How do you tune 4 stroke engines.

[Biggles' Elder Brother - Moderator]

Hi Craig,

 

I've no experience with an ASP four stroke but I'd be absolutely amazed if "5 clicks" and "a quarter turn open" would be rich!

 

In most 4 strokes I'm familar with, rich is between two and quarter and two and half full turns open.Note full turns - not clicks! A typical running position, once the engine is run in, being in the range of 11/4 to 11/2 full turns open.

 

Unless ASP's are very different - or I have seriously misunderstood what you are saying - something is wrong here.

 

Hopefully someone with some experience of ASP's can pick this up?

 

BEB 

[Martin Harris - Moderator]

Sure it didn't say 5 turns?

 

I know some ringed 4 strokes advocate the initial run so rich that it may be necessary to leave the glow connected. I can't put my hands on instructions covering the 61 but the 160 twin instructions state 3 1/2 turns (well "tunes" actually!)

[Craig Spence]

Hi BEB,

 

I havent got an ASP?lol. However you are right it is five turns open.

Haveing read the instructions again (for the third time lol) I think Ive cracked it.

So they say the first tank should be run through it with the carb fully open (they mean the needle and not the throttle) with a rich mix.

So I will do this for two tanks. Then they say before opening up the throttle full for the first time that the needle should be five turns open from closed.

 

Hi Martin,

 

after speaking to a mate he said that if I need to I should leave the glow connected.

 

Ill see how it works out today.

 

Cheers all.

[Craig Spence]

One last question for all reading this.

 

I have wondered for a while now with both types of engines (two strokes and four strokes) if prop selection would make a difference when running in.

 

My thoughts are this, if you use the lower reccommended prop on the engine you will get higher rev's, would this run it in faster? or possibly cause damage?.

If you use the higher end prop the engine will have to work harder, would this put stress on moveing parts? and take longer to run in.

 

My point is should we be useing a certain prop to run the engines in, in order to achieve the best effecincy from the engine. If I run it in on a 11/7 then went to the feild and used a 13/5 shurely the engine would be running in again.

 

Thoughts on this please, I think its one to ponder over.

[Craig Spence]

Hi all,

 

I have put three tanks through it now, very impressed and pleased. I put the first tank through with the needle open two full turns, opened it up on the last tank to five turns to go full throttle.

Full throttled fine and closed it back down to two turns from open, opened it up and sounds good.

Ill try and get about five flights through like this, with it rich, then lean it out to optomise performance.

 

Cheers all.

[Biggles' Elder Brother - Moderator]

Hi Craig,

 

sorry about the ASP confusion - I was getting mixed up with Steve - still all well that ends well etc.

 

Re prop choice and running in. In my view it depends where you are running in. I always run in on the ground, so I use a lighter duty prop. The reasoning behind this is that on the ground the prop cannot unload in the way it does in the air. If you were to put a heavy load prop on the engine under these circumstances you are - in a sense - over prop'ing the engine and it wont be able to rev out to the level you really want to - eventually at least - on the ground.

 

So, in conclusion, I use a lower spec'ed prop on the ground and then switch to something in the middle of the engine's range for the first flights. Once the model has had 10 or so flights and the engine is happily run in I examine the prop issue again and decide if I want to change it for performance reasons.

 

BEB

[Craig Spence]

Hi BEB,

 

your explation makes alot of sense actually, I removed the 13/5 prop and used a mid range 12/6, but in the future i may use the lowest range. As for the next SC52FS it will be getting tuned almost exactly the same as this one as they are going in a twin.

 

Once they are both well run in on my PC9 they will be getting put in a Mosquito with 13/5 props on.

I have been told that with a twin you can go larger on your props than normal, so if the max size on the engine when its on its own is 13/5 when you use it with another you can go up.

Does anyone know a formula for this, how much in Diameter and pitch can you go up?.

 

Cheers.

 

Craig.

[Glenn Philbrick]

Hi Craig.

 

I have experiance of several twins with 4 strokes all inverted, Me109, lightning and a mossie. I would not prop up, why would you want to do that ? you will only make the motor labour and prone to stop. Use the correct size prop to get them running sweetly. Set the engines by sound you will not be far out ( within a couple of 100rpm which you will not notice) if the model requireres trimming then use the rudder to ofset any problems. The lighning can be flown on one engine but the Mossie most definatley not.

 

Good Luck

[Craig Spence]

Hi Glenn,

 

thanks for the feedback. Ill just go to the higher end of the recommendation then I think which is 13/5.

As for the Mossie on one engine down I think the only solution with one engine down is to cut the other, I hope never to find out.

 

Cheers Glenn.

 

Craig Spence.

[Steve Hargreaves - Moderator]

Hi Craig.....I have a couple of ASP 4 strokes & these are the same as the SC range apart from the badge....they are all ringed motors so rich mixture running in is what is required. I have heard of this 5 turns open on the main needle before & am frankly staggered that the motor actually starts.....thats a very rich mixture indeed. 2.5 turns should be more than enough.....

 

As to props I think you are way too big on a 13x5 prop on a 52 4 stroke. I have an ASP61 (which is basically the same engine as a 52 but with a slightly bigger bore to get the extra capacity) & I have a 12x6 on this motor. It pulls my Pitts around just fine. My ASP70 has a 13x6 prop on it & again this pulls my YAK54 around in a very scale manner.....

 

The range of props suggested for the ASP52 is from 10x6 to 13x4 with 11x6 suggested as the best start point & an 11x4 for running in.....as someone else mentioned over propping will simply cause overheating & unreliability......my personal view would be to use an 11x6 or possibly a 12x5 to get the extra thrust....

 

PM me your email address if you'd like a copy of the ASP instruction sheet....this was written by the late Paul Landels of Just Engines so its in real English rather than Chinglish!!!

[Craig Spence]

Hi Steve,

 

"I have heard of this 5 turns open on the main needle before & am frankly staggered that the motor actually starts.....thats a very rich mixture indeed. 2.5 turns should be more than enough" I agree with you on this, I tried to run the engine on 5 turns open and it does run until you take your glow starter off, a friend said that some manufacturers say to leave it on. Not for me im afraid, I run mine on two turns open and this was quite rich.

 

As for the props, id agree again, I did eventually decide to run it in on a 12/6, still a little big by what you say but the engine run fine. 

 

I will PM you later for those instructions, really appreciate it thanks.

 

Craig.

[Klippy]

Hi Craig, couple of small points, the oil bleed, do not use too long a length of pipe, otherwise the oil just bangs backwards and forwards in the pipe! Another thing, you can use a small microswitch for your onboard glow, just arrange for the throttle linkage to press in the button when it's close to closed, that way you'll extend your battery life, since you don't need the glow at higher rpm's