It's just not right....

Standard back in the late 1970s for Jotas was 140 mains; these days it's 122 give or take, so original standard jetting means very little in 2025. Meet that bloke once or twice as well.
 
markQLD said:
For your information about pilot sizes for a Corsa, from our forum member '2622'
View attachment 96895
I know this bloke and it is always worth listening to what he advises.
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I was fortunate to ride Mr. 2622's Corsa when visiting down under a couple weeks back. '81 Cico 180 too. Both ran like Swiss watches. The 180 near as vibration free as the 120. He's the maestro.
 
Indeed the oversized idle pilot ( its not just that, it is the off throttle stop transition/light throttle cruise also ), has 100% to do with the original BTZ single step advance and nothing to do with the best operational parameter for the PHF carbies. Massively over jetted to compensate for the pinking of 32DBTDC at low rpm. Part of history now, or it should be, the information from 2622 is based on wider experience, mine also setting up a proper ignition on a horrible jetting from the factory.

The ludicrous "145" mains i witnessed in Australia on series 1 motors was not for our climate to say the least. The 30 or so i had removed from owners bikes i used to solder up and redrill for test jets, about all they were good for.... HTH j *** series 2 motor will achieve around 17km per litre with good off idle response when jetted and ignition corrected. j.
 
Thanks again people.

Ok it looks like I need to source smaller pilot jets as well as another attempt at cleaning out the carbs....

Just gotta try and find the time.

cheers
Tony
 
Ok so yesterday I took the carbs out again and tried the carb cleaner tip as suggested here. To my surprise all the galleries were clear on all three carbs and the carb cleaner squirted out the venturi exactly as it should.
However I did discover a couple of issues. When I rebuilt the carbs I did each one separately. This time I partially dismantled them together and noticed that one of the springs on a mixture screw was shorter than the others! Well that isn't going to help! Also noticed than one of the idle jets was blocked which was strange because it wasn't when I last had it apart. No idea where that bit of sh*t came from as the fuel filters are lovely and clean. Anyhow, so long story short, two of the carbs were compromised.
I also looked at the choke plungers and the rubber seal on one looked damaged maybe...
So I have ordered three new mixture screw assemblies and choke plungers from Wolfgang to go with the smaller pilot jets I'm waiting on and I will try again.
cheers
Tony
 
Yes hard enricher plungers can cause problems and sounds like you,re making progress. did you use Liqui Moly or some other cleaner?| That plugged idle jet was probably the result of using the cleaner that dislodged the particle from elsewhere
 
The spring for the mixture screw won't have any bearing on what goes to the motor - it simply applies pressure on the screw so it stays where you want it. If they were overly long they could bottom out before the tip does, giving a false setting at, say, 1 1/2 turns out, but you don't reach ideal mixture setting based on the position of the screw; that comes from fine tuning.

Carb work needs to be very methodical. As you've discovered, you think you've done everything thoroughly but anything missed will create woes later. Good that you've on the right track.
 
..not forgetting the easily lost metal washer on the fuel ( idle mixture ) adjust screw and spring. HTH j
 
piranha-bro2 said:
The spring for the mixture screw won't have any bearing on what goes to the motor - it simply applies pressure on the screw so it stays where you want it. If they were overly long they could bottom out before the tip does, giving a false setting at, say, 1 1/2 turns out, but you don't reach ideal mixture setting based on the position of the screw; that comes from fine tuning.

Carb work needs to be very methodical. As you've discovered, you think you've done everything thoroughly but anything missed will create woes later. Good that you've on the right track.
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Thankyou, but doesn't the spring also hold the washer and o-ring in place? If the o-ring isn't being held securely against the carb body isn't there a chance of more air entering the system?
 
TeddyG said:
Yes hard enricher plungers can cause problems and sounds like you,re making progress. did you use Liqui Moly or some other cleaner?| That plugged idle jet was probably the result of using the cleaner that dislodged the particle from elsewhere
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No I didn't use a cleaner like that, just an ultrasonic bath. But you are correct. It must have been lurking somewhere.....
 
Re5Guy said:
Thankyou, but doesn't the spring also hold the washer and o-ring in place? If the o-ring isn't being held securely against the carb body isn't there a chance of more air entering the system?
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Minimal, not enough to throw the entire idle system off. Lots of older carbs don't have any form of sealing of the idle mixture screw, VHB Dellortos for example, they work perfectly well without.

piet
 
Re5Guy said:
Thankyou, but doesn't the spring also hold the washer and o-ring in place? If the o-ring isn't being held securely against the carb body isn't there a chance of more air entering the system?
Click to expand...
It would only be a problem if:

a) - too short and didn't provide sufficient spring pressure
b) - less so, but too long and didn't allow the screw to bottom out
 
Just an update everyone, I've been away for the last 2 months plus so just back into it now...
I have changed the pilots to 55s, replaced the choke plungers and the pesky short spring mentioned earlier. It is now better but still definitely not right.
I can now get some change in engine speed playing with the fuel mixture screws but the bike is still rough between idle and 2,000rpm.
It will now pop and backfire on the over run when slowing down (which it didn't do before the changes above) and it just feels unhappy. Get to 2,000rpm and all is well.
I have looked for air leaks where ever I can think to look and tightened everything up. The only thing I haven't done yet is remove the inlet manifolds and double check them for any cracks/leaks...hopefully this weekend.
It still starts and idles well after it's warmed up.

This is all part of the "FUN"...right? :LOL:
 
Re5Guy said:
I have looked for air leaks where ever I can think to look and tightened everything up. The only thing I haven't done yet is remove the inlet manifolds and double check them for any cracks/leaks.
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A quick way of checking for inlet manifold leaks is to spray some carb cleaner on them in turn. Engine speed will change
 
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