I have a 26 +/- cc gasser, it is weed eater converstion engine, I started it up this morning and it ran like a dream. then 60 seconds after takeoff It started to cut out on me, it would run but only at an idle, somthime it would try to rev up but couldnt. Does anybody have any Ideas what the problem could be?

Thanks for your help.

Ignition failed?

To check your CDI, take the plug out and with it firmly mounted in the rubber boot of the CDI hold it against the cylinder head and with ignition on slowly rotate the prop past the magnet on the prop shaft. See if it sparks when passing. Make sure your CDI batteries are charged etc. Also- check the fine fuel filter in the carby. There is a thread in the Gas forum somewhere that explains what you need to look for.
Have you got plenty of air flow to the engine head etc - the engine may be getting really hot as well.

If it idles the ignition works....

As TOM indiicated if the engine starts ok and idles then the ignition is working. This sounds like a dirty carb filter screen.

Karol

Put the choke closed about 1/2 way or more then see if it will rev up more. If it does you may have crap in the carb. What other things can you tell us about it? Thanks Capt,n

Sounds like a weak battery to me, charge or change your battery, I bet the problem goes away.

Diaphram in the carb is stiff, it won't allow enough gas in to run in the WOT position, but will run on idle. Have had that happen a number of times.

Thanks everybody for your help. I checked a few of your ideas but will certainly be checking on the rest of them. I tend to think of it as a fuel problem, I tried to adjust the screw but to no avail. I will pull the carb and check for junk.

captn' I know little of the engine, It has not been started in years. I just got the CDI back from being fixed, hooked it up and the engine fired and ran as good as I have ever seen one go. It did cross my mind that dirt or dust got into the carb from sitting so long. I was running with out a cowl, so heat was not a problem, and it was only 25 deg. at the time.

Thanks again guys for your help.

mr,
You didn't mention if it ran the same on the ground, after the flight. If it is an inflight problem and you are using a Futaba PCM radio, and the RX battery is low, you could be seeing the RX going into battery Failsafe. Check the capacity of your Rx battery.

Jerry

If it was an inflight PCM Failsafe problem he would be posting this in the "crash and rebuild" forum.

WRONG,

Battery Failsafe is a program in the receiver that will drive the throttle to the idle position if the receiver battery voltage drops to near a dangerously low level. It has nothing to do with the programable failsafe.

If the Rx battery is low or too low capacity, the flight loads on the servos will drag the voltage down, then the engine goes to idle. Also a maneuver that loads up a servo will set it off. Moving the throttle stick to idle will reset it to normal operation.

I'm not using a Futaba Radio. I have it set up with two batteries, one for the cdi only and one for the rx. I now belive it was the battery. I ran it at the shop for a better part of 8 minutes with no problem, that was on a different battery. I will try flying it again this weekend and hope for better luck.

thanks everybody for your help.

So was it the battery? I'm just checking to see if I was correct or if it was something else?

I dont know, It is still doing it, as of a week ago. I can only get to the field to fly on saturday mornings, and I dont dare run the engine much at the house with all the neighbors and kids trying to go to sleep. I checked the carb out and th filter needed some attention and I am going to try a bigger batt this weekend.

What about the switch? If the battery at the shop worked, and you are using that same battery now in the plane and having the problem again....replace your switch and retest.

Have you properly tuned your carb?

Do you have any pictures of your engine install....cowled and uncowled?

Okay guys, thank you for your help so far. I still have the problem. I have checked my fuel sytem. This I think it is my spark. I have two questions, first is a 4.8 volt 1100 mah battery enough? It is a good battey, its been on the cycler. My next question is this, is there a special spark plug to use? I just got a new one from napa. Is that okay?

Thanks again.