RBean

I've got a DLE 20 in TF Mustang. It ran fine on the ground but after flying a while would start sagging, wouldn't take throttle, quite. Several engine out landing, damage etc. Finally was running it on the ground it the real hot weather we had last week and started doing same thing on the ground. I have the aluminum Slim line XL fueler, and I felt the cap and it was real hot. Probably vapor lock from the fuel too hot. So I moved the fueler from its location in front of the fire wall to behind. Seemed to help some but still same problem, so on advise of "expert" at club I cut out most of the bottom of the cowl. Same problem but takes longer to develop. runs ok flying as long as half throttle or more but after throttling back problem cames back. I think thats because when running fast the fuel is flowing through and the air fuel mix going through the carb keeps it cool enough but when flow slows it heats up. I have a pitts muffler and it is right under the carb.

I think there is little air flow in the upper rear of engine compartment and carb is getting heat soaked from the muffler. So I have closed in the bottom front of the cowl and installed and air dam/ flang, in front of the air exhaust hole to creat a low pressure area and hopefully help pull the hot air out. Also use old flexable exhaust tubes to duct cool air from front air scoop to upper rear engine compartment above the carb. Idea is to create high pressure area there and hopefully the air will be pulled down past the carb and past the muffler carrying the hot air from the muffler away from the carb and out the bottom. Here are some before and after pictures.

Any other ideas? Not much room for a heat sheild between the muffler and throttle linkage. About 1/8 inch.

RBean

Forgot to add, after it sags and quits, can't start. Will run a little with the choke on but will not run without the choke. After it sets for half hour and cools down, it runs normally. Has to be a heat problem, but engine never get tight as piston/ring binding etc. I think the cylinder is not over heating, but the carb and fuel lines are. Any suggestions other than what I have done. Will test soon and let you know.

captinjohn

Install a heat dam between carb and muffler. Get the material from a small engine shop....they sometimes clamp between engine port and muffler. Not saying you need to do it that way...just use the material for a heat dam. Capt,n

soarrich

My Feedback: (98)

I would get a beer in an aluminum can, drink it, then cut the can so that I could make a heat shield for the carb against the radian heat of the muffler, screw it to you plastic motor mount. Some foam from a Doggie bag container would work too, but I like beer. I would also try to make the spoiler right behind that last rivet for a bigger opening and a taller spoiler.

Tired Old Man

My Feedback: (1)

You have discovered the problems associated with stuffing a large dimension, hotter running engine into a tightly cowled small airframe. The problem will not be resolved until the engine has cooling entry air hitting the right places in the right volumes with enough exit area strategically placed to cool the engine. No, the scale look will not be maintainable.

The fact the engine runs afterwards with the choke on tells you the cylinder is indeed overheated. An over heated engine will only run when it is excessively rich.

Valve floater

I would remove the riveted panel over the plug area. Like the first pic. Leave the cylinder open to airflow.

RBean

I flew the plane twice today. It was running a little rich and not quite as hot today. No over heating problems, not sagging, good idle, landed ok. Five minutes after the flight engine started and ran ok. Next flight ok, leaned out just a little. If this works I will leave it alone. If not and still over heating I'll have to work out some sort of heat sheild.

RBean

I flew the Mustang twice today before the cross wind became too much for me. Had it leaned out and running great. Good transition, no sagging, good idle and LOTS OF POWER. No over heating. I think I have the problems solve. Same fix should apply to any tight cowl situation using a pitts muffler.

soarrich

My Feedback: (98)

What was the fix?

RBean

Soarrich:

Fix was to put flang/air dam in front of opening in rear lower part of cowl and duct cool air from front scoop to upper rear engine compartment. This was to creat high pressure area in upper rear with air flowing to low pressure area created by flang, thus drawing air past the carb and the hot air from muffler out the lower opening. I used old flexible exhaust ducts for the air to the upper rear and aluminum to cover front lower cowl and also to create air dam. Pictures show ducts and bottom of cowling. I glad it works. I've been messing with this engine for months. Finally made progress when I realized it was vapor lock and not a fuel/air leak causing lean running and engine out. I'll fill clean up and paint later.

av8tor1977

My Feedback: (6)

Glad it worked out for you. To me, that exit area still looks a little "shy". The exit area should be two to three times the air entry area. I shoot for three times the inlet area myself.

AV8TOR

RBean

av8tor1977:

Its hard to tell in the pictures, but the exit area is between 2 1/2 to 3 times the entrance area.