Pumper carb


I’m about halfway into this project. So far I have removed the small pick up tube and replaced with a longer metal tube to feed the main jet. I epoxied the fuel transfer slot on the bottom of the carb and epoxied the lower hole at the diaphragm pump side. All I have left to do now is drill a hole in the upper diaphragm hole which will squirt the fuel into the bore of the carb. Anyone have an idea what size hole I should start out with? I think I need to angle the hole where it’s facing more towards the front of the carb as well instead of straight in at 90 degrees. I’m gonna try running this thing on gas and see how it does. I don’t have any methanol. Any ideas? Or am I totally wrong with my ways of how this works?


Dawg 89
Yea you may be off base .
It could work no way to regulate the fuel input .
Im going to say .028
Search sa carb or modifying flathead carb , summerlin carb set up .
There are 3-4 good articles .

Dover Power

I do not quite follow you on the last part.. BUT doing away with diaphram in my opinnion is not a good move.. Doing the single tube on the jet side hole will be a constant adjusting issue.. As the fuel level drops the mixture automatically leans itself down.. Its strickly depending on engine pulse to pull the fuel..

Another wild set up was to eliminate the short tube,, channel fuel from the fuel dump slot over to the small pick up tube hold, then bond a thin shim material over the slot.. Bingo you have forced feed fuel system and can regulate with the exsisting mixture screw...

Most all big mods to these carbs over the last 50 years were done with Methanol,, gas will be much trickier..

Behind the Jet the 2 holes.. lo spped and hi speed.. On gas i would not enlarge them much at all... On Methano. you can enlarge the front quite a bit and as for the rear hole just a tic.. OR that a screw driver that fits in the slot where the holes are and simply knock the entire slot out... Then no holes ...
None of this would be good on a Mini Bike application or something where you'd want to put put around

funky ole

.028 was way too big..... methanol I was running .017, gas I would think much smaller. but as jerry said,gas is much trickier and definitely not a minibike put put carb.