Rcplanedan

It was the only way to get a good idle..if i leaned the ls it would die upon opening throttle mm..also it doesn't seem as though its lean when bringing the throttle through stages either..i ran the engine briefly yesterday while still on glow (inverted) it seemed to like a high idle....but i think it is running alot better on gas with its new carb ..i haven't got a smaller prop for the engine but i know it will produce a decent top rpm with say a 14x6 that was recommended....and yes it is is also wanting a certain amount of mixture for hand start..and its effortless when its right on..but a quick hot with the cordless rattle gun and its away

1967brutus

A bit of warning: if you ran the engine on glow, and changed to gas without cleaning, two oils and fuels that do not readily mix will be mixed in the crankcase. Better take it easy, because until the old crap is flushed out of the crankcase, lubrication is not going to be optimal. This flushing process can easily take one hour of low/medium throttle running, longer if the engine has in the past seen castor oil (and in that case, a partial "re-break in" could be required due to the properties of Castor),
I normally either warm up the engine to 50 deg C (115F or so) and then rinse it out thoroughly with brake cleaner, then re-oil it with the oil I use in the fuel, or if that is not an option for whatever reason, I first let the engine tucker away at idle for at least an hour before I start loading it.

Having said that: That's weird... that it would not accelerate with the idle mixture leaned out to "proper"... That indeed suggests that your solution does have additional side-effects in how the mixture reaches the cylinder (better evaporation of fuel).

16 x 7 indeed is quite a bit too large for the engine, and chances are the large prop prevents normal adjustability. It might allow for normal adjustment without the airbleed when running the more normal 14 x 6. 15 x 6 also is OK.
A possible cause of that loss of adjustability is that larger props reduce carb intake vacuum (for the same RPM, a wider throttle opening is needed, =>less restriction in the intake=>less vacuum=>lower air velocity=>poor atomizing results).

I am very curious if the smaller prop will improve adjustability.

I know that for this engine, and an APC14 x 6, you should see roughly 9000 RPM on the ground for a proper inflight mixture, and on a normal sporty plane you should see somewhere in the neighbourhood of 9500~9800 in level flight.

If I would have to guess, right now you are seeing about 6700~6800 (maybe close to 7K), is that correct?

Rcplanedan

That makes perfect sense..i actually just realised i have a 14x6 prop hiding..well il get that out tomorrow..
well for the engine i gave it a rinse out with some fuel before i hooked it up ..and i got it up and running and let it tick away at a low enough rpm for a while to get it cleared out..it really only seen about 1 litre of glow fuel before i got it on gas..i put 500ml gas through it today..
i will try again tomorrow and see what response i get with the right propeller..until then my radial has no carb ..but i just wacked together a adapter to fit a rcgf 10cc carb that i had once tested on a asp fs120..it was too small for that engine..bit of luck it may work on the radial 3 x 11cc ..should be a good match in terms of size..but i dont know if the fluctuating intake pulse is good enough to run the diafram pump in these carbs..

1967brutus

Wow... 500 ml of fuel is some serious runtime... Full throttle that would be around 1 hr, but I doubt you ran it full throttle all the time.

The RCGF carb should be fairly matched to both the ASP 91 and the radial, if it comes to throat size.
The Radial has three intake strokes of 180 degrees divided over 720 degrees of crankrotation, so there should be 60 degrees of "nothingness" inbetween the pulses. That should be OK... BUT... the RCGF pump is intended for a positive crankpulse, while the Saito generates a negative intake pulse.
That means, that the RCGF carb needs to be adapted by fitting a returnspring under the pumper diaphragm, on the pulse side (the negative intake pulse pulls the pumper diaphragm against the spring, and this draws in fuel. The return spring then effects the pumping action).
It can be a bit of a puzzle to source a proper spring. If you have old broken engines, usually there is a spring behind the carb barrel, something like that could be useful.
The intake vacuum is in the neighbourhood of 0,1~0,2 bar negative, this together with the exposed surface of the diaphragm should give an impression of what springforce you need.
Do not forget to provide some sort of "padding" to protect the diaphragm from chafing against the spring end.
There are fourstroke utility engines with negative pulse driven pumper carbs on the market, and I expect those to have reinforced diaphragms, so perhaps you can find something suitable in the spare parts catalogues of Walbro or Tillotson.

But you can of course first try it "as is" and see if it works, because the diaphragm itself also has some flexibility.

Rcplanedan

yes the solution i come up with stopped fuel spitting out the throttle..and it allows me to reduce idle lower now its got a air bleed before the throttle..the spitting stopped..and i wS able to tweek the lsn to suit ..
i will see if the 14x6 will give back normal adjustability.
It was up there in the 6500 rpm with 16x7..

Rcplanedan

yep ,wow indeed..i hung around the engine a fair bit today..and done other things while giving it a good run in..apart from a slightly high idle after 300ml it was running fairly smoothly thats for sure..i have noticed the throttle slide wiggles side to side while running too..holding a little pressure on it and it runs much smoother so i will make a little attachment on the stand to stop that business from happening..
thats a good lot of information for the walbro..i will give it a shot..

1967brutus

This wiggling is caused by the vacuum pulses, and is usually caused by a too weak spring behind the throttle barrel.
If you are confident, pull out the throttle barrel, and check if the spring is there (it could be a production error) or if necessary, add an additional spring from an old unused glow carb (virtually all twin needle carbs have them).
When a carb is ground like I showed earlier in that video, an extra spring is a necessity because of the increased clearance.
It will indeed make the engine run much smoother, and was at the time an eye-opener for me.

Cat 1

My Feedback: (1)

So the Webra rotary valve 4 stroke showed up today - Pretty little motor and in great shape - Very little runtime - Smooth and very good compression..

Its a very simple engine - not like the HP or first Webra rotaries with the Aspin type valve. Only about 20 G more than an older OS 61 FS - and can theoretically turn higher RPM - I found a video of my engine running (on glow) on YouTube and it sounds neat...


Whats your opinions on the as a conversion - The heat on the valve is my only concern - I have attached a short video showing the valve arrangement.. The brass should transfer heat well and the front would be cooled by the intake charge.


An idea - if this rotary valve is a workable option for a small gasser - you could combine the Cam drive with a 2:1 reduction to the prop - Like the BOMO shown earlier - the rotary setup would be easier to make and incorporate.

1967brutus

That valve is really different in construction than I expected (I was thinking of a vertical spindle and a thrustbearing.

I would, especially given that the plug is not covered by the valve, have very little doubt.. It should work, and if it were mine, I would do it (but then again I am idiotic enough to convert a 50 year old MkI OS Wankel, so don't mind me ).

It would probably not even need a separate lubrication system for the valve spindle, it did not need one as a glow either. Heck, I do not even know if that would be possible, but I could imagine drilling a passage tangentially touching the "bearing" of the spindle and routing the crankcase effluent through there, just to see if some additional oil can be supplied. Oil=heat transfer and it would improve the heat transfer from spindle to head.
I don't know if it is necessary, and I think it isn't, but tinkering is fun, right?

I would however not skimp on the oil. That spindle needs to be "wet"...

I don't think it will be possible to use the "valveshaft" as a propshaft, on account of it lacking a possibility to install a thrust bearing.
It also would mean that the inertia from the propeller, needed to bring the piston hrough compression, transfers via the toothed belt and I do not know what gauge that belt is, but I don't think it is suitable for that. Can be mitigated by installing a flywheel on the now defunct propdriver, but I still don't think it would be a good idea.

Cat 1

My Feedback: (1)

Bert. Think I will give this a try on gas. Has a neat little two needle carb so I think will just try with a simple setup. Ignition setup will be easy too.

For the “cam drive” idea. I agree it would not work well here for many reasons but I’m more thinking about a Custom one. Maybe a conversion of a small “industrial” type with proper bearing provisions and a belt sufficient to take the loading.

Rcplanedan

Cat1 thats a cool engine..i would just leap out and get it on gas..it will be unique and definitely different..

1967brutus

#Metoo...

Way I see it, fiston and running gear is 100% safe. We know that from earlier conversions. Leaves only the rotary valve, and it has all appearance that this particular construction is extremely easy to dismantle and inspect for wear every runhour until you are sure no bad stuff happens.

I would say, go for it, Chris!

Rcplanedan

Well i got the asp fs91 idling well enough without an addition of any bypass..testing with a 14x6 prop sure gets a bit more top end and a bit more responsive..but i like the way it performs with the 16x7 ,produces a nicer thrust and this engine can just pull it up to max without issue..i added a cut piece of spring from a pen to fit in the carb body , to hold the throttle barrel from fluctuating..that was causing abit of issue with idling..so im pretty satisfied now..although i think the spark plug gap was a little off,that may a reason i cant go to low of an idle..
heres a link for the video Done some testing of the walbro carburettor on the fg33, can get a great idle..anything above 1/4 throttle requires alot of tank pressure to keep fuel to the carb..its troublesome for sure..

Raleighcopter

That's why we use the solenoid and controller (and Chris has been experimenting with an air pump which I hope to do if I ever get back to experimenting).

Rcplanedan

yeah i completely understand the es is the way to go..but i thought id try once more on a different engine..i will mark that walbro right off the list...thanks

1967brutus

Did you allready fit a spring under the pumper membrane?
Because what you describe perfectly fits the behaviour of a pumper carb without a pulse drive... And without that spring, a normal Walbro will not respond to a negative pressure pulse.

Raleighcopter

Naw, man. Try any method you think is viable. That's how we learn what works and what doesn't work.

1967brutus

The Britlanders would say: "say, that ain't half bad, ol'chap"....

That indeed runs pretty decent.
That prop and RPM will perfectly match oldtimers, slowflyers and WWI era biplanes. The engine will (contrary to glow ignition) handle that kind of supressed running without issues and basically indefinitely.

On the 14 x 6 you will get a bit sportier performance. Here is my 91 still without the electronic fuel control. Throttle response not as nice as with the electronic control, but still a very decent sporty performance.
Plane is 2,7 kilo and 61" wingspan VQ SpaceWalker.

Plane is still flying to day, performance has not deteriorated one iota, just throttle response is much better and the blue puff of smoke is totally gone, virtually zero residue on the plane even after a full afternoon of flying.

Rcplanedan

i did ..well that should be on the correct side? ..
i have a leaf blower (4stroke) and pulled the sprig from that ..so its definitely the recommended spring rate

Rcplanedan

thats very true..well i should try a little more possibly..the carb was an easy fit ..but to make it work, thats another herdle

1967brutus

Fully agree. Your airbleed idea was a good one and that kind of thinking outside the box is what our group needs.

And just as a thought: I am thinking about starting a parallel thread more directed to "analog" carbs, amongst others because it seems to come up more often, also in e-mails to me, or comments via YT.
If so, that thread would only serve to make it easier for people to easier find the info they are looking for and to prefent confusing info in one single thread. It would NOT be intended to keep things separated for separation's sake, because I do not believe in that.

I will only do so if there is a demand for it, and heck, it does not depend on me, anyone of you guys can open such a thread.
Because i still see the "analog" conversions, whether they are done by fitting a different carb, OR by modding an existing glow carb, I still see those conversions also as a viable option (I flew them for years, remember?) and it would certainly make converting engines to gas accessible to more people.
What is more: I know from experience that not only will modding a glow carb provide better insight in what an engine likes WRT fuel/air ratio (not so much in numbers, but more in "getting a feel for it"), and a pre-modded carb will be way easier to finetune by solenoid than a straight unmodded glow carb.

It is just a thought, let me know what you guys think (or go ahead and start one if you think it is a good idea).

Rcplanedan

that does run very well ..i was thinking to put in a seagull models isport i have hanging..it should match well..and will use 14x6 for sure..

1967brutus

The difference between that and the same engine fitted with ES is night and day, but indeed, analog mods absolutely can run 100% satisfactory.

1967brutus

The leafblower being a single, it has much less volume in the intake tract, and a much greater cylinder volume compared to the radial, so although average vacuum should be roughly the same, the amplitude of the pulse signal is much stronger on the leafblower and weaker on the radial. I think the springrate of that spring is too high. How if you exchange the springs of the Saito carb that is now on the single, and that of the leafblower? The Saito carb has a springrate designed for the radial, and the leafblower has a springrate designed for a single.
I have to admit it is a guess, but I hope it is an educated guess...

Rcplanedan

That is a great guess..it makes sense..
I will test this theory later today..see what happens..
The leaf blower is a 25cc and would have a longer stroke and a larger piston giving one decent amount of vacuum per revolution..and well the pulse from the radial will be more linear once it gets reving