Sup guys. I need to modify a walbro carb for an external pulse. What size fitting should I use?
What size fitting for walbro carb?
- Thread starter Troopermaniac
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Is it the carb you want or the insulator carb?
If its for the insulator block the barb is 10-32
If its for the insulator block the barb is 10-32
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- #3
I want to modify the carb itself. Gonna drill the bottom plate. The crankcase itself will be tapped. I'm assuming the same size.
Just put a pulse port on the insulator block and are you going to an accelerator style carb?
MonsterAir
Lone Racer 🤠
Can someone explain what your trying to do here? This is going so over my head 
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External pulse signal. Instead of using the piss poor one that goes through the intake manifold.
MonsterAir
Lone Racer 🤠
Would that be the 2 pin holes that are on manifold side of carb? and What kind of performance is gained from doing this?
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The one "pin" hole. Performance gains eh, just assures a good strong pulse signal. And opens up for a larger intake design. Normally I open up the pulse hole and make a larger/deeper grove in the cylinder if I'm keeping the intake pulse line. It causes lots of issues in saws and whatnot. Especially if you start deleting base gaskets and using glue to seal the cylinder and block.
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- #9
I don't have an option for the engine pulse port. Its already done by someone else I just was asking for knowledge.
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Ok, it's not a terribly hard mod. Need some epoxy a drill bit and a barb. You drill a hole in the diaphram cover in the unused boss. Tap it or glue the barb in. I don't care which. He'll do both. You can even use a fuel inlet fitting for the carb. Not rocket science. Give me a minuet and ill post up a few pictures
Here my beater 668. Mod is the same for all carbs.
Internal pulse. Forget it exists and make your own gasket, or give it a dab of epoxy. Plug it up somehow. If your not a total slob you can convert back to an Internal pulse.
Here is the boss I would drill, but you can knock off all those bosses and drill anywhere in the area I have circled in red
The punch is where the pulse signal comes up through the carb body, and does 2 90* turns to get to the diaphragm.
Here you can see with the diaphram laying in place, lots of surface area and a tiny little hole trying to make it work.
Like I said not rocket science, just need to make sure you grind off the nipple off close to flush so it doesn't mess with anything, or just drill one of those bosses.
Here my beater 668. Mod is the same for all carbs.
Internal pulse. Forget it exists and make your own gasket, or give it a dab of epoxy. Plug it up somehow. If your not a total slob you can convert back to an Internal pulse.
Here is the boss I would drill, but you can knock off all those bosses and drill anywhere in the area I have circled in red
The punch is where the pulse signal comes up through the carb body, and does 2 90* turns to get to the diaphragm.
Here you can see with the diaphram laying in place, lots of surface area and a tiny little hole trying to make it work.
Like I said not rocket science, just need to make sure you grind off the nipple off close to flush so it doesn't mess with anything, or just drill one of those bosses.
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What is your goal here @Troopermaniac? I'm running a pulse port through my insulator block on my boat to operate an external water pump. It has plenty enough pulse to operate my dual pickup pump. Block can also be drilled and tapped. Maybe I missed something, are you considering liquid cooling an engine? Just curious.
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- #12
Fuel delivery
Problem is high rpm for extended periods. Also some carbs have long fuel inlet needles in them which has a lot of mass too it. It can not follow fuel demand as needed. I seen it first hand up close on the dyno running high rpms. The problem is all the 90 degree turns the pulse makes to get to the carb fuel pump. That is why on our engines we deleted all internal pulse passages on our product and run external only.