anyone hear or experiance this before,i have a spe 26cc engine which runs fine on the stand and also when in the plane on the ground,leans out nice and can get to 7200rpm with a 3-blade 16x8 with a idle down to 1850-2000,as soon as you get to speed after liftoff it drops in power and starts to 4stroke like its rich? land the plane and spool it up and it sounds fine? could i need a velocity stack? any help appreciated,i've gotten lucky so far but its only a matter of time before i lose the model,luckily the flaps have saved my butt to this point,btw its installed on a tt bearcat with a auw of 14lbs.tia........john

You may want to vent the carb's diaphragm to the inside of the fuse, also make sure the slipstream isn't blown across the carb, that will mess up the carb settings also.

it seems the engine runs better with the stream over it! hence when under cowl and up to airspeed it dogs,(the cowl shields the propwash from the carb with about a 3/4 in. clearance)i also heard of the diaphram mod but i want to try things in increments so i'm not all over the place and still not having the problem solved

See the small plate with a hole in it on the bottom of the carby?

I bet the hole is facing into the slipstream.

Turn that plate around 180 degrees and your problem will go away (or at least get a whole lot better).

This is a common problem with the SPEs.

sounds good! i'll give the dia-plate mod a shot and see what happens.........thanks

well i did the dia-plate mod and still no workie[:'(]i even took the plane off with out the cowl on! same ole thing,runs like a champ on the ground but as soon as you put some speed and alltitude in, it richens upone thing i can say is i'm getting good at takeoff at stall speed and doing a circut and landing last thing i try is the velocity stack but i can'nt see that helping,but who knows at this point i'll try anything! anymore ideas? maybe my engine is just a turd!

No, the SPEs are OK. I think you'll find it's just some niggling thing.

The things would check for:

Air leak under the carb. Is the carb tight?

Carb adjustment. You said it sounds like it's going rich and four stroking, maybe it is. 1800~2000 seems to me to be too high of an idle. I'd start by leaning out the high speed jet until it sags, then back off 1/8 turn, then adjust the idle until it dies when you pop the throttle open after idling ten seconds, richen the idle screw up a 1/8 of a turn from that setting, now go back and reset the high speed jet.

Check that you have a good switch and battery for the IE. My friend went nuts for a week with a DA50 that flew like crap, the ignition's switch was intermittent.

all of the above have been done,even ran ei with out a switch to eliminate that,had all the gas gurus have a hand at it at 2 differant flying fields! seems to be some concensus that maybe 14lbs. is too much of a load for the motor which makes some sense if it runs great static but dogs under load,the engine could,nt run anymore reliable,it starts nice idles great and makes a great transition too full, and i can get the idle down lower,i had it as low as 1400 without using the idle screw,its my personal preferance to have the high idle at 2000 with the idle screw,i think for a warbird with a auw of 14lbs. and a wingloading of almost 40oz/in this motor can,nt keep up,maybe at 11lbs. you would be ok,maybe try to trade her out for another powerplant or keep it for a lighter airframe and shop around for another engine for the bearcat............thanks for the help
john

Isn't the load the highest during a static ground run?

You may be right, it is a lot of airplane for a 26cc, but I flew a 16 pound plane for a year with a Ryobi.