Flattening off the bottom end power on a Dellorto PHM 40

Ady · Aug 28, 2007

Gent's
Real broadly speaking ...
I'm finding that after riding through a lot of water, i loose my tickover. So i screw the idle adjustment screw in a bit, but then it struggles to start off the button and generally requires fiddling with the mixture screw..... However, if it were dry, the tickover remains constant.

Maybe this is because i run a 50 pilot air jet. I do this because it deddens the power at the bottom end....
In actual fact, my carb is jetted down in every way, apart from the pilot air jet. I run a DR266, and a 175 main jet.

Recently, i fitted the standard 35 pilot air jet and the lack of tickover improved, but it was still a beast on the bottom end (too much for my liking).
Yes, i'm comparing it to an 06 - 400 Orange machine ... with a lovely gentle bottom end (superb for hill climb's), but wanna get it as smooth as i can.

So, i'm considering ordering my self a fatter needle the K51
Question 1, Considering the above, is this gonna help (alongside the 35 air jet) ?
Question 2, Standard needle is the K35 ... Is the 51 fatter, therefore allowing less fuel in, or is the K32 fatter ?
Guess, i just need some simple clarification.
BTW. In the future, i may try the 'crescent' modification.

thanks
Ady

Taffy · Aug 29, 2007

i wouldn't go outside of K35 or K51. they are the only needles that work.

it's not a PAJ it's a PJ ady.

the best way to soften the bottom end is to fir a /50 slide. you should find when you look under yours that you have a /40. the /50 will make the bottom end fluffier.

that's all you'll need to do.

regards

Taffy

Ady · Aug 29, 2007

Cheers Taffy - thought as much.
Will probably try the crescent mod on my 40 slide, as a new 50 slide was about Ã‚Â£120 at DCR, if i recall.
Will splash out on a K51 needle and see how i get on with that.

Cheers
Ady

Taffy · Aug 29, 2007

i would modify my original slide for sure. good idea.

your bike is old enough to need a new emulsion tube so while you're there i would get the DR270 or even the DR272. we can guide you fairly swiftly to better jetting.

if you only have a 35 and a 50 you need a 40 and 42 IMHO.

regards

Taffy

dsducati · Aug 30, 2007

Riding through water with the bowl vent hose submerged can cause enough pressure to build in the float bowl so that fuel from the tank can't re-enter. After running rich for a bit, the fuel level then is low. All this messes with the idle and is why the guys that run in water vent the bowl upward. Has to be deep water for long stretches to create an issue.
dan

Ady · Aug 30, 2007

That's interesting
I've gone the wrong way then....
I've already changed my emulsion tube, but stuck a DR266 in, thinking it was smaller, thus allowing less fuel in at the bottom end.
Hell, i've got a DR272 and feel like running to the garage now and trying it !!
Soooo.... (using the spares i've got) A DR272, a 175 MJ, a 40 PJ, a K35 needle - on the top clip ???

regards
Ady

Ady · Aug 30, 2007

Hi Dan
I was aware of that, and have previously fitted a T piece to vent it from top and bottom.
Your explanation was excellent though and helped me to understand it better than i did before.

Many thanks
Ady

Taffy · Aug 30, 2007

go into the carburation part of the doc and there are two sets of specs there by heimar and joeusa. joe only recently reconfirmed the work he did to me, that's reconfirmed that he did some work - not to me (you understand, i wouldn't want any confusion to happen so that you know, you thought that he did it to me. you didn't think that did you? oh good, good. ahem o yes now where was i?) and i'll now copy and paste them to you but they really are the same as the link to the thread and i think you should have a go....

regards

Taffy

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Flattening off the bottom end power on a Dellorto PHM 40

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