1967brutus

Not really... I can show you at least 2 vids of unmodified glow carbs that ran perfectly fine in the air, and at least one other that ran perfectly fine on the bench (but rather crap in the air).
I mean, it is NOT impossible, and it also depends on how fastidious one is WRT running behaviour.
I am a bit extreme in that. Not so much the running behaviour itself (I can live with a less than stellar throttle response) but I am extremely picky when it comes to the "quality of the combustion". I hate black crap coming from the crankcase drain, and I hate cleaning piston crowns.

I do not question those people, but not everybody has the same definition of "running well".

I have heard, that those carbs, due to their midrange adjustment, tune "fairly well" for gasoline. Not like the solenoid, but acceptable for applications where demands are not too high.
The engine itself is even pretty good on gasoline, pretty decent heat dissipation.

Rcplanedan

[QUOTE=Cat 1;12766020]Dan.. somewhere between you and I there is a perfect spot to be . - The dam thing just keeps moving up and down.

i bet there is ..😆

Cat 1

My Feedback: (1)

OK... some testing today. Interesting discussion above as this is the first "solenoid" conversion I can quite get right.. 1/3 to WOT is brilliant and easy to set. Idle can be set to run all day long at 2000rpm. Im really struggling with the off idle to mid range - Loading up and leaning causes a cutout. IM thinking the weird intake arrangement is causing some grief - Do you think the weird S bend and horizontal carb could cause loading in the manifold at idle? The cold aid blast on the tube probably doesn't help either.

All in all - it runs great - lots of power - 2 bladed props today - 12x6 at 9300 and 11x7 at 10000.. Easy to start and runs like a top - just have to figure the low end out.. My curve has a very pronounced Post idle dip. Might need a "special" carb.

Here is some media.

1967brutus

I have seen curves like that, and cannot really explaint why not all engines do this, I also have seen many engines that run perfectly fine with that kind os dipped curve, I have a few of those myself too...

What I do know is that there is, for a fourstroken an interference area between the valve's cycle frequency and the RPM. A cure might be to simply move the LS needles a bit to nudge the curve up or down. No guarantee.

Cat 1

My Feedback: (1)

Looking at it again and thinking for a while I have a few things to try. The LS needle is very very sensitive. Will give it a few more tries and then might have to come up with a different solution. I think I’m just running out of Headroom for the off idle dip. Will take the carb apart too just to make sure there are no issues there.

Raleighcopter

can you close your LSN 1 or 2 clicks? that'll bring that end of the curve up some.

1967brutus

That was my idea as well

Raleighcopter

I would shoot for the low end of the curve to be near +50 or so. That'll give more solenoid resolution

1967brutus

More like around "0" would be my first idea, just based on a hunch and previous experience.
What would be even better, would be one of those beautiful Throttle bodies Chris makes...

Glowgeek

I know what you two are saying, not sure anyone else would though. I think you two are talking about two different points on the curve.

Raleighcopter

The left side of chris' curve is really low. There's about 6000 points from full open to full closed but there's only about 1000 useable places that can be selected. The points in between are used by the compensation when the curve gets scaled according to the ideal gas law. If that low dip goes down to about 5% of 1000 that's a solenoid output of 50 of 1000. A change of 1 step results in that 50 becoming 49 which is a change of 2%. That's a huge change. If he closes the LSN he can move the curve up. Say he makes it so the curve low point is now around 25% of range. That's 250 of 1000. A change from 250 to 249 is 0.4%. you can see that raising the curve that way increases the resolution between values so you can get better control over the mixture.

Glowgeek

Yes, I know, however you said "I would shoot for the low end of the curve to be near +50 or so."

"low end of the curve" could mean idle, or it could mean the lowest point on the curve. Also, Chris's radio uses a -100/+100 scale and don't think you want either idle or the lowest point on the curve set to +50.

Raleighcopter

Sorry. I meant idle.

Glowgeek

That's where I start the idle point on a -100/+100 scale. That usually keeps the lowest point on the curve above -50.

Raleighcopter

Sure, but if it doesn't, close the LSN a bit and try again. Obviously, a well running engine is the goal however you get there.

Glowgeek

Yep, whatever it takes.

It's unanimous, we all agree that Chris should lean the lsn, pushing the idle curve point closer to zero.

Cat 1

My Feedback: (1)

Glad you guys got this all sorted out . Sorry for he radio silence but i'm up at one of our Northern Bases again on a "Management Assignment". I will try this but I originally set out with a flat curve at +40 (70%) and i'm not sure now how I got to the end result.. The LSN is super sensitive and I guess i'm just not trained well in that adjustment.... BECAUSE .. I usually eliminate it. I think the carb might have an issue with the needle/nozzle arrangement. I think the issue is being created but how the jet/needle arrangement meters fuel coming off the Seat.. not optimized for the minute amount of gas needed here.

When i'm back I will have another go - I know this engine will run well as the majority of the range is very good and it runs great otherwise. I have a contingency plan in mind too - I won't build a full on TBI carb YET.. But might build a simple throttle barrel and only run the HSN - Basically mimicking my TBI setup but with an adjustable needle instead of the fixed jet. - no LSN or helical slot easy to do and try.

Glowgeek

The lsn, if you have one, IS super sensitive. It is on my Saitos anyway.

I start with 0 on the curve for the idle point and +60 for the wot point. I then make a fake curve between those two points based on experience. I start the engine at 33% throttle using the hsn, set the hsn for wot and quickly begin working my way down the curve toward idle. If at any point during adjustments the curve dips below -50 I lean the lsn, retune the hsn and begin working my way down the curve again. The last thing I want to do is to waste time getting a good idle only to find the curve out of useable range. I hope this makes sense.

1967brutus

I see, we worked out what was meant.

Strange enough, sometimes opening the LS needle until it is no longer active, ALSO works.

On second thought, I see Chris' curve ends at around +40 on a -100 to +100 scale, and that is a bit low...

Now there are two different trains of thought here. If HS mixture is largely determined by the solenoid (relatively wide open HS needle) and idle mixture is on LS needle AND solenoid, that causes the dip in the curve.
The location of the lowest point of that dip is determined by how many points there are in the curve, and whether those points are also X-axis adjustable or not. That lowest point is NOT necessarily where it NEEDS to be according to the engine.
That will always cause a bit of "friction" between engine requirement and curve possibility. Because MAYBE the engine wants a slightly leaner mix where the curve, because of its fixed X-axis, allready rises or vice versa.
The way around this is to open the LS needle to where it is no longer active, and do most of the WOT mixture on the needle, That will end up in a curve that is always ascending over the entire range, and that eliminates the issue of the lowest point not coinciding with where the engine wants that lowest point.

So what I would suggest, IF "closing the LS needle to force the curve up" does not fix the issue, is to open the LS needle a few turns (it should not fall out but also be not active anymore) and close the HS needle to where the solenoid just comes in (appr 70~80 on a -100 to +100 scale) in order to create as much "range" as possible, and run the entire mixture on the solenoid.

I have a few engines where this seems to work pretty well. Idle mixture most definitely is less refined, but it cures the midrange issue most effective. And since I only idle my engines on the ground, I do not care too much for that.
I think that stuff like "the engine has to idle low enough to not roll on pavement" highly overrated. It has to idle low enough for a reliable approach and landing. That is all I need.

Glowgeek

Thanks Bert.......I must admit, I haven't wrapped my mind around it yet but it's something else to try.

Raleighcopter

i like this.

1967brutus

Just saying: your earlier posted way of setting up a curve is a valid one, and one I typically use as well, because it leaves more resolution.
But if you have an engine that, no matter what you do, above idle there is that patch where it seems you just cannot find anything the engine is happy with, you can first simply change the throttle curve a bit, in a "blind" attempt to let the engine requirement more coincide with one of the X-axis steps of the fuel curve but that is really a bit of a blind trial and error. And if that does not help, then there is very little else to do than to sacrifice resolution a bit in order to eliminate the dip in the fuel curve alltogether.

Glowgeek

I have had some success with moving the X axis points to work through "off idle" problems. Essentially clustering them them in problematic areas. That was when I was using a radio with only 7 point curve. With the Taranis and 12 points I have not had to move them on X. Then again, I've not had a chance to fly any of these conversions yet.

I've definitely noticed problems when running the lsn too too lean. After all, the solenoid can't deliver more fuel than what's available.To date, I have concentrated my efforts on needle adjustments that create a harmonious relationship with the solenoid i.e. where leaning or richening on the curve produces an equal resonse wrt to engine behaviour. It's really easy to get out of balance where the solenoid will over-lean the mixture with a small change on the curve but won't richen the mixture unless you raise the curve point a lot. So, I try to land the lsn and hsn where equal amounts of movement, up and down on the curve, results in reasonably equal changes in rpm.

I'm anxious to try richening the lsn more than usual to let the solenoid have more control. There may be some magic to be found there. Anything that can possibly make the curve more linear is worth a try in my book.

Edited to remove dumbazzness.

1967brutus

As far as I have been able to determine, the difference between groundruns and flying does not affect the shape of the curve. It might highlight a lean spot (making it more noticable) but it is not like suddenly midrange has to be noticably difference. Most of the times, if you have a good curve on the ground, one click richer on the HS needle shifts the entire mixture range to where it needs to be for flight.

Dang! You have beaten me at my own game! Never thought of that (and therefore never consciously tried that) but that principle immediately landed in my mind and clicked in place. I think you have a very good groundrule there.
Looking back I think that is where I usually ended up, but I think it is a pretty good way to check whether you're on the right track with the needle setting.

Glowgeek

Good to know, thanks.

On the right track, yes, but safer to be on the rich side of that -/+ hysteresis centerline.

The thought of adjusting needles for a centered hysteresis came to me with the introduction of the temp/pressure sensor. I felt it was important that the change in fuel mixture would have equal effect, whether richer or leaner, with temp and pressure change.

I seriously could be over thinking things.