Food for thought.
- Thread starter FlatheadsForever87
- Start date
FlatheadsForever87
Member
Is there a good gain with the fun power carbs. I hate those things. I have like 10 of them
CarlsonMotorsports
Site Supporter
Yes, there is power with the fun-power carb simply because of the bore, but I only ever knew one guy locally that was real successful doing them 20 years ago or so.
I would say they're not worth the headache.
Bolt on a 22, 24, 28mm slide carb and be done with it.
I would say they're not worth the headache.
Bolt on a 22, 24, 28mm slide carb and be done with it.
What a great picture OVALTECH1. Try this; put that carb on your flow bench and get a good measurement of bulk airflow. Then put a small lump of children's modeling clay or A/C putty on the inside of the front of this air horn we are looking at. Start at about the size of your little finger back to the fingernail. Mold this smooth to cause the air to take a late apex at the turn. You'll will be making the airhorn ID smaller front to back and be surprised how much. You see, air get's in the way of air in a port or carb setting especially at a 90 degree turn. The air flowing down the front of the air horn runs into the air trying to make the turn from the back of the air horn at the apex. After the clay adjustment the carb will be quieter too because the air making the turn will be smoother,,and it will pick up over 1% bulk flow.
Please do me a big favor,,,,, Report back your findings just to compare to what I saw over 30 years ago building outlaw carbs.
Best, WP
Skidude
Member
I’ve got a fun power I reworked 25 or so years ago. I cut the short dip with the jet completely off and milled it flat. I reconfigured the fuel passage to feed into what used to be the air bleed adjustment, making it now a fuel mixture screw. No jet, I just reamed it to the size I wanted. I used a block off plate between the tank and carb to make it pump fuel directly into carb via the adjustment screw. It ran pretty well on a stock stroke stock appearing with a 112alt. I’ll see if I can dig it out and take some picks this weekend.
IMHO the best way to modify the fun power carb is to use the correction air system / air bleeds including the emulsion tube. Jetting will be like any other race car,, change jets and air bleeds in the pit. The smaller droplet size created by the correction air system will have a much wider sweet spot.
When adding gas tank repair epoxy to modify the rotary choke air horn like I described above, the gentle curve of the now reconfigured front wall
of the air horn will work like the "Coanda Effect" and cause the air to turn into the throat of the carb. Even though the ID of the air horn, front to rear, will be smaller the smoother more organized air flow will net an increase in CFM.
Best, WP
When adding gas tank repair epoxy to modify the rotary choke air horn like I described above, the gentle curve of the now reconfigured front wall
of the air horn will work like the "Coanda Effect" and cause the air to turn into the throat of the carb. Even though the ID of the air horn, front to rear, will be smaller the smoother more organized air flow will net an increase in CFM.
Best, WP
FlatheadsForever87
Member
Don't have one of those carbs. But I do have a gx200 style stock carb. Would that make any more power than the pulsa jet?
FlatheadsForever87
Member
I'd like to se a picture of your explanation if possible. I'm sure you have explained it perfectly but my dumb a** isn't able to see it in my imagination.
That was a long time ago, no pictures. If you have access to a flow bench, put a small dab of clay there as I described and as you begin to shape it on the flow bench you'll get the hang of it. Take a picture of the clay modification before removing it to install the epoxy. The epoxy will remain soft long enough for you to adjust it to optimum air flow.
You'll have to drop the tank to change the jets on a fun power carb. When you modify it for stock appearing alter the air bleed area and build some various ID air bleed jets you can change out with needle nose pliers. Then you only have to remove the air filter in the pit to fine tune the fuel curve. These along with the proper emulsion tube pattern will make the best use of this big bore carb.
Best, WP
You'll have to drop the tank to change the jets on a fun power carb. When you modify it for stock appearing alter the air bleed area and build some various ID air bleed jets you can change out with needle nose pliers. Then you only have to remove the air filter in the pit to fine tune the fuel curve. These along with the proper emulsion tube pattern will make the best use of this big bore carb.
Best, WP
FlatheadsForever87
Member
I'm in the process of opening up a normal flathead carb right now. I think I have it opened up good enough. Just taking my time matching the velocity stack and the air horn. Then I'll polish it up and try to mate it to my block the best I can. I really worked my fingers off rounding out the transition from air horn to venturi. Should I epoxy the back section inside behind the Welch plug?
FlatheadsForever87
Member
I have one just gotta get the green fluid for my Simmons carburetor comparator. So far I have this done. The seam is smoother than the photo appears.
FlatheadsForever87
Member
How did u do yours? I'm using porting tools a file, sand paper scotch Brite and wd40
Badrooster
Member
I love this Thread! Flatheads, FTW!!!! They may be coming back. And, why wouldn't they??
Last edited:
FlatheadsForever87
Member
Yeah I was hoping this one inparticular thread would take off a little better than it did. But beggers can't be choosers.
