procharger Posted February 11 Report Share Posted February 11 Someone said to lean the carbs. out from the engine in the cold weather what is that supposed to do to make the engine run smoother? What would change in the carbs, by doing that? Quote Link to comment Share on other sites More sharing options...
Madhatter Posted February 11 Report Share Posted February 11 Leaning carbs in cold weather is opposite what you would do even if the premise is valid for this discussion, which it is not. Quote Link to comment Share on other sites More sharing options...
Roger Lee Posted February 11 Report Share Posted February 11 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. Quote Link to comment Share on other sites More sharing options...
Tom Baker Posted February 11 Report Share Posted February 11 Yep, cold weather will make your run up a little rougher, and a bigger RPM drop due to it being leaner. If you have the clip set so it is leaner than it is supposed to be it is really rough when it gets cold. Quote Link to comment Share on other sites More sharing options...
Roger Lee Posted February 12 Report Share Posted February 12 If you want a little roughness taken out when it gets too cold then you richen the needle clip down into the #4 slot. Quote Link to comment Share on other sites More sharing options...
procharger Posted February 12 Author Report Share Posted February 12 I was asking about tilting the carbs out not trying to make the carbs leaner?? Quote Link to comment Share on other sites More sharing options...
Anticept Posted February 12 Report Share Posted February 12 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. Quote Link to comment Share on other sites More sharing options...
Roger Lee Posted February 12 Report Share Posted February 12 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. Quote Link to comment Share on other sites More sharing options...
Anticept Posted February 12 Report Share Posted February 12 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. Quote Link to comment Share on other sites More sharing options...
Roger Lee Posted February 12 Report Share Posted February 12 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. Quote Link to comment Share on other sites More sharing options...
Madhatter Posted February 12 Report Share Posted February 12 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. Quote Link to comment Share on other sites More sharing options...
GlennM Posted February 13 Report Share Posted February 13 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. Quote Link to comment Share on other sites More sharing options...
Anticept Posted February 13 Report Share Posted February 13 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. Quote Link to comment Share on other sites More sharing options...
Skunkworks85 Posted April 6 Report Share Posted April 6 On 2/13/2024 at 7:35 AM, Roger Lee said: 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? Neither will burn "better" at the same ratio, Ideally stoichiometric. The more dense air will allow more fuel to be burned, in turn allows more chemical energy to be transferred to mechanical energy quicker. But they will still burn the same. Quote Link to comment Share on other sites More sharing options...
FredG Posted April 6 Report Share Posted April 6 Skunkworks85 post has me go back and read some posts on this thread. After 100 years, carburetors still confuse and mystify. On 2/13/2024 at 2:08 AM, Anticept said: "there's only so far they [the carburetors] can go for mass compensation because they do use a spring, and that doesn't change with air density. Corey, the spring doesn't change with air density, but the position of the throttle slide most certainly does change with air density and in doing so, they adjust for air density. Although CV carburetors may not meter perfectly (ie, maintain an exactly ideal air fuel ratio), but compared to non-CV carburetors, CV carburetors do compensate for air density over the range of densities typically encountered by light sport aircraft (which means they compensate for altitude and air temperature, which are major determinants of air density). Quote Link to comment Share on other sites More sharing options...
Anticept Posted April 6 Report Share Posted April 6 What I am saying is there is only so far they can go. It becomes more inaccurate at higher altitudes or extreme temperatures (this affects how well fuel atomizes), hence the off the book suggestion of changing pin positions from 3 to 2 if you are operating from denver for example. In fact, that is one of the reasons these settings exist, since these are modified motorcycle carbs. These carbs are tuned for a certain richness at low altitude, that richness gap doesn't really change as you go higher because the slide doesn't compensate proportionally. While the slide continues to operate and meter, there's nothing compensating the offset from peak, so as the air thins, they subtly but gradually increase fuel air ratio. Pressure carbs are much better able to compensate over the entire operation range but we don't have those. Quote Link to comment Share on other sites More sharing options...
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