Oops, I did it again...Brought home another DB30S (New Project)

Daniel Coop

Daniel Coop

Well-Known Member
#84
#84
My .670 bore "stock appearing" big bore carb wasn't quite up to snuff on the big end anymore and I had a GX390 sitting unused in my garage, so I decided I'd rob it of it's big genuine Honda carb and try to mate it to my thirsty little 212...
I had heard the intake adapter plate was problematic and would require an extra piece when mounting the motor flat so I searched up different options and ended up settling on EC Carbs 458INT intake that eliminates the fussy issues of the adapter along with the plastic insulator.
Came with all necessary hardware and gaskets, but I also had to buy the larger filter adapter.

Just have to finish figuring out the throttle linkage.
GX390 carb's butterfly opens the opposite direction. I about had her done, but then the snow and cold set in within a couple hours. Supposed to be mid 50's again Wednesday, so hopefully I will be able to finish it and test it out. I threw in a pilot and main jet that was a hair to rich from a big bore carb I had laying around. I have no idea where to begin with jetting, but hopefully, I will get lucky.
 
noseoil

noseoil

Active Member
#86
#86
Daniel, if the 390 isn't working right, try the genuine Mikuni (VM22-133). I hear it's sort of a crap shoot sometimes with that carb on a 212, not sure why or what the problems are. The Mikuni's a good fit for a 212, has a 1mm larger throat (22mm with the Mikuni vs. 21mm on the 390) & is really easy to swap out the main jet. There's a bolt on the bottom of the bowl which has the jet attached. Just a 10mm wrench, 6mm for the jet & then replace the bolt. No gaskets or seals to deal with, I like simple.

If you decide to go to the Mikuni, try the 130 main jet with the needle in the middle position as a starting point. If you get the assortment from 100 (the normal jet size is too lean) to 190, you will have what you need. Sometimes cheaper to buy the assortment than to go with individual jets.

GPS makes a manifold that fits well & you're up & running. Not sure if they have one with the vacuum inlet for your pump, but they're good guys to deal with on the phone, really knowledgeable & helpful on this stuff.

Waiting to see how you like the GX390 & how it runs with the jetting that works, never tinkered with one on a build.
 
Daniel Coop

Daniel Coop

Well-Known Member
#87
#87
I actually ordered that GPS intake the other day, but to try and use with a Chi-kuni I have laying around on a different engine. But then I sold the damn Chi-kuni (with the crappy angled intake) the next day, so I will have an intake, but no carb so it could be an option. We'll see how the 390 carb works out. I've heard and read all the same shit about them but was told many issues we're attributed to the carb adapter plate and not having it lined up just so...
 
Daniel Coop

Daniel Coop

Well-Known Member
#88
#88
The GX390 carb on EC manifold conversion was successful. I managed to keep it gravity fed from the stock tank by just adding a 3/16 in line fuel filter and short piece of line and made a crude but very functional throttle setup using an $8 clone throttle linkage kit and a piece of the original governor/throttle rod.
[video=youtube_share;30S0unbvEX8]https://youtu.be/30S0unbvEX8[/video]
Think I even managed to guess correctly on my jet sizes first time out...
 
Fisher1983

Fisher1983

Active Member
#89
#89
Returning after a long break. Can't say enough how cool this build is. Thanks for sharing the tire size too...I think the big-n-little combo looks old skool hotrod-ish especially with the chrome fenders.
 
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