Large Model Association Forum

Having some bother with the above, whatever is done, it does not seem to pull the fuel through, the seal just does not seem there, others have said put a servo on, but this seems to struggle, its quite a shove to get the choke leaver over centre, even when the buttefly is closed, the draw is not good, ive found, in my box of bits, a tatone choke, bit like a sprung flap, that bolts under the carb screws, then the choke operates very much like the 4 stroke rubber pad system, but i only have one of them, starting the 70cc roto twin is a doddle WHEN it gets fuel, as are the 2xdle 32cc motors, do others struggle with this?

Allan,I have had this problem in the past,and I cured it by soldering over the hole in the choke flap which then gives you more suction.
To check it out before soldering put a small nut and bolt through the hole,and if it works remove the nut and bolt and then solder.
Whatever you do don't leave the nut and bolt in, because there is always a chance of it coming loose and falling into the engine.
ps.if the choke flap is not closing fully you will swing all day and get nowhere.Hope it helps..Brian.

The servo method is best Alan. you are right about the difficulty of the servo to operate the flap. the solution is to carefully remove the choke flap from its rotating spindle, then carefully remove the spindle from the carb body. Take care to watch that the ballbearing and spring doesnt jump into the venturi! Once the ballbearing and spring are removed, refit the choke flap and the choke will operate easily. It will then need to be operated positively with servo control as there will be no way of keeping the choke on or off. Hope that helps . .
I have heard of damage to the engine occuring if the choke is completely sealed Brian. If the choke isn't used diligently, the fuel can be drawn in with such force and in such a pressurised state that hydraulic locking is possible - especially when trying hard to start a stubborn engine.

CHEERS GUYS, many thanks, i will sort the beast, and report back

Aren't the small screws that secure the choke butterfly to the spindle 'flared' at the ends after factory fitting to prevent easy removal? If they are removed, the slight increase in thread diameter can damage the soft brass spindle meaning when it's replaced the screw is a fraction loose?

I'm sure this is the case with Zenoah's........not sure about other brands of engine though.

To overcome the force issue when using a servo, I have screwed/glued a longer horn to the small steel choke horn to give more leverage.

Phil

Phil, that is correct regarding the fixing screw.I have just checked 5 old carbs 2 bings and 3 walbros, and all have the fixing screw either
swaged or slotted and splayed, which I assume means not for removal. PS. Allan the only engine I have the choke servo operated is my Moki radial,and I have just checked the length of the extended arm,from the center screw to the servo hole it is 16mm, but as Glenn rightly states use the choke diligently.