fORCE 28 Carb Conversion
it was suggested that i start a new thread on this conversion and post pictures. This was the last post under a different thread.
I picked up a Force .28 carb on E-bay for $14.00. I had to turn down the base to get it to fit in the engine and build a new (longer, offset to the right) throttle arm, and i had to cut a notch out of the roll bar to be able to adjust the LSN, but other than that, it was a simple conversion. Right now i am geared 17/36 and it is crazy fast. The engine sounds like it turning much faster on the top end, Throttle response is crisp and the low to midrange transition is smooth. What impressed me the most, was how easy it was to tune. 1/4 turns were resulting in noticeable and forgiving changes not the 1/8 to 1/16th adjustments that i was having to make on the stock carb. i hope to get the GPS on it soon to check the top speed. Its barely able to lift the wheels from a stand still, but i am only running 20% fuel at this time. i plan on switching to 33% and lowering the gearing some.
Today i wote:
I do have the advantage of having a machine shop at my disposal, so turning down the base was no problem.
The size of the carb is close to the stock unit with the exception of the slide valve.
This required modifying the throttle linkage. it had to be longer and offset to the right. I also had to use the outer hole in the motor mount and flip over and make some custom bends to the throttle rod.
to make the arm, i installed an old engine block into the chassis with the carb install. since the EZstart was in the way. i had to remove about 2mm of material from the bottom of the stock throttle arm, i then formed a new piece out of an old servo arm and shaped to fit, i then used an industrial adhesive to glue the pieces together. Knowing that if that piece ever came off, it would go WOT, it installed a small screw and wrapped the two pieces with fine copper wire, then coated the wire with a quick set adhesive.
I then had to work the angle of the carb to clear the EZstart, the angle of the pivot pin to get smooth throttle movement. The roll bar had to be notched for adjustment purposes only.
Today i made the mistake of doing to many things at once. While i had the carb off for pictures, i took a measurement and noticed that it was only 1mm larger (7mm) at the slide than the stock carb (6mm). so i bored it out to 8mm. Nothing fancy, just used a Dremel tool and calipers. i also slapped on a 14T clutch bell with a 36T spur gear. Last time i had the 14T bell gear, i had not set my shift point down and broke a piston from over revving. Now if it has traction it does violent wheelies, or just spins the tires, shifts into second and then takes off. Still the best part is how easy it is to tune. i kept leaning the HSN until it bogged on launch, then opened it a 1/2 turn out, gave it a high speed pass, had a good smoke trail and a crisp exhaust note, i then leaned it a 1/4 turn, no bog, good note, but a little light on smoke, so i backed it out 1/4 and called it good. I started to lean the LSN until the RPMS started to take off, then opened it a 1/4 turn, I noticed it had a slight studder on launch, opened it another 1/4 turn and all is good, nice low idle, very stable, never dies and fires up instantly when hot and starts good cold, ( i preheat using a heat gun) sorry, i dont have a temp gun yet so i cant give yo any heat numbers. After looking at the pictures, i think i am going to move the return spring to the hole on the throttle arm.