This one is a WT-38. There are several others all similar though. I think with the pump, it would stand a bigger venturi though.

The linkage on this particular model is a bit awkward, so I will need to take the standard arm off, drill and tap the shaft and put something else on. Done that before, not too fiddly.


The Edge 540 is a candidate for the converted motor, although it ain't got much bulkhead and it might not go in. Not got much else big enough to take it. The YAK now has an SPE with a bigger 11.1mm carb, which is where the SC 180 came from. It has a big bulkhead into which I could make a hole for the carb. But the SPE is going great on it's new carb now, so it's a keeper in that plane.

I'll let you know if the big end lasts on 20:1 mineral oil, once I find an airframe

It sould be fine with the 20:1 mineral oil for some time.

Keep in mind that the ASP is the same as SC and you can get another rod from Just Engines a couple years from now if you need one.

the big end of the rod will be the critical wear point of interest.

I can't speak for ASP but my converted Saito 91 big did just fine at 22:1 fuel/oil. I took it apart when I put it back on glow, to clean and inspect, and found everything in the bottom end to be in absolutely mint condition. It had somewhere between 30 and 50 hours of run time on gasoline using Redline Two Racing Synthetic oil and Pennzoil Two Cycle Air Cooled. I think most will know the Pennz is mineral based and I couldn't tell the difference between the Redline and Pennz in performance. As I mentioned, it ran on both and looked perfect when I took it apart to inspect it before putting it back on glow.

It is now powering an AeroWorks Extra 260 doing 3D and I need every last bit of power at the absolutely lowest weight possible. That is the reason for the conversion back to glow.

Ok, Sounds good. I'll stick at 20:1.

P.S. My friend just took the big end out on his Moki 210 petrol with 40:1 synth [:@] We had a discussion before the sudden stoppage along the lines of "Ow much???!!!" but he wanted to try it and knows the risk. He has a new rod to fit now and will be back in the air on more oil than 40:1 soon!


More on carbs:- 22 size is too small and holds the RPM back. 24 without accel pump stumbles in the mid, but the top-end and the idle are great. 24 with accel pump seems to be the best combination, although a 28 with pump will probably be good. 28 with no pump has similar top end to the 24.

I modded the butterfly on the (slightly worn out) 24 with pump to increase air over the idle jet:- it seems better still, although with the worn spindle I'm not convinced. WOT in a hurry after a minutes idle is pretty good, with good mid. WOT in a hurry after 10 seconds idle is great and so is mid!

So accel pump needed for 4 stroke 180 and bigger than 22 as far as I can see.

Brrom! Brooom!

The Walbro WT-38 is common to the <font face="Times New Roman">STIHL FS 51, 61, 65, 85 AND 90 TRIMMERS</font>

Hopefully this will avoid any 'oil drop in the pulse line' problem.

I also am converting a asp 180 FS and plan to use a WT454 from a ryobi can the intake pulse be taken from the inlet manifold on the adapter plate and do away with the fuel lines?
Also the breather, could this run to the adapter plate also for the oil return.
Is the WT454 ready to use as is or does it need modifying for the intake pulse.
dogshome any further updates on your conversion, the video sounds great and idle is very smooth.
Could I suggest you use 5 cells on the ignition as I have found it gives higher rpm and reliable running.

Good luck on your conversion. My might consider starting a new thread for folks to follow your project.

The WT454 carb appears to need a positive AND negative pulse to operate. It's not set up to get it's "pulse" from the intake only. It could, perhaps, be modified to work like a WT-456-1 which IS set up to run from an intake-only pulse. See the instructions how this could be done yourself, assuming the pump cover and the carb body look like those in the picture. http://www.rcuniverse.com/forum/m_93..._4/key_/tm.htm
If you use a carb that is set up to run on intake-only pulses, then you don't need to hook anything up to the breather(crankcase vent).

This arrangement works "Two stroke" carb and no diaphragm springs required!





Seems very happy on a 4 cell pack, with a big fat blue spark so staying with that for now. I'll bear it in mind and try at some point though.


The carb you've suggested........[:@]
WT 454 is only 20/64ths venturi. This will definitely affect power badly []
No accelerator pump on it either []

That's 8mm venturi. Could be better but should work for a first project. The lack of accelerator pump is a big deal. Does your carb look like the pictures I linked to? I've never quite understood how that return tube running from your carb back to the intake doesn't just attenuate your diaphragm pulses, both positive and the negative one. The dry side of the pump diaphragm, seems to me, should be isolated (except, of course, for the pulse line) so all the pressure changes act on the surface area of the membrane. Right?

Why have an lossy RMS signal to the voltmeter when you could just go DC? [img]{akamaiimageforum}/micons/m9.gif[/img]

Cutarug,
Does your carb pump cover and guts look like those in the link I provided (for possible conversion to negative-only pulse)?

I think ac is the way to go Don't remember DC with those horrible bakelite fittings and open frame switchgear in the house - was it Victorian? I bet somebody on RCU does All the industrial motor control is ac or brushless DC now as well.


Another scribble for you?

Nice electrical analogy chart. You've come a long way since that original plumbing diagram. [img]{akamaiimageforum}/micons/m6.gif[/img]

I like your inductive circuit explanation because it makes my point. As with any inductive circuit, the voltage drop increases with speed. So your fuel pumping capacity will be reduced at WOT, just when you need it most.

That will keep me awake tonight [X(]


What about the resonant frequency??? Maybe it will pump so much at one speed that I'll get a 10ft flame licking out of the intake!! [] Worse, I could have made a ticking time-bomb!!!! [:-]

These carbs are available at up to 13.5mm venturi with the same pump. It takes quit a bit less fuel flow to feed a 30cc four stroke. I wouldn't worry about a thing.

I channeled my buddy, Nikolai Tessla. He says don't call the fire dept yet. .....he said something else that resonated too, but I can't remember what it was.

I noticed that dogshome has used the RCEXL ignition unit.
The instruction of this unit says that the timing should be set at about 28degrees BTDC.
The datasheet from this unit says the unit advances a minimum of 4 degrees and 10 degrees at 2000rpm till 35degrees at 4000rpm.

Question: Shouldn't the timing be set at 0 degrees because the CDI does the advancing? I know the manual says to set 28degrees pre ignition but i'm concerned if the pre ignition isn't way to much if the unit is adding 4 - 35 degrees pre ignition.

datasheet: http://www.rcexl.com/upfile/200994/2...1492067926.pdf

It's not a very clear data sheet []

I think that the retard with very little RPM (long period between pulses) is probably 0 degrees to enable setting the full advance timing. I imagine that as soon as two pulses are seen together in quick succession (i.e. engine has started) that it then retards fully. As the engine speeds up, then the retard is reduced.

10~35 is 25 degrees. If I set it around 28, then I get 3 degrees at low RPM and 28 at full RPM. Sounds reasonable [8D]

Note that the very low compression industrial engines (like SPE) need at least 35 degrees advance to get full power. I think that is why advance is stated as 10 to 35 degrees.

Yep, not very clear on that pdf file. But most companies don't share any of their table. I think what the manual is saying is the PIC chip inside is programmed for 4 degs advance at idle (they determine what is "idle" in the PIC table), 10 degs at 2000rpm, and 35 degs at & above 4000 rpm. These are points along their curve. These aren't step functions, it is a linear increase in advance (or removing of retardation). I think when you're trying to start, the ignition is at full retard, 35 degs. I'm guessing as soon as the engine fires and sees, as Dogshome said, any close pulses (close compared to trying to start the engine), the box interprets it as 'running at idle' and gives you 4 degs advance right away. That can rise very quickly if you happen to start at a wider throttle opening.

So, I'd guess, when you're hand flipping it to start, your spark is close to 35-28=7 degs AFTER top dead center. This is a very safe, reliable angle to hand start an engine because there is little chance of firing before top dead center either injuring the user or just running backwards.

I have a 27% Cap232 with a CRRC Pro 50cc engine in it. It starts backwards about 50% of the time and it's only set to 31degs BTDC. Of course, there's no telling what CRRC's advance (or retard) profile looks like. CRRC makes their own ignition and they don't share the PIC table.

Piccys

Nice work Dogshome.   There are no bad looking engines.  Looks like that cowl was set up for some big 2 stroker originally, eh?  Lets see some pics without the cowl?  Well, you're almost there already .  Has this flown?

Thanks! [sm=thumbup.gif]

It's had an SC60, ST 90 then the ASP 180 FS glow. Not flown as a gasser yet.

Still a dog to fly - although it flies nice at speed. Prop hanging is difficult/impossible (short ailerons and bad roll coupling to rudder) and landings fast (heavy with small tail). No lead required with the 180. Never crashed though


Seagull Edge 60. How they though it would ever fly nicely on a 60 I have no idea. The 90 was marginal. Room for a 40CC 2 stroke in there!

5 flights at the weekend on 20:1 mineral oil. Big end feels fine