Dellorto PHM40 - mixture and idle

loonyberg · Jul 24, 2008

I've had my dellorto jetted by Taffy. New needls and emulsifier tube. PJ changed to 33 and choke jet changed to 40. Also had stator rewound by S[arks. The bike now starts first or second kick from cold and I have time to close the choke knob and it keeps going. The idle is sooooo much better and the performance of the bike is stunning (or awesome for the US readers).
Tafft and Sparks...what can I say...superstars.
Now the autodecomp needs sorting due to a weak spring then I might be getting towards getting the monster started on the button.
Judgement day is getting closer

Taffy · Jul 24, 2008

after explaining to paul (loonyberg) why a 45 was too big, he trusted me and bought a 40 choke jet. as i explained, the bike may need a 45 choke jet for the first kick but with mixture on the ports, valve faces, piston and linar: the next kixk with a 45 is way too rich added to this the bike HAS tried to start and the cumbustion chamber temp is already going up.

for the next few kicks therefore a 40 is more than enough as it comes within the bikes radar. so although he may well fail on the first kick, it means on the next 7 he is on the money and she should go in 2-7.

hope you were all following that at the back! this will go in the doc if someone else with a well set up bike tries it.

forget all this "i kisk with ignition off for three, then choke for one, then no choke for 7" etc etc. all that does is give you half choke via turning it on and off and kicking to reduce thew very 'wetness' i described at the beginning of this post.

one for the doc methinks.

this is my first input back into the dell orto since i ran one. the other thing i did for paul was put the choke on the left of the bike. it goes on a 1cm hollow dowl and longer inlet stub screw. all you do is angle the knob away from the head and down towards the clutch drum.

this allows you to rev the bike while still on choke.

regards

Taffy

Coastie · Aug 4, 2008

Hey Simon
Turning out the idle did make a bit of difference. It returns to normal idle speed straight away now.
It's 4 and a bit turns out.
The mixture screw still doesn't seem to respond when wound in and it's a real ***** to start from cold.
Hot start is OK but could be better on estart - 1st time on kick but estart cranks over for a few turns sometimes with a few pops out the exhaust.
In reading Taffy's posts above it sounds like the choke is a bit rich from cold. I have to do the choke on / choke off routine for it to start and it won't idle with the choke on. I've got a 40 on order.
I think it's a bit rich all round cos the plugs still a bit sooty so I'm gunna go down to a 185 main as well.

Simon · Aug 4, 2008

Hey Coastie,

That's good news that winding out the idle speed lets it settle to idle as it shows us the idle circuit was getting too much air in its previous state so that's at least one thing out of the equation. As you say, now it's possible to get down to some fine tuning.

As you probably already know, if you can wind the idle mixture screw all the way in, it is a sign that the jet is large so while you're at it, I'd suggest it's a good time try the smaller idle jets now too and at the same time triple check to make sure you haven't got any dirt in the float bowl or idle circuit.

Remember, only do one thing at a time and I'd humbly suggest first going to a smaller idle jet or two to see how the mixture screw responds, then the main jet and then the choke - at least then you'll know what does exactly what.

All the best,
Simon

Coastie · Aug 4, 2008

OK simon will do.
I'm running a 38 idle jet now.
What would be your next step down, 35 or skip down to around 33 maybe?

Simon · Aug 4, 2008

Coastie said:
OK simon will do.
I'm running a 38 idle jet now.
What would be your next step down, 35 or skip down to around 33 maybe?

You may as well get both idle jets Coops because either of them could end up doing the job then just go step by step again dropping down one size and checking response on the mixture screw, then dropping down one more size to check that too. At least then you'll get a good measure of how your particular carb is working, because lets be honest, the variation in product out of the factory from Dellorto has always been a bit funny :wink:

Cheers,
Simon

Coastie · Aug 4, 2008

Yeah OK mate no worries.

Coops

Dellorto PHM40 - mixture and idle

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