Another tuning question on a four stroker

[acerc]

I have a Valach 170 four stroke and believe it is tuned fairly well. I notice I have a gurgle at mid throttle, my throttle is literally linear. I am guessing this gurgle is actually because the top end is rich being I have it slightly over propped with a 32x12x3 of which it holds the max rpm's down 6-8 hundred rpm. Should I, after getting it to operating temp, throttle up to the gurgle and lean the top just enough to remove this gurgle?

 

[Snoopy1]

Have been working on and getting a Valach 210 to work with a struggled with the motor most of last summer. Had the standard exhaust from Valach. Well after trying everything and nothing worked took the muffler off and built two straight pipes and out the bottom with a couple of 90 degrees elbows. This eliminated almost all our problems. One do not over prop the engine it will run hot every quickly and difficult to tune. Run the recommended two bladed prop until you are Familiar with the engine. Tune the to have a good idle and as lean as possible and then a good transition to full throttle.

 

[acerc]

I have not had any issue with the engine, it has performed well from the get go. I put the three blade on and last time out I noticed the gurgle. I think the prop loading it just a bit is causing the rich condition. I did the usual re-tune but it changed nothing. I am thinking because the prop loads the engine, about 600rpm at full throttle on the ground, is why a ground tune may still be well rich by way of rpm. Next time out I will lean the top 1/8th turn and see what happens.
I have yet to get a temp above 180° on the hot head and 160° on the cool head in flight, running this cool may also be a factor in my tune. I have baffled about a third of the engine and will see next flight about that.

 

[Snoopy1]

One thing we did Learn on the 210 if we went over 5200 rpm with the prop the engine did not like it was difficult to tune. As long as propped at around 5100 all worked better. But get some time on it it needs a couple of gallons through it before it really starts make some hp and Gets easier to tune.

 

[acerc]

So far the max rpm was 5000 on a down line, average is around 4400-4600. Tomorrow I am pulling the cowl to baffle the smoke tubes wrapping the headers and will work on the tune some as well. It runs really great, I am very pleased with the Valach, just want to get that gurgle gone. I know it went away with the lower needle but it messed with the bottom so I will try the top and see what I get. I know it is running rich on one of them by the amount of residue out of the exhaust. I also know that both needles are in operation around 2/5th's throttle and that is where the gurgle is so it just seems to me that either can be the culprit. Just so you know, I have on-board tele that I can watch live on my lap top as well as manual set ups visible on the plane, both are used during ground running. I like to see what I'm doing as well as record it to study later. I will post my findings tomorrow.

 

[acerc]

Forgot to say, I found strait exhaust is best as well, any of the other methods I recorded a loss of rpm. The one that blew my mind was the Y, I used it to attempt to aid the smoke in coming out better but even it dropped the rpm.

 

[Snoopy1]

The exhaust that was one the Valach was the one that fitted under engine. One muffler with two small pipes coming out of the the same muffler straight down looked beautiful but it did not work. One thing that was a pain was the oil that the engine pushed out the crankcase man is black and dirty and hard to get off the plane built a big plastic bottle to catch it and clean it out every now and agin.

 

[acerc]

The problem with the mufflers is not only the volume of air exiting but the short pulse returning, it has to be absolutely free to move. I have a pill bottle as well, read about that oil on a German site, so fixed that right off.

 

[acerc]

Well, after about three hours, I have the gurgle gone and it is purring like a kitten. Ended up richening the bottom by a 1/16th and leaning the top by about an 1/8th. This carb has fine threaded needles but it don't take much, 1/4 turn either way and it's dead, but that's where it ended up from prior setting's.

 

[Snoopy1]

Good hope you enjoy the engine.