I have yet to see or touch a ASP engine that I didn't have to tinker with and fix the carb on. Actually so far all the mainland Chinese engines have had flaky carbs on them. I must have bad luck and only see the engines they make just before the weekend starts.
Someone had two of these ASP .61 four cycle engines and they were simply not working well at all. So he asked me to help him out. We took the engines off his twin engine plane so i could bench run them. Both engines ran horrible, false needle settings, rough running, you couldn't lean them out, and even then the engines' RPMS were all over the place, up and down.
So I got to take apart the carb on one of the ASP 61 four stroke engines. I found a tiny burr on the tip of the main needle. So I used a extra fine stone hone to gently and carefully remove the burr. I tried to get a pic of it, but without a 8x magnifier, it is hard to see, but you can feel it with the fingers. The idle jet rod was sort of, kinked off center a little, so I straightened it. The O-rings look OK. But as a test, I used some silcone grease and carefully greased the O-rings, and threads on the needle valves and reassembled the carb. i will try it out again on the engine stand tomorrow sometime. I'll see if that helped or not. I also thought about the carb's barrel throttle, but it seems to be a fairly tight fit, so sucking in air around the barrel may or may not be likely.
I tried to get a pic of the burr on the needle tip. You can just make it out as a faint line sticking up slightly on the lower edge of the tip in this pic.
The next day...
OK, I saved the ASP 61 four cycle engines and made someone very happy as the engines now work very well.
First problem was the guy had used old glow plugs. I made him go and get a couple of new Fox Miracle glow plugs for the engines. Second problem, I had to sleep on it, but I decided the engines had lower compression than I am used to. So I broke out a jug of my old 20% nitro glow fuel (16%synthetic and 2% castor oil). Then last night I had lightly greased the O-rings on the carbs and ground down a burr on one needle valve tip and straightened out the idle jet needle on one carb. I also added a piece of silicon tubing on top of the needle valve where it screws into the carb as well.
Then then I fired the engines up, they ran like I expected them too. Solid and firm, no funky stuff like false needle settings and so on. The main needle valve was sucking air pretty good. The 20% nitro made them run good too. I think the compression was lower, more in line with USA consumer needs as everyone likes to run a lot of nitro over here. My normal fuel choice is FAI or 5%, which is what I use all the time for most purposes.
Now the engines are running pretty good. He can put them back into his airplane now, knowing they'll work OK. They still seem to smoke at just off of idle, but they idle good in either case. Now we can see how long the engines hold up a last as he uses them. If he doesn't crash and total out the engines, we'll find out if they case hardened things like the camshafts or whether the crank bearings wear out prematurely.
Before the changes to fix the engines. You couldn't get a consistent tach reading at all usually you couldn't get a tach to read over 9.3k rpms but the readings were jumping all over the place. Now the engines hold a pretty solid 10.1k to 10.2k RPMS using a Zinger 11x7 wood prop on 20% nitro fuel.
Since the carb is working OK now, one can probably run lower nitro fuels. But I didn't test that thought. 15% Nitro fuel is very likely OK.
That is a small piece of extra large silicon fuel tubing on the needle valve like shown here.
Here is a short video clip (1 minute 28 seconds in length) of one of the ASP .61 four cycle engines I bench ran.
[URL=http://s248.photobucket.com/albums/gg171/earlwbollinger/Newer%20Engines/ASP%2061%20Four%20Cycle/?action=view&current=ASP61_Bench_test_Run.flv[/URL]
s248.photobucket.com/albums/gg171/earlwbollinger/Newer%20Engines/ASP%2061%20Four%20Cycle/