[Noin]

I have just mounted my evolution engine. This is an engine that I just purchased used from a fellow modeler this summer. I had not seen it run before I bought it but I was told that it ran well. I tried to run it today in my garage and did not get great results. The engine would idle fine and start reasonably well but anything above half throttle and it would surge and fall then surge and fall. It would repeat this over and over again. The high speed needle seemed to have no or little effect on this surging cycle. I had actually screwed the needle in completely and the engine did not change a beat. The head tempurature was low at 100* so I wrapped some foil around the cylinder and the head. The tempurature then climbed to about 190*-200* but never went above. The needle seemed to have more effect when the foil was on the engine helping to get a higher head tempurature, but it was still very eratic. I changed the plug to a new O.S.8 and had no noticeable difference. I am running Cool Power 15%. The carb is inline with the centerline of the tank. Fuel tubing is new. The engine has a very respectable amount of compression. I am using the 3 bladed prop that comes in the box with this engine. A note on the prop I know that 3 bladed props are not the best choice I just threw it on for the testing.




I just want to be clear that I am not looking to start the debate of running model engines in the cold. I am just looking to find an answer to this problem.

[skypupnut]

does your needle valve still have theturns restrictor on it
if so remove it it will alowe you to turn it in ( lean ) more
have seen some of those with lock at wrong position
( supposed to have been adj. at manufacture ?????)

[AJCoholic]

Ted,
I assume you are running muffler pressure. Just for fun try running the engine without the pressure line from the muffler to the tank.

I would also not be afraid to pass the preset stops. I had to on mine that I tested (but just a little) this summer.

I had a few engines that surged like that. They were running excessively rich on either the top, low end or a combination of the two.

If you are at least 200F then I would nt worry about damaging the engine. I know Dave Gierke uses a higher temp but speaking to other knowledgeable engine people in the recent months and also from my own tests, if you are running at 200F you will be fine. And the reading you are getting with the IR temp gun is probably a little low (they usually are) anyhow.

I would first try leanign out the low end a little and then carefully run it and see how it transitions, and (starting with a rich top end) slowly lean out the top and see if you can get it to transition up cleanely and past 1/2 throttle.

[Noin]

Yeah I had to remove the stop. After I removed the stop, I then tried to lean it out and thats when I slowly screwed in the needle about a1/16 to 1/8 of a turn at a time all the way tp fully closed. The engine was still running even with it fully closed. I can get it to run a full throttle, it just sitges the whole time. The low end seems fine.

Andrew, what did you do to solve the surge problem you mentioned?

I will try no muffler pressure.

[AJCoholic]

Well, on one engine I had it would do this surge no matter what I did with the needles. Only when I tried to run it without muffler pressure would it run like a top. Its worth a try...

What about any leak where air can enter casuing it to lean out and surge? I would also check the gaskets, head and glow plug seals, etc. Around the carb especially.

If the engine has good compression then it shouldnt be "over the hill" so to speak... is there any excess leakage out the front bearing?

If the NV is fully screwed in and it still runs then perhaps the needle was not properly fit at the factory. I have had engines in which the needle was not pressed through the thimble far enough and you couldnt lean it enough.

Just throwing some ideas around... if you screw in the needles can you still blow air through the carb (throiugh the fuel nipple, with a short length of tubing on it) You should be able to seal it off completely...

[Noin]

I will definitely try it without the pressure. I will also try to blow through the carb with the needle screwed in completely. If I can't blow through the carb then I wll assume that it is ok, but I would be surprised if I can't blow through it because as I said the engine still ran for a while with the needle fully closed. The other thing I noticed is it is consuming fuel at an alarming rate. If one of the above things doesn't solve the problem I will start sealing the carb with silicone. I will also check the head. Do you know Andrew if the head on this engine is supposed to have a shim or gasket or anything between it and the cylinder?

When I wrapped the engine with foil I used plain aluminum foil. I have heard someone mention (maybe even you Andrew...lol) using foil tape. Do you know if it is hard to remove the tape after you no longer need it?

Something else I should mention is that I have one of those Dunro 45* exhaust deflectors on the muffler. Do those accessories add alot of back pressure. I have used them alot before without problems.

[AJCoholic]

Ted,
The exhaust deflectpr shouldnt do anything bad. I use them all the time.

I did suggest using aluminum foil tape but the tape is HARD to remove without using a solvent like lacquer thinner. As long as the foil stays put its fine. You can wrap a little copper wire around the foil to keep it there too.

If its using up fuel and also surging I think it may be a rich problem... I have had an engine or two that just would not go lean enough... perhaps its the needle? Its so hard to say without seeing it and playing around with it...

[Noin]

I'm sorry Andrew, was that an invite to your place to "play around"?











lol

[AJCoholic]

Actually Ted I am heading to Frank's (father in law's) Christmas day and will be there for a few... you should head to Tillsonburg and we can run it up in the garage Maybe I shoudl talk to the in laws first... I can only imagine what fun they have planned for me (I refuse to do ANY snow shoveling! )

[Noin]

Good news, I took the needle valve assembly completely apart and I noticed the there was no reciever (I don't know what else to call it) inside the needle valve body for the needle to mate with. There fore when I screwed the needle in all the way it did nothing because the fuel just flowed around it. This engine has had the remote needle valve assembly broken off before and then replaced by the owner. When it was reassembled the guy didn't put the little brass reciever for the needle to mate with and thus cut off or restrict the fuel flow. I haven't gotten out to the garage to run this engine but I am fairly confident that it will run like a top now as it ran pretty good in the low end with the needle completely ineffective.

As for getting together Andrew, guess that will have to wait for another time. I would like to meet you someday to shake your hand and thank you personally for the help you have given me. Until then....