I have a Turnigy 50-HP engine that refuses to go over 5,000 rpms. The owner could not get it to run properly so he gave it to me as part of a trade.

The engine used to run strong, then one day it would not start. He could not figure out why, so he got a new carb from Hobby King and a replacement TGY ignition. The carb looks like this one from HK's website.

With the needles set at approx. 1.5 turns out it starts easily, idles nicely, and revs smoothly up to 5,000 rpm. Above 5.0 - 5.2k rpms it dies. Richening the needles does not help. I am running a 22 X 8 Xoar prop at 32:1 gas/oil mix (Pennzoil).

I replaced the ignition with a spare RCGF module I had available, but the problem persists.

I understand that this is a XYZ 50-HP engine re-branded by HK. It is a rotary valve engine.

Any ideas or suggestions would be appreciated.

Thanks in advance,
Ted

Check the timing, I have seen this a couple times with older DA 150 engines and it ended up being a cracked prop hub that retards the timing enough to have a large drop in rpm.

Another imposrtant thing that comes to mind is that may be there is an air-leak some where and the engine is sucking in air , hence above a certain RPM, in your case , 5000, it leans and shuts down ?

The only way to check that is to close the inlet after removing carb with a piece of old cycle / car tube and metal plate and two appropriately sized bolds ( may be 5mm size) and doing the same with the silencer port / hole in the engine head and then make sure your piston is at the Bottom of stroke cycle and pumping air through the nipple in crankcase or some other way and spraying some Fairy / dishwashing liquid mixed water to see BUBBLE coming out from seams / gaskits or anyother places on your engine.
2 stroke engines during their service life can seize on you if they have a leak from where they are sucking air and going borgerline lean on you .....sometimes you would not even notice that as you think your engine is cracking good and well tunned...
If the leak is significant, it would die on you after a certain RPM is reached, beyond which it might not have fuel to keep on going...
This is my thought on it.

I would definately check the timing on this engine with any timing kit , viz. Hobbyking does one. It should be 28 Degree advance.

Many of these engines seem to be a little loose and I think the air leak is a good start point. A Bowman ring also would be a good suggestion as the one I had was lacking compression and showed similar traits?

Well, the problem was finally solved.

I took the engine apart, cleaned up all parts and discovered that the ring was stuck. There was too much carbon on the piston, and I it took a few evenings of using solvents and heating it up to get the carbon off and to free up the ring loose without breaking it. But in the end it all worked out and I put the engine back together using Yamabond to seal the case from air leaks.

I eagerly put i back on the bench and fired it up. NO GO! Same problem. It would start fine, rev up to about 5,100 rpms and then die. I even tried a smaller prop 20X10 but it did not help at all.

In desperation I got on the phone with Bill Jensen of BJ model engine repairs in CT, a great shop that other folks at my field have used in the past. Bill quoted a fair price to send the engine in for checkup and repair, but he also made an observation:

"The fact that the engine goes up to 5,000 rpms and then dies no matter what the High needle valve settings are may indicate that there is a blockage somewhere. The engine just runs up to these rpms through the Low end passages while the High end may be blocked."

Bill instructed me to take out the High needle valve, spray some carb cleaner in the passage and blow it all out. After doing exactly that, I fired up the engine and ..... YESSSS! It happily revved up to 6,900 rpm turning a Xoar 22 X8 prop.

So, the engine runs nice and strong now and I learned something new in the process. Thank you everybody for your input and suggestions and a special thanks to Bill Jensen for the expert advise. He is not only an engine repair professional, but a gentleman and true hobbyist as well.

Ted

You had the answer, when you found the Hi-speed did not help. That tells you most likely the Hi-speed passage was plugged up.

You are right, I should have thought of that possibility. I guess I didn't because the carburetor was brand new, never used before. Live and learn captin.
BTW: I never met an engine I did not like either

QUOTE=tedev;11842436]You are right, I should have thought of that possibility. I guess I didn't because the carburetor was brand new, never used before. Live and learn captin.
BTW: I never met an engine I did not like either [/QUOTE]


I have two of these engines NIB. I had heard that they were not all that strong for having that much displacement, but I also heard that they were good running, reliable engines that could last quite a while if properly cared for by the user. Good to know. You couldn't beat the price when I bought mine.

Ed Cregger, NM2K

Ed
You can never have too many engines?

Words more true were never spoken!! Just ask my ex-wife....

AV8TOR