Fruitless flipping...almost

[Steve Hargreaves - Moderator]

Hoooraayyy!!!...he's one of us...he's one of us!!!!!!

Well done Tony....sounds like things are getting a bit more positive. Certainly a flat glow battery & no fuel will make starting very hard......!!!!!

The idle needle is usually factory set & shouldn't need more than a 1/4 turn either way to finalise it...you didn't touch it did you? You did??!! Ah!!!

OK here's what we do...main needle set to run setting....carb open just a crack (2-3mm) & lightly screw the idle needle home (lightly so you don't damage the taper.) Piece of fuel tube over the fuel nipple & blow down the tube (swallow yer spit first though in case it rots the bearings!!!!). Slowly open the idle needle until you can just hear the air hissing through the carb (& you turn a lighter shade of purple!!). Run the engine again & drop the carb to idle....after about 20 sec idling open the carb (steadily at "servo speed" don't wack it straight open) & see what happens. If it stops dead it's too lean...if it picks up slowly with much coughing & smoke its too rich. Stop the engine & tweak the screw about an 1/8th of a turn (screw in makes it leaner (less fuel)...out makes it richer, (more fuel)) & try again....keep doing this until you get a nice clean pick-up. (by which time you'll probably find the engine's worn out & you'll have to go & buy a new one!!!! No I'm just joking!!!)

Once set you shouldn't need to adjust either needle more than a click to compensate for the weather unless you change the plug or fuel...you should just be able to prime & glow...I mean go!!! Don't join the unhappy band of needle twiddlers who are forever screwing needles in & out every time they start the motor...it just isn't necessary....once it's set it should be fine...if you need to make major adjustments something else is wrong...blockage, duff plug, stale fuel etc

Wouldn't worry about the oil bubbles from the rocker cover either (assuming it really is the rocker cover ;-) ). This is usually a metal to metal joint & they all seep a bit....if it's the head to barrel junction then we have a bit more of a problem.

Final thought....you will need to set the needles with the glow start removed as the glow start will have an effect on the settings.

Final final thought...always tune slightly rich....trade a few hundred revs for a bit of smoke & your engine will love you...a lean run will kill it very quickly & four stokes will run longer, leaner & hotter than a two stroke.

Here endeth the lesson.....

[Tony Patman]

Steve Hargreaves said: "The idle needle is usually factory set & shouldn't need more than a 1/4 turn either way to finalise it...you didn't touch it did you? You did??!! Ah!!!"

*sigh* I'm sorry, I'm a fiddler. Anything mechanical, I have to twiddle everything. Anyway, I did pretty much what you described to reset the idle needle and hopefully managed not to damage the carb when I had to tighten the nut. In doing so I worked out what the screw on the side was for :)

Yes, it definitely was the rocker cover. Yes, I did have the glow start removed (I'm just cooking with gas now).

I'd heard the thing about always running slightly rich before: I assume this is to do with there being enough lubricant getting through. BTW, I do put after-run oil in too.

In the name of the fuel pump, the glow and the holy needle valve, Amen.

[Steve Hargreaves - Moderator]

Fiddling is the best way to learn...once its in bits you have to learn how to put it all back together again....plus its a good way to increase your supply of small 'O' rings, screws & springs as you always seem to have one or two left over...h'mmmmmm!!!

Yes rich is good....lean mixture equals less lubricant & also burns hotter which means more friction & more heat until something siezes or melts & your wallet has a coronary!!! (You know about setting the needle valve with the nose of the model help up to make sure it won't go lean in the air...yes??)

After run oil is good too (I can see I'm going to have to pat you on the head & give you a chocolate drop at this rate!!!) but don't use too much of it as it can easily cause a hydraulic lock, particularly in a 4 stroke so turn the motor over carefully by hand when you come to use it again just to make sure it's OK (Hydraulic lock is when the cylinder is full of oil (or other liquid, like fuel) & the piston won't go over top dead centre because liquid is incompressable) Too much force at this point will bend the rod or snap the gudgeon or crank pin....not good!

Only one thing for it now....go fly it!!!

[Alan Shipley]

Hi Tony, your not a plant are you and having us all on. Now read the instructions again and they might make sense. Happy flipping.

[Tony Patman]

Alan, yes, dammit, you've rumbled me: I am, in fact, a large aspidistra.

No, I'm not a plant! I'm not sure whether you mean "he actually knows what he's doing and is faking ignorance" or "he's ignorant and out of his depth"! I just read books and things, and fiddle about down in my cellar. I really am a beginner: I can't even fly yet. A few circuits a few times is the most I've done: getting up so early on Sunday mornings is so hard...

Certainly I've put much more time into building over the winter; but I always suspected it'd be like that with me. Probably I just haven't been out flying nearly enough yet. When I can go solo, then I can go to the field whenever I want, and now the summer is here I hope I can focus on achieving that.

[Gary Binnie]

Are you still having starting trouble Tony?

The one and only time I ever had trouble was with an OSFS 40, I took the model in to work and was trying to start it in the lunch hour and it just would not go.

A non-aeromodelling friend suggested I used the 'Hi-amp' glow plug setting on my power panel, I had switched it over for another model, doh!!! Instant fire up after that.

Gone electric now and can't remember the procedure for the OS 'F' plug, certainly worth trying it out of the engine to see if you are getting a healthy glow.

Just a thought.

Cheers

Gary

[Alan Shipley]

Hi Tony, I'm glad that you watered your plant and its out the way.
I still have concern about starting and running your engine. what method are you using to keep carb barrel in one place? (yes I know it sounds daft)
1&1/4 turns out on main needle seams a bit lean. Let me explain, you said it was purring at idle and then stopped.The setting on idle may be near, but the main is not being used in this position and that is why it will run. As soon as carb is opened it starts to use main needle and if this is set too lean the engine will stop.

Now try this. Get it running at idle again and turn main needle to 21/2 turns out which is one more turn, and open carb litte bit at time. If it stops dead its still too lean. Get to the point where the carb is full open and leave it there, as it runs then fiddle in or out with main needle. At this point the more you turn it out the slower the egine will be and you'll do it no harm. If you turn it in a bit at time the engine speed will be more untill its screeming its head off.
All the best, Alan

[Chris Beer]

with an engine like that to solve the problem i always use my trusty engine hammer, or you could try engine matches.

[Alan Shipley]

Don't think anything wrong with engine, just needs a bit of help

[Tony Patman]

Alan:

"what method are you using to keep carb barrel in one place?"
I don't think you mean "how are you attaching the carb barrel to the throttle arm?" so, assuming you mean "how are you controlling the throttle?", then it is held by a pushrod attached to a lever fixed to the test stand. The lever bearing is a tight screw squeezing the lever between two washers so that the friction stops the throttle moving unless I move the lever. I should provide a pic of this to show what I mean; but the upshot is that the throttle is firmly controlled.

I understand what you are saying about the main needle setting. The 1 1/4 setting was achieved like this: start up, close the needle to the point of "screaming its head off", then open a few clicks to ensure good lubrication. The engine slows down slightly but, as someone said, losing a few revs is a good price to pay for a well-lubricated mechanism. On reflection, I think my engine stopped last weekend because I was trying to find the lowest possible throttle for idle, and closed it too much :)

Am I right in my understanding of the relationship between the idle and main needles? The main needle valve is the source of the mixture for most of the travel of the carb. barrel, but, as you close the throttle, there is a point where the main valve is cut out and the idle valve is cut in (presumably with a slight overlap so that there is no break of fuel supply). If either needle is too lean or too rich, the engine is likely to stop when this point is crossed toward the incorrectly-set mixture.

Going back to the throttle control, this raises a point about finding and using the idle. Clearly there is a physical position of the throttle arm/carb. barrel which is the minimum at which the engine will continue to run, assuming that the idle needle has been correctly set. In flight, you'd want this position to be at the bottom of the throttle stick travel, wouldn't you, so that the engine couldn't be stalled accidentally and the cut-off switch needed to be used to stop it deliberately on landing? My reference book doesn't mention such a set-up, so do people not bother and just try not to close their throttle stick too much, or is this achieved by cunning push-rod length judgement, or by trimming the throttle throw on the TR?

What jolly fun this all is. I should have got into it years ago.

[Peter Miller]

Hi, I just thought that I would check the needle on the SC 3o FS in my Bonzo. It was set at 1 1/4 turns open and that was what it flew at a couple of weekends ago.

[Steve Hargreaves - Moderator]

Tony....in t' olden days setting up the throttle was a real pain...getting just enough movement to go from full chat to a nice idle tested your mechanical skils no end...plus there was no servo reversing then so you had to make sure it all worked in the right sense as well as getting just the right amount of servo travel......!!

With modern radios life is much easier...you can reverse the servo to get the right mode (ie push forward for open & the ATV (Adjustable Travel Volume) to make sure you get the required amount of movement. If you set the ATV to 100% each way & use the correct holes on servo arm & throttle linkage to get it somewhere near & then tweak the ATV to fine tune it.

What you want to achieve is fully open at stick full forward with out stalling the servo & at the other end (at least this is how I set mine so this is a personal thing) stick fully back, trim forward gives fast idle which I use for normal flying so the motor doesn't cut at the bottom of a spin or during a stall turn. Trim halfway back normal slow (but still reliable) idle for landing...trim fully back..motor stops. My radio doesn't have an engine cut button. I've no experience of setting these up so your on yer own there matey.....!!! Half stick should give throttle half open or thereabouts. The throttles on our engines are pretty crude (unless you have one of these wonderful heli engines with pumps & lots of needles for idle & mid range et al) but this should give you god results & smooth throttling

Please do spend a bit of time getting the mechanical side nearly right though...it's true that you can adjust the ATV to get around most things but this can make the operation horrible with 0-90% throttle in the first half of the stick movement & the remaining 10% in the second half.....what we want is a steady linear increase in revs from idle to full chat as the stick is moved from fully back to fully forward.

Hope this helps

[Peter Miller]

I find that the best way to get a really linear throttle response is to use 30% negative exponential. This closes the throttle quite fast at the start of the stick movement and then slows it down for the last part.
I use throttle cut on my FF8. Get the idle right at low throttle and then operate the cut switch. If you can select the switch use the one on the left. I find that 40% travel is normally needed to get a good clean cut, That is 40% on the throttle cut of course, not the throttle stick.

[001]

Having followed this thread for the near two months it has been running, there seems to be 2 possible reasons that this engine is difficult to start. 1) that it has very low compression. this could be due to manufacturing tolerances and that there is a larger than average clearance between the cylinder and barrel. If there is low compression because the cylinder head or valves are leaking, then the engine should have been returned.
2)Earlier in the thread it seems that a small glow plug supply was being used and later a starter was being used from a 12 v electronic supply.
Assuming that a 12v battery, power panel and starter are NOW being used,so that the glow amps. can be monitored then if the engine is new it should be able to made to run in some fashion, even if very smoky and throwing out oil (good). Following on from the last, if it has low compression, the glow plug should be being supplied with enough power to burn off the excess (comparatively) fuel and oil, and the starter motor will need to bring the engine up to a fast speed to give it some chance to fire and continue to run..Normal 4 stroke model engines need to have a good clearance around the piston for oil to pass by the piston ring to lubricate the area below the piston (crankcase)and its contents.
It should be noted that the compression ratio of a two stroke is specified as a geometrical one and does not allow for the fact that the height of the bore below the top of the highest opening in it (port) does not contribute to the feel of compression when you turn it over by hand. Whereas the whole of the stroke of the four stroke is (in theory) compressing the mixture into the combustion chamber. At low rotational speeds some air will pass by the 4 stroke piston, so it will seem to have low compression.In ABC type 2 strokes the fit between piston and liner is made deliberately tight (at the top) so they seem to have very high compression. (When cold).Hope that helps.

[Myron Beaumont]

Very interesting Richard .I have been wondering since i bought my 1st 4st(fc52) how the bottom end was lubricated efficiently. Seems a bit hit (Spray ?)& miss but obviously works. I had considered the addition of a long length of fuel tubing or a little reservoir (as well perhaps) attached to the breather nipple to keep the pre & after running oil in & around mains/big/little ends.Do you think its a good idea or unnecessary?

[001]

Myron do not extend the breather more than about 30 mm. The main reason is to make sure that dirty oil is allowed to pass out of the crankcase and not get sucked back in. There are thousands of model four strokes that have given years of service with little attention apart from a supply of good quality fuel and no modification..

[Tony Patman]

Richard - I am still using the little glow-start, and flipping: I can't afford to buy any more equipment at the moment. However, the engine does start much more readily now that I have worked out how to "stoke it up" adequately. Perhaps it will get even better when I can afford more controllable and powerful starting gear.

I think the main reason for my difficulties has been my lack of experience.

[Matt Yorke]

Richard - regarding breather, am sure I saw an article in RCM&E years ago suggesting connecting an old film container to the breather as a "puke tank"

[Steve Hargreaves - Moderator]

Hi all.....just returning to this epic to ask Tony....hows it going?????

Are you managing to get yer motor going reliably now.....?? Its been in my mind cos I've just bought a new ASP61 & like Tony gound the compression very low initially....like nothing there!!! It didn't half improve after 3 or 4 tankfuls through the motor. Its as the point now where you can't take it over compression unless you have a prop fitted.....huge difference!!!

Also I found 2.5 turns open on the needle gave me a very rich setting for running in with lots of oil to keep it cool & smooth (& put a big stain on the patio!!!) & it now runs at 1 & a third turns open...I also had to lean out the idle setting by a half turn or so.....

Motor now starts first time every time (electric starter) & has an idle so slow it makes me yawn!!!!

[Tony Patman]

Yes, I got it going ok, and it's now firmly bolted to the model. Sadly the model has come out rear-heavy, and would seem to need at least another 6oz in the front to move the CoG to the right place. This seems an awful lot.

Steve, it sounds like your experience matches mine quite closely, including the stain on the patio...

[Steve Hargreaves - Moderator]

Tony...what model is it?? 6oz of lead does sound a lot for what I guess is a pretty small model given the SC30. Plus 4 stokes are usually heavier than 2 stokes so nose weight is not usually required....

Where's the radio battery? Can it go further forward...under the tank maybe?? Bigger battery perhaps? The weight might as well work for you......

[Tony Patman]

See this thread for the origin of the model.

The model is a pod-and-boom design, so the engine is at the back, as a pusher, and the battery is shoved right up into the nose along with the present 5oz of lead. The design suggests that 4-6oz of weight should be enough to place the CoG correctly. The pod is mainly ply, and the wings and tail are almost entirely balsa. The boom is an aluminium tube, and was difficult to source at all, so I suspect that it is of a thicker wall than the one used in the prototype. Hmm. I suppose I could remove the tube and see if I can find someone to bore it out a little. Any ideas?

[Steve Hargreaves - Moderator]

Sounds like a bit of a weird machine to me......why can't you just start with something nice & boring like an Irvine Tutor or somesuch???

I think I can anticipate the answer...."Because it's boring!!"

[Tony Patman]

Actually I've already got a Tutor 40, but I wanted to build something myself. I got that book and, well, it's quite good at holding one's hand through the building process, so I thought it would be ok.

[Peter Miller]

From very long experience and watching many people including myself incur nasty injuries, I can say that propellers in unconventional places normally result in propellers in very painful places.
I would also say that learning on a well proven design is a far wiser way to go. However I do promise you that your test flights with a stange device with masses of nose weight and heaven knows what other peculiarities will NOT be boring. Exciting, terrifying, disasterous, tragic but never boring. It won't last long enough to be boring.
Having said that., I am truly and honestly delighted to find someone willing to exeriment but I feel that experimenation would be even better once you can fly.