F4U Corsair

My Feedback: (22)

A friend at our local club has a JC 28cc engine that's giving him fits. It keeps quiting on him in the air after just a lap or two. On the ground we have checked both the low and high needle valve position so we know it's not in the adjustment, he has 3 or 4 gas engines and the other ones run great. One thing we can't get rid of is a constant engine surging at wot on the ground. At 1/2 or 2/3 it's nice and smooth. He did the pressure mod, where you solder in a tube and run the line back into the fuse to get into calm air. He has replaced the spark plug, installed a new EI battery, and the throttle arm is not moving when at wot. No metal in the throttle control arm either. He has run 3 or 4 tanks through it on the ground at low to med. throttle without it stopping or overheating. Any idea what can be causing the surging, and could this contribute to his deadsticks? Is there a way to test your EI to see if it has issues? DG

av8tor1977

My Feedback: (6)

Sounds to me like the high speed needle is lean.... Unless it is "four stroking" during the surging, then it would be too rich.

AV8TOR

w8ye

My Feedback: (16)

Normally this problem is like Av8tor says

But just the other day on here a guy had this problem and it was air blowing by the carb entrance.

Turk1

Surging means mixture changes periodically.Bubbles in fuel feed?

NM2K

My Feedback: (14)

Look for a kink in the vent or fuel feed line. Kinks let enough fuel by to run the engine at medium speeds, but sometimes not at high speed. Good luck finding the problem.


Ed Cregger

coralcape

My Feedback: (4)

Try spraying WD-40 around the carb base, throttle shaft and insulator, at medium speed. Might be a air leak, and this test should make it surge. Good luck, red

ahicks

My Feedback: (2)

Have him hold the nose of the plane straight up while at wide open throttle, just like we used to do with the nitro engines when double checking our HS adjustments then. Not something you're going to want to try by yourself, but just as effective troubleshooting something like this. I screwed with one plane for 2 weeks prior to having this suggestion made by a club member - and of course doing this allowed me to figure out/fix it immediately. Not a lesson I'll soon forget.

Ih82crash

Another thing to check is the fuel filter. Check the carb screen and ensure it is not partially blocked.

captinjohn

Also sometimes a bad throttle servo can cause simular running. Capt,n

speedracerntrixie

My Feedback: (29)

All good suggestions, I have one more. A long time ago I had a DA 150 in a Fiberclassics 202. The 202 cowl shape seemed to dump a buch of air right on the diaphram breather hole. I added a nipple to the cover and ran the tube into the motor box and the engine ran worse. It takes force to move air through a tube, try breathing through a garden hose and you will know what I mean. My resolve was to take a CF plate and put it over the diaphram cover with some spacers under so it left a 3/32 gap. No air could directly hit the vent hole and it was ables to breath easily.

F4U Corsair

My Feedback: (22)

Thanks guys for the suggestions, I will pass them on to him this week. I'm positive it's not a too lean or rich condition, as I personally adjusted it both ways just to check and it didn't make a difference. The servo is not moving, I checked that too. One thing I remember is during the surging, I saw the gas tank moving slight forward and backwards like pressure in the lines was causing it to move. After your suggestions, I'm leaning toward an air leak or pinched line. I have him check these out.


By the way, I went up to Urbana, Ohio today and got to see a large number of B-25's fly-in and practice for a fly-in at WPAB next week to celebrate the remaining Doolittle raiders. How cool to see these beauties up close and personal and to get a chance to see them takeoff and land and do flybys down low. These came in from all over the USA, and they had some on static display with the bomb doors open and loaded for bear. I counted 19 with a few more still in route. A P-51 did a low flyby about 30' off the ground and then landed to join the fun. Windy as hell, crosswind of 30-40mph gust, but it didn't seem to bother them except for a few wing rocks on landing approach. What a day!

FullSpool

My Feedback: (12)

The old JC28 were alittle problematic, see if Milton is still running the trade in program . I think he was offering new jc30evo for your old jc28 plus