Dellorto on Cub

[trialsrfun]

22mm Dellorto fitted to 199cc Triumph Tiger Cub

For best performance how far out do you set the mixture screw, also needle position. Currently mine has mixture screw around 1 3/4 turns out, clip in top groove so needle lowest. Took care setting the float level as bike seemed rich, adjusted float to 25mm so fuel level slightly lower, Dellorto say 24 + / - 0.5mm. Carb is as supplied for a Triumph Cub. Slow running seems better now but will need a trial to know.

Edited January 21, 2017 by trialsrfun

[goudrons]

There's no easy answer to your questions as what might work on one bike doesn't mean it'll work on another.

Carb tuning can be a little tricky and it's tempting to keep at it, chasing something better when perhaps you're already there!

 

Warm the engine up and turn the idle speed up ever so slightly.

Start with your mixture screw at 1 and 1/2 turns out as your base setting and adjust in 1/4 turns.

As you alter it too rich the engine will sound dull and fluffy, too lean and the revs will "hunt" ie, the idle will rise and fall unevenly.

Once you have it idling smoothly (as possible), reset the idle back to normal.

 

The needle setting effects the way the fueling acts as the throttle opens and the fueling changes from pilot circuit to main jet.

Start on the middle groove.

You'll need to ride the bike around and see how it acts on slow and sudden throttle openings.

Lifting the needle up (low clip) with cause a little more fuel to pass = richer, lower the needle (high clip) less = leaner.

(It's been a while, but I seem to remember mine had the needle lifted quite high to over come a stutter on sudden throttle opens).

 

Float height can also cause rich and lean running, too low and it can lean out, too high and it can flood up as can the angle the carb is fitted, particularly up and down hills.

 

But like I wrote, it all depends on the bike and what parts are fitted, air filters and exhausts can effect setting as can altitude .

Then there's Cubs that are fitted with R cams, they just don't tend to idle too well to start with!

 

Edited January 21, 2017 by goudrons

[trialsrfun]

Thank you goudrons for your really useful information, needs riding more to really find out if what has been done has made an improvement.

[totalshell]

buy a set of needles jets etc.. make sure bike is warm before making a judgement.. change one thing at a time and note every change it may take some time but its worth it .. you dont need acres of land to try it out you can get it right in a very small space as long as there is some gradient my driveway is two car length and a fairly nice slope and proved ideal.. you ll know when its right.. and when its right DONT CHANGE IT.. thats the best advice..DONT CHANGE STUFF WHEN ITS WORKING

[2stroke4stroke]

If you search for Amal carb tuning you should get a leaflet telling you the various stages of tuning a conventional carb which should translate to the Dellorto.

[carl ekblom]

Well, I have some experince of the PHBL carb.  I see Dellorto UK list the D40 needle for Tiger Cub. Replacing the D40 needle with D34 will make the mixture slightly leaner at low throttle openings. Idle mixture screw at 1-2 turns out is perfect.

Needle chart is here http://www.dellorto.co.uk/wp-content/uploads/2015/05/E-D-Needle-charts.pdf

[trialsrfun]

Thank you I have downloaded both the Amal and Dellorto tuning guides, am sending for a D34 needle, mine has the D40 as supplied. Other settings are 40 slide, 260BZ atomizer, 105 main, 35 pilot, 60 choke jet and 200 needle valve all as supplied with the carb.

[trialsrfun]

Have fitted a D34 needle as suggested above, initial results are encouraging certainly seems smoother running, needs choke on for longer until engine warms up will be much wiser after the next trial. Thank you all for your helpful suggestions.