I posted this in the Puppeteer thread but here it is again. On the last of six flights the other day, my Saito 56 which had been running absolutely beautifully sagged and died just before take-off. And I wasn't able to get it started again. No, that's not quite right. It always starts right up. But always dies at full throttle.

The next day I had a new fresh can of fuel (which I had suspected might be part of the problem) but it's the same thing. Here are the symptoms: 1) idles a bit higher than usual 2) good revs at middle throttle 3) sags considerably in the top 1/3 of the throttle and then dies 4) after even a short run engine seems hotter than normal and there's some smoke coming off the muffler (which I don't usually see). All this suggests to me that maybe it's running lean, but how does an engine suddenly from one flight to the next, runs lean when it's been flying beautifully all day?

I have the exact same problem with a Saito 80. I got to the point of taking it out of the plane and spent a half day on a test stand.
Talk about pulling your hair out...[:@]

I can get it to run if it's sloppy rich but then I don't have the power. If I tune to peak the mid is fine but full, she drops rpm and dies, and is HOT.

I was told there may be an air leak and it's leaning out.

At this point may fix was to replace the 80 with an 82 while I'm waiting for rebuild parts to arrive. []

Good luck and I'll be watching this thread.

Bob

The strange thing is that I had really started to trust this engine and several of the guys at the field had even commented on how great this engine was running, including our resident Saito expert. It seemed absolutely rock solid and I haven't had to touch the needle and haven't experienced a single deadstick.

But...this WAS an engine that I was having problems with in the past and sent it back to Saito to have the bearings replaced. And I had pulled it out of the Puppeteer previously to run it on a test stand and found a greater than usual amount of oil pooling during a run.

So air leaks? Where do they occur and how does one deal with them? Honestly, I'm also feeling like replacing the engine!

You may want to post both of your messages on the "Club Saito" forum. There is a fellow (Dave Hobbes "hobbsy") that is great at diagnosing Saitos and is the moderator of the forum. Dave is a member of my RC club and he flies exclusively Saitos and has for a long time.

http://www.rcuniverse.com/forum/m_33...tm.htm#8716815

Thanks for the link! I've already reposted my comments. Dang this is frustrating. I was just settling in to a routine of getting in a hour of air time each day and now it's out of commission.

New plug?

I had a similar problem with a two-stroke which had a partially broken engine mount. Itheorized that the extra vibration was foaming the fuel, causing a sudden Lean condition > overheating and fuel starvation.
Is there some new source of vibration on your plane?

Damn! I'm now having exactly the same problem with the Saito 56 on my Legionnaire! That leaves me grounded until I find a solution!

Allan, I'll check on the vibration thing. Our club Saito expert spend almost an hour looking everything over and couldn't find anything out of the ordinary and couldn't find a solution. Both he and others felt it could be a fuel delivery problem so I'll check the plumbing.

Pulled the engine out of the model, mounted in an a test stand, and fired it up. It runs without apparent problems. No sags. Stable idle. Good high end. So what have I screwed up on the installation? This engine is mounted upright in the round metal cowl of a Flair Legionnaire. There's a dummy engine but with two "missing cylinders" for air inflow and a wide area above and behind the cylinder head for air outflow. Tank is pretty much on the carb center line.

In the case of the other engine, it's mounted sideways (needle valve pointing up) in a Flair Puppeteer. Also behind a dummy with cutouts for inflow and lots of space for outflow. More to the point, why was I able to fly the model (the Puppeteer) without problems of any kind for almost 8 hours over the past two weeks without any problem until just now? I haven't changed anything on the model or the engine. It just stopped working.

BTW, I notice the the fuel foams pretty badly on the test stand but it doesn't seem to affect the engine at all.

well if the engine runs ok on the stand that leaves either the tank and plumbing or the cooling.have you tried running in the aircraft with cowl removed?

Yep, this afternoon at the field. Same problem. So I guess that narrows things down a bit. Though honestly, I can't see how the plumbing could just "stop working" from one flight to the next. On two different models.

you may want to run the engine on the stand with the tanks from the plane to see if trouble follows.over the year I have had the brass tubes crack inside the stoppers and gave me a fit tracking down that problem,

Sometimes I feel more like a heart surgeon than a modeler. And sometimes the work seems never-ending.

and the result was?

And the result was that that the engine seems to run perfectly with the same tank and plumbing combination used in the model. I even tried moving the tank up and down relative to the carb during the run and encountered no problems. No overheating problems, no smoke after the run, and the engine was cool to the touch a couple of minutes after the run. In short it performed perfectly.

So what does this all mean?

Upon inspecting the model, here's what I think. It appears that there many have been a constriction on the fuel tank tubes as they passed through the hole in the firewall. Minor shifting then starved the engine for fuel. So I enlarged the hole, reinstalled everything and will give it another shot. If this isn't it, I'm all out of solutions.

I also added a guide tube for the driver that I use to adjust the hex bolt in the end of the needle valve. I had one already but it was too big and the driver couldn't find the nut when the engine was running. Doing it this way is more of a hassle than just having a wire extension (or the old trick of using a small allen wrench) but I wanted to try this out since that's what I'm doing on my more serious scale models, where it's not ok to have a wire sticking out the side of the model.

Of course, there's not gurantee that this is the problem on the Puppeteer as well, but it at least gives me a place to look.

post your results as my curiosity is peaked.I use the alleen head braised on the needle valve trick myself and wuse a ball end to adjust.hadto do this when I was running ductted fans and it worked great.

That seems to have been it. It started right up today and though it died the first time I went to full throttle on the ground, thereafter it seemed just fine. I shut it down and restarted several times and it always ran without any indications of the prior problem. No smoke after I shut down and the engine cooled off normally after a run.

I did two short flights and had no problems with the engine.

So now I need to check out the Puppeteer.

Now that I know what to look for, I inspected the fuel lines on the Puppeteer and found what I believe is the problem. The Puppeteer is constructed differently from the Legionnaire with no hole in the firewall. Rather the engine tank bay is open to the engine area. So it wasn't a constriction of the tubes passing through the firewall. Instead it looks like the fuel line got "kinked" like a garden hose and thus the same ultimate effect as on the Legionnaire. By clipping off a 1/2 inch of tubing made this unlikely to happen again.

Odd that such similar problems would crop up on two models at the same time. Probably speaks to poor plumbing skills.