Correct slot in needle 503

[nickjaxe]

Hi guys still working on my rough running mid range revs 503sc,

Had a look at the needle tonight mine has 4 slots and the circlip is in the next to bottom slot, its marked 15K2,

Does this sound right, theres no info in my rotax manuals regading this.

Nick.

[ICEMAN]

Hi nickjaxe,

I had similair problems, it seems that there are two types of needles, each one with a differant main jet requirement and also differant circlip settings.... My problem was that i had "type a" needles matched to "type b" main jets. (so idleing was fine and full rpm was fine but getting through the midrange was rough)

One of the A/P`s sorted it out within minutes and the improvement in midrange performance was like chalk and cheese.

Sorry i cant remember the jets and needles specs but im sure that any supplier or AP can give you the specs.

Might be a good place to start.

[Morph]

For a single Carb serial number after 3785372

Jet Needle 15K2 - Circlip position #3 from top
Needle Jet 2.72
Main jet 185 at Sea Level
Idle Jet 45
Idle screw 0.5 turns out from closed

Prior to 3785372
Jet Needle 8G2 - Circlip position #3 from top
Needle Jet 2.74
Main jet 180 at Sea Level
Idle Jet 45
Idle screw 0.5 turns out from closed

[nickjaxe]

Mmmm may be getting somwere here thanks for that iceman,

Morph those part numbers you have given me, you say there for a single ignition engine mine is duel ignition does that mean they will be differnt from above.

Nick.

[Duck Rogers]

Nick......I think you have a single carb though. The numbers Morph gave you should be the same if I remember correctly. Morph?

[Morph]

Sorry I meant single carb

here are all the 503 options in this order Mainjet, Idler Jet, Needle Jet, Jet needle, Clip from top, Air screw

Rotax 503 SC
Up to Serial #3785371 180 45 2.74 8G2 3 0.5
Rotax 503 SC
After Serial #3785372 185 45 2.72 15K2 3 0.5
Rotax 503 DC 158 45 2.70 11K2 2 0.5

More details here

http://www.ultralightnews.ca/bing/bingjetchart.html

[nickjaxe]

Many thanks Morph I am going to take my carb apart today and check it out,

I wonder if you would know were I can find my engine number, had a look cannot see it.

Nick.

[nickjaxe]

Stripped my carb today and checked the jet number and they are all matching,

So its back to the drawing board, I just cannot get my head around why the revs at around 1/2 to 3/4 throttle 4000ish to 5000ish rpm should very so much, around 1000rpm without altering the throttle postion,

Maybe it has somthing to do with the transition from needle to main jet

HELP.

Nick.