Rotax 503 engine lag
in 2 Stroke Technical Questions
13 years ago
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by Geoff Storey » 13 years ago
ignition is DCDI set timming with a protract as suggested in the last forum, carbys have been syncranised .it has me baffeled why it is doing this.
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by Nick Axworthy » 13 years ago
I was hoping somebody else would add some input to this one,
Bit of a head scratcher...I'm clutching at straws here...but is the exhaust sys the correct one for the engine and not bunged up...do you have choke on the carbs...is yes have you experimented with the at the problem RPMs to see if adding a bit of choke helps or make things worse,
If you have choke...are you sure they are fully closing....did I remember you say a while back that you had a spare set of carbs,
What method do you use to sync the carbs...it does sound like a carb prob.
Nick.
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by Geoff Storey » 13 years ago
Hi Nick l though there might be more input also , the exhaust is brand new suit 503 the old one was cracked on both sides of the radious l was told thats probably what caused the piston to grab making it run lean.
l have the lever chokes and yes l have a spare set of carbys and l swapped them over and still had the lag.
On another forum l was told l may have a leak between cylinders at the middle crank seal and it only shows up at low rpms ,l am going to do a leak test on the weekend .
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by Nick Axworthy » 13 years ago
So would that be a leak passed the big O ring between the crank halfs...did yours have one on ??
A hole in the impulse pump diaphragm can cause all kinds of probs at low RPM as it lets neat fuel into the engine casing and it makes the motor bog down but run more or less normal at high RPM...and s it maybe a small hole it still pumps up to the carbs as well,
Only ever had it happen on an outboard...and it took some tracking down....it had more or less the same pump as a Rotax s 2 stroke,
Worth checking before you tear the motor don again.
Nick.
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by Geoff Storey » 13 years ago
l fitted new orings on the bearings l didn't know there was a seal in the center of the crank you cant see it because of the aluminum sleeve that is over it cant be replaced unless you split it in two ,the pump is new but will check it out never know it could be faulty..
l will start a new topic on the 4 stroke soon as l have just bought a Zenith ch 701 with a 912ul it misses and shakes l will start checking out shortly..
cheers Geoff...
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