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It could be the manifold vacuum signal. My engine was always a little
unstable below 2000 rpm but I didn't have the vacuum tap in a very good
location. I'm not sure why it would be worse some of the time unless
you're getting some sort of resonance under just the right conditions.
Bob W. (Just a WAG)
On Fri, 20 Jun 2008 21:21:00 -0700
"Mike Wills" <rv-4mike@cox.net> wrote:
> Well, I'm pretty sure it's not a burnt valve. :-)
>
> In the early tuning stages I was all over the engine with starting fluid, soapy water, you name it, looking for vacuum leaks. Never found a thing. Timing is set per Tracy's manual.
>
> Odd thing is the lack of consistency. Most of the time it runs great. I think if there was a vacuum leak it would be more consistent.
>
> Acts to me like there is something just a little off in the tuning. Get everything in just the right (wrong) condition and it sets up a resonance. Most of the time this doesnt happen. Changing mixture kills the resonance and its fine after that.
>
> Mike Wills
> RV-4 N144MW
> ----- Original Message -----
> From: Greg Ward
> To: Rotary motors in aircraft
> Sent: Friday, June 20, 2008 8:56 PM
> Subject: [FlyRotary] Re: The SAGA continues; More checking basics and development progress
>
>
> I hate to say it Mike, but in a recip, that's a sure sign of a burnt valve or a major vacuum leak. Maybe in this case, there's a leak in your intake? A bad gasket or loose bolt could do it. Timing is a possibility for sure.
> Greg Ward
> Lancair 20B N178RG in Progress
> ----- Original Message -----
> From: Mike Wills
> To: Rotary motors in aircraft
> Sent: Friday, June 20, 2008 8:33 PM
> Subject: [FlyRotary] Re: The SAGA continues; More checking basics and development progress
>
>
> I too still have intermittent surging issues that havent been fully conquered. Doesnt happen all the time. Always in the 2000 - 3000 RPM range. Usually happens when I'm taxiing and back off the throttle. In my case the A/F reading is useless. The engine surges rhythmically at about a 1Hz rate with RPMs varying several hundred, MAP varying from high to low (hard to pin down exact numbers - its moving around too much), and the A/F bouncing back and forth from the rich stop to the lean stop. Fiddling with mixture always stops it, but its a little disconcerting (and embarassing) when it happens (usually as I'm taxiing away from the crowd at the local EAA chapter while everyone is watching). For a while I thought adding some capacity to the MAP sensing line (Dave Leonard's suggestion) had cured it, but not entirely. I'll need to get this figured out before it flies. Could be a real problem if it happens on short final.
>
> I occasionally have a pretty good backfire at the secondary staging point. The operational solution seems to be to not linger in the area - just advance the throttle or retard it right on through and it seems to be OK. Advancing the throttle too slowly almost guarantees a big pop! I'm told it's particularly impressive after dark!
>
> I havent worked on the tuning in months while I've been tweaking other little issues in prep for my DAR inspection. Just about ready to get back to it. I'm sure i'll get it more or less figured out eventually.
>
> Mike Wills
> RV-4 N144MW
> ----- Original Message -----
> From: Mark Steitle
> To: Rotary motors in aircraft
> Sent: Friday, June 20, 2008 7:06 PM
> Subject: [FlyRotary] Re: The SAGA continues; More checking basics and development progress
>
>
> Chris,
>
> As you've probably read from the archives surging is usually caused by an overly lean air-fuel ratio. What is your A/F reading during the surging?
>
> Mark S.
>
>
> On Fri, Jun 20, 2008 at 8:41 PM, Christopher Barber <CBarber@texasattorney.net> wrote:
>
> Well, to continue the saga, I have not run the new 13b much since I got it running a few weeks ago due to the EM2 not showing oil pressure as it should. It was giving me erratic readings like -1, -3 etc. I hand propped the engine before I ran it and oil pumped through the system fine....much onto the hangar floor...alas, the sacrifices for certainty ;-). Also, during my short runs everything heated up in the oil system evenly and the oil temp stayed pretty much in line with coolant temp. BUT, since I was not sure if this was a gage/sender issue or an actual oil system problem I was very cautious about my few short engine runs.
>
> Well, today while dreading the idea of dropping my pan, I happened across an extra oil pressure sender (still in the package) I happened to have. I had seen it laying around for a while, but didn't give it much thought until I was thinking about dropping the pan. Low and behold, The problem was the sender. I am getting good pressure reading now, along with coolant and oil temp. Yeah. I am surprised at the temps as they seem to be staying in check considering the 95 + degree Houston weather.
>
> I am able to start the engine, shut it down and restart it (something I was not able to do with the old engine). It is somewhat difficult, but seems to be getting easier as I continue to tweak things (ie timing). I am trying to do the various tuning via Tracy's manual. To be honest a lot of the information in the manual is seemingly abstract until I actually get to the step and/or problem. So, tonight, I got it to run, and it seems to run better, but......
>
> I am having a surging problem. It seems intermittent, but it just may be I have not been setting the throttle quite the same way as I get use to it all. Also, I have had the coil C/B pop on me several times now....it seems as if this is when the engine is near or at idle. I have not had a chance to look into this as of yet. Also, I have gotten a number of horrendously loud/powerful backfires. Not sure what changes as the engine may have run fine. It backfires when attempting to start. I wait a few minutes and it may then start. Gee, isn't inconsistent crap fun <g>
>
> I just did a search of the archives on the surging issue, but have just started reading the 105 post on the topic. Seems our own Mr. Slade had the same problem back in the day <g>.
>
> Well, it is the middle of my work week and I gotta turn in soon, but I wanted to share that it seems as if actual progress is being made (hmmmm, wonder what will screw this positive statement up<g>) as the Saga continues.
>
> All the best,
>
> Chris
>
>
--
N93BD - Rotary Powered BD-4 - http://www.bob-white.com
3.8 Hours Total Time and holding
Cables for your rotary installation - http://roblinstores.com/cables/
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