OS 61SF Idle Problems
07-14-2011, 10:06 AM
#26
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RE: OS 61SF Idle Problems
Just an after thought, and rather elementary If I don't say so myself, and that's the glow plug.
You probably already thought of this, just though I'd mention it.
For example: when you start your engine and remove the battery from the glow plug and the engine looses RPM
then your plug is to cold for the fuel you are using or its going to fail soon. It will significantly effect your idle.
You probably already thought of this, just though I'd mention it.
For example: when you start your engine and remove the battery from the glow plug and the engine looses RPM
then your plug is to cold for the fuel you are using or its going to fail soon. It will significantly effect your idle.
07-15-2011, 10:29 AM
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RE: OS 61SF Idle Problems
Amazing info about the different bearing size - didn´t know that.
I will have to check my SF and RF engines for that detail.
I will have to check my SF and RF engines for that detail.
07-19-2011, 12:54 PM
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RE: OS 61SF Idle Problems
OK, here is the latest on the poor idle:
As per Atlanta 60 I checked the amount of fuel pumped per compression stroke. I connected a long fuel line to the OUT that was marked at 10". The fuel line was suspended vertically above the engine so the pump was pushing against gravity. After a several tests, the fuel moves about 1" per stroke (10 strokes for 10" of fuel line). This is quite a bit more than the 1/4".
I got the O rings and replaced them in the carb. The carb was clean with no residue in any of the passageways. The O rings appeared to be in good condition, but I replaced them anyway along with a new needle valve assembly.
I put in a brand new OS #8 plug.
Basically everything has been repalced (except the pump).
Sad to say, it still will not idle or run under 5,000 rpms.
I have a couple of FX's so I may try to adapt one of those carbs and try it on muffler pressure. I'm not sure the big carb will work very well on muffler pressure alone. Not sure what to do with the pump connections if I try muffler pressure. I don't have a spare non-pump backplate.
Does anyone know what the adjustments on the pump do and what is the proper procedure for adjustment? I haven't changed anything, but since the paint seals are gone, someone else may have changed them.
As per Atlanta 60 I checked the amount of fuel pumped per compression stroke. I connected a long fuel line to the OUT that was marked at 10". The fuel line was suspended vertically above the engine so the pump was pushing against gravity. After a several tests, the fuel moves about 1" per stroke (10 strokes for 10" of fuel line). This is quite a bit more than the 1/4".
I got the O rings and replaced them in the carb. The carb was clean with no residue in any of the passageways. The O rings appeared to be in good condition, but I replaced them anyway along with a new needle valve assembly.
I put in a brand new OS #8 plug.
Basically everything has been repalced (except the pump).
Sad to say, it still will not idle or run under 5,000 rpms.
I have a couple of FX's so I may try to adapt one of those carbs and try it on muffler pressure. I'm not sure the big carb will work very well on muffler pressure alone. Not sure what to do with the pump connections if I try muffler pressure. I don't have a spare non-pump backplate.
Does anyone know what the adjustments on the pump do and what is the proper procedure for adjustment? I haven't changed anything, but since the paint seals are gone, someone else may have changed them.
07-20-2011, 07:08 AM
#30
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RE: OS 61SF Idle Problems
I cannot locate the internal notes we had on the old pump used by the O.S. Max .61 SF/RF pumped engines, but I think it's something like this:
First set the high-speed needle on the carb to exactly one turn out from closed. At full throttle, with the engine running, you adjust the top screw on the pump to get the high-speed mixture leaned to peak. Retard the throttle to idle and adjust the idle mixture. Adjust the lower screw to set the point where fuel returns to the carb. You have to work between the idle RPM, idle mixture, and screw adjustment to get things set where the engine will have a good top end, a good idle, and good transition.
First set the high-speed needle on the carb to exactly one turn out from closed. At full throttle, with the engine running, you adjust the top screw on the pump to get the high-speed mixture leaned to peak. Retard the throttle to idle and adjust the idle mixture. Adjust the lower screw to set the point where fuel returns to the carb. You have to work between the idle RPM, idle mixture, and screw adjustment to get things set where the engine will have a good top end, a good idle, and good transition.
07-28-2011, 12:42 PM
#31
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RE: OS 61SF Idle Problems
The saga goes on . . .
I was able to adjust the pump as per Bill's instructions; I was able to peak the rpms with the top adjustment, and control the fuel return with the bottom pump screw, but still could not get the engine to run below 5,000 rpms.
I have a carb off an old Super Tiger .75 that happens to have the same od as the 86 carb and is also held in via clamp system (as opposed to screws). Since it was a perfect repalcement for the big carb I tried it with muffler pressure and was able to get a reialble idle of about 2,000 rpms. The top end suffered from the smaller venturi with the best rpms at 10,800 vs. 11,300 with the big OS carb. This is with an APC 12-8 prop. When running on muffler pressure I connected a piece of fuel line between the "IN" and "R" and another piece between the "OUT" and "S" on the pump. After running the Super Tiger carb I put the OS carb back on. I blocked off the return line from the carb. The top end rpms were a little less than with the pump, but more than with the Super Tiger carb. The results were the same on the low end: the engine will not run under 5,000 rpms. I also tried the OS carb with the return vented, but the results were the same.
I have had the OS carb apart a few times now, but cannot find a problem. I looks to me like there is only one way that this carb with the mixture control and all can be assembled; hard to mess it up.
Right now I'm fresh out of ideas, and without another known good carb to try I may have to either use the Super Tiger carb or switch to one of my FX engines.
I was able to adjust the pump as per Bill's instructions; I was able to peak the rpms with the top adjustment, and control the fuel return with the bottom pump screw, but still could not get the engine to run below 5,000 rpms.
I have a carb off an old Super Tiger .75 that happens to have the same od as the 86 carb and is also held in via clamp system (as opposed to screws). Since it was a perfect repalcement for the big carb I tried it with muffler pressure and was able to get a reialble idle of about 2,000 rpms. The top end suffered from the smaller venturi with the best rpms at 10,800 vs. 11,300 with the big OS carb. This is with an APC 12-8 prop. When running on muffler pressure I connected a piece of fuel line between the "IN" and "R" and another piece between the "OUT" and "S" on the pump. After running the Super Tiger carb I put the OS carb back on. I blocked off the return line from the carb. The top end rpms were a little less than with the pump, but more than with the Super Tiger carb. The results were the same on the low end: the engine will not run under 5,000 rpms. I also tried the OS carb with the return vented, but the results were the same.
I have had the OS carb apart a few times now, but cannot find a problem. I looks to me like there is only one way that this carb with the mixture control and all can be assembled; hard to mess it up.
Right now I'm fresh out of ideas, and without another known good carb to try I may have to either use the Super Tiger carb or switch to one of my FX engines.
07-28-2011, 01:20 PM
#32
RE: OS 61SF Idle Problems
alaflyer,
I did read this thread for a while and have this simple question, “Do you use an electrical starter motor?†(or maybe I did not read it?)
Why this question?
When not using an electrical starter motor, starting by hand, the first problem of a bad piston liner set is, you are not even able to start the engine (without tricks).
If you use an electrical starter motor you can start the engine with bad compression, but the engine will have a bad behavior in low revs. Exhaust gases will enter the crankcase and destroy the breathing.
I always start my engines by hand and so do have a good feeling of the compression.
So, how is the compression, the quality of the piston and liner? Maybe a bad pistonring if there is, or the ring locked? in the groove of the piston or a groove in the liner.
Mechanical condition is the first important fact to check.
Another important check is also the fit of the crankshaft in the crankcase. Maybe the engine did his duty for a while in the past with bad bearings so there is too much leakage?
If I missed a post about these subject, than I am sorry. good luck,
Cees
I did read this thread for a while and have this simple question, “Do you use an electrical starter motor?†(or maybe I did not read it?)
Why this question?
When not using an electrical starter motor, starting by hand, the first problem of a bad piston liner set is, you are not even able to start the engine (without tricks).
If you use an electrical starter motor you can start the engine with bad compression, but the engine will have a bad behavior in low revs. Exhaust gases will enter the crankcase and destroy the breathing.
I always start my engines by hand and so do have a good feeling of the compression.
So, how is the compression, the quality of the piston and liner? Maybe a bad pistonring if there is, or the ring locked? in the groove of the piston or a groove in the liner.
Mechanical condition is the first important fact to check.
Another important check is also the fit of the crankshaft in the crankcase. Maybe the engine did his duty for a while in the past with bad bearings so there is too much leakage?
If I missed a post about these subject, than I am sorry. good luck,
Cees
07-28-2011, 04:20 PM
#33
RE: OS 61SF Idle Problems
There are a lot of folks on the forum that use the OS 61SF APC-P engines. I would think you could find someone near Montgomery that could visit to bench run your engine and swap out the carb and or pump to determine where the problem is.
07-28-2011, 06:08 PM
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RE: OS 61SF Idle Problems
Not an expert either and I have several of these engines as well, rear and side exhaust. These carbs are quite unique in that they have a flat butterfly instead of a throttle barrel. I'm thinking you have a small obsticle partially blocking one of the passages. This butterfly valve has a small hole on one side where the fuel enters into the venturi and may be partially blocked or the passage to the butterfly ispartially blocked.
I read that you completely disassembled this carb. Did you by chance remove the complete needle valve assembly? I would also would try to blow air backwards through all the passages to see if someglow fuelvarnish is blocking the passages.
Surging before it quits is usally an indicator that the engine is running lean. Which suggusts to me some type of blockage in the idle mixturecirucit. IMHO
Regards,
Bryan
I read that you completely disassembled this carb. Did you by chance remove the complete needle valve assembly? I would also would try to blow air backwards through all the passages to see if someglow fuelvarnish is blocking the passages.
Surging before it quits is usally an indicator that the engine is running lean. Which suggusts to me some type of blockage in the idle mixturecirucit. IMHO
Regards,
Bryan
