Rotax 503 has me baffeled.

[skyfox1]

Dazza wish they would have a duel might fix the problem .i will correct my spelling in the future.

 

Cheers Geoff

 

 

[dazza 38]

Dazza wish they would have a duel might fix the problem .i will correct my spelling in the future.Cheers Geoff

No need to Geoff, I make just as many mistakes as everybody else. Just mucking around. No offence intended.

 

 

[Guest Maj Millard]

Hi Maj the engine that grab was an engine that i bought 2 years ago was running perfect did about 180 hrs then after about half an hour into flight lost power landed pulled engine apart found mag end piston had grab and scored the bore .i have rebuilt the engine myself which l have done many 503s before none have ever had this problem before will go back to the 50-1 mix see what difference is thanks for you input Maj

Maybe run - in wasn't done correctly, they go well if done right by the book.

 

 

[Guest Andys@coffs]

So for clarity the engine currently on the machine, and a spare you have fitted have exactly the same issue., correct?

 

If so was it a complete swap over or was there any common parts?

 

If complete then your left with the fuel system and ignition switches....is it possible that one of the mag switches is failing and you have a transient short to earth? easy to disconnect one mag switch at a time and wire a replacement in place to test. If it is failing then what you are seeing is the expected rev drop when running on a single ignition system?

 

Other than that what about the suggested checks I mentioned in my last post for fuel and tank...other than prop that's the only thing common to both engines.

 

Andy

 

 

[skyfox1]

No offence taken Dazza got to have some fun .

 

 

[skyfox1]

Hi Andy the swiches are one common thing l haven't checked l do a mag check and both work fine could be some intermittent problem will change them see what happens fuel tank breather is all clear replaced fuel pump as well fuel bowls are at correct level .and yes both engines have the same problem it must be some thing simple which l cant see l have swapped old parts back no change.

 

 

[flyerme]

Did you rebuild bottom end ? And was crank replaced or checked ?

 

All seals replaced?

 

Did you run it in per rotax specs ( takes an hour) and note all temps etc...

 

Also just as important as correct warm up is the cool down .

 

Here's my 503 -run in specs...( no cht on the nieuport )

 

Also the same for my 582...

 

I have been a 2stroke mechanic( mainly moto x works machines) for 26 years now, never come across an intermittent RPM rise of that calibre due to outside temp?...Have had loss of RPM intermittent .. Turned out dad and son mixed fuel different, dad added extra100 mls to jerry can making a strong rich mix, lol.

 

What oil do you use and have you changed oil brands?

 

Did you fit piston per specs or by replacing it as it came out of engine? I ask as I had an apprentice once who removed a piston and refitted by noting the old piston position , however the old piston was backwards ( arrow pointing back) yes it made another mess of the customers kx 250 requiring another full top end replacement including the kawasaki power valve. Grrrr cost me $$$$$

 

What spark plugs are you using?

 

No worries

 

The More info the better :)

 

Good luck

 

 

[aj_richo]

Extra oil in the mix will give it a rich mixture throughout.( makes it little sluggish)

For a given size jet, I thought increasing oil amount in the mix would reduce amount of fuel... making it leaner?

 

 

[Phil Perry]

Could some shed some light on my rotax 503 scratched my head some much l going to go bald .l rebuilt my 503 some months ago since then when the weather temp changes so does my engine set it up for static 6200 rpm on the ground cold day about 10 to 15 degree day full power in flight 6800 .when the weather is about 20+ degrees can only get 6000 rpms .carbys set and jetted for sea level as l am only 150 above sea level put new carbys change cdi coils, new plugs ,new fuel pump air cleaner even changed stator .nothing makes any difference .if l change the prop pitch to get to the 6800 full power on clod day it gets to 7200 which is not good .

put your thinking caps on hopefully give an answer please.

 

Cheers Geoff.

Hiya Geoff,. . . . I have a Rotax 503, fairly early model, bought in 1991,. . . .with a single carb and points ignition. May I ask in what what config you are using it please,. . ie, pusher,. . or tractor ? My R503 has suffered though 1,080 Hours, and one 'B' type gearbox. . . . It still has the original pistons, although I broke the crank into two neat pieces about twelve years ago. . . other than that, it's been brilliant. ( The forced landing was exciting. . .but that's another story. . .! )

 

My Guru Ronnie Rotax, the famous Ron Bates, of Stoke onTrent, UK, looked after mine for the first couple of years after purchase of the trike,. . .and told me that it ought to run ( In my Gemini Flash 2 trike - ie, "Pushing". . .) at around 6050 RPM on a static ground test, and no more than 6350 whilst flying, otherwise the engine life would be reduced.

 

That engine has been operated to his specs ever since, and, apart from a coil failure a few years ago, it still gives perfect service. . .ie, it has not failed unless I, as the IOC ( Idiot in command) have failed, for whatever reason,. . to keep it supplied with fuel. I use Silkolene Comp 2 premix oil, never used anything else,. . .at 50:1 mix, and the thing does not require a head off really, for around 250 hrs - 'ish,. . .and even then, there's no soot, and I shouldn't have bothered.

 

I have a three blade warp drive carbin fibre prop on it, it came supplied with a two blade wooden propeller, which is sitting here in the hangar, leaning up the wall, all varnished and lovely looking,. . . right next to where I'm typing,. . .( anyone want it ? ) I got the carbon fibre prop for a song, but was quite miffed when there was no apparent difference in performance of the aircraft,. . .apart fro the much longer delay in reaching full power every time I screwed up a landing approach,. . the timber prop, with it's low inertia, gave instant thrust,. . .the plastic bugger was a bit more sluggish in that regard. . . but it DID put up with hail and rain stroms well, and didn't fragmentate. . . which has been nice, in rainstorms, when I've been transiting either to La Belle France over La Mer, or over the bloody Irish sea to the Isle of Man. . .( 10 miles further ! )

 

Two stroke motorbikes could often be revved to over eithteen thousand RPM,. . .but in my experience,, we had to rebuild them after the race,. . .you don't really want to be doing that often to the engine in your flying appliance really do you ?

 

Keep the revs down a bit mate,. . . anything over 6500 on a R503 is taking the wee a bit,. . .the engine life really Will suffer., and if you've got twin carbs,. .then there's even less reason to thrape the engine really. . . .

 

Phil

 

 

[Phil Perry]

For a given size jet, I thought increasing oil amount in the mix would reduce amount of fuel... making it leaner?

That is EXACTLY what will happen. Causing LESS lubrication, . . . . . . . .oops.

 

 

[flyerme]

Yes correct what goes through the engine is a lean fuel mix or oil rich mix ,

 

I should have been clearer sorry :). " a rich OIL. Mix" lol. Resulting In a lean fuel intake ....

 

 

[skyfox1]

Hi Tim yes replace crank and new seals and all my engines l rebuild go though the proper rotax break in process. Plugs l use are br8es and oil is castrol 2t .

 

 

[flyerme]

Hi Tim yes replace crank and new seals and all my engines l rebuild go though the proper rotax break in process. Plugs l use are br8es and oil is castrol 2t .

All perfect... So now IDE be ruling out engine and look at fuel system, electrics.

If prop change doesn't do any thing. It has to be fuel system or electrics surely? Real head scratcher

 

 

[skyfox1]

Hi Phil the motor is in pusher configuration in a Drifter sound like you have had great run out of your engine .

 

 

[skyfox1]

Yes Tim thats what i recon but nothing l do makes any difference the thing that gets me is go flying on a cold day runs perfect runs good temps full power couldnt ask for perfect set up soon as the outside temps rise 5 to 8 degree wont get full power loose up to 800 rpms .

 

 

[flyerme]

This is a bit out there but, what fuel filter/filters do you use? 2st motorbike or paper like a z14? Oh and do you have a fuel pressure gauge? Also Do you have an auxiliary fuel pump fitted? Clutching at straws here

 

No wuggers

 

 

[skyfox1]

Fuel filter is glass type with cleanable mesh .no fuel pressure gauge or electric fuel pump but l did fit temporary fuel pump and no change to full power check carby float levels all with in specs .still scrathing my head i will find the problem .

 

 

[facthunter]

Have you done a fuel flow rate check? Is there any way air can get in on the suck side of a pump? Nev

 

 

[skyfox1]

Hi Nev no l haven't done fuel flow and l replaced fuel lines and suction line as far as l can tell all looks tight .

 

 

[smokeybear]

Could some shed some light on my rotax 503 scratched my head some much l going to go bald .l rebuilt my 503 some months ago since then when the weather temp changes so does my engine set it up for static 6200 rpm on the ground cold day about 10 to 15 degree day full power in flight 6800 .when the weather is about 20+ degrees can only get 6000 rpms .carbys set and jetted for sea level as l am only 150 above sea level put new carbys change cdi coils, new plugs ,new fuel pump air cleaner even changed stator .nothing makes any difference .if l change the prop pitch to get to the 6800 full power on clod day it gets to 7200 which is not good .

put your thinking caps on hopefully give an answer please.

 

Cheers Geoff.

Try using a digital master tachometer to check actual revs first, also what oil is used in gearbox 85W140?

 

 

[pylon500]

New to this thread, but used a 503 some time back.

 

What I did spot reading this is 'no electrical fuel pump', but I assume you are still using the Rotax supplied Mikuni diaphragm pump?

 

If so, have a look at the tiny bleed hole from the pulse line.

 

It should be pointing downwards (not always done), and may have gummed up a bit, differing temperatures may change the viscosity of the 'goo' in the hole, changing fuel levels in the float bowls?

 

Maybe a bit of a grab, but nothing else has cured it yet?

 

 

[skyfox1]

Hi pylon 500 found the problem it was the fan belt when it was cold the belt must have been slipping slightly as all temps were good did show up but hot day belt must have gotten bit more sticky grabbed better loaded the fan up properly took away the revs all sorted now after all that I am in the process of put 582 on it now thanks for everybody's input cheers ..

 

 

[WayneL]

Thanks for the update Skyfox1, for those of us that still own a R503 we will commit these symptoms and your fix to memory for future reference.

 

Wayne.

 

 

[Guernsey]

Stone the crows I have posted too late now that the problem has been fixed.

 

I was going to suggest wood chips blocking up the carby or the air filter after scratching your head so much.

 

Alan.

 

 

[facthunter]

You might get another belt too if you keep up the funnies. Nev