Flathead Breather with Pulse Barb

#3
I make these. They're perfect if you're looking for a crankcase pulse. This design incorporates fuel hose and o-ring to secure a stainless barb. Should last a while. View attachment 300978 View attachment 300956 View attachment 300957 View attachment 300959 View attachment 300962 View attachment 300975 View attachment 300976 View attachment 300977 View attachment 300978
Very nice idea!!!!!

If you get a chance??? Can you hook up a vacuum/ pressure gauge to that barb, with the stock valve/pcv working and read vacuum/pressures at different rpm.

I've tested this on some clones and was shocked how much pressure was actually in the crankcase with the stock pcv's.

There was no increase under the 4000 rpm mark, but some showed a huge bounce in pressure (15-20 psi increase) as low as 4500 rpm. Got worse with higher rpm. This kills power and slows the piston down.

Engines with more hrs, showed more increase.

I started using 2) 1 way check valves, without the stock pcv, and never see over 10 psi at over 5500 rpm. Idles 2",/2 psi at 2000 rpm now.


I was jus curious about the b&s crankcase vacuum/ pressures.

Good job.
 

Minimichael

Well-Known Member
#5
Very nice idea!!!!!

If you get a chance??? Can you hook up a vacuum/ pressure gauge to that barb, with the stock valve/pcv working and read vacuum/pressures at different rpm.

I've tested this on some clones and was shocked how much pressure was actually in the crankcase with the stock pcv's.

There was no increase under the 4000 rpm mark, but some showed a huge bounce in pressure (15-20 psi increase) as low as 4500 rpm. Got worse with higher rpm. This kills power and slows the piston down.

Engines with more hrs, showed more increase.

I started using 2) 1 way check valves, without the stock pcv, and never see over 10 psi at over 5500 rpm. Idles 2",/2 psi at 2000 rpm now.


I was jus curious about the b&s crankcase vacuum/ pressures.

Good job.
That's interesting stuff. I won't be spinning this flathead too fast just yet, as the billet safety stuff is not in the budget right now. So pricey.

But yeah I'll try to remember to look into the psi. You've got me wondering what psi may be needed (or too much) for the pumps I'm using. And I'll add that I discovered on my last pulse set up (3hp) that the pump wouldn't work reliably with the stock pcv as the only point of exit for case pressure. Know what fixed it? Adding an additional opening to atmosphere, inline with the pulse/pump vacuum hose, after the pump. It was a fluke I even tried that because I was sure it would thin the strength of the pulse to such a low psi that the pump wouldn't operate. I was wrong tho. So yeah, last summer's flathead runs with a stock pcv, as well as a 2-way barb to the fuel pump and then open to atmosphere. Granted, I restricted the open end a bit with a straight barb fitting with a smaller opening – to try and preserve some of the pulse strength...because I'm superstitious I guess.

(And with that change, I also noticed that engine was no longer weeping oil from its case gasket after a long ride.)
 
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Minimichael

Well-Known Member
#7
Yeah I suppose I could eliminate the stock pcv altogether, but i think my current design may satisfy the purists out there. Massacre, you doubtless run a catch can from those valve cover plates, yes? My design puts the barb's port at far upper exhaust side to limit oil mist, and I am merely running a modified (ie: poked thru) fuel filter as catch capsule, rather than a big can. No problems yet! And like you validate, the valve cover pulse works great. It also seems a really convenient place for making your other case venting mods. I had been making them with plastic barbs and any odd rubber seals I could find, but it works so reliably that I upgraded to this design for simplicity as well as durability.
 

Harquebus

Well-Known Member
#8
Despite this mod and its merits, has anyone run into issues using Briggs' standard way of dealing with combustion byproducts, i.e., the way the oil mist is pumped back into the carburetor, through the aluminum tube, to be burned off (basically a second time)? It's basically a simple EGR valve. . .

Is it detrimental to performance in any way? Maybe more so if the engine is getting worn (and emitting more oil) or when the engine is at the upper limits of performance; does it pump more waste materials back into the engine that you don't really want?

A catch can does 'good work' catching and isolating all that stuff.
 
#9
Yeah I suppose I could eliminate the stock pcv altogether, but i think my current design may satisfy the purists out there. Massacre, you doubtless run a catch can from those valve cover plates, yes? My design puts the barb's port at far upper exhaust side to limit oil mist, and I am merely running a modified (ie: poked thru) fuel filter as catch capsule, rather than a big can. No problems yet! And like you validate, the valve cover pulse works great. It also seems a really convenient place for making your other case venting mods. I had been making them with plastic barbs and any odd rubber seals I could find, but it works so reliably that I upgraded to this design for simplicity as well as durability.
Yes, i run a line to a catch can from that location, plus another line from the side cover to the same can.
 

Minimichael

Well-Known Member
#10
Despite this mod and its merits, has anyone run into issues using Briggs' standard way of dealing with combustion byproducts, i.e., the way the oil mist is pumped back into the carburetor, through the aluminum tube, to be burned off (basically a second time)? It's basically a simple EGR valve. . .

Is it detrimental to performance in any way? Maybe more so if the engine is getting worn (and emitting more oil) or when the engine is at the upper limits of performance; does it pump more waste materials back into the engine that you don't really want?

A catch can does 'good work' catching and isolating all that stuff.
I found that it reduces performance. If you think about it it's what didn't burn any further the first time so it's certainly not going to the second time around. I tried it with and without, and it definitely seemed to dull the combustion process. The idle dropped when hooked up as an EGR. Not as a signal of efficiency tho. Rather as a sluggishness, and slowness to fire.

Just two cents.
 
#14
This is a drag only bike. Runs on methanol.
Once the engine is happy with the oil level, it doesn't push that much oil into the catch can.
12 oz of Lucas junior dragster oil seems to be about right for my application.
Keep in mind that the engine idles at 4-5k and runs to 9-10k RPM
so lots of pressure
 

Minimichael

Well-Known Member
#16
This is a drag only bike. Runs on methanol.
Once the engine is happy with the oil level, it doesn't push that much oil into the catch can.
12 oz of Lucas junior dragster oil seems to be about right for my application.
Keep in mind that the engine idles at 4-5k and runs to 9-10k RPM
so lots of pressure
Very cool. Yeah I put a can on a 3hp flathead and just never caught a single drop of oil.
 
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