attacking a monojet

[boxer3main]

I am sizing up a unique 4cyl project. 108ci

the barrel for my singular barrel intake was for a thing called singular point fuel injection..can't use it anymore, going extinct like an earthquaking island. The intake is very nice, and the last year for the castings, a bit larger..kept it to revive an old engine...without a carb choice, except for a one barrell.
It is huge compared to the chevy vega monojet at 1 and 5/8ths inches...and found the next monojet that went to the 2.5 liter up to the 292 is a better match. The cams are bigger than the injected as well. I am guessing it can handle it.
my question is ...

can I use the smallest jet from this list on the bigger venturi?
my own guess is yes, as monojet should have been in the 30s mpg way back when, and they were not. leaning out is an option.

so... little main jet, bigger venturi? that is the question.

this is a boxer intake as well, so a centered 22 Hg of vacuum is there at all freaking times. no wobbly intake runner games with the weirdo inlines this particular monojet typically came from.

am going ahead regardless of answer, but am curious, maybe a beetle owner played around with this already.

[STINEY]

Seriously, if you want great economy and excellent throttle response - - a single venturi 40mmish carb on EACH head is the ticket.

Dual carbs yes, but much improved efficiency due to the extremely short intake runners. No time or opportunity for fuel to drop out of suspension and wash down the cylinder walls when it does get sucked in, like a single carb on a shared LONG runner intake that a Boxer layout demands.

I hit 40 mpg with a 1641cc with twin 40mm carbs, and that was NOT babying the throttle at all. That was fun poke-it-n-shift-it type driving.

If you have a pair of those carbs you are talking about, why not build short intakes for them and give them a try, they are sized about right?

[dieselgeek]

Barry, you seem to have the aptitude for a DIY EFI installation. You should consider giving it a try.

[boxer3main]

I like the thought of the injection, that is why I kept 1400 miles of the cables.

the spfi unit will be getting used for the round cable wrap throttle linkage, and back in the parts bin it goes. it is a smart piece.

the two carbs is awesome on single cam engine.. the ea82 has two belts. I even use igntion wires to dial it in (nearly equal length). the centered intake is a win.

injection would also be an easy goer there with as much as I did to center draft.

the long runner is still a short one...the way subaru built the ea. I'll photo with carb on top, the monojet looks like a skyscraper.

edit: I finally found one reasonable, and not only that.. it has electric choke, idle pitch stop and possibly electric vent (I love using those in my locale). the barrel is large enough where idle draft can lose when the big flapper shuts quick. Remember carbs do not have air bypass like injection...the answer back then was to pitch slow the idle electrically. This way big air like injection can happen, and slo enough to keep running without choking, then shut the valve entirely, preserve for next start.




I'll call it a rare gem (I love carbs) this is a 1977-1979 for a 250ci, and on its way to a new home..
108 ci is >100% less than a 250, but did find jets for a 2.5l that fit the traditional monojet (middle venturi size, not the little vega, and not the v8 one)

[boxer3main]

I got this cleaned up, back tyogether, mounted on the intake..
broken air idle screw (no way ) and ordered one from mikes carburetor dot com.

I set the power piston linkage so needle meter is snug. I had to have it front of me to realize I had tinkered with a monojet more than 20 years ago. I loved that carb.

Up next is the capped secondary setting below the main jet.. may experiment with a needle below to get some lean. the air is big...making a snappy rocket may need some adjustments. I never did get to extra think with it.
this thing is a rock.

210 cfm to 108ci is 600cfm to a 324ci..

why the little boxer gets large is no mystery.

[boxer3main]

drilled into this today. Found the little needle was way open..took several turns to find a closed seat from where it was originally.

I have it at 1 turn out now...getting closer to mount the intake on engine and start. I also found a plastic plug with a handle, fit snug into the new hole. lucky pile of pack rat parts bin I have.


I also remembered another nuisance, the cover for hot idle bleed (left photo). looked new in there,delicate operation with gas and oil proof silicone to ensure cover sealed, and back together.

[boxer3main]

did some aligning today. I wanted it towards #1 cylinder, the offset linear stuff.

this is what I came up with...and a little vortex



I let carb leave impression on loosely placed tape...insead of subarus "centered" hole, I wanted this towards the cylinder jetting out there on the passenger side. the drivers side sits back, passenger side in the stratosphere and forward. thi should get the big barrel evenly.


I also am in the process of making this planum..a ufo look outof a stanless sauce pan. I did find the top air bleeds,and will be making something precise for the top of carb.. needs to be seated tightly.


and that is digusting tobacco in the background.
this weekend should be mounting. I verified choke pulloff is failed, but choke works, and a new idle air screw is due tomorrow. choke pulloff is also on the way.
both items, less than 20 dollars total. this whole deal is under $100..
I do know what I am doing, that saves alot, like alot of us.

I am optimistic as the engine is a bit more motorcycle on my cams setup..adding f1 sized air for the displacement could be very surprising sounds from a liquid boxer. The math plays out with the monojet..it is as big as it goes for the little ones.

[boxer3main]

the new idle bleed needle. not like the old one exactly, but made it work. A different taper and length. seems very soft as well. the nut is from my pc parts bin to set some tension..the new spring had no function even with screw all the way in,and the old spring is too big.
close fit. this is parallel to the intake, so a screwdriver of any size gets in to adjust. the little lack of annoying things add up decently during runtime.

[boxer3main]

7 inch hard lead out to side, the stainless steel holding fuel line is an old soup ladle. I remember my 250ci six cyl had a monojet. the intake used to vibrate off the engine, the carb rumbled off its seat..the savior was the hard mounted fuel line. Acted like a strut. the sube intake is a brick in comparison, but did this not only for memory sake, it stables the needles.

once on the car, a round of carb medic by gunk, and the sube spits off the ionization in realtime. the cleaning has been many hours. this carb, as luck would have it, smelled like a cow farm, a basement, and the finale seems to be the soapy car wash stuck in the float bowl. This was so dirty, the choke did not know how to ground anymore. It started wokring after the first several hour soaking submerged in lysol 4n1 bathroom cleaner. Returning it to petroleum is easy with the carb spray cleaners out there...and the sube, in its electrical happiness, does not get dirty often. I have cleaned the 25 year old hitachi just once, and never the insides. this monojet is going to a heavenly spot.

on a to do list, as the car is mid 80s with a return line..is add a regulator on the end of the line in photo, hard mounted, no rubber links. I found the subaru uses its return line, even on a 3psi setup in the spring, and early november..and sits dead the rest of the year.

[boxer3main]

yet another memory trigger. I was looking over the monster sized fuel vent and thinking how to make it smaller. lo and behold I moved the pressed in 3/8ths thin tube with my fingers, and removed it. I then found this overpriced piece from summit I was going to use on a gas tank in my bucket.
being tapered and stainless, I started turning it in without a tap, aluminum is soft.
I stopped at 4 threads or 3/16ths..with the leverage of a socket wrench, I felt out how tough I could go.
the way this barb worked is a solid lower end, not a cheap hollow. this weight of solid will win a long time. I paid almost 15 bucks for this..not very smart with the nickels and dimes that day. I am getting a good use today.

if anyone remembers the tops of monojets...holy cow. stuff unknown to man hangs out there. a good stainless piece is not a bad idea.