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Trouble shooters?

scottsville

Registered User
I have a problem that we can not figure out! I have a SC 150 with Penn Yan overhauled motor with 500 hours on it. I bought it with 220. Since then it has never ran to the rpm that prop manufactures say it should. Sen 74/56. Full throttle level flight 2500 rpms max. Borer 82-44 2600 max rpm straight and level with 2400 rpm climb out. So we put a new carb on and full At Lee dodge exhaust with hot rod muffler and went from generator to a new alternator. Checked mags. normal drop and timed right. Now it has less power than before. Very doggy specially at low rpms. Messed with idle mixture and got it flyable. But still very doggy, not peppy at all. In the process of doing this we found a broken primer line that we fixed and the throttle cable was not anchored so it was giving different throttle responses. We figure that was probably the main problem. But to no avail! Has anyone ran into this problem? Adjusting the idle mixture helped some. But per the carb manufacture it says its not effective over 1400 rpms. It sounds like it is flooded but no real signs of it being to rich. It runs like a old diesel truck. Very sluggish. Any advice would be appreciated?

Thanks Scott
 
What kind of mags? Did you check internal timing? Was this a new/rebuilt carb or just different one? What is the RPM drop with carb heat at 2400 RPM? How many degrees of EGT can you lean before you get peak EGT? Did you do a resistor check on the plugs? Do you have a 4 cylinder EGT/CHT?
denny
 
Bendix mags. Just checked timing. They have about 550 hours on them. It is a new rebuilt carb from Avstar. At 1800 drops 80-100. did do a mag test in a climb under full power 2400 rpms. The same about 80 and engine run smooth. No resistor check on plugs. About 50 hours on new tempest plugs. No engine monitor. Was thinking on tying it to a tree and using a laser heat gun to check the exhaust pipes and see if I am getting same temps on each cylinder.
 
Have you verified the accuracy of the tach. Sounds like your missing 100 -150 rpm.
Common for a tach to be off that much.
 
Bendix mags. Just checked timing. They have about 550 hours on them.

Did you check the INTERNAL timing of each mag or just the timing of the mags to the engine? Then pull the plugs and measure the internal resistance of each one. What's the history of the plug leads? Out of the box or cut to length and hand terminated?

Web
 
Have you verified the accuracy of the tach. Sounds like your missing 100 -150 rpm.
Common for a tach to be off that much.

Yes last December at annual. It was right on. I have a 160 SC here and there is a huge huge difference in performance between them.
 
Did not check internal timing. Just timing. One was 25 and 26. Not sure on the plug leads. They look good. Was completely rebuilt in 2012
 
Or cam timing. My 0-320 just came back from overhaul and it ran very similar to what your describing (like ****)

First give away was not making peak RPM. Second was it was a little “poppy” or “snarky” when pulling the throttle back from full to idle.

Engine shop had the cam timing one tooth off on the cam gears.


Sent from my iPhone using SuperCub.Org
 
I have new exhaust. I did do a run up at 1500 rpms and check temps on exhaust pipe right out of cylinders. all ran in the low 500's and one ran in the low 600's. Maybe not getting enough fuel in that cylinder?
 
Is anyone have trouble getting to 2700 rpms with a 0320 150 at straight and level flight with a borer 82-44 prop? My understanding it should have no issue hitting 2700 even in a shallow climb?
 
I was being a smartass since you're asking the same questions you asked 2 weeks ago.

44 pitch is a lot for 150 hp. When I had a fresh 160hp and a brand new prop 8242 netted 2700 in low altitude level flight.
 
I was being a smartass since you're asking the same questions you asked 2 weeks ago.

44 pitch is a lot for 150 hp. When I had a fresh 160hp and a brand new prop 8242 netted 2700 in low altitude level flight.



Since I asked that question I replace the exhaust and carburetor. The old exhaust was really messed up inside. All the new exhaust and new carb did was make it worse. Borer prop stc shows that a Sc 150 should min produce 2300-2400 static rpms with a 82-44. I have friend thats had over 6 150 SC and he never had a problem redlining a 82-44
 
I had a stock Sen 74-56 on it before and Don at Sensenich said I should get 2700 rpms no problem with that prop on a 150. and never saw over 2500 rpms.
 
Since I asked that question I replace the exhaust and carburetor. The old exhaust was really messed up inside. All the new exhaust and new carb did was make it worse. Borer prop stc shows that a Sc 150 should min produce 2300-2400 static rpms with a 82-44. I have friend thats had over 6 150 SC and he never had a problem redlining a 82-44

I am unclear exactly what was made worse but I have a hard time believing a new exhaust would be the culprit. I have always been leary of new carbs.
Edit. It sounds like your exhaust was really messed up inside. It could possibly been the problem and previous carb was ok and new one could have issues? It is tuff sometimes to diagnose when more than one change is done. Good luck with your issues.
 
Last edited:
I have a problem that we can not figure out! I have a SC 150 with Penn Yan overhauled motor with 500 hours on it. I bought it with 220. Since then it has never ran to the rpm that prop manufactures say it should. Sen 74/56. Full throttle level flight 2500 rpms max. Borer 82-44 2600 max rpm straight and level with 2400 rpm climb out. So we put a new carb on and full At Lee dodge exhaust with hot rod muffler and went from generator to a new alternator. Checked mags. normal drop and timed right. Now it has less power than before. Very doggy specially at low rpms. Messed with idle mixture and got it flyable. But still very doggy, not peppy at all. In the process of doing this we found a broken primer line that we fixed and the throttle cable was not anchored so it was giving different throttle responses. We figure that was probably the main problem. But to no avail! Has anyone ran into this problem? Adjusting the idle mixture helped some. But per the carb manufacture it says its not effective over 1400 rpms. It sounds like it is flooded but no real signs of it being to rich. It runs like a old diesel truck. Very sluggish. Any advice would be appreciated?

Thanks Scott

Altitude?

Have you confirmed that the throttle linkage is allowing full travel on the carb?

Where are you located?

9/10 it is something simple.

Tim
 
We ran a spectrum on the the motor in December and the rpm was right on. Engine showed it ran very smooth. better than average. The throttle linkage it good. hits full stop

I wanted to change each item and then fly it But the generator hit the new exhaust so we went ahead and put a alternator on it. So that caused us to have to replace all of it at once.
 
On hot cylinder, look for induction leak, broken gasket, loose tube going into sump(you have to reswage tube to tighten)
 
What condition made you feel the old exhaust was "messed up" compared with the new one? What exhaust did you have before and then now? For example a freer flowing exhaust can create a leaner fuel mixture in some engines. Lean mixtures can lead to light tan to white colored exhaust stains inside the muffler outlet. Too rich and they are dark tan to black. Same for spark plugs.

Gary
 
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