skyfox1 Posted September 20, 2015 Posted September 20, 2015 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.
jetboy Posted September 20, 2015 Posted September 20, 2015 Is air cleaner same type? I used to use the K&N dual air cleaner I liked better than foam pod filters EGTs showing normal? Float needle valves get old but you should have new ones with the new carbs Other than intake leaks or crankcase seals that leaves the muffler I liked the 503 for its simplicity and never had that sort of variation on either of them. Ralph
skyfox1 Posted September 20, 2015 Author Posted September 20, 2015 Hi Ralph i am using the k&n dual aircleaner and have changed muffler also sealed ports did a pressure test on case no leaks .i love 503s also in all the years l have used them never had this change in weather conditions.
Guest Maj Millard Posted September 20, 2015 Posted September 20, 2015 What EGTs are your running at high takeoff power........? Sounds to me like your are running on the rich side and iceing up your main jets.
skyfox1 Posted September 20, 2015 Author Posted September 20, 2015 Hi Maj 1100 on both EGTs runs the best on cold days hot days loose 800rpms i have changed jetting makes no difference.
Tomo Posted September 21, 2015 Posted September 21, 2015 I'd be checking your muffler - muffler and carbs have to be calibrated (for want of a better word) on those two strokes.
skyfox1 Posted September 21, 2015 Author Posted September 21, 2015 Hi Tomo have a new muffler and have sync both carbs with a carby mate . 1
Cosmick Posted September 21, 2015 Posted September 21, 2015 FYI mine has a fixed Bolly, revs on the ground change with temp and humidity. Usually around 6400 (powerband on 503 6100 to 6400) up a Thousand feet and lucky to get 6300. Not to resolve your issue but for some comparrison. 1
Guest Andys@coffs Posted September 21, 2015 Posted September 21, 2015 Do you still have the old stuff? If so start swapping new for old one at a time......Could be that new isn't exactly the same as the old......
skyfox1 Posted September 21, 2015 Author Posted September 21, 2015 Hi Andy l had the problem after rebuild l pull motor apart and rechecked everything was right nothing changed so then i started renewing bits to try and elimanate the cause put new on then back to old still cant resolove it what ever is causing it has done the same on my spare engine even Wal at bertflood cant work it out.
Guest Andys@coffs Posted September 21, 2015 Posted September 21, 2015 ok so we are looking for something way out there....... What does the EGT look like when normal compared to when down on RPM's is there enough of a difference to suggest anything? How does the fuel tank breath? is there a a breather hole that might be blocked where that blockage is temp dependant... like gummy varnish etc..... when running at RPM is it possible to loosen the fuel cap to see if the RPM's are then affected in any way suggesting a vacuum forming in the tank.... sorry those are pretty wild..... But I had fuel issues on a 582 when I added an inline fuel flow meter...the meter had an orifice that could be added for low flow engines...582 was neither low or high using the sensor manufacturers documentation and I added the restrictor.....in retrospect a stupid decision cause fuel restriction to the engine had a much worse impact than a gauge being a bit more inaccurate...... Has any fuel related work been done at the same time such as extra instrumentation or changed instrumentation or replacement fuel lines etc? When running at full power when the RPM's are down if you kill the engine what about the carbie bowl fuel levels as soon as the engine stops....are they at the usual level as compared to when it develops full power. When you changed the carbies were they completely new or was some parts transferred across to new? Andy
Guest Maj Millard Posted September 21, 2015 Posted September 21, 2015 1100 is a little cool/ rich...raise your needle by lowering clip..you should be looking at 12o0 - 1250 at max power on takeoff. The reason you loose RPMs on hot days is the air is thinner, and you are running even more rich. Best mixture is around 15-1...fifteen parts air to one part fuel, called the stoinochic mixture.
horsefeathers Posted September 22, 2015 Posted September 22, 2015 stoinochic Try stoichiometric EGTs are affected by the load on the engine as well, so you can also try playing with your prop. pitch. EGTs on my 582 had more than a 100 degree temp change when I altered the pitch by 1/2 degree.. 1
skyfox1 Posted September 22, 2015 Author Posted September 22, 2015 Dont have a problem with temps its just that yesterday in the hanger start the engine warm it up go full power get 7100 static cool day without touching or doing any thing start up following day same procedure warmer day only by 7 degree static full power 6000 rpms .
horsefeathers Posted September 22, 2015 Posted September 22, 2015 Leaky/cracked rubber carby boots???
skyfox1 Posted September 22, 2015 Author Posted September 22, 2015 Hi Maj i had a one piston grab and since i have rebuilt the engine l have been run extra oil 50 mls per 20 lts fuel do you think that would make that much difference in the rpms on different temperature days. Cheers Geoff
Yenn Posted September 23, 2015 Posted September 23, 2015 I don't know what the cure is but I don't think adding extra oil to the fuel mix ill prevent a piston grabbing. My understanding is that a grabbing piston is usually caused by using full power before the engine has fully heat soaked. We used to run our 2 strokes for a short while to warm them up, then shut down for a few minutes to allow the heat to soak right through the cylinders. Then re start and go flying. Never had any more problems, but that doesn't mean our theory was correct, just that we may have been lucky. Someone with more 2 stroke knowledge than me may have a better idea.
flyerme Posted September 23, 2015 Posted September 23, 2015 It's the rings that grab usually from wear and jumping there locater The exhaust is a tuned pipe designed to block the exhaust outlet with sound waves for power band,Extra oil in the mix will give it a rich mixture throughout.( makes it little sluggish) Temperature shouldn't affect the rpm much . Atmosphere will but only slightly... Is your 503 points or cdi? Dual or single carbie? 2 air filters or 1? And the big question. Do you have a tiny tach fitted or can you borrow one to confirm it's not a gauge issue? Sorry if already posted? It's very strange . Would then look at prop... Good luck keep us posted Tim
skyfox1 Posted September 23, 2015 Author Posted September 23, 2015 Its duel carby duel cdi with oval aircleaner which l changed for single k&N filters no difference. Have changed tachos to see if it was that but still no difference .also got a brolga three blade prop swap out the ivo three blade still no change .when l get it all sorted out hopefully soon l will try your warming process Yenn.
dazza 38 Posted September 23, 2015 Posted September 23, 2015 Its duel carby duel cdi with oval aircleaner which l changed for single k&N filters no difference. Have changed tachos to see if it was that but still no difference .also got a brolga three blade prop swap out the ivo three blade still no change .when l get it all sorted out hopefully soon l will try your warming process Yenn. Jeez I hope you mean dual, I would hate to see your carby and Cdi units having a shoot out.Tongue in cheek, just mucking around. Duel is OK, well sort of. 1
Guest Maj Millard Posted September 23, 2015 Posted September 23, 2015 Hi Maj i had a one piston grab and since i have rebuilt the engine l have been run extra oil 50 mls per 20 lts fuel do you think that would make that much difference in the rpms on different temperature days.Cheers Geoff Geoff, No generally not a good idea to add additional oil for any reason...50-1 is 50- 1. By adding additional oil you are actually leaning out the mixture...think about it. I ran a 582 for around 650 hrs on my Drifter without as much as a hiccup....always kept added oil spot on the number. As far as snicking up a piston....many possible causes there...inadequet cooling on one cylinder, incorrect oil qnty in fuel, loose fan belt if fan-cooled, piston incorrect orientated on rod, rings incorrectly fitted to piston and not orientated toward intake side instead of exhaust outlet. Synthetic oil use causing ring jamming and lack of movement on rings. Etc etc....who rebuilt the engine ??...
skyfox1 Posted September 23, 2015 Author Posted September 23, 2015 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
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