96 replies to this topic

[DarkHand]

Wait wait wait. It only affects the idle mixture? So if I spend 95% of my time MOVING on the interstate, rather than running the engine at idle, will THAT fuel economy be affected? My MIXTURE doesn't change as I apply throttle, does it? I'm absolutely confused. This is the first carbed car I've had. It seems simpler in theory, but not in mechanics, but I'm still not USED to it. I was under the impression that the fuel/air mixture ratio is FIXED and only adjustable by that screw, and applying throttle increases fuel AND air flow in the same proportions. I'm in Florida, it's always fairly warm, so I'm not super concerned about cold starting, but...well, it would be NICE to start easier, but as long as it starts RELIABLY... I'll be good. Mostly, I want to INCREASE my MPG on this car. I'm barely getting 30 now, and I KNOW it's better than that. And it's all in the carb, I'm sure of it. And I'm fairly certain I'm running rich, and if the devac and carb rebuild I'd like to do don't take care of that, but a devac renders it richer than normal anyway, I SHOULD just be able to manually adjust the mixture to compensate, right? Or am I missing some fundamental of carburetor operation here?

You've got the idea correct in general... Mixture is generally a static thing; whatever size jets, emulsion tubes, etc are in the carb will deliver a set amount of fuel for a given amount of airflow no matter what (unless they're clogged). The idle jet is a little different. You can change its flow by adjusting the idle mixture screw on the back of the carb. The term 'idle mixture' is a bit misleading however... It does alter the mixture at idle, but alot of your regular driving is actually done on the idle jet, up to a few thousand RPMs. So it's not a waste to be adjusting it.

A devac will make you more rich overall, but if you're running rich already you may just have a clogged air passage somewhere, lessening the amount of air compared to the amount of fuel that's going in, resulting in a rich situation (which is why a rebuild is always a good idea). Also don't forget that USDM carbed cars use the CVCC system, where the cylinders aren't ignited directly by the spark plugs... They're ignited by the flame from a small prechamber that the spark plug lives in. The small prechamber is very rich on purpose (to provide a flame that shoots out and ignites the lean mixture in the cylinder... lean enough that a spark plug can't ignite it on its own), so you can't reliably read your spark plugs to tell if you're running rich or not... They'll always read rich!

[Captain Regular]

Well, I just ordered the stock carb rebuild kit from O'Reilly. I think it was about $36, which is GREAT. It'll be here tomorrow. I called a couple Honda parts departments in the area, and they all have a GASKET SET, but they're not sure what's in it, and that would cost me like $42. The prices are approximate, but the O'Reilly kit was cheaper and they said it was the whole KIT. Is there anything else I need to get, like chemicals or special tools or anything? I read that to adjust my fuel/air mixture I could use a propane enrichment kit. Strangely enough, I already have 2 propane bottles, and I wonder if I could use a loaner tool from one of the big 4 auto parts stores in the area (we have an Advance, O'Reilly and AutoZone within like 5 minutes of my house, and a NAPA downtown) and do that AFTER the devac to get my mixture just perfect and maybe get my MPGs up where they belong. Any further advice I should be on the lookout for? This car IS my "daily driver" but if it takes more than a weekend, I DO work the midnight to 7am shift, so I can steal the wifeys Jeep for a while. I'm excited, I can't BELIEVE how helpful this forum is.

[DarkHand]

A can of carb cleaner and a can of compressed air is probably all you need (skip the can of compressed air if you have a compressor of course). A gasket scraper could be handy if any gaskets are really caked on, but I've never needed to use one.

EDIT: You'll also need a large (#3) Phillips screwdriver to separate the two main halves of the carb, and something to remove the pin in the float hinge. I used a small nail; a pin punch would be the proper way to do it.

[Captain Regular]

Here's another off-the-wall question about this whole thing. I have the entire vacuum system removed and undone, and am starting to remove the carb itself. How much of it should I be taking off to do the rebuild and devac? I see the pics at the start of this thread, and they have the whole intake manifold (right term, right) right up to the head removed. I'm not having to remove THAT, right? It doesn't seem there's that much on it that needs removing or even cleaning. I'm not sure of the terms for what I SHOULD be removing, but I THINK there's the "baseplate" and then that is under the carb itself.
Here's what I have. I already backed out the bolt that holds what I've been calling the baseplate(partially circled in green) to what I've been calling the intake manifold(below the blue) while I can just undo the four bolts, one of which is right above the loosened green circled one and take the carb ITSELF off, and I started doing that (the loose bolt is since tightened back down) but a bunch of coolant started coming out, I need to drain some of that off, and I THINK that's what I should do, right? I'm not going to need to remove the manifold or baseplate, just the area above the red, right?

[DarkHand]

You're exactly right on everything.

Now that you've got the baseplate loosened, you can clean up and reseat it to eliminate it as a potential vacuum leak. It's only held on by 4 more bolts just like the carb, it's no biggy at all.

Coolant flows through the intake manifold and up against the underside of the carb to help warm it up in cold conditions, just wipe up the excess and you'll be good.

[Captain Regular]

Ok, so I got the carb off and all seems well in the engine bay, nothing special. I've read about the red fuel tank vent line that currently goes to the charcoal canister, and I see the charcoal canister USED to go via a larger, but softer rubber hose into the large port on the drivers side of the carb. I'm wondering how I should replace that system, maybe just keep the charcoal canister and extend that rubber hose? The canister has ports for smaller vac lines that don't go anywhere (I didn't remove them, I think this car was partially devacced by the previous owner. I don't want to just vent fuel vapors into the engine bay, especially with that metal corrugated exhaust tube now wide open, but I am going to cap that - but still, doesn't seem like fuel vapors in the engine bay is a good idea. I've seen somewhere (I think on 3geez, maybe?) pics or ideas of putting a T-fitting in with the red vent line in one side, a small air filter, and then an adapter to the larger hose to the carb. No idea how this works yet.
Also, there's what I think is the EGR system. The metal exhaust pipe that used to go to a black thing. Then the black thing went into my air intake. It was removed in the devac that started this thread, and I removed it in mine. I feel confident in removing it because I'm sure it couldn't have been working well, if at all. You see, it rattled. Like there was a bunch of loose crap or gravel inside it. When I turned it over, what looked like yellow flakes of rust started coming out. What it DID was go into the air cleaner, recycling exhaust gas, right? Here's my question... Outside air vs recycled air, supposed to heat the engine up faster, but not let the intake air get TOO "exhausty," right? Controlled by the little vacuum-operated device in the intake pipe, right? Well, my "intake air control diaphragm" was only connected by a regular vac line to one of the ports on the inside of the air cleaner. That's it. No way in hell there's enough positive OR negative pressure there to make that diaphragm do a damn thing. So it was either hooked up wrong or missing some other source of power, but either way, it hasn't been doing me a damn bit of good, has it? Should I just pop the whole thing out, or is it worth hooking to something?
And last but not least (for this post, anyway) comes what I THINK is the "air jet controller." The little Keihin box with A-B-C on it. All three lines ran directly to the carb, no other interface with the rest of the vac system at all. What does this do, should I leave it hooked up, or partially hooked up, and could it improve my MPG (my most important goal with this rebuild-devac)? In the pic, it was originally mounted right behind the driver side vac control box, but it's unbolted here for the pic.

Here's the "air jet controller" (I think) and what I'm pretty sure is the air conditioner control solenoid, which I've left, but vac lines are disconnected and taped off now. I have an A/C system, but a pipe has been busted open and it's depressurized, and the belt is off the compressor. I'd like to get it working one day, but that's further down the road. Another thread, another time. What to do with this guy?

Oh, and also: I got my kit from O'Reilly Auto Parts. It's a Walker, number 15898. The receipt has the normal price as $67.78, but the price I got was $39.58. The $67 is what a kit for the Keihin 2bbl seems to be online, so I was happy. However, when I opened it, I noticed that there's no float. I was under the impression that a carb rebuild should have a new float, as they get saturated or corroded with long term exposure to being submerged in gasoline. Should I try and get a new float by itself from somewhere? Or are these floats more resilient and don't need replacing? Or is there something else I should do with it, or might my kit just maybe be missing a part?

I'll make another post with lots of pics when I actually get in gear to taking the carb apart and doing the rebuild itself. Might even start a dedicated stock carb rebuild thread.

[DarkHand]

I've read about the red fuel tank vent line that currently goes to the charcoal canister, and I see the charcoal canister USED to go via a larger, but softer rubber hose into the large port on the drivers side of the carb. I'm wondering how I should replace that system, maybe just keep the charcoal canister and extend that rubber hose? The canister has ports for smaller vac lines that don't go anywhere (I didn't remove them, I think this car was partially devacced by the previous owner. I don't want to just vent fuel vapors into the engine bay, especially with that metal corrugated exhaust tube now wide open, but I am going to cap that - but still, doesn't seem like fuel vapors in the engine bay is a good idea. I've seen somewhere (I think on 3geez, maybe?) pics or ideas of putting a T-fitting in with the red vent line in one side, a small air filter, and then an adapter to the larger hose to the carb. No idea how this works yet.

The charcoal canister doesn't work quite right after a devac, those small vacuum lines you mentioned are for opening and closing it under different circumstances; that functionality goes out the window with a devac so typically that gets removed too. The amount of vapor is minimal; in fact the float bowl has another vent that's always open anyway (the bronze diagonally cut opening at the top of the carb by the secondary throat), so you're not adding much more by unhooking the canister. If you remove the port on the carb and block it off like I did there's practically no difference.

Also, there's what I think is the EGR system. The metal exhaust pipe that used to go to a black thing. Then the black thing went into my air intake. It was removed in the devac that started this thread, and I removed it in mine. I feel confident in removing it because I'm sure it couldn't have been working well, if at all. You see, it rattled. Like there was a bunch of loose crap or gravel inside it. When I turned it over, what looked like yellow flakes of rust started coming out. What it DID was go into the air cleaner, recycling exhaust gas, right? Here's my question... Outside air vs recycled air, supposed to heat the engine up faster, but not let the intake air get TOO "exhausty," right? Controlled by the little vacuum-operated device in the intake pipe, right? Well, my "intake air control diaphragm" was only connected by a regular vac line to one of the ports on the inside of the air cleaner. That's it. No way in hell there's enough positive OR negative pressure there to make that diaphragm do a damn thing. So it was either hooked up wrong or missing some other source of power, but either way, it hasn't been doing me a damn bit of good, has it? Should I just pop the whole thing out, or is it worth hooking to something?

You can pull that whole system out. EGR does help a bit with warming up a cold car, but it's mainly for emissions. The EGR system takes some of that raw exhaust and reburns it in the cylinders for more complete combustion, and less pollutants out the tailpipe.

And last but not least (for this post, anyway) comes what I THINK is the "air jet controller." The little Keihin box with A-B-C on it. All three lines ran directly to the carb, no other interface with the rest of the vac system at all. What does this do, should I leave it hooked up, or partially hooked up, and could it improve my MPG (my most important goal with this rebuild-devac)? In the pic, it was originally mounted right behind the driver side vac control box, but it's unbolted here for the pic.
Here's the "air jet controller" (I think) and what I'm pretty sure is the air conditioner control solenoid, which I've left, but vac lines are disconnected and taped off now. I have an A/C system, but a pipe has been busted open and it's depressurized, and the belt is off the compressor. I'd like to get it working one day, but that's further down the road. Another thread, another time. What to do with this guy?

Yep, that's the air jet controller. You know, I've been thinking about that one myself lately. Those lines connect to ports on the carb that feed directly into the primary and secondary throats. The devac caps them off, cutting off air and is probably the source of most of the richening that happens; opening them would allow alot of air into whichever port is opened, leaning it out. Completely uncapped, however, is too much air. The air jet controller seems to meter a set amount of air into each throat depending on altitude. Whether this system would be better off getting pulled, remaining on the carb or even being modified is something I plan to look at soon. The 3geez people seem to be on to this already, the 2nd picture in this link shows it connected. Some of the other routing in that picture is not quite right though, so I don't completely trust it yet (partially because it's for an accord, but they've got the distributor advance hooked up to manifold vacuum? That won't work right (EDIT: Further research is showing they may have been right about this all along. Stay tuned)). They seem to have the right idea though.

Oh, and also: I got my kit from O'Reilly Auto Parts. It's a Walker, number 15898. The receipt has the normal price as $67.78, but the price I got was $39.58. The $67 is what a kit for the Keihin 2bbl seems to be online, so I was happy. However, when I opened it, I noticed that there's no float. I was under the impression that a carb rebuild should have a new float, as they get saturated or corroded with long term exposure to being submerged in gasoline. Should I try and get a new float by itself from somewhere? Or are these floats more resilient and don't need replacing? Or is there something else I should do with it, or might my kit just maybe be missing a part?

I'll make another post with lots of pics when I actually get in gear to taking the carb apart and doing the rebuild itself. Might even start a dedicated stock carb rebuild thread.

I haven't run into a bad float yet, which is good because no rebuild kit seems to come with one. You can buy one separate here, but it's $28 by itself!

[Captain Regular]

Ok, question. Real quick. The red one. Capped or uncapped or hooked up to something. It's capped in the first pictures in the thread, so I capped it, but it hasn't been on the car yet or anything. The original picture poster said he had some trouble, and had questions about ports on the rear of the carb. Other than that, I do have a question regarding the power valve, but that's for another thread.


Ok, I'm bored at work, so my question for the power valve is this: What's the effect if it's fully open? Like the top filed off and the guts removed? Oh, and how many ports and which ones on the manifold itself get capped? There are a LOT from the little plastic thermovalves, but I hear they aren't an issue, and there's a big one on the drivers side that obviously (right...?) gets capped, but posters are saying there are "other" ports on the back of the mani? Larger ones? Should I just pop off my manifold and do this, or is this something that's easier than I'm thinking it is?

Edited by Captain Regular, 06 November 2008 - 02:19 AM.

[harm]

I'm curious about the power valve too - mostly on fuel consumption issues. Has anybody blocked it off completely after devac and seen a change?

Anassa - thanks for the write-up - I did cross-reference a few different threads during my devac, mostly yours and DarkHand's - and then the more recent thread from Soobie - my car is purring like a kitten and I feel like I owe you guys at least a big thank you. i dunno if it's legal to mail people a beer or two. hmm.

[Captain Regular]

I'm curious about the power valve too - mostly on fuel consumption issues. Has anybody blocked it off completely after devac and seen a change?

Anassa - thanks for the write-up - I did cross-reference a few different threads during my devac, mostly yours and DarkHand's - and then the more recent thread from Soobie - my car is purring like a kitten and I feel like I owe you guys at least a big thank you. i dunno if it's legal to mail people a beer or two. hmm.

I've been running with mine OPEN since I did my devac, filed open like DH did, and I've been getting a consistent 36 MPG, 38 on the highway. But I'm in Florida and it's flat here, and I drive kinda like an old lady. Not too much hard accelerating, I open the choke as soon as I'm on main roads, which probably isn't much, but it leans it out a bit sooner than the automatic system would. I have my idle set at about 1100, too. Seeing as how I drive it like I do, I really do want to plug the power valve one of these days, but I've got a 20 month old and a 3 month old kid now, and car time is pretty much limited to keeping it running. If I ever get to find out what the thread measurements are, I'll just put a screw in there, if I can find one. Or maybe see if I can pull a power valve out of the junkyard next time I go.

[kaymo]

i know i said it somewhere else, but if you do the devac you should do something about your float vent other than leaving the cap off it. as long as your float bowl doesn't overflow, you should be alright, but if your needle and seat start leaking, or the O rings, and gas overflows your bowl, it will flow right out that vent into your alternator. easiest way to fix this is to remove the float bowl vent diaphram, remove the guts, and reinstall with a cut to match piece of beer (or soda) can. there is a rubber o ring that you will reuse and should seal up just fine. now if it overflows, it will go up that brass "straw" as i call it that points to directly above the middle of the secondary throat. better for the engine to eat the gas than to get it all over the engine bay and possibly start a fire.

remember, if you smell gas, stop and check. its better than catching fire and hoping you're close enough to a fire department to not loose the car

[anassa]

Holy Crap!!!! over 7k views..


So I update the first page with some links to some good threads by other members who have a lot of good information, including bike carbs, sidedrafts, and mods to stock carb. I'll post the links here too:

Some additional info links of others:
Scoobiewrxsti devac thread
HONDA KEIHIN CARBURETOR REPAIR
Darkhand Carb mods

Bike Carb setup info:
Bike Carbs
EuphoricBlue bikecarb How- to

Side Drafts:
Official Side-draft mikuni/weber thread - OG Wagon

Weber 32/36 install:
Weber 32/36 - ydennek




Sticky anyone? One giant thread that has all the info? lol.

EDIT: Thanks Darkhand for checking the links. Fixed!

[DarkHand]

The first Darkhand link is messed up, and the second one (bike carbs) is actually EuphoricBlue's post.

[Toneco]

Just did a devac on my sedan, engine was pretty heathly before i did it, rebuilt carb full tune up etc. i was running the stock set up for 7k miles and now is when i decided to go throught the devac car turned on but rpms shot to 5k on cold start it took a while to slowly lower and once it seems it was about to idle it just turned off any insight to what I need to do or check. I used this thread as a guide through it all.

-Toneco

EDIT figured it out

[pdc]

Thanks for this information. I just pulled everything off last night. What an amazing amount of hoses! Picking up vacuum caps today. I should know by tonight or tomorrow how it turns out.