DwightFrye
Active Member
I don't post much, but when someone goes out of their way to provide good service I have to share the story. Over the last handful of months my engine has started to run rougher when pulled back to idle. In particular, if I have to throttle up to go around it would stumble quite a bit before settling down into making good power. In cruise at higher power settings (and higher fuel flows) it ran great.
Different people had different theories, and I explored them all. One of the theories was heat and vapor lock, but that didn't pan out. Then Don Rivera at Airflow suggested a theory. He thought that maybe the slide valve in my flow divider had gotten sticky or blocked and wasn't closing all the way. We both felt that would explain the engine's behavior.
Weather finally allowed me to fly down to Don's shop and we dug into the engine. We pulled the flow divider and the initial check seemed to imply that the slide valve was seating fine. Dang, there goes a good theory, I thought. But in the spirit of being thorough Don put the flow divider on the flow bench and checked it out.
At higher fuel flow settings (i.e. out of idle) it seemed great. All the outlets were flowing identical amounts and were right in sync. However, when it was pulled down into the idle regime one of the outlets .. the one for cylinder #1 .. was flowing less than the other three. This was the first hint of something wrong that would explain the behavior seen, the only question now was to find out why it was flowing less.
Don took it off the flow bench, and pulled it apart. The little slots (and way down in the idle range, those slots are very small) seemed clear. However, on the base of the flow divider where the slide valve would seat was some crud. It was small, but a very visible little ring of crud had accumulated there. We hypothesized that it might have kept the slide valve from fully seating and this might be the source of the problems.
We cleaned it off, double-checked that the slots were open, and put it back together. When back on the flow bench we now saw all four outlets flowing in lock step, just as they should.
We put everything back on the engine, and while we were at it Don double-checked my flow rates in general and made an adjustment to tweak that a bit. We also checked and reset my idle mixture. Finally, I also had one cylinder which tended to peak before the rest, so we swapped out a restrictor in one of the injectors to balance things better.
When it was all said and done, things behaved MUCH better. Awesome!
This, my friends, is the kind of service we wish all vendors could give us. It helps that I'm only an hour flight from Don's place and can visit in person. But the real take-away is that Don genuinely cares about supporting his customers. I felt that he deserved a shout-out for the fabulous support. Thanks, Don!
Different people had different theories, and I explored them all. One of the theories was heat and vapor lock, but that didn't pan out. Then Don Rivera at Airflow suggested a theory. He thought that maybe the slide valve in my flow divider had gotten sticky or blocked and wasn't closing all the way. We both felt that would explain the engine's behavior.
Weather finally allowed me to fly down to Don's shop and we dug into the engine. We pulled the flow divider and the initial check seemed to imply that the slide valve was seating fine. Dang, there goes a good theory, I thought. But in the spirit of being thorough Don put the flow divider on the flow bench and checked it out.
At higher fuel flow settings (i.e. out of idle) it seemed great. All the outlets were flowing identical amounts and were right in sync. However, when it was pulled down into the idle regime one of the outlets .. the one for cylinder #1 .. was flowing less than the other three. This was the first hint of something wrong that would explain the behavior seen, the only question now was to find out why it was flowing less.
Don took it off the flow bench, and pulled it apart. The little slots (and way down in the idle range, those slots are very small) seemed clear. However, on the base of the flow divider where the slide valve would seat was some crud. It was small, but a very visible little ring of crud had accumulated there. We hypothesized that it might have kept the slide valve from fully seating and this might be the source of the problems.
We cleaned it off, double-checked that the slots were open, and put it back together. When back on the flow bench we now saw all four outlets flowing in lock step, just as they should.
We put everything back on the engine, and while we were at it Don double-checked my flow rates in general and made an adjustment to tweak that a bit. We also checked and reset my idle mixture. Finally, I also had one cylinder which tended to peak before the rest, so we swapped out a restrictor in one of the injectors to balance things better.
When it was all said and done, things behaved MUCH better. Awesome!
This, my friends, is the kind of service we wish all vendors could give us. It helps that I'm only an hour flight from Don's place and can visit in person. But the real take-away is that Don genuinely cares about supporting his customers. I felt that he deserved a shout-out for the fabulous support. Thanks, Don!
I wouldn't expect anything else.
