dual carbs GX200

#21
Tomorrow I will level this "thing" out, unhook the TC, wipe off the dirty carb and try to start the motor.
No gas to the back one yet, I just want to see if there is much change or not
as it is. Rear carb has idle screw out, jets in front one 140/17.5 IMG_20181205_163021738.jpg
 
#23
#27
Hey Bro. DCarbide, I know what's made in your home-town. This was my new one 30 years ago, 375 Cat.
IMG_20181210_054530289.jpg

Anyway, here's a better video of the 2-barrel.
https://photos.app.goo.gl/MK7SiYD3ijr6jPSRA
Will be working on another thumb throttle today.
If theoretically the motor can use/fire a Huge amount of gas is there any chance it could
blow-up/demolish the block or head? Or not?
Hey Phil, I bought this motor stock and have built it piece-by-piece over the last 5 years;
bigger=heavier; the power- to- weight ratio of small-blocks is remarkable.IMHO
 

delray

Active Member
#30
If theoretically the motor can use/fire a Huge amount of gas is there any chance it could
blow-up/demolish the block or head? Or not?
the only way that motor would blow-up is if you where running some crazy amount of compression and methanol fuel and the motor was built to run 8000+ rpm's,big ports/valves...etc.... just ask Charles he can tell you how they blow-up. other wise if it comes unglued that's on you for not building it correct.
 
#31
the only way that motor would blow-up is if you where running some crazy amount of compression and methanol fuel and the motor was built to run 8000+ rpm's,big ports/valves...etc.... just ask Charles he can tell you how they blow-up. other wise if it comes unglued that's on you for not building it correct.
Charles is @minidragbike on the forum. He is the man for making 30+ HP with a smallblock.
 
#32
1. FPMinis: I don't know what to expect; after thinking the idle would be fast even with both
idle screws backed out;, a decent idle took screwing both back in a bit. Either throttle by
itself works well and when one is open a bit, the other one comes in seamlessly (you mentioned
"irregularities in the airstream". But obviously this is at low rpm, I dunno what's going to happen higher up. When the motor gets to that point
where it can't use any more will it start running too rich/lean, will it pop and raise hell, start missing, sound funny?
2. delray: " if it comes unglued that's on you for not building it correct." I know you're right.
I needed you to tell me that too much carb won't be a concern, 93 octane and about 11.5 CR
and wanting acceleration not top end so much.
3. DCarbide: When minidragbike and his 'scriptures' come to mind I 'believe' that fast can always
be made faster.

Thanks for sharing, it is highly interesting and helpful to hear from you.
 
#33
Idle speed could be adjusted on one carb, with the other shut fully, or on both. Either way is fine. If each carb had been on a similar build alone, idle may have been high, but the massive plenum volume and 90 degree turn are minimizing the divided signal.
Overcarbureting won't manifest itself in any dramatic fashion. It'll just sorta nose over since it can't draw fuel hard enough and with enough velocity to keep it atomized. I predict it'll act lean on top, but have raw fuel markings on the chamber, piston, and exhaust port. If it's set up with a large area of tight squish, and enough timing, it may crutch the issue.

I'd gear it tall enough to run 1000 below max revs on one carb, then ease the second open, watching the tach and EGT. You may have to gear even taller if I'm wrong and the second carb adds appreciable power.
 
#34
FPM, Got another throttle put on yesterday. Nice here today and so here I go
this afternoon to see what will happen. Your notions of "divided
signal", manifold structure and linkage and gearing are all noted.
I will try WOT on one at about 20-25 mph and quickly crack
the other to see if the results are dramatic enough to keep the 2nd carb.
Enter into the mix a 6-stage 40" header, 1", 1.125, 1.25, 1.3125, 3, 2.
Seems it might help air flow on the bottom-end but hurt the higher revs?
 
#35
I'm happy to say the dual carb set-up is a huge win. Smooth as silk
at any and all positions of the two throttles, and either one can be used
alone; however the real thrill is using them simultaneously...just a slight
push on both revs the motor several hundred rpm. To go WOT on both at any speed delivers
phenomenal torque/acceleration and will have you leaning forward a lot.
.( Spark plug looks great). I'm very happy
with the amount of added power and the ease of adding it.

Thanks to all who helped!
 
#36
"So I have worked with snowmobile, dirt bikes, atv and utv engines for a few years and have seen several dual carb setups. On a single cylinder it is completely pointless in all honesty with the specific carbs you are looking at. Just too much air and fuel to efficiently burn"
"It would be a bear to tune and it would end up being too much carb"
"Couldn't agree more. Nice explanation!"
"I hate to be that guy who says it won't work"
"Like I said, I really hate to tell you it won't be worth it's weight in power"
"Overcarbureting won't manifest itself in any dramatic fashion. It'll just sorta nose over since it can't draw fuel hard enough and with enough velocity to keep it atomized. I predict it'll act lean on top, but have raw fuel markings on the chamber, piston, and exhaust port".


Actually, it works so well you'd think Honda put em' on at the factory and dyno-tuned the engine.
Extraordinary throttle(s) response! The rpms rise so fast at WOT that it's hard to stay in it
for very long because it pulls so hard it's scary. IMG_20181213_145712089[780].jpg
 

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