attacking a monojet

[Barry Donovan]

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.

[Barry Donovan]

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)

[Barry Donovan]

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.

[Barry Donovan]

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.

[Barry Donovan]

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.

[Barry Donovan]

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.

[Barry Donovan]

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.

[Barry Donovan]

threaded fuel vent



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.

[Barry Donovan]

updated choke pulll



forgot to grab a photo of this. I remembered this update from my 74 chevelle. the original choke pull has two errors..misalignment to be useless to open choke, and the plunger had no relief to function in the first place (very bizarre manufacturing error- found on all oem setups). I am aware the screw with washer goes in another spot..I just grabbed two to verify room behind powqer steering (there is plenty). the new pull off is notably larger.

the choke is designed to work slowly, the bimetal using engine heat as another factor. Days like today (headed for below zero) the choke could stay shut for a long time. the updated pull off is very needed. It does not allow choke to stay shut while engine is running. I liked that update alot. My old chevelle started as strong as a carbed subaru all year..

I surprised more than one with my version of monojet. the big car with little engine even burned its tires.

[Barry Donovan]

vent final

brr. its cold out. headed for a february version of below zero. as cold as it gets. full radiators are missing 25%.
anyway..rummaging through a parts pile, I found a metric piece that used to go into the intake for a brake booster. very thick. A smaller exit than oem rochesters vent, yet can take the same 3/8ths hose. Strangely rugged piece.
this vent is my final version. Bolted in stubborn, all the way to very tight. this even sticks to its own aged patina.


I ponder metric and SAE overlap as if a riddle for this one. jet sizes in mm coincide with cubic inches. the barb added in fit perfect. the subaru throttle circle bolted on ended up being its own full throttle pitch stop exactly at full throttle.. coincidence or not...works good for me.

[Barry Donovan]

wrong idle screw



the 2mm jets on the way, I took out the idle screw and thought back to high school days.. 1990 or so.
this screw was a nightmare. we had a quadrajet screw in a monojet, like above. this did not work. but neither did the monojet on a 292 that was at 8 miles a gallon its whole life. getting fuel correct led to a bad engine. the desoaking killed itself in correct stoich. that is a rare occurence, and goes to show some old dogs can't learn new tricks. fun while it lasted in the 20s mpg.
I hope this new order is the correct one.. it is a different part number running on the same photo. Goes with the worlds dumbest criminal internet sales..watch out.

on another subject, gaining density..I knew to check shaft play as it has been on the intake torqued down for a few days..sure enough, this carb was in a gas soaker. the shaft is a bit looser than when it showed up in the cold mail. Cold is not the only density changer. the destination of its mount is. the original jet seems to be a #109. the engine it came from must have been single digits in fuel. To get this one started and swell the magical aluminums will need the choke working, full warm engine and long idle time...of course correct idle screw.The bottom of the carb where throttle is, the material is alot like a subaru. morphing and changing and being an iron man..it drives me crazy if I did not know better. my first lessons in this morphing wierd stuff (very patiently guided by a shop teacher) was a 1974 kawasaki snowmobile engine in the late 80s. Not many hang onto them..not enough knowledge was given to why they went that freaking pansy that fast. As crazy as blowing studs out of subaru heads. Hence this is a go..looking forward to it. I centered another dead vacuum port today on intake, with drilling and seating stainless barb. this will help even the two boxer banks. ready to go.

the 43mm throttle centered to two 35mm openings venturi into the head, now round after porting..this should be oem like, discipilined vacuum in inches, and whistling like a teapot at idle. the part throttle and full throttle should be a surprising gain (that is what I am after). the power valve needle finishes its primary taper at 2mm. this is why I know not to get a jet larger than 2mm.
no fuel dynamics if to go larger, that means fuel dump.

c/n: needle must be the long one for monojet, and preferrably stainless steel. cannot use quadrajet like the mikes carburator website claimed.

[Barry Donovan]

custom idle air screw



still not knowing if the correct one is in the mail. Mikes carburator web site has a few goofy things going on there. 2 pictures the same with 2 part numbers, and same description...
I'll just make it my own damn needle. A post earlier is a "before" photo. Above is after my caveman grind with a dremel and diamond bit. I had to lengthen this to just stick the tip out into the throttle hole, like oem rochester..and got it done. I kept the head fat, as the engine is a 108ci. An oem needle may be too big, even brand new. So, will try this fat one first before the replacement. This grind also allowed the new spring to gain a tension without nut or washer, locks in like oem intended. not too much, not too little...just right.

up next is the seating of holley jets in the monojet. I am guessing it won't need much..the holley is a bit tight, will wait patiently and see.

[A/Fuel]

I hope I'm reading this right, and it's a long shot I know. But...if you are steping on the gas peddle the idle mixture screw has no effect any more.
And....I could be wrong, but your stainless fitting looks to be a little crooked....It could just be pic angle though.
I'm following this with intrest, the best that I can!