Electronic Carburetor/Roto 85 FS Install

[TonyHallo]

My search for a servo that has high operating temperature was a failure so I decided to use a Savox SV1250MG servo, same servo used on the GP178 EFI engine. It's rated at 111 in-oz of torque at 8 volts, it is referred as a micro tail rotor servo, the case is smaller than the standard size Hitec servo previously mounted. The return spring on the ZAMA is rather stiff and the servo wasn't happy at higher throttle settingso the spring was unhooked, now the servo current drops to zero at any throttle setting. The Roto 125FS engine comes equipped with a servo mounted on the throttle and it uses a Savox servo as well, the best I can tell, they use a SV1332MG rated at 69 in-oz of torque. This the my first exposure to Savox and looks like a quality product.

 

[dhal22]

I have a needs to be rebuilt 120cc Edge 540 with these servos. It had serious tumbling power back before I tore the landing gear off…..

 

[AKNick]

The 1250's are nice servos!

 

[TonyHallo]

Had a little extra time today before going to a late lunch with old friends. Decided to see see if the engine would run. The solenoid is normally open so without power its wide open. Flipped the engine over at high trim with the controller off, no choke, after 15 flips or so it started, shut off and powered up the controller, the engine came to life, however I could not lower the idle speed below 3000 RPM. I left the idle stop screw in. Had to remove the carb to gain access to the screw. Hopefully tomorrow I'll get the carb back on and set the throttle servo. Then run the engine

 

[TonyHallo]

With the carb back on and the throttle servo reset started and ran the engine, lowest possible idle when leaned out was about 1600 rpm, this engine would tick over at just over 1000 rpm with the WT 962 carb installed. When I look at the throttle disc you find the small slot where the idle jet is and there is also a second slot about 160 degrees across, I have not seen this second slot on other carbs.
When I compare the slot in the WT 962 carb it is much smaller than either of the slots on the ZAMA. I would estimate the slot area to be about 6X that of the WT962. I would like to have the idle set before completely the final tuning. Going over the gaskets and heat isolators, might find an air leak.

 

[TonyHallo]

Found a smaller carb used on a 35 cc chain saw, got it in hands yesterday. The original electronic carb bore was 17 1/2 mm, the new is 15 mm. Had to make a new throttle arm and the pump is driven by hose connection rather than through heat insulator. A little bit of lathe and mill work and should be ready to go.
I think the original carb will be good for a 12o cc four stroke.

 

[Snoopy1]

It does not take much of an air leak to have rpm pickup quite a bit. I have older YS 120 love the engine the last season I could no longer shut the engine of with the throttle. I thought I had an air somewhere, could not find it. After quite a lot of work I fond that the throttle plate was worm ever so little. Could not fix it and the engine was to old no parts so I just live with it. It idles ok but cannot shut it down.

 

[stangflyer]

I would love to see a video of the Roto 85 running with the electronic carb.

 

[pawnshopmike]

I would love to see a video of the Roto 85 running with the electronic carb.

+1
And welcome back brother! Great to hear from you. How you been?

 

[TonyHallo]

Yes, welcome back and you will if it is successful, need to make two gasket and it is ready for test run however it's just a tad too cold right now,