Setting up Dellortos Idle jet

[Jota Rob]

Im in the preliminary stages of setting up a brand new set of Dellorto and all is going well.
I suspect that the pilots are too lean, but given I started with a clean sheet, it it pretty close. This is my race motor which was running the Mikuni RS38's.
With the Dells its currently on 130 mains and 60 pilots.Its the pilots Im concerned with as I cant get to a dyno or ride the thing on the road.

Positives:  
Balance the carbs on idle and on throttle open
Idle down to 700 rpm
Reasonably clean pick up from idle
Negatives: It I set the mixtures screw at about 1.5 turns out, its a cleaner pick up but the throttle hangs if I rev it to approx 4k, UP to 3k is fine but 4k or 5 k and it hangs at about 3k on the way back down. If I richen the mixture screws until it feels too rich on idle, (ie idle slows right down and less smooth) it will rev up and not hang so much on way down but doesnt feel as clean as before.


My feeling is the pilots jets need to go richer and this concurrs with the Delloroto manual which states:  PROPER SELECTION OF THE IDLE
JET
Generally, if the selected idle jet is
too big, the engine may tend to stall
and responds to the accelerator
slowly with a deaf and feeble sound,
usually overcome by closing the throttle
temporarily.
If, on the contrary, the jet is too
small, the engine responds better to
the accelerator (except when it stalls
when the jet is much too small), but
when the throttle is closed, the
speed (rpm) doesn't decrease immediately,
and the speed remains high
for few seconds before settling down
to idle.
So my question is do  you think I should  fit a set of 65's or could there be other factors causing this ?..

CHeers Rob

 

[Grant]

Is it safe to assume that we are not talking about 32mm PHFs? So, 36mm PHFs ot bigger?
Also it is assumed you have a 1200 motor?
1200s originally came with 65 pilots, although the odd one may have escaped the factory with smaller ones.
If the pilot jet is too small this would show as the adjuster screw needing to be out about 3 turns or so. Fitting a 65 would allow going back to around 1.5 to 2 turns out.
I assume you have made sure there are no air leaks at the manifold.

Also a gas flowed head will flow more mixture so may respond to larger jets all round. When I fitted a Corsa-spec head to my old 1200 I had to fiddle with pilots and adjuster screw settings, no other changes to the motor.

 

[Jota Rob]

Yes Grant, dont want to give too much away yet but same size ie 38mm. I'll go with your findings thanks and my understanding of what I've read.
I guess if I'd asked for advice on what shade of pink I should paint it or whether I should fit speedmasters or TT100's, I'd have got a plethora of responses !!  
Cheers

 

[Laverdalothar]

Hi Rob,

are the float levels equal and set right? You can make idle richer with higher float levels, too and vice versa, you can lean out idle a bit with lower float levels. so make sure they are not to high...

Then, 3.000 revs, 4.000 revs means not to much - what throttle opening do you have in the area you mean? If that is below ore around 1/3, it's the area where the slider cut-out comes into play. If it's around 1/3 to 1/2, it can be both the needle/-position or the slider cut out. Above 1/2 - which I don't assume you mean - it would be needle/needle-position. At around 7/8th it's mainjet mainly.

See the graph in the Dellorto Manual, please. For further steps, it helps a lot ot understand where which part of the carbs comes into the game.

I would set it to optimum idle and raise the needle by setting the clip one notch lower and see what happens...

 

[Jota Rob]

It's on about 1/8 to max 1/4 throttle.
Ive noticed the movement on the throttle is now 2 bloody handfuls whereas on the Mikunis it was one comfortable one. Same throttle which means the ratio at the carb end is different. To make it the same means to make a new throttle sleeve with large diameter pulley , then the throttle will be even heavier.. Subtle things like that, make riding fast harder grr.

Anyway, I haven't checked the float heights as I know how the Italians work and clearly it will be put together with the best of care, I did actually ask and even the accel pumps are set and sealed, which will suffice for now.

 

[sfcpiet]

Negatives: It I set the mixtures screw at about 1.5 turns out, its a cleaner pick up but the throttle hangs if I rev it to approx 4k, UP to 3k is fine but 4k or 5 k and it hangs at about 3k on the way back down. If I richen the mixture screws until it feels too rich on idle, (ie idle slows right down and less smooth) it will rev up and not hang so much on way down but doesnt feel as clean as before.

Rob,

Got a hunch your problems are more ignition related than carbs...

Attach a strobe and check what your ignition is doing on return to idle.  Too much ignition retard will prevent the revs to drop cleanly, usually they hang around 1500-2000 depending on how rich you have set the idle mixture, before finally dropping to around 1000rpm, but not for long before the motor starts stumbling.  Give it a rev and it starts all over again.  Sound familiar? 

I'm assuming you still have the Ignitec, set idle advance to at least 5?BTC, 8-10? even better.  Will clean up rev pick-up and the carbs will respond better to mixture screw adjustment.

Float height should be 18mm.  Softer/shorter springs work a treat when coupled to a larger actuating quadrant, had mine down to 90? turn at the throttle grip.

HTH,
piet

 

[Vince]

What I have found re jetting is you need to make big changes to get a dramatic change.Needle clips are a good example.Its really hard to notice the difference 1 notch makes,move 3 notch's and its plain as day.
Using the choke helps too,especially with Dels.Add choke and its better and the base setting is lean.You need to see an effect,the lack of change with tiny adjustments tells you nothing.Thats from 6 months of carb changes attempting to fix a cam timing issue with me.Rego helps as well,its frustrating not being able to test ride straight away after a change,been there with the illegal dirtbikes.Don't know how Chrispin handles testing having to trailer to a track day but it would drive me nuts.

 

[Jota Rob]

Ok thanks Guys, some useful points in there that I would not have thought of. Cant run today as Im working on a breather mod and have the motor hanging out sideways to sort out the cam box, but will look at it hopefully this eve and 1st thing, check the timing, although of course it was great before, different carbs I guess change everything..and easy to play with and put back.

Normally Id get it to the dyno but Nicks gone on holiday !

 

[KERMIT1200]

Hi Rob,
Set the mixture skrew to what ever the motor requires to get the highest idle speed.If you are approaching 2 1/2 turns out then I'd say you require bigger pilot jets.
I'd be more concerned with main jet,because thats the jet that you'll use most on the track.Also it affects the needle (mid range).
A fuel check on a dyno would be good but is'nt going to happen for reason mentioned.
The first thing I would suggest is taking a selection of main jets to Mallory and try and run a plug chop on your first run.The second thing is contact the VMCC and enquire whether anyone is setting up (portable) dyno at Mallory for the weekend.
To be honest its pointless wasting to much time on the idle side of things until you've set the main jet.

Have a great time at Mallory,I'm off to Snetterton,
Andy