After a few gallons of fuel there should be minimum wear. I think the waste oil is fine to recirc BUT, not post venturi. My methanol engines run great recirculing crankcase oil pre venturi i.e. into the velocity stack with no noticeable change in running behavior. The methanol OS 4 strokes I've run with factory recirc into the intake tube ran noticeably better disconnected, venting to atmosphere instead.

I've not tried recirc on a gasser but one thing that I've noticed running gasser 4 strokes is it appears there is a significant reduction in overall wear. Better oil? Inherent lubricity in gas? Not sure, but one thing for sure, it's many more hours of run time between valve lash adjustments.

With the recirc' through the orfice in the intake runner, there's an increase in crankcase pressure that develops with the varying rpm / blowby... the GF40 with the gas walbro carb was affected by the increase pressure on the fuel pump diaphragm, which affected throttle transition / response... The idea is sound, just not well executed... try blocking the PCV valve on your vehicle's engine and see what happens with oil forced out the crankcase seals... if they want to implement a recirc' PCV system on a model engine, there needs to be a means to scavenge the crankcase, but that won't work well with the walbro fuel pump system... there's no need to over complicate things with such a small displacement model engine.

Over complicate? PCV? Lost me. Couldn't be more simple to add a nipple to a velocity stack. A tight fitting hole for the 1/8 brass nipple and JB Weld to secure it. Done. Oh sorry, you DO have to remember to plug the crankcase vent tube into the nipple. And it scavenges just fine.

Well, over complicated in terms of mimicking the big engines... what you state is true, simple... recirc' blowby on the atmosphere side of the throttle valve / plate works better than on the manifold side... but PCV properly implemented, requires a bit more than a one way check valve as the crankcase breather pcv, and a small orfice in the intake runner... especially with a single ringed piston... tight tolerance engines can get away with a small fixed orfice PCV system... but a single ringed piston with a check valve acting as a PCV valve.... a small orfice in the intake track that can't pass the blowby volume in the lower rpm range with ring collapse... it causes inconsistent fuel mixture.

Remember the GF40 is a positive / piston driven forced ( with a check valve ) PCV system... there is no relief path when the crankcase positive breather system is over pressurized by excessive blowby.

Thanks, John. Is there a GF40 thread that describes the issue you mention with the PCV system? Hours of searching and reading has yielded nothing so far.

Update: Found a little info on flyinggiants about how the PCV system is intended to work and how the crankcase inlet check ball can leak at high rpm. Interesting system with the tiny hole at the exhaust valve to aid in lubrication of the exhaust valve train, then expelling excess waste oil out the exhaust. Does the exhaust lifter or it's bore have a slotted passage?

I didn't start a thread on it, but I mentioned it in a few replies over in the rcg engines forum.

The so called PCV valve is in fact just a sprung loaded one way check valve allowing a small volume of air drawn in and then closes on the down stroke of the piston... the crankcase breather / blowby gasses get forced up the push rod tubes through a small passage cut in the cam follower bushings, and then down a small orfice in the intake runner under the rocker cover, just behind the backside of the intake valve... the orfice is too small for much of a scavenging effect, but small enough not to allow a large volume of gasses to be forced through that small orfice... so pressure builds in the crankcase in the lo / mid throttle range... the fuel pump pulse pressure port is in the backplate just above the PCV check valve, it's visible externally as a short piece of transparent tubing connected to the fuel pump pulse inlet nipple in the carb.

I ended up removing the rocker cover and blocking that orfice with a small allen set screw ( drilling / tapping )... and then adding a large threaded nipple in the rocker cover to vent the crankcase blowby and lubricate the valve stems / rocker assembles... you can remove the ball and spring from the pcv check valve, but I choose to leave them in place, as the vent nipple I put in the rocker cover was large enough to vent the crankcase efficiently... I made a threaded nipple from some brass round stock with a 3/32" ID... worked a treat, the engine ran much more consistant and got rid of the burble through the lo / mid throttle transition.

In the GF40 pdf manual, there is a drawing showing how the PCV system works.

Fact... Breaking in also takes longer.

Sorry for having been gone for a while, guys... But life dealt me a rotten hand (better said, my employer did the dealing) and life has been a bit helter skelter lately.

Haven't been sitting idle (in fact, buried myself a bit in hobby projects to not have to think about the misery in life) and it just so happens that where last leave period it was a steam powered boat, this time it's a bit closer to this topic. Still a boat, but at least powered by a converted-to-gasoline ex glow engine.



No solenoid system however, but that has a reason: The RPM (1500 approx, or 25 revs/sec) and the control frequency of the solenoid (30 Hz) are too close to each other, and I cannot be bothered to start messing with synchronized solenoid operation.

It's a continution of a project I did about 7 years ago, but for which back then I had a very unsuitable hull...
Did not feel like "engineering" lately, just wanted something to keep my ands busy and my brain disconnected from reality.
Haven't flown an RC plane in about 4 months, didn't trust myself with that kind of stuff...

Slowly getting back to where I am supposed to function, so...

And I'm not the only one that is slowly getting back to life:
Hasn't run in about 6 or 7 years...

what carrier frequency are you loooking for on that boat engine controller? that's just software and easily modified, especially if you're using one of my controllers.

It would have to be synced with the engine on the intake stroke, even a bit of asynchronicity, and the valve does not open during several intake cycles. The RPM is not 100% rocksteady.

But I think, for this thing it really would be only bling and no noticable advantage. It's not sensitive to mixture at all... Or better put, mixture affects this engine just like any other, but due to the governor it somehow does not matter (richer=>RPM drops=>Governor compensates=>me not noticing that it runs rich=>me highly confused)...

to do that would require a rewrite of the controller code and i'd need to monitor the ignition pulse from teh RPM output and then calculate how long to wait until the engine is at the intake stroke before opening the solenoid for the proper duration. yeah, that's a fairly big change. what about changing to a 50 or 60 hz carrier frequency? a higher carrier makes the solenoid behave more like a modulating valve rather than a 2 position valve but that would probably have detrimantal effect on atomization at the spray bar.

To be honest: I don't know what direction to take... This is really completely different than anything else out there. Imagine this: The carb is taken from a .06 cu.in engine. That is tiny.
This engine (the fourstroke, not the donor engine) runs with throttle openings so small that that .06 would not even consider turning over, let alone run...
I have no idea about air velocities, intake manifold pressures and what not. Looking at fuel consumptions in the order of magnitude of 20 ml per hour (2/3rd of an oz).

I am like a blind man, feeling my way around here, and no idea what does, and does not work.
I have allready reworked the camshaft, because valve timing intended for 10K does not function very well at 1,5K. So I reground camprofiles such that valves open and close as near to their respective dead centers as I could get it. It makes the valve train a bit noisy, but because of the very low speeds, I do not think there will be an issue with that.

so what are the expected minimum and maximum RPMs you expect/want?

1500... But it needs a bit headroom and footspace for starting up and getting the governor to engage. That is the trouble... I need some manual control during starting, and bring the engine to within the range where the governor will engage, but from there it's on the governor.

The thing is: once the governor takes control of the throttle, there is no functionality for a TX based curve for the fuel.

Interesting project Bert... you could rewrite the sketch so it turns on the solenoid valve on the induction stroke via a small magnet on the side of the cam gear... hall sensor mounted on the cam cover... do away with the 50hz (PWM) modulation, and vary the on-time using (PDM - pulse duration modulation) via a varing delay, vary the on-time via the channel mix curve.

If the throttle is managed by an onboard governor, there's essentially no throttle position available at the transmitter to slave a mixture curve to. It would require adding a throttle position sensor and moving the mixture curve to the controller and everything that entails. It's a major rewrite of the code and additional hardware (probably a magnet and hall sensor) to read throttle position.

If thats the case, put the governor controller in the solenoid driver sketch managing the throttle servo pulse width based on rpm... then vary the solenoid PDM based on governor / throttle servo pulse width and engine rpm... add a PDM bias to trim the fuel mixture via a spare channel on the trans.

Truly Amazing project Bert... Love the sound... Variable pitch to control speed??

Do you think a custom carb with a very small venturi high help out - I know a guy..

All in all it seems to run great!

That is exactly the bump in the road...

But I decided to go the analog McGyver way and solved it like that.

The challenge I had was that a glow carb from an AP .06 Wasp (1 cc glow engine) had to supply an ASP 30FS running at 1500 RPM, fixed RPM variable load.
Since RPM is fixed by governor, increasing load actually DOES force the governor to open the throttle, but since the RPM does not rise, that means carb vacuum and thus fuel draw reduces.
It is the same effect that forces us to use a servo-slowdown when opening the throttle, only, in my case the RPM won't come up.

So I was having an engine that went from slobbering rich at low load to too lean at high load at constant RPM (meaning you cannot really determine what is going on by ear).

Given the very low RPM, very low fuel consumption (this thing, even slobbering rich, only consumes less than 1 oz of fuel per hour), there also is no visible smoke plume to go by...

What I did, was attach about 1 1/4" length of 1/8" OD Brass tubing in front of the air intake, that serves as a restrictor.
At low load (throttle barely a pinhole sized opening) the throttle barrel is the main restriction, at increasing load the throttle opens, the airflow increases and the Brass tube becomes the dominant restriction, shigfting the vacuum area to in front of the carb barrel, increasing fuel draw at increasing load.

I can tailor that vacuum bias by varying the length of that Brass tubing, and at the moment I am (based on sparkk plug colour) probably just ever so slightly on the rich side at high loads.

It looks rather improvised (and that is because it IS improvised), but this is that restrictor.


So far, it works like a charm, the engine is running pretty consistent and so far absolutely reliable, it starts really easy, and the only "thing" procedure-wise is that you have to start it on manual throttle, and once running you need to bring RPM to within a certain range close to set RPM or the governor won't engage. Without a visible tach, that is a bit of a trial and error thing, but no big deal. Once the governor engages, it basically runs until the tank is empty.

Cooling is done by a tiny 42 mm electric fan, and more as a gimmick than anything else I added a commercially availlable themperature controller (very cheap Proportional controller, nothing fancy) and changed the NTC resistor for a FrSky probe, which conveniently brought the regulating range to 70~100 deg C.

The weird thing about this cooling is, that when I ran the engine without cooling, it never got over 110 deg C as far as I can tell, and the other ASP 30FS I have runs way hotter.
I do not believe for one minuten that this tiny fan has any significant effect on engine temperature, because even an idling prop generates a 100 times more air movement, but alas, without the fan the engine refused to run reliable, and needed a belching rich mixture (judging by the pitch black exhaust residue) while using that tiny fan, I'm now fairly close to Stoichiometric: the exhaust residue now is a light grey oil/water emulsion and the tailpipe does barely get over 30 deg C.

Haven't been able yet to determine engine temperatures due to the shrouding on the fan (no access for IR temp gun).

But who cares if it appears to run right all day long, right?

Yup... Variable pitch indeed. An old Marx unit, 50 mm prop, 15 degrees reverse to 45 degrees forward blade pitch angle. These things have been discontinued for at least 30 years if not longer, but 7 years ago out of a clear blue sky I managed to find 2 new ones (both NIB, never used).
Pretty decent quality, triple bearing double sealed sterntube, the hub has 5 ballbearings out of stainless (one for each blade, and two in the pitch control mechanism). Entirely maintenance free, yet the hub is taken off in 5 minutes if needed.

I know you know a guy, but the issue for this carb is adjustability. Right now I can trim that air intake tube, and as long as it works, I'm not going to change that...
It took me 7 long years to come up with this idea (remember I mentioned once that a lot of my solutions are "brainwave-based" and that I have little control over where or when they pop up? This was one of those... )

THis is a more clear vid of governor response:


As you can see, I had to extend the throttle lever by a "huge" amount to reduce barrel movement, and mind you, this is a carb intended for a 1 cc engine feeding a 5 cc engine.
Throttle bore is something like 2,5 mm in total, and at 0 load, the throttle opening is even barely visible with the eye, at full load it is maybe 1/3rd of its stroke opened.
It's a weird set of parameters to work with, I can tell you...

Had to read the intake restrictor theory a couple time before it sunk in - Brilliant.. What are you using as a governor control Bert?

I had to chew on that carb issue for 7 years before the solution came floating up...

But before that, there were several issues that needed to be solved (that happened 7 years ago btw), such as that a tiny throttle orifice and a wide intake port (about 5 mm diameter) will lead to a near zero mixture velocity leading to oil pooling in the intake port. I solved that with an insert in the port, up to as close as possible to the valve area, reducing the inner diameter as far as I dared to go. Made that insert out out of POM, same stuff I made the carb header from.

Valve timing was another issue that I fixed last week. Strong reversal in the exhaust at the beginning of the intake stroke caused enormous amount of fouling of the combustion chamber.
Ground away the cam profile until there was virtually no more valve overlap, now the combustion chamber stays clean.

The governor is a Futaba GV1, intended for IC helicopters, a very weird controller, acually...
It wants to see the engine RPM as input signal, but its set value is the rotor RPM, and to make that work, you have to tell it the reduction ratio.

It has a working range of 1000 to 2000 RPM (rotor RPM...)

So I had to put 10 triggers on the flywheel and tell it there is a reduction ratio of 10:1 in order to trick it into thinking it sees 15K rpm, in order to achieve the desired 1500.

But hey, as long as it works...

So... let's call that the "vacuum bias carburettor"...

I suspected its was a HELI governor but have played with them a bit and was wondering how you "tricked" it..

"Theoretical Idea Moment" - What if we built a "carb" with two throttle elements with and spray bar in between - No venturi per say . If we controlled both inlet and outlet with fixed curves and delays we should be able to control both the flow (speed) and the mixture profile.. Not an improvement on the solenoid in my opinion but a different method of control.

For certain applications, that would most definitely work, although I would place the spraybar in the 2nd throttle barrel just to keep a good atomisation (turbulent flow at the point of fuel supply).

Such a set-up can even be done as a strictly mechanical thing, varying the bias by means of the lever geometry.

I see that as absolutely viable, but very limited in application. It could be an ida for helicopters though, because my .50 gasser heli also was impossible to tune properly, and relied in essence on the governor FORCING the RPM to be constant. A second throttle in front of the carb, even simply mechanically actuated, might have proven very benificial to the point where a governor would become obsolete. A "no governor situation" would have in turn allowed for the solenoid and TX-based fuel curve to function properly (although dialling in the curve would have been a real challenge.

But although the solenoid and electronics are the subject of this thread, it sometimes is good to at least explore analog ways for mixture control, even if for no other reason than to learn about mixture requirements, and the physical conditions that influence mixture and in what way they do that.

Learning is the essence, the results of the knowledge gained is the goal.