Surging RPM Rotax 503dcdi
in 2 Stroke Technical Questions
11 years ago
Hi guys I wonder if any of you guys would like to comment on a problem I had when flying my trike a few days ago,
The 503dcdi fitted to my trike was brand new about 12 months ago one of the last available here in the UK,
When I first fitted it I was not happy with the EGTs running at 650c 1200f at cruise 5000rpm and 625c 1160f WOT with all the factory std jetting and needle positions suitable for use in my area...the agent I bought it off said to me it should be fine at those settings and to leave it at these std Rotax settings,
But I was still not happy running at max EGT...so I raised the needles one notch and this had the designed effect of getting the EGT down to 625c max 1160f at cruise 5000rpm,
I have ran it like this for the last 12 months totally happy with it...but around 2 months ago I thought the fuel burn was higher than normal so I dropped the needles one slot back to factory spec and test flew it...still hitting 650c or a tad more as it was when I first fitted the engine...so I lifted them back again,
A few days ago I had a flight in my trike on a very hot day over here for us anyway...it was 20c 70f
And had a prob I have not had before...the RPM would not hold steady at cruise power...it was ok at WOT and lower RPMs but the mid range it would surge from my normal 5000rpm to over 6000rpm,
I would close the throttle a bit to get back to 5000rpm only to have it drop to around 4700rpm, I would re adjust again to 5000rpm...only to have it back at 6000+ a short time later,
As I say it was an unusually hot day over here and the EGTs where quite low at around 560c 1040f...I suspect a rich mixture problem,
I have been reading this very interesting artical,
http://www.challengers101.com/ExhaustGasTemp.html
And was wondering what you guys think of the idea from the artical of giving my prop more pitch,
This will take my RPM down from the 6250 static 6500rpm climb out I am getting know which are in line with Rotaxes recommendations but I maybe able to get my needle back to std Rotax setting with more pitch if it works out...but I dont want to mess about in this area if its not a good idea,
Any ideas will be most welcome.
Nick.
The 503dcdi fitted to my trike was brand new about 12 months ago one of the last available here in the UK,
When I first fitted it I was not happy with the EGTs running at 650c 1200f at cruise 5000rpm and 625c 1160f WOT with all the factory std jetting and needle positions suitable for use in my area...the agent I bought it off said to me it should be fine at those settings and to leave it at these std Rotax settings,
But I was still not happy running at max EGT...so I raised the needles one notch and this had the designed effect of getting the EGT down to 625c max 1160f at cruise 5000rpm,
I have ran it like this for the last 12 months totally happy with it...but around 2 months ago I thought the fuel burn was higher than normal so I dropped the needles one slot back to factory spec and test flew it...still hitting 650c or a tad more as it was when I first fitted the engine...so I lifted them back again,
A few days ago I had a flight in my trike on a very hot day over here for us anyway...it was 20c 70f
And had a prob I have not had before...the RPM would not hold steady at cruise power...it was ok at WOT and lower RPMs but the mid range it would surge from my normal 5000rpm to over 6000rpm,
I would close the throttle a bit to get back to 5000rpm only to have it drop to around 4700rpm, I would re adjust again to 5000rpm...only to have it back at 6000+ a short time later,
As I say it was an unusually hot day over here and the EGTs where quite low at around 560c 1040f...I suspect a rich mixture problem,
I have been reading this very interesting artical,
http://www.challengers101.com/ExhaustGasTemp.html
And was wondering what you guys think of the idea from the artical of giving my prop more pitch,
This will take my RPM down from the 6250 static 6500rpm climb out I am getting know which are in line with Rotaxes recommendations but I maybe able to get my needle back to std Rotax setting with more pitch if it works out...but I dont want to mess about in this area if its not a good idea,
Any ideas will be most welcome.
Nick.
