Stuttering 360

Mags

Don't know if his applies, but I have had bad intermittent engine sputtering and temporary rpm drop in a few planes.

Troubleshooting, thought it was plugs, fuel and other things. It ended up being bendix mag condensers. They ran great cool and during runup of course.

When they get warm is when the problem showed up. Nerve wracking in singles.

In my case I don't think it's a mag issue because turning the LASAR system on and off has no effect.

I went to Don's shop today and he was extremely helpful. Due to the installation method of the gascolator, we decided to leave it alone for now because it would have been a pretty big job to remove it. He did make the following changes:
1. Moved the fuel lines to and from the injector servo 3 or 4 inches further from the exhaust
2. Raised the injector lines higher above the cylinders
3. Put smaller restrictors on the injector nozzles

I flew about 5 hours today after the modifications and I can report several improvements:
1. So far I have not seen the problem in the air (previously it was very common on final)
2. GAMI spread (fuel flow difference between first and last peak) is 0.1
3. The engine runs much smoother LOP. I had it at almost 150 LOP without any noticeable roughness (previously I couldn't get much better than 50 without noticeable roughness)

Unfortunately, I still have the problem on the ground so at some point I will try removing the gascolator to see if that helps, but so far it seems like the changes we made today have improved the situation. A big thanks to Don and everyone at his shop!

btw - whether you have a problem or not, I highly recommend checking with Don on the nozzle restrictors. At 10500 ft I was doing 165 KTS TAS burning less than 8 GPH at 50 degrees LOP. I pulled it back to 100 degrees LOP and dropped down to 155 KTS and less than 7 GPH. At 100 LOP I only had about a 15 degree variation between the hottest and coldest EGT.

bjohnson1234 said:

1. Moved the fuel lines to and from the injector servo 3 or 4 inches further from the exhaust
2. Raised the injector lines higher above the cylinders
3. Put smaller restrictors on the injector nozzles

I flew about 5 hours today after the modifications and I can report several improvements

Click to expand...

Glad to hear you've had some success, even if not fully cured. If you have the opportunity when you do the gascolator work, it'd be great to see a photo or two of the changes to line routing that were made -- how the route from servo to spider ended up, and how the injector lines were raised.

Thanks for the update. I have not had the opportunity to make a major changes but will be paying close attention to this thread.

Ken

I recently purchased an RV-6A and I think it has this same problem. I took a video of the stuttering at idle after it has been run for about an hour:

https://www.youtube.com/watch?v=pzI3RUR9KNg

Is this what other people in this thread have been seeing?

Note the tach is fluctuating about ~50 RPM but there is no fluctuation in the fuel pressure. Pump and mixture have no effect on this. My stuttering occurs with less frequency/severity in idle flight but on the ground it is pretty bad.

My -6A has no gascolator, an in-cabin electric fuel pump, and has the blast coolers for the mechanical fuel pump. Given this, I think the problem is probably after the fuel servo. All of those lines are wrapped in heat shielding up to the spider.

This might be a similar problem, but it's hard to see in the video. Mine had about a 50 rpm drop every 2 to 4 seconds. Yours looks more erratic, but I can't really tell.

neonbjb said:

I recently purchased an RV-6A and I think it has this same problem. I took a video of the stuttering at idle after it has been run for about an hour:

https://www.youtube.com/watch?v=pzI3RUR9KNg

Is this what other people in this thread have been seeing?

Note the tach is fluctuating about ~50 RPM but there is no fluctuation in the fuel pressure. Pump and mixture have no effect on this. My stuttering occurs with less frequency/severity in idle flight but on the ground it is pretty bad.

My -6A has no gascolator, an in-cabin electric fuel pump, and has the blast coolers for the mechanical fuel pump. Given this, I think the problem is probably after the fuel servo. All of those lines are wrapped in heat shielding up to the spider.

Click to expand...

I recently found a very small leak going into the gascolator. It was only noticeable with the fuel pump on. The leak is fixed, but the temps haven't been high enough to see if it had any effect on the issue.