TOPIC: 85 Subaru carb W/ thin iron throttle body

Hi Orrist, Yes I have heard of the Carburetor Enhancer.

I bought the little kit from Eagle Research years ago. As you may know it's simple. Concept is to use manifold vac. tapped from the PCV hose, to put a SLIGHT pressure drop (vacuum) on the air in a carb's float bowl. It's adjusted w/ a needle valve so it can be fine tuned how much pressure drop. and the resulting gas vapor is drawn into the PCV's manifold vacuum source.

Carburetors main and idle feed systems work based on the difference in atmospheric pressure between the air in the float bowl and the air flowing thru the venturi(s). As air flows thru a venturi the air speeds up as it goes thru the "bottleneck" narrower section. This lowers the air pressure at that bottleneck- -and there is a discharge tube right at that bottleneck that connects thru the internal passageways of the carb. to the main jet.

The fuel in the float bowl "sees" atmospheric pressure above it (the carb bowl is usually exposed to ambient air pressure thru a vent that opens up to filtered air inboard of the air filter). But at the discharge tube in the venturi there is a pressure drop from the Venturi Effect at engine speeds/throttle opening above idle. SO-the fuel is PUSHED into the discharge tube and out into the airstream in the venturi by the difference in air pressures. (we think the engine is sucking the fuel in, but in reality its atmos. pressure pushing on it).

SO if you can lower the air pressure in the float bowl just a bit, you reduce the pressure pushing fuel in as well. This is completely separate from the fuel pump pressure.

It does work, but doing it on different carb's depends on the float bowl vent design. It also ought to be noted that earlier folks here were talking about carb. bowl vents, the kind of vent that would lead outside the carb. to either a charcoal canister or the atmosphere in pre-smog carbs.

A carb may/may not have this type vent--but all I have ever seen always have a regular bowl vent to expose the float bowl to outside atmospheric pressure. IF a Carb. Enhancer kit is used, it will only work when the "smog" bowl vent is closed. George Wiseman At Eagle-Research.com is a great site George Wiseman has a lot of stuff/info there.

TracyG

Hi all, TracyG here w/ an update on the carb and my Subaru.

2 weeks ago I Grooved the iron throttle body/base from the junkyard carb thats same as on my Subie. First of all I used a cut down carbide ball bit to start grooving, then switched to the medium bit to actually groove it. The carbide bit was only vaguely like our bits, but it got me started.

Used low speed and plenty of cutting oil on both bits. The Medium bit IS still useable!! I'm just glad there aren't many iron carb throttle bodies around!!

I wound up w/ about a 3/4 groove didn't go under the thin section by the big screw, didn't want to risk using epoxy there. I wound up digging thru the throttle disc using a 30 degree angle to groove. Switched the disc from my original carb to fix that.

While the carb was off i attacked vacuum leaks-replaced 6 or7 original equip vacuum hoses, this engine has plenty of 'em! When reinstalled the engine ran badly, I pulled the Pulstar plugs that had maybe 15k on em. One had its center electrode all worn back, so I junked 'em and used new NGK stock style w/ added 20% gap. I won't use Pulstar plugs again.

Also did a wet/dry compression test, one cyl. is down 13 lbs. from other 3.

With new plugs it ran a lot better, my cap, rotor and wires all seem good. I did a computer relearn on this car, but I'm not sure that did anything, remember its an '85 and a feedback carb.

I still suspect 1 or 2 possible vac. leaks, but overall the car seems to be gradually improving. There is no dramatic power increase, but if you drive gently the power seems to increase i.e. speed builds w/ a steady throttle.

Tried backing initial timing off several degrees, it didnt like that reset to 11 deg. initial w/ advance hose plugged then reconnected after timing. Still have to calculate MPG, hard to say yet.

I think the Groove is pretty big in proportion to primary bore size of 1 inch. Sometimes it feels like the car has better power, other times like no change. But- this car has always been iffy like that. It is underpowered to begin with, but is far better than when I bought it yrs ago.

I do have a 5 cent theory about groove placement. Ron and Karl in Tacoma said to back out the throttle idle speed screw to fully close the throttle then do the Groove. Ok fine- but when you install and set curb idle this places the throttle disc/plate into the groove.

Might it not be better if we leave the idle speed screw alone and groove where the disc is? Maybe I'm forgetting or misunderstanding something--any input is welcomed here!!

Thanks, TracyG

The reason I recommend (EVERYTHING is a "recommendation") setting the idle screw to its minimum setting is that the engine will invariably pick up on the idle. This comes from the more efficient burn created by the waveform The Groove generates, requiring the idle to be backed down anyway!

As The Groove functions best the closest to the throttle plate, reducing the idle setting first only allows for better placement for efficiency's sake.

Additional adjustments using the idle air screws is also beneficial. By reducing the amount of air allowed to pass around The Groove forces more air INTO The Groove, thereby further enhancing gains at idle.

Does this answer your question, Tracy?

Hi Ron, yes it does in part. I was thinking about the recommendation you made re: closing the throttle to groove carbs. Partly due to the way this subaru engine runs and the fact it has ALWAYS had idle quality issues. It has always had a bit rough idle esp. when at operating temp. The carb and emission controls are a "weirdo"; lots of solonoids on vacuum lines, the whole feedback thing that seems to be metered air added to internal air bleeds in the carb. '85 was a year for lots of emissions crap on cars esp. carbureted ones. bottom line this engine has always had me guessing... Also I'm at 4500 ft altitude or so here in Reno and that hurts power. I'm No expert on anything, though I have seen someplace that a carb generally wants the idle mix. to be a bit rich, I have usually tried to lean out this carbs idle screw (turning it in a little) but that only works so far. Fixing vacuum leaks has made a difference on this car, another vac. line worked loose today, I reinstalled it and "fixed" it with something from the Sporting Goods Store that goes in air rifles...wow no more leak!! I'll likely end up fixing more vac. hoses this way, there are like 2 dozen separate hoses here. I also relocated the vac line that goes to the MAP sensor from one end of the manifold over 2 intake ports and tied in to another going right to the central plenum. I'll try the "close the idle mix screw and turn in the curb idle screw" trick as a deliberate experiment and post the results. Thanks again, Ron! TracyG

Thank you, Tracy!

That is EXACTLY what we have to do: experiment with different settings.

You're a great G-Man,Charlie Brown!

Ron

PS: Did you notice the changes in your earlier posts? If you could folow that example, my tired eyes would be so much happier!