Tuning Rotax 503 or others

[bushpilot]

My Rotax 503 needs a tune; it is running a bit rich - exacerbated by my strip being at 2,800' ASL I guess..

 

Is tuning these (dual carby) something that can be done as a self-maintenance thing? Any clues on how and equipment needed?

 

Thanks,

 

Chris

 

 

[Ultralights]

the mixture is controlled by the position of the jets, when i first got my 503 it was on the leanest setting and getting no where near full power, after a top end rebuild and adjusting the needles to the book setting it runs up to 6300 ( i have a 18deg cruise prop) where before it would only do 5000 max. though on the book setting, it would gt the EGT up close to the red when at reduced power, so i adjusted the needles to 1 stage richer, now she runs nice and cool at lower power settings and still gets max power.

 

 

[drifter_driver]

hi chris, you can adjust the mixture in 503 engines by adjusting the position of the circlip(retaining clip) on needle. the needle in 503 usually have three settings.to lean the mixture raise the circlip one or two notches higher.if it is already in the top position consider buying another needle next size up.it is relatively simple to do and you don`t need any special tools.just open two top bolts of carby and pull out slider mechanism(carby piston).then squeez down the spring with your thumb and push out throttle cable through the bottom of slider and move it sideways to release it through larger hole.vice-versa for putting it back togather.

 

to reach correct mixture setting I usually run EGT`s in the range of 1100 and also keep an eye on the colour of the spark plugs.

 

cheers

 

 

[bushpilot]

Thanks for the advice guys.. Can I assume then that in making these adjustments that I do not have to worry about balance between the 2 carbies? ie if the same adjustment is made to each, say the circlip adjustment - then they will be balanced OK?

 

(BTW: I dont have EGT - only CHTs)

 

Txs

 

Chris

 

 

[drifter_driver]

if you keep same setting on both the carbies you should`nt have any problems.

 

cheers

 

sunny

 

 

[Guest Perry]

Chris,

 

By making adjustments on the needles of both carbies will NOT take care of the balance - be careful as mixture and balance are two completely different tasks. As correctly pointed out, adjusting needle position and jet size will take care of mixture control - get an EGT installed on each exhaust port as for a couple of $$ could save melting the pistons...

 

As for getting the carbies balanced...the simplest method is to remove the airfilters and check the position of the inner slide pistons at varied settings (with engine off of course). By adjusting the cable tension on each, one can set the position of the slides accurately - the fully open position (max RPM) is most critical.

 

Regards

 

 

[bushpilot]

This is all useful advice; thanks heaps to all of you for helping... Will be into it next weekend...

 

BTW: Any hints on buying /fitting EGTs?

 

Cheers,

 

Chris

 

 

[Knighty]

Hi Chris

 

Wade Marlo (Wadeair) at Springhill 63655111 can supply units over the phone via credit card transaction. Probes are fitted 100mm (4 inches) from the piston skirt, simply drill the right size hole for the probe and use the clamp supplied to secure. Really simple mate, no dramas!

 

Knighty

 

 

[facthunter]

EGT's & tuning.

 

Just buy one of the type mentioned, and swap them over to check each cylinders performance. ( block the other hole when not in use). 2 indicators can read differently anyhow. I would not change the carb. setting from standard without an EGT reading to reassure me that things are OK. By the way, the full throttle fuel mixture is controlled by the MAIN jet size. The needle position only affects up to about 3/4 throttle. Remove the manifold to drill the holes or you might get shavings back into your engine . The idle speed is set by the idle stop screw, (one on one side of each carb ). To set them, close the throttle fully, & with the air cleaners removed, adjust each slide by means of the screw, so that the opening is equal on each slide & about the average of the two (assuming that the previous idle speed was OK) You may have to back off the cables to permit the slide to fall to the close position. After the stop screws are set equally, increase/ decrease the idle speed as required by moving them an equal amount. Ensure that there is an equal amount of slack at the carb. end of the cable outters, suggest about 2 mm max., and that should ensure that the slides move together. Check through the range of throttle movement. Ensure that you obtain full throttle on both Carbs Nev...

 

 

[Yenn]

To balance the carbies the recommended way is to use a plastic pipe with some water in it. this hangs in a U shape connected to the nipple on the side of each carby.

 

Be careful not to have too much water in the tube which should be about 2 or more m. long. The theory is that each carby will pull the same pressure and the water will be the same height in both legs of the pipe. If the water is not level you adjust the slide to get them level. Not easy to explain in words but there should be people around who have done it.

 

For a mine of information on Rotax engines get hold of a CPS catalogue. CPS is California Power systems and you should be able to contact them at:- [email protected] or www.800-airwolf.com

 

 

[facthunter]

adjusting balance.

 

That idea will work, but I personally don't like adjusting an engine standing that close to an active prop. I don't think it is that critical in practice, that sighting the opening by eye,(or using a piece of wire as a gauge) WITH THE ENGINE STOPPED, doesn't give a good enough result. Nev....

 

 

[Guest micgrace]

Hi

 

I'm a coward when it comes being near an active prop. I might add I originally used a device, a sort of flow meter, that let you see how much air went into each individual cylinder. This made tuning a cinch. For idle and transistion only though.

 

Micgrace