Corsa Carb Settings

  • Thread starter Thread starter Grant
  • Start date Start date
Surprised about the recommendation to put smaller pilot jets, this is not my experience, I always finally went between 60 and 65. Anyway the number of turn to the mixture screws let no hesitation. Going too small on the jets may cause also some transition problems.
 
For sure it is easy to establish if the pilots are too small or too big as the motor talks to you.
Too far in or out on the mixture screws will be self-evident.
 
Finally started getting into the Corsa and learning it's secrets.

Today I took the carbs off. Here is what I found:
Pilot jets: 65
Main jets: 118
Emulsion tubes: AB250
Needles: K1
Slides: 60/6

The float valves were not all the same, as in 2 were with red tips and one was with a black tip (well worn in a groove)

I am assuming the red ones were new replacements, but recall the material the tip was made from indicated it's resistance to modern fuels.

Can anyone tell me which colour is best? I assume the red ones, but may be wrong.

I have always used AB265 emulsion tubes in my 180s, any reason why 250s should be used in the Corsa?

I also thought the slides were ALWAYS 60/2, why change to a /6?

The connection from bell crank to slide was by solid rod. I think they moved to this from braided cable due to the type of vibration found in 120 engines.

I can only assume the carbs are as they left the factory, although the float needles look to have been partially changed at some point.
No wish to move away from standard settings, more of a heads up and to ask why the carb brassware varies so much from typical 180 carbs.

I will change the float needles as a matter of course and maybe the K1 needles (for same).

So my questions are:
- float needle tip type for best fuel resistance
- slide type
- emulsion tube type

 
I think to remember that my green SFC had 60/6, too. AB250 sounds very lean though, I would change to AB265; other settings sound right (65 Pilot, 118 Main, K1, 2nd notch).

The red tip is the only thing you get now as a replacement as far as I am aware. Not sure what the change of color means (just "replacement part" or "new fuel ready"), but I think to remember that some people had issues with them. Not sure though with which fuel, might have been 95 Octane which has more Ethanol (at least in Germany) than the 98 Octane.
 
I think the number after the 60/ indicates the slope or timing of the ramp to activate the accelerator pumps, so a change from a /2 to a /6 must be a significant difference.
Anyone any idea what?

All my 180s loved 60/2 slides, K1 needles and AB265 emulsion tubes, but I am wary of moving away from stock settings to base it on a 180 set-up without any validation.

The jets appear stock for the Corsa, already discussed in a previous thread.
I will not change the sizes although I would be tempted to go for a 60 pilot jet. Will wait until I get it up and running first.

All the insides of the carbs are thoroughly covered in a fine dispersion of rusticles, so I will do the old trick of immersing in Coca Cola tomorrow once I have been to the shop. I first used that on my 750/4 carbs and they came up a treat.

I will also fit new float needles while I am in there. I see no point in replacing much else due to the low mileage, just a thorough clean and polish will do for now.
 
http://www.thisoldtractor.com/gtbender/mg_manuals/dellorto_manual_a_guide_1.1.pdf

See page 19. Unfortunately I could not find the addendum with the data, maybe someone else has?!?
 
Hi Grant

for the slide accelerator pump actuation, I don't know if /6 is earlier or later and more or less than /2 or not. Easy way is just to compare the ramp on a /2 slide and the /6 slide. The ramp higher on the slide is earlier, the ramp lower on the slide is later.

slides are surprisingly expensive, if they are not worn, I would use them as is and leave any possible change of slides to the tuning process after the bike is running. Don't forget that in addition to the slide ramp timing the onset of the accelerator pump, you can also change the volume of fuel pumped with the adjusters on the pumps themselves, or you can just disconnect the pumps altogether as some do.

Paul LeClair
 
Lothar, good reading, but short on critical data as you said.

Paul, luckily I have the carbs on the 3C to be able to compare slide profile side by side. I have not opened up the 3C carbs yet but assume they will have 60/2 slides.

The Corsa carbs are very unworn, as befits 4223km from new. Just a minor section of wear on each slide, but I have seen much, much worse function perfectly so I will not be in a rush to replace them for a while.

My take is that over the years (and with varying levels of carb knowledge, starting at zero) I have run triples with Dellortos in all kinds of configurations and levels of wear and tear. It is only when you experience a well set up set of carbs do you realise what you have been missing.
I do have a set of carb repair kits so I will go over the carbs with a fine tooth comb and fettle accordingly.

It is a weird feeling not having to scrape years of corrosion, goo, gum and oily grit to see base metal on a set of carbs. Also they appear quite unworn so any 'issues' I find will be down to my fu fettling of them.

Luckily everything is or will be standard, from exhausts to airbox and filter. The only thing missing is the rubber trumpet that exits out of the back of the airbox. It is supposedly only for noise suppression so I am hoping it doesn't affect any running conditions.
 
Stock settings were given by redfox in his post on this subject and as fitted to my '85 Corsa.  What you have found is different.

The red tipped float valve needle is current Dell'Orto supply.  

The solid lifters were used on later 120s to address the vibration failures experienced by some.

Can't find a spec for the /6 slide accelerator pump ramp profile.  Dell'Orto document lists 1-5 only -  http://www.dellorto.co.uk/editor/uploads/images/Pumpramp.pdf
 
The underside of the slide has the 60/ cat in and obviously a removeable plug with the following number. The plug leaves the area as a raised circle, and mine displays the number 6.
I can take photos later.

I asked previously ablut the stock settings for Corsa carbs without having removed mine at the time.
Today was just to document what I found and compare and contrast with exisiting data.

I now want to understand why they would go to a 60/6 slide and AB250 emulsion tubes.
 
Grant said:
I now want to understand why they would go to a 60/6 slide and AB250 emulsion tubes.
Click to expand...

Could be something to do with the speed the engine shifts air. You can speculate all you like about carburator settings whilst sat at a keyboard. The way to work it out is with an exhaust gas analyser and a running engine. Have you actualy been for a ride on the bike yet Grant?

  Keith.
 
Fucking thread merge, thanks mods...
Makes sense I suppose, just seems intrusive.

Keith, there was no way to run the bike when the tank was literally full of loose rust particles.I looked in the float bowls when I got the bike and when I saw the brown crap everywhere I decided not to try to star it. That plus the fact it had not run in several years made me want to dig into it first.

From what Jacques posted I am surprised at the emulsion tube and slide differences.
I cannot believe the previous owner would make these changes and as he was the only previous owner I have to conclude that is how it left the factory.
I also conclude that the factory more than likely had a better clue how to build a stock Corsa than I do, so I want to try to understand these differences, not necessarily to jump in and start changing things to make it how I think it should be.

I don't get the tank back for a few weeks yet so by then I should have finished all the fettling and furtling. Then I will run it.
 
Grant,

By all means, get yourself a set of AB265s, you're going nowhere witht the AB250s!  These will seriously disrupt the mixture.  Why they were fitted can only be speculated.   To my knowledge, all triples were fitted with the AB265 needle jets.  To get the 250s working you will definitely need a different needle to restore mixture over the complete working range of the carb.  I doubt that anybody will have experience of fitting AB250s in a triple.... finding a suitable needle will at least be frustrating, if you find a solution at all.

The "removable plug" is just a replaceable stamp fitted to the mould of the slides.  It is not removable, just looks it.  While the accelerator pump ramps might have a slight influence on rev pick up, the 60/6 slides should be OK to start off with, you can always replace them with 60/2 or 60/3 slides if need be.

If mixture had been an issue, slides with a different cut-away would have been fitted together with the AB250 needle jets.  But staying with a 60/x slide doesn't change anything in the way of air entering the mixing chamber.

piet

PS, haven't got around to check your wish-list, send a pm when I do.
 
Piet, good to know. I may have a spare set of AB265s kicking about here, if only I could bloody find stuff since moving (3rd move since leaving the farm).
If not I will soon get some. I will stick with the 60/6s in the meantime.

I assume the rubber inlet stubs have been changed for RGS ones at some point, as the ID of the rubber stub is more like 32 than 36mm. I will reshape them to fit 'while' I am at it'.

Let me know if you have anything we can trade then. Sooner the better, as I have just placed big orders with Slater and Wolfgang this week.
 
NickNZ said:
I have a Corsa in the workshop at the moment.  Jets are 118 and 65 as Brad says, the mains are fine but the pilots are way too rich on transition and it is being a pig.  My gut feel is that around 58 will be the final solution - which I don't have, naturally!

This bike still has the strange sex-aid only fitted to 120's, and a Unifilter.

PS. How the f@#$ did I end up with this avatar???
Click to expand...

You can keep the avatar I was intending to change it :D

Scrumpy
 
Grant,

The rubber stubs were always the same on RGS or 1000SFC, no reason for them to be different on the Corsa.... re-shaping will weaken them to some extent.  If they are still OK and not porous, best to leave them as they are.  If you really need the extra performance, probably be easier to change over to the alloy/rubber set up from the last 180s, but you will then run into clearance/fitting issues regarding the intake bellows to the air box.

piet
 
About the rubber stubs, Wolfgang had nice replacements, exactly similar to the originals but with a brass sleeve inside to avoid a direct contact between fuel and rubber.
 
Grant,
From the description given my Liz it sounds like Pablo loved playing with the bike, I suspect your jetting is not factory original. 
The carbs and inlet rubbers are 32mm on all 120's, even when the ports are 36mm.  At least on the surface it seems like a bit of a half-arsed job by Laverda, were they not wanting to buy small batches of 36mm carbs or were they deliberately doing it that way for improved midrange etc?  Maybe Piet / Uwe Witt can enlighten us?
Cheers
Steve B

(a bit hung over from Club Lav NSW Christmas party at our place last night)
 
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