I’m having issues with my Alpha 40 trainer. I have had the plane for about 3 months, and flown 20 –25 times. I am now having issues with ‘surging’. When I get my throttle from about ½ way to full throttle, the engine is very slow to get to full RPMs. Sometimes it is totally unresponsive from ½ throttle to full throttle, staying at the same RPMs or VERY slowing winding up. We can see some bubbles in the fuel line from the needle valve to the carb. At full throttle especially. The engine is also surging lower then higher at full throttle as well. We have made it richer and leaner as much as possible, and it has not resolved the issue .

Based upon several suggestions, I dismantled the card and the needle valve (did not remove the jets), and flushed it with Isop. alcohol. Hopefully this would remove any gunk clogging the jets. I lubed it up again with a little 3 –in- 1 oil, and reassembled. I tested again, and I am still having the same issue at full throttle, and it is slow to rev up to full RPMs.

Any suggestions… New needle valve?

It's still a possibility it can be too lean. Remember, turn the needle valve one click at a time. Also the engine can be lean on the low end. Try and richin up the low intake valve and see what happens. But make sure you only richin up a 1-3 clicks at a time, because that screw is very sensitive and can be hard to get adjusted properly. If you have already tried these things and is sure it isn't that, then it can possibly be the fuel tank itself. Because needle valves don't go bad that often unless it's constantly being abused and stripped. And that wouldn't cause bubbles in the fuel line. After trying this and nothing happen, replace the fuel tank. I personally prefer the ultra flex fuel tanks.

GoodLuck

Will try the fuel tank. I and the instructor tried
[quote]ORIGINAL: Technito20

It's still a possibility it can be too lean. Remember, turn the needle valve one click at a time. Also the engine can be lean on the low end. Try and richin up the low intake valve and see what happens. But make sure you only richin up a 1-3 clicks at a time, because that screw is very sensitive and can be hard to get adjusted properly.

Hey Mike, Sounds like a problem I was having with my Avistar with an LA 40. Mine would start fine and when I throttled up it would cut out and run erratic. It sounds like you have an air leak somewhere. Check the back plate on the back of the engine. The screws could have come loose. If they are phillips type like mine had you may want to replace them with allen head type and locktite them. Also check your fuel tank clunk to make sure it isn't binding and can swing up and down all the way. Check your fuel tank plug or stopper that the fuel lines come through and make sure it is not sucking air in there. Lastly, check the fuel line in the tank that the clunk is attached to and make sure it is in good condition and not split. They fuel line in some of the tanks is pretty cheap and can break easily and you'll be sucking air in through there. That happened with mine. I installed the fuel line that came with the tank and it cracked in a short time. I could start the engine and hold the plane up and see tons of bubbles coming up though the fuel line. When I took the tank apart I found the fuel line split right where it connected to the tubing. Good luck. Let us know what you come up with.

I agree with the lean suggestion but how about replacing the line between the carb and needle valve. I t could have a small hole in it that would be very hard to see. That's of course you already did not do this.

What engine are we talking about here?

Oops. Thanks Bubbagates. That is very likely as well. I forgot that one. (replacing the fuel to the carb.) That happened on mine as well. It seems like everything that could happen on my Avistar did happen. I sure learned a lot though.

No problem. I had that happen to me once and now if I run into it it's the first thing I do. It's amazing just how many I have fixed like that, especially Evolution engines. There is usually a small hole right at the needle valve and since this is usually a clear line it's very hard to see it.

He did mention that the bubbles were in the line between the carb and needle valve so it was the first thing I thought off. Assuming the line from the tank to the needle valve has no bubbles in it I would replace the line first then do everything else that everyone else suggested.

The fitting may have loosened up that the line attaches to the main needle. Mine is a brass barb, and was loose by about a half turn or so.

You also may have a build up of "fiber hairs" down in your needle valve. you can take the needle valve out and blow down into the carb opening and blow it out. I have had that happen from time to time andthe engine goes right back to normal.

Bingo,

That is one I forgot about, good catch. Some of the Evo's have that and it will loosen which can drive you nuts trying to track it down.

Once bitten......

As long as you are seeing fuel bubbles you will never be able to set the engine to be reliable.

A few Bubbles in the fuel line are usually a result of foaming in the fuel tank. If the tank is foaming a few bubbles manage to get to the fuel line. I have found that most of the time fuel foaming is caused by jamming the tank hard up against a former. However if the tank used is too large or the foam is packed too tight or there is no foam at all the engine vibration will be transmitted to the tank. The result is fuel foaming and dead sticks.

Balancing props can help to remove the source of vibration but often we don’t balance them. Latex foam rubber is also much better at absorbing vibration than other types of foam.

Twins and fuel foaming: With twins an engine out is usually critical. On my last twin project I went to considerable extra effort to size the tank compartment exactly 1/2 inch bigger than the tank on each side. Half-inch latex foam rubber was used. Velcro was used to control the tank pressure against the foam. No foaming has been observed in the first 25 flights.

I have replaced the line between the needle valve and carb, as well as tightened all the fuel nipples on the needle valve and carb. The back plate was real tight as well, with allen type bolts. I flushed the needle valve with alcohol, but did not blow it out. The bulkheads are designed in such a way so that the tank is held snuggly in place, so I am not sure it is a foaming issue.

I will try to blow out the hairs in the needle valve and replace the fuel line going from the tank to the needle valve. I will check the clunk as well. I will let you know if that works.

Thanks, Mike

Mikecdrew,

I have a new Evolution 46 and have the same problem of surging lower at full throttle. I have replaced all the lines cleaned the high speed needle vaule checked back pressure....Even had the club Evolution experts look at it and they can't find the problem.....I have had someone mention that heat off the engine might be causing problems with the remote value.

Mike :
Sometimes they leak between the needle valve and the body that it screws into. Slide a piece of fuel line over the joint where it screws into the body. needs to be a tight fit over both. Suggestion; do one change at a time, otherwise there is no way of knowing which one fixed it

I also have an evo .46 that was acting up. You could put it at full throttle and it would take 2 or 3 seconds or more for it to reach full
rpm. I ran fuel thru the high needle (took off the line to carb) to clean out any dirt. It transitions better now but still not as good as my OS .46's. My high needle at one point I had screwed out 5 full turns and it acted like it was opened by only half a turn. You could see the needle turning by itself on full throttle!!! I had to adjust the little ratchet on it.

Dave...