Hi!

I'm not so much a noob but I thought I'd post this question in this forum all the same.

I have a trainer, 20-25cc 2 stroke but my 25 cc 2 stroke is a big hunk of junk so I installed my .46 2 stroke in there, fits fine works great, haven't flown it yet.

These are my assumptions:

1. If I have some counter-balance for the extra 300grams in the back of the plane it should be ok.
2. The extra OOMPH may allow it to fly apart so I've set the controller only to allow it to get to 2/3 power.
3. The fuel is the same, I'll have shorter flights but this I don't mind.

Ok so can someone please tell me if this is DANGEROUS. If it is then please tell me why it is dangerous. If it's not dangerous please tell me if I should still use the .25cc propellor or if I should use my .46cc propeller. I'm guessing I can stick that .25cc nylon properller on there and have a ball, I think the .46cc is too big.

Please let me know before I find out on my own.

G'day Mate,
For a start I think you mean a 0.25Cubic inch 2 stroke, or 4cc, usually with a 9x6 or 10x4 prop. A .46Cu engine is about 7.5cc, nearly double, & it uses an 11x6 or 12x4or5 prop.
Next we have the weight difference, just balance it, with the 0.46, to the CG, that you had with the .25, you may have to move batteries back or add weight to the tail, whatever.
Don't restrict the throttle, learn to use it instead, in other words don't fly it at full throttle, use maybe half, or whatever it takes, to fly.
Don't use the .25 Cu prop, put a .46 size prop on it, or it will be badly under propped, & over rev, which can cause engines to FAIL dramatically.
PS why do you say that your .25Cu motor is a hunk of junk, what is it, what prop are you using, & what fuel.

Wow thanks Alan.

Well I say this because it's one of these engines with the needle way at the back and it leaks air into the fuel line in tiny bubbles. I can't figure out where it is coming from and I covered that part in epoxy cement and some bubbles have stopped but not all of them, I just need another remote needle but I'm too lazy.

I'm glad I can just use my trust .46, yes it's cubic inch, I always get those mixed up! The .46 has taken me through many crashes and has been broke in (unlike the .25cu inch). .46 propeller is wooden and quite large. I will have to be a little careful on landings that I don't smack it on the ground. Only a couple inches between that and the cement! Oh well, it's just wood, it'll break and they're cheap anyhow.

Now I hooked up that .46er and there are no bubbles in the fuel line, and runs like a charm. These engines can really take a pounding!

G'day Again,
Have you changed the fuel tube from the needle valve to the carby, they can have very small holes in em, & let in air. Don't buy a needle valve assembly, it is more than likely a fuel hose leak.

I've checked and replaced all the lines and pumped into them separately. It's the needle valve. It's not the gas tank either because I can suck the gas out of the tank fine through the tube when it's not connected to that valve but once the valve in connected the air bubbles start to appear. I'm sure this piece is cheap and I'll probably replace it later on but right now I really don't have the patience to play around with something like that. Maybe later on but that needle balve as completely eluded me.

The air could be coming in right from the adjuster needle throttle, in that case the whole thing is junk and will need to be replaced.

Actually it's quite common to have small bubble in the fuel line that goes from your remote needle valve and the carb. They don't affect the performance any, so I wouldn't worry about them if I were you. The only time you need to worry about bubbles in the fuel line is in the line from the fuel tank to the needle valve.

Ken

Prop Clearance May Be An Issue larger Wheels May Be Needed.A Test For The Needle Valve Is When You Have It Running Wiggle The Needle To See If You Can Produce Bubbles ( Not To much Force,You Can Make It Leak).
The Reason Being That The O-rings On The Needle Or Were It Screws Into The Housing Are Worn Or Cut.

Wow thanks for all the support.

I'll let you know how it goes tomorrow and if I'll need to get larger wheels.