Symptoms of initial float failure ?

by nicola di biase in 912 / 914 Technical Questions 9 years ago

Hello ,

during last months my Rotax 912 uls (year 2008) not affected by recent floats bulletins with 390 hrs total and all maintenance and sl,sb done is begining to start perfectly without starter use.

With starter on is very difficult to start and runs horribly rought. Without starter it is perfect. Now with summer it seems more evident but this defect was also present during winter/spring.

Because i had checked usual items(pneumatic sync ok, idle rpm 2000, starter jet ok, starter linkage ok, cdi unit new ,battery voltage ok) i have one question.

If a float begins to be only slight defective witch are first symptoms ?. Are they compatible with this defect ?

Can a little higher fuel level in bowls/slightly rich mixture do not hurt performance but only affects starter phase?

Thanks

Nicola di Biase

Re: Symptoms of initial float failure ?

by Roger Lee » 9 years ago

Roger Lee

128 5.28k 4.98k

Hi Nicola,

Does your engine use the choke (enricher) or does it have a primer setup?

Your symptoms and high idle suggest a slight flooding problem at start.
You may have the idle set too high at 2000 rpm. This would be my number one guess and the first thing I would adjust. This may be causing a slight flooding issue when you add choke or primer and this is why it starts better without using the choke because you already have extra fuel going to it with the advanced throttle high idle. Before I started changing and working on everything else I would reduce the idle rpm to down between 1700-1800. This will reduce the amount of fuel at start. Try that with the choke and see what happens.
Next with a high idle at 2000 rpm you can't afford to give it any more throttle at start so this would cause the hard starts by flooding.

If you suspect a heavy float remove them and weigh them as a pair. They should be under 7 grams or less than 3.5 each. New and dry out of the box they are around 2.75 grams. Just because you didn't fall in the SB for heavy floats doesn't mean you couldn't have one.

If during your float check you may have inadvertently tweaked or bent the float armature that controls the float level. If this happened you would need to remove the carb and have it upside down to make this adjustment. Try the first suggestion first about reducing the idle rpm.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-349-7056 Cell

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Re: Symptoms of initial float failure ?

by Richard Guzzo » 9 years ago

Richard Guzzo

0 1 0

This is just an FYI on this float topic. I am not an AP but do have a 912...and I slept at a Holiday Inn last night.
My 280 hour, perfect maintained, 2007 engine ran so smooth and strong until one day the idle started to lower...I kept flying and taxied with just a pinch of throttle. maybe 6 hours later, idle lowered more and on run up, ignition A was normal but B sounded like plug wire (or 4) was off and rpm drop was too significant for take off so, to the hanger where I pulled plugs to find on side(left) 4 fouled and black plugs. At high rpm there were no noticeable problems...Only at below 2500rpm. Sunk floats...runs rich!
So, my carbs have no trays and with a pry on the spring clamp(close to off but not completely) loosening Phillips screw of the $90 dollar rubber collar(welcome to Airplane ownership) a slight turn of the carb and Voilà! One..I repeat 1, sunken float! I weighed it...over 4 grams. It's mate was 2.9g. WHY ONE BAD AND NOT 4! I left it out for 48 hours and weighed it again to approx. 4 maybe 3.9g's.
Cleaned plugs of course, put floats back in (BTW, no probs with gaskets but in case I had two on order..which came before I took this on) and much to my surprise...... MY 912 was back to perfect! smooth idle, purrrrring like a kitten. 15 minute job, cowl removal was hardest part. What's the A&P charge on that for a signature? I say, DON'T DO ANY ADJUSTMENTS BEFORE YOU WEIGH FLOATS! You may muck it up for yourself and have to synch those babies.
All I can say is I ordered and have new floats which will be installed today(been up to Osh...tried to talk to rotax guys but they were talking amongst themselves so I didn't bother). I will save the good old floats for spares. It seems to me after 3 years this float went bad. That's all! Floats go bad! I wanted to know what the real prob was with advisory on floats. Maybe some guys new floats went bad in a week. If anyone can get the attention of Rotax guys, ask will ya?

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Symptoms of initial float failure ?

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