So here’s a few questions. I’m way to close to the down tube for any kind of air filter so I need to turn that carb out 45 - 90 degrees (which I think would look pretty cool) to make this work. Other than making up something totally from scratch is there anything out there I could repurpose for this. If I used tubing, how critical is the inside diameter of the tubing, does it have to match the intake diameter already there perfectly. Would a rubber, silicone whatever elbow of some kind be ok. Anything not metalic I’ve found so far is not really rated for fuel. I’ve seen some posts on this board building something to convert a Bonnie head to a single carb but this should be simpler. Just an elbow and a couple of flanges. Any suggestions would be appreciated.
If you turn the carb at 90 degrees, you'll have a rich mixture on one cylinder (away from the carb) and a lean mixture on the other cylinder. It will cause you shit trouble and probably melt a piston, while the other cylinder misfires from being too rich.
i've got a cobb on mine, works great. No fuel balance issues. I'm thinking about trimming it down a bit though so it doesn't stick out so far.
If it works for you I guess it should work for me. I may try to fab up something myself and see what happens. I can always go with a short, really short velocity stack as oil field money suggested.
In theory if the straight section after the bend is long enough the airflow will straighten out....
However on a running engine it may not work out that way as the fuel might fall out of the air flow and cause what Pete is mentioning.
But if it works out ok for you that's fine.
I made an elbow for my sigle carb Triumph; sort of a knockoff of the Cobb but not quite a 90. Exhaust bend and a flange, I used a rubber boot to connect the Mikuni i had. Worked great, no tuning issues.
I have heard about the starving/rich issues regarding this type of intake....Not sure just how much they hold water since I have seen a boatload of different types of "intakes" on different motors....I would like to hear more regarding this. If issues regarding "impossible to tune" with this style intake surfaced...I would first look at a possible intake to head leak, then valve adjustment...
I am just guessing.....like I said, I would like to see more info.
I will add this....I am running a Super B on my shovel, and the opening is 90 degrees from the motor.... if I do not have a air cleaner I have a issue with off idle acceleration due to to air turbulence.....I have read air passing by the opening will suck air out causing problems...hence the need for the filter...
I didnt believe it until I put the filter back on......
Thanks for all the input guys. Gonna have to find me a nice smooth 45 degree, or more, steel bend with ID 30 mm and give it a try. Just learning to weld (got a Licoln 175 square wave) so this could be good practice.
If the angled intake runs for about 2 inches after the bend and dumps into a "log" or common plenum...Then two individual intakes for the two ports.... It would deliver an even mixture to each cylinder.Similar to a tunnel ram on a drag car...
I put an SU on a 45 degree manifold sometime just after the last ice age. The only way I could balance the fuel was to put an adjustable divider in the air flow from the carb to the "Y". Not 100 % successful but worked ok for the road. This was for show, not go!
I say it will only work at low throttle and high manifold vacuum. There's enough vacuum to keep the fuel vaporized.
At full throttle (not enough vacuum to vaporize), where the fuel is still droplets, it will all go toward one cylinder.
It should be OK for anyone in the USA. You blokes don't ride at 100 mph. (Maybe more like 50 mph).
Well,the guys with bad fuel distribution ride at 50 MPH, but the rest of us ride like demons. We don't need no fucking speedos to tell us we're doing the ton
A rough texture the full length inside intake runner will create turbulence, helping to keep fuel/air mixed. Of course compression ratio, cam profile, carb condition, elevation, etc etc etc will have bearing on this issue. Keep in mind tho that if you can get it close but not perfect , experiment with spark plug heat ranges and manufacturers. My $0.5 (inflation adjusted)
...any chance of posting pics of intakes that have been proven to work (along with motor, carb, cam info), and others that have caused rich/lean issues? this may aid in the future for others when looking at either going this route or possibly fabricate one.
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