nitro engine stalls in when held vertical

by Jim Buckley
(Roseville,MI)

Hello,

I have an MDS .60 that is stalling when I hold the plane vertically for more than 8 secs.

I have gone back and forth with both high and low end needles (note: with low end needle at flush it will not start, that seams to need to be out quit far to run well at low rpm.)

When I first go to vertical it revs up as expected and 3-5 secs later slowly revs down and stalls.

Checked lines, filter, changed to hot heat glow plug.

Could this be caused by carb seal? It Runs very well at level and pointed down. I also Check the clunk and length of the line in the tank.

Any help appreciated.

Comments for
nitro engine stalls in when held vertical

Average Rating

Click here to add your own comments

Apr 11, 2009
Rating

Missing parts... Not good..... lol
by: Matt

Are you referring to item 38 and 39 on this drawing?

39 is the low speed needle. Yea, it's pretty important! lol

Or is it 37?

There is a groove in the carb barrel that is cut in a spiral shape. 37 is a screw that sits in the groove. This is is what causes the carb barrel to move side to side when the carb barrel rotat. This side to side movement is what controls how much fuel comes out of the spray bar.

By moving side to side, the low speed needle moves in and out of the fuel supply opening on the spray bar. See the picture at the top of the page.

No matter what part is missing, I am sure your engine will run much better when you replace it!

Let me know how it turns out!

Matt

Apr 11, 2009
Rating

Thanks
by: Jim

Thanks for the quick response matt,

I have spent the morning on the carb and I have discovered that i may be missing a piece. lol.

Let me ask ya, On the top of the carb, (air intake),next to that there is a small tapped hole that there is nothing in, so I went online to look at a pic of an MDS motor and there is a screw and spring in that same hole.

Could this explain why My low end needle needs be so far out to start (it may be drawing more air than its supposed to be?)

I have had this Extra 300s for approx eight years, I have run it on table a dozen times, flew it once about 3 years ago and I was real rusty.

(long break from rc) it stalled at low altitude and I had to float it into the tall grass. (needed very minor repair).

So, now I am pretty much just getting back into rc and I am not sure what that adjust screw even is but i am on my way to hobby shop to get it.

Thanks Again

Apr 11, 2009
Rating

Hmm
by: Matt

Man, these nitro engines can drive you nuts can't they?

I guess it could be the seal between the carb and engine block. But if that were the case, it would not run well level or pointed down.

When the airplane is pointed up, the engine must work harder to pull the fuel into the carb because it's working against gravity. So if the carb is set too lean, it may run OK when its level, but not when its pointed up.

Make sure to perform the "pinch" test described on the top of this page. If the engine doesn't increase in speed when you pinch the line, then it's definitely too lean. Be care, running your engine too lean will ruin it in a hurry!

Also, (this is pure speculation) there could be a pin hole in the fuel line. If there were a pin hole close to the top of the tank, the engine would run fine until turned vertically. Just a thought.

There is one important piece of info that I didn't see on your post. Are you running the engine at idle vertically when it dies, or at full throttle?

If it dies at idle, then the low speed is probably too lean. If it's dying at full throttle, then the high speed needle may need turned out a bit.

Please let us know how it turns out.

Good luck!

Matt