OS 70 running rough
07-06-2004, 11:19 AM
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OS 70 running rough
The engine runs very rough. Seems to surge as if the fuel was foaming, but I have checked it and it was OK. I get 7800 rpm with a 13-6 MAS. I richen it to 7200 or so to fly and it seems to be too lean in the air. I replaced a .46 with this engine and it doesn't pull as well as the .46. Any Ideas?
07-06-2004, 01:19 PM
#2
RE: OS 70 running rough
The engine should be running close to 10,000 with that prop.
Bad fuel will cause one to run like this.
Use OS "F" or H9 Super Plug
15% fuel
The surging is typically caused by a build up of pressure in your tank whereby the increased pressure causes the engine to run rich whereby the pressure decreases and the engine goes leaner. Some people can adjust it out with the needle valve. Others have disconnected the pressure line from the muffler.
enjoy,
Jim
Bad fuel will cause one to run like this.
Use OS "F" or H9 Super Plug
15% fuel
The surging is typically caused by a build up of pressure in your tank whereby the increased pressure causes the engine to run rich whereby the pressure decreases and the engine goes leaner. Some people can adjust it out with the needle valve. Others have disconnected the pressure line from the muffler.
enjoy,
Jim
07-06-2004, 05:40 PM
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RE: OS 70 running rough
Thanks for the reply.
It does seem to have a lot of pressure, it blows a lot of oil out the front bearing and everywhere else.
The fuel may be the problem, it is wildcat 10%, 18% syn. I am going to try 15-20 next time.
Thanks again
slopoke
It does seem to have a lot of pressure, it blows a lot of oil out the front bearing and everywhere else.
The fuel may be the problem, it is wildcat 10%, 18% syn. I am going to try 15-20 next time.
Thanks again
slopoke
07-06-2004, 07:29 PM
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RE: OS 70 running rough
I fought with an OS .70 for a while that I bought used which had not been run for a while. It turned out the engine was OK but both the high and low speed needles were all out of whack. I started out by making sure both needles were set very rich to the point that the engine would only run with the glow igniter attached. I found it would idle well at a lot of different (and incorrect) settings while I was messing with it. The key was to get the low speed needle set correctly first then move on to the high speed needle. Like yours, mine seemed to spit out tons of oil and run rough until I was able to get it sorted out.
With both needles set rich start the engine and let it run at as low an idle it will maintain without quitting.
Next, repeatedly lean the low speed needle by 1/8 turn and then remove the glow plug until the engine no longer quits when the plug is removed. This will get the low speed needle in the ballpark or somewhat close to the factory setting from when the engine was new which should still be a bit rich.
Once you are comfortable that the engine will idle reliably without dieing when the glow plug is removed you can move on to doing the same thing with the high speed needle.
Setting the high speed needle is basically the same as the low speed needle except for a couple things...
1. The throttle should be wide open instead of at idle.
2. Adjust the high speed needle by a half turn at a time until it will run wide open without the glow plug. After that adjust it by a quarter turn at a time or less - be careful not to go too lean or you could cause damage.
At this point the engine will still be running rich but the transition from low to high speed should be getting better.
Now is the time to go back and tweak the low speed needle to try and get a good low idle. The thing to look for here is how the RPMs change when you remove the glow plug. You want the engine to run the same either way. If the engine slows down then it is still a little too rich. Remeber, whenever you adjust the low speed needle it is always in 1/8 turn increments or less as the low speed needle is much more sensitive than the high speed needle.
If luck is on your side your engine should now have a nice reliable idle and the transition should really be coming on. Just be sure not to make it too low as it will lean out a bit in the air when the tank gets low. It is best to use a tach at this point to make sure you are in the recommended RPM range.
Now go back and tweak the high speed needle by making quarter-turn adjustments. A tach is almost a necessity at this point because your adjustmenst to the needle will affect the engine but the last few hundred RPM won't result in much change in sound so adjusting by ear at this point is nearly impossible. Holding the plane in a nose-up position is a good test at this point to make sure it isn't going to lean out on you in the air. If the engine slows down during this test you are too lean and need to richen by a quarter turn until the engine no longer slows down. Then richen it another quarter turn to be safe!
In my experience with this engine it runs rough when it is too rich. Of course, if it is too lean it won't run at all and may result in damage so avoid that if you can.
Hope this helps!
FlyerBry
With both needles set rich start the engine and let it run at as low an idle it will maintain without quitting.
Next, repeatedly lean the low speed needle by 1/8 turn and then remove the glow plug until the engine no longer quits when the plug is removed. This will get the low speed needle in the ballpark or somewhat close to the factory setting from when the engine was new which should still be a bit rich.
Once you are comfortable that the engine will idle reliably without dieing when the glow plug is removed you can move on to doing the same thing with the high speed needle.
Setting the high speed needle is basically the same as the low speed needle except for a couple things...
1. The throttle should be wide open instead of at idle.
2. Adjust the high speed needle by a half turn at a time until it will run wide open without the glow plug. After that adjust it by a quarter turn at a time or less - be careful not to go too lean or you could cause damage.
At this point the engine will still be running rich but the transition from low to high speed should be getting better.
Now is the time to go back and tweak the low speed needle to try and get a good low idle. The thing to look for here is how the RPMs change when you remove the glow plug. You want the engine to run the same either way. If the engine slows down then it is still a little too rich. Remeber, whenever you adjust the low speed needle it is always in 1/8 turn increments or less as the low speed needle is much more sensitive than the high speed needle.
If luck is on your side your engine should now have a nice reliable idle and the transition should really be coming on. Just be sure not to make it too low as it will lean out a bit in the air when the tank gets low. It is best to use a tach at this point to make sure you are in the recommended RPM range.
Now go back and tweak the high speed needle by making quarter-turn adjustments. A tach is almost a necessity at this point because your adjustmenst to the needle will affect the engine but the last few hundred RPM won't result in much change in sound so adjusting by ear at this point is nearly impossible. Holding the plane in a nose-up position is a good test at this point to make sure it isn't going to lean out on you in the air. If the engine slows down during this test you are too lean and need to richen by a quarter turn until the engine no longer slows down. Then richen it another quarter turn to be safe!
In my experience with this engine it runs rough when it is too rich. Of course, if it is too lean it won't run at all and may result in damage so avoid that if you can.
Hope this helps!
FlyerBry
