Tale of 2 carburetors

Thanks to Josef for moving this thread into the correct chat room. Hopefully, it'll be more useful here. Happy New Year and safe flying!

Chris

Dammit......I can't figure out how to move this entire thread over to 'Tech Help' where I meant to post it in the first place. Gotta remember that when I click on 'New Topic', it always places it in the first forum on the list which is this one (Suggestion Box) and I forget to switch over. Any suggestions for how to get it moved out of "Suggestions"?

Anyway, the carb is back and installed. I ran it up for the first time today and no more leaks. Now if it's dry tomorrow, I'll declare her airworthy again after my mechanic looks it over and makes the appropriate log entry although not a lot of flying is taking place in general these days in South Dakota. Temps dipped to minus 30 a few days ago and now, most of the snow is melted and they're forecasting rain and possibly thunderstorms tomorrow. The little C-85 is pretty warm-blooded. I put the Knipco heater on it for about 30 min to bring everything up to a reasonable temp for starting and she still kind of hiccups until there's been a fair warm up time, maybe 5 min or so. Not complaining though. It's just my little engine speaking to me and I'm doing my best to listen. She says, "Don't put the power to me until I'm good and warm or I'll crack a cylinder or engine block and show you just how expensive airplane ownership can get!".

Bob (The Stromberg Specialist) came through as advertised and all the work was done under warranty. As usual, it came with a full explanation of what he found and he said that he just couldn't get the needle to seat properly in the valve so he went ahead and replaced the whole mess again and then pressure tested it at 1 PSI for an hour with no leaks identified. He sent it back once again with all new gaskets and install hardware attached. It's really a beautiful work of engineering to behold.

One little tip that might help someone in the future. It's very hard to install the carb using the OEM castellated nuts with cotter pins. They require the right number of washers to bring the nut up along the shank of the studs so that the cotter pin will engage the nut properly. Doing this while getting all the geometry right for all 4 attach points takes several tries if you've never done it before and is done almost completely blind (by feel) since once your hand is up in there it blocks any chance of seeing what you're doing. Keeping the washers on a downward facing stud while trying to start the nut means many lost washers and frustrated cursing. Then the hole in the stud for the cotter pin is almost always oriented so that it's impossible to rack and bend your fingers to the angle required to get it in and/or once you do, it's impossible to bend the cotter pin properly. THE SOLUTION: Bob sends along steel lock nuts instead of new castellated ones. They're not the kind of nylon lock nuts used in most other installations requiring such hardware. Instead, they're hardened steel nuts that have been 'pinched' just a tiny bit to make the opening slightly oval-shaped so it likewise pinches the bolt or stud and creates enough extra friction that it won't back off. They're much easier to install and my mechanic approves of the substitution and says they're just as safe.

Happy flying.

Chris
Sioux Falls, SD
415C, #508

Update:

As I thought, the engine ran (and especially idled) much more smoothly with the overhauled carb installed. The idle mixture screw works fine and the mixture control is much more responsive now.

Unfortunately, it leaks. If I let the plane sit overnight without turning off the fuel valve on the panel, it leaks about an ounce of fuel in 24 hours. Actually, I DO turn off the fuel valve but it needs new gaskets so there's always a little trickle to the carb. Bob the Stromberg Specialist and I have been back and forth about it and he's made several suggestions but nothing worked and I finally had to pull it off the plane and send it back to him. In fact, I just put it in the mail yesterday so we'll see what he comes up with. We're both pretty sure it has something to do with the needle valve and/or it's seat. He replaced them in the overhaul with new parts but interestingly, he doesn't trust the OEM parts that he receives (and says are made in China) so he has them re-machined by a local shop so that the fit between the walls of the seat and sides of the needle are to closer engineering specifications and tolerances. Also, adjusting the float position has a lot to do with how the system seals itself and he'll be checking that as well.

Bob says it'll be warranty work. I'll probably have an answer in about a week or so and will check back in then.

Chris
Sioux Falls, SD
Ser# 508

Yes Bob can be full of himself at times but he is the only guy to send a stromberg to. I had a simulator story about 5 years ago with my carb and it was been perfect since. My Ercoupe is hand propped and the engine started on the first blade. A minor tweak to idle speed and have not touched it since.

Kevin

So how did the carb work out?

Man, this airplane ownership comes with a lot of heart and headache. I am still working on making my 415C airworthy and capable of carrying my grandchildren without reservation. The whole story of how it was mis-represented when I bought it and my journey to airworthiness is too long for this venue. Save to say, beware even the most honest appearing guys who are sure that their 'coupe is the best bargain on the planet.

However, I thought the carburetor issue was worth bringing up in this forum. It might save some folks a little trouble and makes for good hangar talk.

My C-85 engine came with a guarantee that the carb was up to date and recently (within last 3 years) overhauled and certified. However, I noticed she didn't run very well at lower rpm's, confronted the seller with this and got him to agree to send the carb back to the most recent overhauler in the upper midwest. It came back very nicely assembled but when installed, didn't solve the problem. The idle mixture needle had to be screwed completely in to the carb body for the engine to run anywhere close to smoothly and even then, it was obviously too rich.

I then contacted Bob Kachergius (the Stromberg Specialist) at Unitech Air Management. At first, he came off as kind of an over-enthusiastic salesman and I have to admit I was a little nervous about taking his word for it, but in the end, sent him the carb.

I got it back yesterday and what a beautiful work of engineering art. As it turns out, the prior overhauler messed things up so badly that the upper half of the carb casting had to be discarded. He not only sent this back but included a detailed explanation of how it was messed up with red 'Sharpie' markings on it to detail where the errors were made. The documentation that came with it is extensive and thorough including a well constructed logbook entry to paste in documenting what was done. More specifically, and as he'd predicted before even receiving the carb, the famous SB 73 had not been done properly so that it was running too rich in the idle circuit. Apparently, this is a common problem and has to be addressed very carefully to fulfill the letter of the SB.

I haven't had time to install it on the plane yet but suspect that things will be better once I do. In any case, beware the Stromberg carburetor that has not been properly overhauled and certified. I don't see a lot of accidents on the NTSB site attributable to engine failures related to this but was so impressed with my experience that I thought I'd share. The pic is of my new carb after Bob's overhaul, ready to install in plane. He sent all new hardware for installation along with and included new gaskets. The workmanship is beautiful and even if it doesn't solve my low rpm roughness problem, I know now that the carburetor is up to the highest standard and safe to fly.

Will update after installation.

Chris
415C, ser # 508
Sioux Falls, SD