Bendix PS-5C Pressure Carb Tuning

cgrossl · #1 10-08-2009, 02:41 PM

I have a Bendix PS-5C pressure carb on a Lycoming O-360. It has been overhauled, and flowed for an O-360. The engine is stock, other than a 4 into 1 exhaust. It runs great, but the mixture at WOT and cruise is a little leaner than I would like. The plugs are very clean, with some light tan, and grey coloring. I have been keeping the mixture at full rich. Correct me if I'm wrong, but at full rich, and 60 degree ambient temperatures, I would expect a full rich mixture setting to leave some darker deposits on the plugs. I'm afraid that after the weather turns colder, that the mixture will be too lean.

I do have the Bendix installation and adjustment manual, which details how to set the idle mixture, and the enrichment valve, both of which are set correctly. I have tried enrichening the mixture by adjusting the discharge nozzle, but I end up making the mixture in the 1100 -1500 RPM range too fat, causing the engine to run rough.

I do understand how the carburetor functions, but I will admit to having almost no experience with a pressure carb. It seems to be hard to find anyone that is familiar with them. I did call the shop that did the overhaul. They want to set it up on the flow bench again (at my expense). I kind of doubt that they would get different results than they got when they did it in the first place. To me, it sounds like the main metering jet needs to be swapped with one that is a size to too larger.

Are there any gurus out there that are willing to share some tuning info on these carbs? Am I being too picky?

Thanks,
Cameron

skygazer6248 · #2 05-07-2010, 04:19 PM

I just ran across your post as I was doing my homework on pressure carbs. I ran across another website/blog that also was talking about the PS-5C-- I don't know if it will be helpful to you or not, but it's worth looking into. You can go to http://www.biplaneforum.com/forum_posts.asp?TID=462 to find it. The guy (Brad) that replied to the original post may be able to help you. He sounds like he may know a bit about pressure carbs, if you're still working on yours. Take care!

cgrossl · #3 05-19-2010, 11:12 AM

I've got mine to a point where it is acceptable. The mixture is still a little too fat in the 1100-1500 RPM range, but I have just been living with it. Other than that, it runs great.