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Carbs leaning out ?


procharger

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Carbs run leaner in cold weather and richer in hot weather. Unless you know what you're doing you may cause detonation and have a very expensive bill. leave it alone unless you have someone who knows what they are doing and what the readings on your instruments are telling you. Other Rotax owners in cold country don't usually mess with it. If you lived at high elevations and flew at high altitudes then dropping the clip one notch wouldn't be a big deal. One clip position leaner has approximately 80F increase on EGT's, but that's shouldn't be your sole info to use.

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I have never heard about tilting the carbs for any other purpose but to try to richen the rear cylinders and lean the front ones. I tilt mine a couple degrees inwards.

I do that to help with how dark the front plugs get, that's all.

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Rotax says carbs are not to be tilted. Plus if you mess with these things you may step into a detonation situation that will be very costly. People all over the world fly in cold conditions and some extreme, but they aren't altering their engine without first hand knowledge of what the consequences might be. A yes there have been many who have trashed their engine.

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Don't really care what rotax says on this. They're being ultra conservative which is reasonable for tort defense. They are not the only ones who are capable of evaluating modifications however.

Been doing it for years. Before I started doing it, the front plugs were black and wet with gas when I pulled them out after a runup. The tiny adjustment makes front and rear an even dark gold and dry on top plugs, slightly damp on lower plugs, and more balanced CHTs.

The intake is unbalanced and suffers from the same issue straight intake continentals do that don't use calibrated fuel injector nozzles.

You have to look closely to see the tilt. It's so barely inwards that it is practically within margin of error.

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Tilting unbalances the two floats. Then one is higher and off from the other. Floats are to be equal in the bowl and push up or down equally in the bowl. There are other ways to deal with some of these items and some items aren't really worth messing with.

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Making changes to aircraft and powerplants without understanding the physics behind it is very risky. You may get away with it for some time or may just be lucky, but there may be a day when you do some maneuver that isn't compatible with the modification. Some things will bite you when you least expect it. There is also the legality in doing some of these things,  especially after publicly making it known. 

For many years I have changed a number of aircraft configurations, several of them quite significant and involved. I spent many months researching these changes and consulting with experts in the industry. I was successful on several significant modifications, both on certified and non certified aircraft. It takes a lot of time to do this to understand everything possible as there is no room for error. 

When I did the vg's on the CT I probably spent three or four months doing this. I consulted with some of the top experts in the industry and incorporated one aspect of it recommended by NASA. It was a lot of work to get it right.

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On 2/11/2024 at 3:43 PM, Roger Lee said:

Carbs run leaner in cold weather and richer in hot weather. 

I thought these constant velocity or depression carbs compensated for the differences in temperature because they have the slide which varies the fuel due to mass flow through the carb throat.

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Fuel also atomizes/vaporizes much more readily in warm weather, if given the same blend. The carbs won't compensate for that, and there's only so far they can go for mass compensation because they do use a spring, and that doesn't change with air density.

I flew with the oat at -40 back in 2018. Engine ran very mildly rough. Running carb heat cleared it up,soon as I took turned it back off, back to mildly rough.

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10 hours ago, GlennM said:

I thought these constant velocity or depression carbs compensated for the differences in temperature because they have the slide which varies the fuel due to mass flow through the carb throat.

You forgot air temp effect on burning. It's not about flow here for the original post. It's about outside air temps. If an engine gets nice cool dry air vs hot humid air which fuel mixture will burn better? 

This was part of the original question. It was about cold air temps.m Plus even with our carbs they can only adjust so much and then it's more about air pressure not temps..

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