My Balsa USA 1/4 scale Sopwith Pup fuselage is constructed to the point where I can now start worrying about mounting my Evolution 7-35 radial. I have purchased a SonicTronics on-board glow system to keep all of the plugs hot at low throttle settings. (Don’t tell the wife about the price)! As I start to lay out what holes to drill in the firewall - it forces me to decide what to do about the choke problem on the Evo.
I have no experience with engines that require a choke. If I use the stock Evo carburetor on my 7-35 I will need to construct a recessed (and fuel-proofed) box behind the firewall for the choke-valve diaphragm and that will force the fuel tank farther behind the CG. Also, reading this thread tells me that using this stock carb will require expert tinkering with the needle settings (I'm not very experienced with this fine-tuning)!
I am used to pre-starting any of my existing Saito engines (all single-cylinders from .82 to 1.25) using the procedure where I hold a finger over the exhaust and rotate the prop until a little fuel comes out of the exhaust and there is a slightly ‘juicy’ sound indicating fuel is in the carb. BTW ~ there is a pressure tap on the exhaust collector ring of my 7-35 Evo.
So, here are the questions ~ [I'm hoping that the answer to question #2 is yes - then all the others won't matter]!
> Question #1: Is the choke necessary for starting the Evo 7-35?
> Question #2: I want to follow the advice of many contributors to this thread who recommend replacing the stock carb with the one for the Saito 90 radial (Saito carb stock # is SAI-90-R3-382-1). If I use this replacement - I notice the Saito carb has a priming nipple on the carb intake. Will priming using this method mean that my Evo won't need a choke?
> Question #3: If I do use the Saito carb - but a choke is still necessary - the whole choke assembly location for the Evo will need to be completely re-engineered to fit the Saito carb intake which faces straight-up - whereas the Evo carb intake faces straight-back (into the firewall). Has anyone used the Saito carb replacement and then moved the Evo choke assembly to work with the Saito carb? One difficulty in doing that is that - on my engine the choke assembly cannot be removed. None of the grub-screws on the back of the mounting plate will unscrew! The metal used for the grubs is too soft and it appears that some very aggressive thread locker was used.
Any help will be appreciated ~ thanks!
–Dave Johnston