rmenke
Posts: 1777
Joined: 6/25/2004
From: Merced, Ca., CA, USA
Status: offline
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JS615:
Ohhhh. Gonna be mad at myself for this, I am not a OS fan just as I am not a General Motors fan. Will not forgive either, GM for their desiel Cad and OS for their super cheepie berings and sleave material. Back to the subject. The OS design is good, copied a bunch simply because of the original design, including the carb. They are designed for the majorty market place, sport. If you want fast, you gotta pay for the Farrari. Jett, Nelson, Profi. So far, only Jett produces a high quality sport motor capable of go-go rpm, and will still idle better than most sport engines. Yes, I'm a Jett fan, proven to myself that the engines are cheep in the long run simply because of the quality which tends to run foreaver. Not unusual to see Jetts still running very strong after 6 years of hard use. Your would have replaced that OS at least 6 times in that period used in the same manner for the same duration.
To work! First, replumb your tank with all new interior copper and flex fuel line to the carb, carefully leaving 1/8-1/4"clearance at the clunk, and be sure the vent also has clearance. Make another flight to be sure the problem is not corrected. Lets also be sure you have that OS carb pressure cleaned and the idle circut correct. The idle circut will effect the top end on most modern carbs, a happy engine is one that will idle for over a minute and then transition cleanly. Open your carb idle screw 1/8 turn. Start it up and get the high speed needle to where the engine is running cleanly, but still a fine smoke trail. Go to idle, Run her for a minute and then open it up. If she staggers, work the idle and high speed needles until it will transition correctly after a minute of idle. Spend the day if you have to, but get that idle. Then fly. Fixed? I suspect not, but do the idle anyway. Like most glow engines, they don't like their plug stuck in the oil and fuel when inverted. So, install an a OS-F plug and do away with that tentency. Notice I did not say a idle bar plug, only used as a last resort for junk engines. Fixed? No, you may still have the muffler/fuel pressure problem that is obvious. Whats going on is that the pressue from the muffler you are useing is not about the same as the OS muffler it was designed around. So, you have some obvious options. 1. Buy a new cowel and install the original OS muffler like Bob's 27 did. 2. Throw money at pitts muffler systems until you find one that will work with your installation. Different manufacturer designs will give you different pressures to the tank/carb system. They all have different outlet locations and sizes, and worse yet, interior baffels that do not always get installed at the same location. 3. Here we go, save some bucks and work at it. If you do not have a good drill index with drill bits in 1,2,3,4, sequencial sizes, you need one. The pitts muffler nipple should be brass, if not get one. Find the size of the niplle hole, start around .076 which is the size of a YS 60. Drill out the nipple 1 drill size, clean and go fly. Adjust both needles as needed, check idle and go fly. You are going to have to drill on that muffler nipple until the engine is running as it should. A little trinkit of interesting (to me) information. Sorry I dont have a OS 60 or 90. A OS46AX niple opening is .070, a Webra 50 and TT46 , the same .070. 3 sport engines, all the same nipple opening. Now, the Jett 50 size is .046 all per my drill index. I have yet to find any engine, 2 or 4 stroke that transitions and idles as well a a Jett, from the 35 to 90. Sorry I'm sounding like a add for Dub Jett!!!!
Ok, if you cant come up with the bucks for the best overall Jett engine, 60LX in my not so humble opinion, get a Webra 55. Not a 50, or 40 or 60, a 55. Break in per Jett's web site instructions, add apc 10 X 10. Yes the Jett 60 LX will outrun you, but not by a whole bunch. In the meantime, you are lapping the other guys, probably at least twice against the OS types in 10. No No you say? Well, ever run for pinks? I'll even fly it in a Avi-Star trainer!!!
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RE: Sundowner 50 Arf - 
