TeeDee 049 with Medaillon sliding exhaust throttle

OVERLORD Sat Apr 27, 2019 2:59 am

Why not mounting a sliding exhaust throttle to a Tee Dee to control revs?

I assembled a TeeDee with a n°6 cylinder. This cylinder has 2 ports and no SPI. To give enough space for the throttle, the NV assmbly needs to be turned around and a washer must be fitted between the carburator body and the NVA. I used a 0,8mm fiber washer. Also the corner of the black plastic that reinforces the veturi mount needs to be cut away for the aluminium ring to fit.

The set up looks like this:

TeeDee 049 with Medaillon sliding exhaust throttle Imgp5518

Yersterday, I mounted the lot for testing. The throttle was connected to a rubber band to keep it fully open for starting.

TeeDee 049 with Medaillon sliding exhaust throttle Imgp5517

Testing didn't take long because it doesn't work. Once the carb adjusted, I closed the the throttle and the revs remained the same. The sliding plunger only acts as a muffler. Does this mean that on a medaillon, the speed adjustment is only done by the rotating spray bar?

1/2A Nut Sat Apr 27, 2019 3:57 am

It should have suppressed the rpm some, any idea how much perhaps by 7k?

Surfer_kris Sat Apr 27, 2019 5:04 am

The original throttle kit for the medallion came with several washer that one could put at the end of the "plunger" before attaching the throttle lever. This way one can tune how far in the plunger will travel as the throttle lever comes stops against the aluminium part. For a low idle you'll really need to seal off the exhaust pretty well. So check for leaks around the cylinder and adjust the stopper so that it will completely close off the exhaust.

The rotating intake on the medallion will not do so much on its own, I think it is more there to ensure a good a fuel draw at low rpms.

OVERLORD Sat Apr 27, 2019 5:48 am

Thanks for your comments. I didn't know about any extra washers but I found a possible cause. The thick parts of the plunger don't have equal lengths. The part with the groove is about 1,5 mm longer than the other one. It was the short bit that covered the exhaust opening and indeed the gap was too big. Now mounted the other way around, the opening is much smaller. I will test again, maybe this afternoon.

TeeDee 049 with Medaillon sliding exhaust throttle Imgp5519

getback Sat Apr 27, 2019 6:36 am

Yes the plunger is in backwards from the pic , keeps us tuned in . Small Cox Logo

Surfer_kris Sat Apr 27, 2019 1:15 pm

Yes, the plunger is on backwards in the first picture, the groove on the plunger is there to identify the end that should be towards the rear.

Here is what it looks like on one of my .049 medallion engines:

TeeDee 049 with Medaillon sliding exhaust throttle Img_0414

TeeDee 049 with Medaillon sliding exhaust throttle Img_0413

1/2A Nut Sat Apr 27, 2019 3:14 pm

With best efforts made for the TD you may need to close the gap further.
The fit and finish lacks enough precision to seal well, you can add a smaller washer
as shown to completely seal off the exhaust exit. The manifold still leaks out but
there should be enough to drop to a good idle.

Note very easy to damage the small flat head set screw, before issues arrive and you can no
longer obtain a good bite to hold the exhaust throttle in position swap out for a hex head.

TeeDee 049 with Medaillon sliding exhaust throttle Imag9627

OVERLORD Sun Apr 28, 2019 1:58 am

1/2A Nut wrote:With best efforts made for the TD you may need to close the gap further.
The fit and finish lacks enough precision to seal well, you can add a smaller washer
as shown to completely seal off the exhaust exit. The manifold still leaks out but
there should be enough to drop to a good idle.

I was thinking about some way to get the plunger deeper into the tube but that was before I noticed the thing was mounted the wrong way. I will look for a small enough washer to insert if needed. I remember from my Jerobee engines that the exhaust gap is very very small for idle speed. Thanks for the pics.

OVERLORD Fri May 03, 2019 1:49 pm

After reversing the valve in the body, I tested the engine again and now it stopped as the port was fully closed. I then added a washer with good results. The engine idles without stopping.

https://www.youtube.com/watch?v=WTsI0aSnbLY

Levent, to answer the question you asked on Youtube, I had to look hard to find out the make of the prop. The blades are not marked (anymore) but I could distinguish some letters on the hub. I took a picture of the hub and found FK, so it's a Kavan prop.

TeeDee 049 with Medaillon sliding exhaust throttle Imgp5526

getback Sat May 04, 2019 9:28 am

That's a interesting run , i believe if the plunger had a little less tapper to it would make it more responsive to rpm change ,, seems to be either wide open or idle at this point , i guess that's were the spray bar movement makes the difference ?!? This Site Rocks!

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TeeDee 049 with Medaillon sliding exhaust throttle

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