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Flooded Again


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  Tried to start Ct again today with no choke, no start again tried several throttle

positions which did not help, I then tried choke still no start, pulled plugs and they

were soaked again with fuel, after letting it sit for hour with plugs out I put them

back in and it started right up.

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I have a question, actually.


Procharger: next time you have trouble starting, disconnect the softstart connections to the starter solenoid and ice the modules. See if it starts then. Just humor me :-). I am curious if you had an extreme bout of bad luck and ended up with some super funky broken modules.

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Are you using choke to start up during the first start of the day?  Maybe try leaving the choke OFF.  Possibly something set wrong/backwards in the choke circuit, causing you to run pig rich all the time and turning choke on leans it out too much for a cold start?


Just guessing.  Certainly something easy to try.

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I would turn on the fuel right before you are ready to crank. Give it just a couple seconds to top off the float bowls if they are not full. No choke, as you are cranking start pulling in a little choke as it cranks. Mine even when it's cold out doesn't require full choke to start right up. (although I always have the oil tank and block heater plugged in for a while when cold). But giving it a chance to fire without the choke first is a good idea as Andy suggested (IMO). I have my screws under the carbs leaned out slightly and I can start it on a warm day without any choke.. just bang and it's running smoothly, and maybe half choke on cold days. Little different setup but worth trying maybe...


What are your idle air fuel mixture screws set at on the bottom of the carbs? They run pretty rich at the recommended 1 1/2 turns as is.. if they are set wrong, it might be a little too rich although I would expect you would notice it running a little crappy after it starts as well if it's that rich....


just some thoughts...

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  • 2 weeks later...


I just finally fixed my own problems with starting. Turns out I installed the chokes incorrectly. I had the choke discs installed on the correct carbs*, but I made the mistake of installing them with the dot towards engine, which effectively renders the choke useless. I put these together last summer while the aircraft was being repaired from the student wrecking it, but I didn't fit it to the engine for months and so it's no surprised that I missed that, as the engine and intake are usually my references...

I had originally written off my carbs as having a problem because I was able to start fine back in January when we had a rather hot day for mid winter (70's!!!), and I didn't have any in flight problems with them while relocating the aircraft. I had to have a lot of other work done, such as some extensive repairs to avionics**, and just today finally had good enough conditions for a battery of tests.

Since it's not a true choke, rather more like a throttle plate bypass, it only functions as long as the throttle is at idle. Once you open the throttle, the bypass stops working as it's a rather high resistance and low capacity for airflow. That's why incorrectly installing these will only show problems when starting or at idle.

While trying to start while I was using the choke, the engine would kick, but it would not turn over. I had done this several times up until now. When I took the carbs off after trying to start several times, the bottom of the intake had fuel pooling on it. I too had "wet plugs" as well. I suspect it's because there wasn't enough fuel staying mixed with the air before the ignition event. Fuel condenses when it's forced to aerosolize, which includes on the cylinder walls, spark plugs, and the intake manifold. Not a problem on a hot engine because it's a lot harder to stay condensed. It's this reason that we have a choke, to temporarily compensate for this cold engine issue. Even injected engines shoot extra fuel and then leans out once it's started. 


Anyways, the last thing I did was finally opening the carbs to check my work on them. The very last thing I did was pop off the choke body... I saw the orientation of the disc compared to the bores and knew I had to have installed them wrong and was pretty damn sure that's the cause of my problems. Fixed the orientation, put everything back together, tried to start... no go. Then hit the choke and tried (did this on purpose to test my theory!!!) and she fired right up!

*Each disc has a stamp on them, one L, and one R. The one stamped L actually goes on cylinders 1 and 3 (right side from pilot seat), and the one stamped R goes on 2 and 4 (left side from pilot seat). I suspect they are stamped this way because these carbs are originally for BMW Boxer Motorcycle engines, which have the throttles and choke control inwards towards the engine, not outwards like in most Rotax installs. There's only two distinct differences in the carb bodies themselves (not all the little parts, just the machined body) that I can think of off the top of my head from the motorcycle version of the carbs. First, the throttle is spring loaded to full throttle (idle on motorcycles), and second, the ULS 100HP version carb needle jet seat has a small semicircular shield that doesn't exist in the 80HP UL carbs, nor on motorcycles. That leads me to conclude that Rotax switches the left and right carbs for aircraft engines.

**The shop doing repairs had reversed two connectors during avionics pod reinstallation, and the damage affected all of the dynon equipment and the autopilot.

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Hi Corey,


"Since it's not a true choke, rather more like a throttle plate bypass, it only functions as long as the throttle is at idle."


Define idle rpm.



I have a point after you do this.

What I mean is when the plate is physically less than barely open, that enrichment circuit is operating. It tapers off after that very fast.


For CTs with a correctly functioning system and prop, it should be 16-1800. 1750 seens to be the sweet spot.

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I was hoping for a different answer. I was fishing and you didn't bite very hard. :bravo-851: .

Idle rpm is up to as high as 2500 rpm even though no one sets it up there. That is at the upper idle jet range. The enricher can be in play up to that point. You can in fact crack the throttle up to 10% and still have it in play since most people have idle rpms between 1600-2000 rpm. (average is around 1700-1750).



So people that have idle rpms that are 2000+, use the choke and crack the throttle usually have starting issues with flooding.

people that are in a more normal setting around 1700-1750, use full choke and crack the throttle usually start much easier.

people that have low idle rpms around 1600 and only use the choke sometimes have starting problems especially on cold mornings.


Cold weather makes engines that are on the edge of good starting setups and pilot technique may have some issues.

When a warm engine is involved then some of those borderline issues go away.

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