Delorto tuning

A

andre

Senior member
Chaps, some advice please

My Motodd with bored to 36mm delortos has taken a 'dislike' to running at low speed through town (who wouldn't?), and so it fouls or wets up the left hand plug. I presume I might cure it by smaller pilot jets or it's been suggested to me that even idle mixture adjustment might be the cure. Any thoughts?

And I cant recall where to download the Delorto manual from on line. Can someone remind me of the link?

Thanks
 
Hi Andre, about jetting I don?t know much but her is an interesting link from Gregory Bender, mainly a Guzzi site but with much other interesting stuff. Take a look around!

http://thisoldtractor.com/gtbender/mg_manuals/dellorto_manual.pdf

grtz,  Ren?
 
idle mixture can be changed by screwing out the idle mixture screw (most right)... standard setting is 1 1/2 turn out
technical_carburetor-dellorto-manual_03d.jpg

this controls the ammount of air on idle... out is leaner, in is richer
 
TinTin said:
idle mixture can be changed by screwing out the idle mixture screw (most right)... standard setting is 1 1/2 turn out
PHF36.jpg

this controls the ammount of air on idle... out is leaner, in is richer
Click to expand...

Ok TinTin have another guess :D
                   
            DAVE
 
Dels can be either depending on model. Some are an air adjustment and some are fuel.

All the ones I know on Guzzis, Lavs and Morini V's are fuel. Out is rich, in is leaner.

1 1/2 is the usual starting point. The Alpino has a recommended 3 turns out!!!!!!  :o Not always the same.

With the bike idling, you may need to adjust the idle up a bit. Make sure you twist the throttle before you screw athe adjusting screws in or you will wear the seat on the slide. Turn the screw 1/2 turn either way. Is the bike idling faster or slower? If faster go another 1/2, if not go the other direction. Again, faster or slower? Do this until you are in the centre of where it is happiest. Cut down to 1/4 turns and so on. It is often difficult to pinpoint the exact location so if it is worse in 1/4 or 1/2 a turn in either direction you must be as close as it matters.

If it doesn't appear to change at all then the other cylinders are possibly carrying that one. Adjust the idles down on the other carbs until the mixture screw does have an affect.

If it is as you say then reducing the pilot jets may be the cheapest option but the main culprit now is probably the slides. You possibly need a bigger cutaway in the slide to reduce the lower pressure in the venturi, reduce the draw of the fuel up the pilot jet and therefore lean out the low throttle mixture.

Drop the idle jets and see if it improves. Other cheap option is to go one heat level hotter on the plugs to redfuce fouling. Experience any pre detonation and get rid of them immediately.  :o

Colourtune is a useful tool for getting an idea what the bike is doing at idle, especially if you are new at it. If you don't have an exhaust per cylinder then a vacuum gauge of some form is a very good idea. Still a good idea anyway but you can at least judge the fueling balance by feel if each pot has its own outlet.

Just how I do it.

Rod
 
I don't know if this will help but I set the Slide Stop Screws Equal on both carbs of my SF buy placing a Allen Wrench or say a Hex Screw Driver End Attachment in the bore of the Carbs on which the Slides will REST and set the Stop Screws accordingly. This will give you a REFERENCE POINT of Constant Flow on which you can further adjust your Throttle Cables and Slide Stop Screws for idle. It's about perfect when you twist the throttle and move the slides all at once and, upon release, don't hear them bottoming outta sync. I've use this method for years and have had great results in Synchronizing the Carbs all the way through the power band - That's not including Jetting or the size or height of the Needle.

From my experience Jetting and Size & Height of the Needle is dependent on the Size of Carb Vs Exhaust System - Not including Compression, Valve size or Cam - That's another story.

Ensure your Cables & Carbs are clean with floats set. Maybe your Enricher is needs attention not adjusted upon seats or has cracked seals which will flood a cylinder.
 
While it may well be an adjustment problem, If it has taken a sudden dislike and only on one cylinder I would have a look at the float level and the needle and seat. Your description sounds like it is flooding. A check of the ignition components for that cyl. would also be in order also.
 
dja981 said:
TinTin said:
idle mixture can be changed by screwing out the idle mixture screw (most right)... standard setting is 1 1/2 turn out
PHF36.jpg

this controls the ammount of air on idle... out is leaner, in is richer
Click to expand...

Ok TinTin have another guess :D
                   
             DAVE
Click to expand...

why, what is wrong here?
 
Hi Andre - Boring out the 32's to 36 moves the needle jet holder down by 2mm -  although the slides will drop (theoretically) the same amount into the new counterbore we only took enough "meat" out to enable the slide to shut enough to stop a high tickover - this tends to make the mixture slightly richer at some throttle openings. this tended to work well with the whole"head job" package we used to do. However, in the rare cases where it caused problems such as yours, we found that increasing the slide cutaway by half a mill usually cured the problem. This involves carefull filing  - and would be done at your own risk and could not be an absolute guarantee of success. If your problem has "suddenly" appeared then disregard this posting!! - HTH - Phil
 
TinTin said:
dja981 said:
TinTin said:
idle mixture can be changed by screwing out the idle mixture screw (most right)... standard setting is 1 1/2 turn out
PHF36.jpg

this controls the ammount of air on idle... out is leaner, in is richer
Click to expand...

Ok TinTin have another guess :D
                   
            DAVE
Click to expand...

why, what is wrong here?
Click to expand...

As Dave says :D, you've got it arse about face.The diagram you've used to illustrate your point shows a carb equipped with a mixture screw, not an air screw. Mixture adjustment screws are downstream of the main jet [ie on the engine side] Air adjustment screws are upstream . You've described the procedure for adjusting an air screw but illustrated it with a mixture screw. A mixture screw needs to be opened to enrich the mixture [to allow more fuel in] whereas if you open an air screw it allows more air in, and leans the mixture. It's an easy mistake to make.
 
If it was running ok before, you don't want to start playing with jets. Do some basic checks on the carbs: cleanliness, balance, wear, float height and stop there.
Then check ignition, fuel quality, general engine wear.
Ciao
Paul
 
TinTin said:
what's the correct picture then  :'(
Click to expand...

For    a    Laverda,  the    picture    you    supplied    was    correct,    it    was    your    explanation    which    was    wrong.
 
Normski said:
If it's fitted with a choke is it seating correctly?
Click to expand...
With Morini VHB carbs this also causes mixture problems at low speeds.... would explain why only one plug is fauled. But I'd replace all when you're at it...
 
Thanks guys. All good suggestions. I gave the hotter plug / 'lean up' the mixture screw a try but felt it was addressing the effect not the cause. Agree that slide cutaway may be a fix. Might just see if Dave Cole will take another look. Runs great 'on the throttle'.

They are very old carbs now, and have no doubt had many 'experts' fiddling with them over the years. My SFC1000 carbs are stock, had the minimum 'fiddle' over the years , and run sweet.

Mikuni RS36... gotta get the money for them together...

Cheers
 
RCGBOB44 said:
As were talking carbs, can anyone tell me why the slides on my jota do not quite clear the bores when opened fully?  Is there a way of making them clear the bore on a wide open throttle?
Click to expand...

There is a throttle stop screw on the bridge piece connecting the mixing chambers.  Make sure this allows full movement of the opening quadrant, the bit the cable hooks up to.  Failing that, the linkages and their bushes will be worn... probably are anyway!  Also check the little levers under the shiny domes above the mixing chambers.  These are fixed to the actuating axle by a screw through both.  These often work themselves loose after a while.  When all the slop is accounted for and taken up, the slides should clear the carb throat.  Might find that one does and the others still don't, even while they are in synch initially... that's where the fun begins!! :D

piet
 
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