till it does.
 
Its not revs,its throttle position.The first 1/8 of a twist of the grip is controlled by idle jets and mix screws.
So thats idle and just off idle.So riding at 100kph and just cruising at a tiny application of throttle is controlled by idle jets at that point.Thats my understanding,hope I got that right.Its a bit counterintuitive.
 
For your mixture screws you can use 1 1/2 turns out at a starting point then balance your carbs after you have wound up the idle speed about 2500 rpm then after balancing return the idle speed (the large verticle knurled adjuster) back so the engine settles to about 900RPM then wind your mixture screws out or in to get the optimum idle a lot of the time the position of these screws is determined by the size of the pilot jets and these could range from 50- 70. but most likey to be 55 or 60.
M.
 
Right here goes, Warmed the engine got it to settle at about 1800 reves and adjusted the mixture screws foe max revs on each screw.

Then connected the vacume gauges and balanced the carbs (the easiest bit!).

Now, can I get the bugger to tick over?

No Wuckin Fay.

The engine appears to run a lot smoother without the original hint of knocking but at the expence of no tick over.

Should I back out each micture screw by a 1/4 turn at a time to see if it help?

Any advice would be appreciated.

Regards.
 
RCGBOB44,

Not sure of the history of your carbs, or how long you have had the bike. Assuming unknown history, this is what I do every time:

Take out the idle screws and make sure nothing is left inside the carbs (you will often find old flattened rubber "o' rings and maybe the odd steel washer..  ::) ). You will need a powerful torch and some good quality picks to get in there. BE CAREFUL! Don't scratch anything!

Get new rubber "o" rings, springs and washers for the idle screws, as required. Get some new idle jets, as they are possibly worn, abused or have a thin layer of crust/emulsion (and maybe mains while you are about it). Replace the carb stud 'o' rings. All these parts are available from Delorto and others and are pretty cheap.

Setup carbs so that all three slides come off the bottom at the same time. Set float heights to correct level.

Set all three idle screws to 1 1/4 turns, warm the engine and do the idle adjustment at around 1000-1200 revs. There is no strict rev point, you just need the bike to run on its own.

Once idle is as good as you can get it (may still be pants), put on the vacuum gauges and balance the carbs. As you balance, you may need to raise or lower the revs to keep them as close to 1000 as you can. Whilst doing this, you might need to go back to the idle screws, if the carbs were way out.

With some patience, it will all come good.  It takes time to learn how to set these up, but after a bit you will get a feel for it.  It's astonishing how often they are way out of wack and I have had a few triples arrive here that are so far off you would not believe it. The uneven firing masks the imbalance.

All of this assumes your carb bushes are not worn, stubs are not leaking air and slides are in good condition.

HTH

Pete

 
Pete/s advice is good,also check that the rubber o rings have not been forced into the carb body,i have come across this,Mig wire with a small hook on it will get them out,if you can;t get a reading when useing the screws on tick over with the gauges on ,ie you screw in or out on each carb but doe;s not afect the gauge for that pot then some thing is not right as pete says it takes time. :) :) :) :) :) :) :) :) :)
 
First set mixture screws.
Once done, do not touch any more.
Ajust using idle screws for reasonable tickover..
Then balance.
Remember that it's not at idle that you want your carbs balanced.
All this presuming the carbs are in good condition.
Paul
 
Paul Marx said:
Don't forget to thoroughly warm up your engine first.
Click to expand...

and to state the obvious,, that includes all carburettors.
i.e.  take it for a fang down the road, or at least get a fan blowing warm air back over 'em for a while.
i reckon a just warm engine and cool carbys,, is just pissing in the wind.
cheers
 
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