I have a os 70 surpass mounted in a aircore colt. When it is cold it starts up great and runs pretty good. But after a few seconds at full throttle the engine will start to surge about 300 rpm. I also notice the smoke density changes. I also notice bubbles in my fuel line. The tank is mounted right to the power cartridge so there is no room at all for foam around the tank. Also when I shut the engine off and try to restart it when hot it will not start. I can prime it till fuel is running out of the carb and it wont even try or kick back. I have messed with the needle valve setting and it does it no matter how rich or lean I set it. I also noticed when I bring the engine to an idle it will idle very nice for about 5 seconds then it will start to smoke and u have to move the throttle up to keep it from dying. Where do I start? thanks

When you say the smoke density changes, does it increase or decrease? (more or less smoke?)

It seems like when the rpm drops at full throttle the smoke increases. I had this engine in a astro hog about 8 years ago and it had a surging problem back then but it did start better. But I was also using an electric starter then and starting it by hand now. This is the first time I have ran it in about 8 years but it still runs the same as I remember it. It acts like it cant hold a needle setting. Also the engine has very low usage on it. I'd say 15 to 20 flights. I have taken the carb apart and everything looks fine. I noticed the needle valve was loose so I put some fuel tubing over it. Did not help. I also ordered a prop balancer thinking maybe the fuel was foaming by extra vibration.

I cannot understand how a large and experienced producer like Aircore, makes that Power Cartridge, without fully isolating the fuel tank from the engine's vibration.

This is, as Sherlock Holmes would say; Elementary, my dear!

And the cost is just a couple of cents per unit.


...Well, as some products are manufactured today: So what, if it doesn't work right? Who the H@ll cares?...


Kattoomman,


The position of the needle is of no importance, before the engine actually runs.

If there is the right amount of fuel in the combustion chamber, it will fire.
If it doesn't fire and it is not flooded, twiddling the needles all you want will not make it fire.

Did you check/adjust the valve lash lately? If it is too small, a valve can leak, or burn and your engine will show all the troubles you are seeing. If tool large, a valve may not open sufficiently.

...And the bubbles could be a result of a pin-hole somewhere in the fuel line.

Well I checked the valves and they were a little loose, but nothing that would cause my problems I dont think. The exhaust was about .004 and intake was about .005. Anybody else?

Yeah....get rid of those air bubbles!!!!

You can twiddle needles, and adjust valves until the cows come home and you won't fix anything as long as the engine is drinking foam.

Either your fuel is foaming, the tank is garbage or the lines are leaking somewhere. The motor absolutely will not run properly until you get this ironed out.

I just dont think it is a fuel foaming problem. I have a dubro inline filter maybe this is causing the problem. The engine did the same thing in my astro hog and I had the tank wrapped in alot of foam. I'm going to try it without the filter. Also does it matter where the pressure line is in the tank? Right now I have it about in the middle. I had an aircore trainer with an 0s 40 in it and I didnt have any problems with fuel foaming. I cant remember if it had bubbles in the fuel line though. Thanks for the help.

Another key factor is you say it will idle fine for about 5 seconds and then it will die. If you only have about 15 flites your just barely broke in. Your low needle has to be set. Sounds like it is too rich and loading up. That would acount smoke differences.

The .70 is a pretty large engine for the Colt, I have owned a USAC KnightHawk and am on my third Colt, the KnightHawk was flown with a SuperTigre .51, first as a glow engine and then as a Diesel. The Colt was flown with an Enya .46 MKII, foaming was never a problem but those are smooth engines. The .70 probably shakes the plane pretty hard.