Hello All,
My RV-12 (912-ULS) has a little over 100 hours on it now, and I am loving it. However, there is a fairly decent vibration from 1800 rpm up to 2600 rpm. I have been to the Rotax inspection class, along with the LSRI class. Definitely not claiming to be an expert by any stretch, but I do have a good understanding of the systems.
The roughness in that range made me immediately think of carb synch, sinking floats, clogged idle circuit, or debris in the enrichening circuit.
So, here is what I have tried so far (with a test run up to 5,000 rpm after reaching operating temperature between pretty much every one of these steps).....
- Changed the screen on the gascolator.
- Carb synch (with gauges) down to the point of perfection. After reading another post, I fabricated “assist” extension springs to aid the Van’s torsion (latest version) springs in keeping the throttle cables tight. What a difference it made on making a carb synch actually enjoyable. They are spot on at idle and 3,500 rpm.
- Weighed the floats, and both pair (less than a year old) are under 7 grams.
- Removed and cleaned the needles, needle jets, and main jets.
- Removed, cleaned, and inspected the float valve. Checked the arms for correct dimension and ensured they are not binding. Tested with the fuel pump on and both working perfectly.
- Removed, cleaned, and thoroughly inspected (with a 10X magnifying glass) the idle jets. They are absolutely pristine...including the small tube running down the middle of them.
- Removed and cleaned the idle mixture screw.
- Cleaned the carburetors with carb cleaner, strands of wire, and compressed air. All passages including the air passage from the front leading to the idle jet, the passage leading from the idle mixture screw to the hole at the base of the butterfly, and the two small transition passages which exit near the same location. I can spray carb cleaner into the idle jet port (with everything removed) while holding my thumb over the idle mixture port, and a nice unobstructed spray will come out of the three small holes under the butterfly, and the brass fitting at the front (the air intake for the idle circuit)....on both carburetors
- Removed and cleaned the enrichening carburetor, including holding the two plates open slightly against the spring to ensure nothing was lodged in between them.
- Replaced the rubbers and gaskets on both carburetors, and re-assembled them.
- Reinstalled the carburetors and did another carb synch.
- Cleaned and re-oiled the air filters.
- Engaged enrichening circuit about 1/8” while at 2000 rpm and things got incredibly smooth.
- Phoned a friend (Dean Vogal) went though everything I have done, and he said to experiment (a very small amount) with the idle mixture screws. I did.....between 1.25 turns out from the seated position up to 1.75 turns out. I could see the effects on EGT at 2000 rpm, but the roughness is still there.
- Moved on to ignition. Replaced the spark plugs (gapped to .025”) and reinstalled with the $100 an ounce paste from Rotax per the manual.
- Checked the ohms on the coils, spark plug caps, trigger coils, and all tests listed in the Heavy manual.
- Did a differential compression test, per the book, and all four cylinders held 78 to 79 psi.
- Removed all the spark plugs to read them, and saw very typical results... #1 and #2 have more soot (and I understand why), while #3 and #4 are more tan.
HOWEVER....the top plug on #4 honestly does not look like it is firing. It is ridiculously clean. The bottom plug on #4 has a tan insulator with soot around the base, but the top plug is still silver.
- Rechecked the coil feeding the bottom plug of cylinders #3 and #4 and the cumulative ohms from spark plug cap to spark plug cap was 15.9k, which is right on the money.
The engine is smooth above 3000 rpm and smooth for a very quick check (gear box, I know) down at 1700 rpm. However, t is still rough from 1800 up to 2600.
I am confident people are going to say its from the float bowls overfilling due to the vibration, but I can run it at 5,000 rpm, reduce the throttle assertively (not aggressively), and it will be vibrating on its way down through those rpm. I would not think the float bowls would fill to the point of flooding in that short amount of time.
Someone else will say, “have you done a dynamic balance on the prop?”. The answer is no, I have not. It is on the list, but the vibration is bad enough at those rpm that I don’t believe the equipment would function correctly. I have a three blade Sensenich with ridiculously light blades, and I do not believe this is causing ALL of the vibration. I am definitely planning on doing it once this is resolved.
Gentlemen, I am asking for suggestions.
I am going to get some fresh 91 octane from WaWa tomorrow so we can rule that out too (unless it fixes it!).
Please tell me your thoughts about the clean plug as well. Ignition checks are pretty much standard +/- 150 rpm on either side and the roughness increases similarly regardless of which circuit is off.
Also, I know the clean plug must be firing (unless it is dieseling) because the #4 cylinder has the EGT probe. The bottom plug is on circuit B, and when circuit A is turned off, the EGT rises. I would assume a 3-1/2 cylinder engine (meaning one plug not firing) going to a 3 cylinder engine (turning off the other plug in that cylinder) would cause more than a little rumble.
Thank you in advance.
My RV-12 (912-ULS) has a little over 100 hours on it now, and I am loving it. However, there is a fairly decent vibration from 1800 rpm up to 2600 rpm. I have been to the Rotax inspection class, along with the LSRI class. Definitely not claiming to be an expert by any stretch, but I do have a good understanding of the systems.
The roughness in that range made me immediately think of carb synch, sinking floats, clogged idle circuit, or debris in the enrichening circuit.
So, here is what I have tried so far (with a test run up to 5,000 rpm after reaching operating temperature between pretty much every one of these steps).....
- Changed the screen on the gascolator.
- Carb synch (with gauges) down to the point of perfection. After reading another post, I fabricated “assist” extension springs to aid the Van’s torsion (latest version) springs in keeping the throttle cables tight. What a difference it made on making a carb synch actually enjoyable. They are spot on at idle and 3,500 rpm.
- Weighed the floats, and both pair (less than a year old) are under 7 grams.
- Removed and cleaned the needles, needle jets, and main jets.
- Removed, cleaned, and inspected the float valve. Checked the arms for correct dimension and ensured they are not binding. Tested with the fuel pump on and both working perfectly.
- Removed, cleaned, and thoroughly inspected (with a 10X magnifying glass) the idle jets. They are absolutely pristine...including the small tube running down the middle of them.
- Removed and cleaned the idle mixture screw.
- Cleaned the carburetors with carb cleaner, strands of wire, and compressed air. All passages including the air passage from the front leading to the idle jet, the passage leading from the idle mixture screw to the hole at the base of the butterfly, and the two small transition passages which exit near the same location. I can spray carb cleaner into the idle jet port (with everything removed) while holding my thumb over the idle mixture port, and a nice unobstructed spray will come out of the three small holes under the butterfly, and the brass fitting at the front (the air intake for the idle circuit)....on both carburetors
- Removed and cleaned the enrichening carburetor, including holding the two plates open slightly against the spring to ensure nothing was lodged in between them.
- Replaced the rubbers and gaskets on both carburetors, and re-assembled them.
- Reinstalled the carburetors and did another carb synch.
- Cleaned and re-oiled the air filters.
- Engaged enrichening circuit about 1/8” while at 2000 rpm and things got incredibly smooth.
- Phoned a friend (Dean Vogal) went though everything I have done, and he said to experiment (a very small amount) with the idle mixture screws. I did.....between 1.25 turns out from the seated position up to 1.75 turns out. I could see the effects on EGT at 2000 rpm, but the roughness is still there.
- Moved on to ignition. Replaced the spark plugs (gapped to .025”) and reinstalled with the $100 an ounce paste from Rotax per the manual.
- Checked the ohms on the coils, spark plug caps, trigger coils, and all tests listed in the Heavy manual.
- Did a differential compression test, per the book, and all four cylinders held 78 to 79 psi.
- Removed all the spark plugs to read them, and saw very typical results... #1 and #2 have more soot (and I understand why), while #3 and #4 are more tan.
HOWEVER....the top plug on #4 honestly does not look like it is firing. It is ridiculously clean. The bottom plug on #4 has a tan insulator with soot around the base, but the top plug is still silver.
- Rechecked the coil feeding the bottom plug of cylinders #3 and #4 and the cumulative ohms from spark plug cap to spark plug cap was 15.9k, which is right on the money.
The engine is smooth above 3000 rpm and smooth for a very quick check (gear box, I know) down at 1700 rpm. However, t is still rough from 1800 up to 2600.
I am confident people are going to say its from the float bowls overfilling due to the vibration, but I can run it at 5,000 rpm, reduce the throttle assertively (not aggressively), and it will be vibrating on its way down through those rpm. I would not think the float bowls would fill to the point of flooding in that short amount of time.
Someone else will say, “have you done a dynamic balance on the prop?”. The answer is no, I have not. It is on the list, but the vibration is bad enough at those rpm that I don’t believe the equipment would function correctly. I have a three blade Sensenich with ridiculously light blades, and I do not believe this is causing ALL of the vibration. I am definitely planning on doing it once this is resolved.
Gentlemen, I am asking for suggestions.
I am going to get some fresh 91 octane from WaWa tomorrow so we can rule that out too (unless it fixes it!).
Please tell me your thoughts about the clean plug as well. Ignition checks are pretty much standard +/- 150 rpm on either side and the roughness increases similarly regardless of which circuit is off.
Also, I know the clean plug must be firing (unless it is dieseling) because the #4 cylinder has the EGT probe. The bottom plug is on circuit B, and when circuit A is turned off, the EGT rises. I would assume a 3-1/2 cylinder engine (meaning one plug not firing) going to a 3 cylinder engine (turning off the other plug in that cylinder) would cause more than a little rumble.
Thank you in advance.
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