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Thread: Idle Circuit Running Rich

  1. #1
    LX User Fixedit's Avatar
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    Idle Circuit Running Rich

    1987 DX
    209K miles (if the dash is original. 5 speed swap wasnít done by me and the dash has definitely been tampered with to cover up the PRND lights)

    Got home and looked down the carb to see solid streams of fuel going down both barrels. Looked to me like the float was stuck up and fuel pressure was just shoving fuel straight through the carb. Just pulled off the top hat and cleaned quite a bit of dirt from the bowl. Been using non ethanol gas to clean things out so I expected a mess in there. Everything looked normal and operated freely (no sticking, just smooth movement and no fuel inside the float). Only now, with everything put back together, it idles rough but I donít see the streams of fuel going into the carb. So that leads me to believe it is running rich only on the idle circuit, but I am unsure what to do about that. Iíve read that the mixture screw is blocked off from the factory as it isnít necessary to adjust. What could be causing a rich idle circuit? My only thoughts are possibly an old gasket but I donít know which gasket would affect only the idle circuit. The top hat gasket looked to be sealing everywhere just fine, and I cleaned off the mating surface on the carb body.

    Car drives down the road beautifully, no hiccups at all. Just idles like crap and stinks up the cat. Idles better if I create a vacuum leak, but that just increases RPM rather than smooth the idle (confirming for me that it is getting too much fuel at idle). Don't know how to check the idle circuit system but I'll keep looking



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    LX User Fixedit's Avatar
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    Re: Idle Circuit Running Rich

    Seems to be an intermittent issue as of the next morning. Fired up smooth and idled well, no issues. Iíll see what happens after work though. I expect the issue will come back after a long enough drive.

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    LX User Fixedit's Avatar
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    Re: Idle Circuit Running Rich

    Drove home great to but Iíve noticed the Er is doing some strange shit. Making all kinds of noise in the intake at idle, I know my vacuum hoses are 100% but going to double check the routing regardless.

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    LXi User InAccordance's Avatar
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    Re: Idle Circuit Running Rich

    Er?
    Originally posted by ShiRen:
    Nice car or not, nobody likes losing a race to an old 4 door Honda.

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    Re: Idle Circuit Running Rich

    Besides your float level I wonder if you have some fuel pressure creep most carbs dont need much fuel pressure to run. Higher the pressure more chance fuel pushes past the needle and seat.
    1988 Lxi owner since August 1995
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    LX User Fixedit's Avatar
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    Re: Idle Circuit Running Rich

    Quote Originally Posted by InAccordance View Post
    Er?
    Gol dang phone thinks itís so freaken smart. Meant EGR lol. And okay, yeah itís a new pump I wonder if itís providing too much pressure? Is the best way to check that just a pressure gauge at the end of the feed line at the carb? New pump and new filters by the way. Also, the float level is set right at the upper most level of the ďokĒ zone. Havenít tried lowering it to see if it makes a difference yet.

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    Re: Idle Circuit Running Rich

    I'd guess the needle valve is tired.
    Dr_Snooz

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    LX User Fixedit's Avatar
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    Re: Idle Circuit Running Rich

    Okay, what are your thoughts behind it? Just a sticking needle whenever it decides to stick, and leaks a little extra in from time to time? I could see that

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    LXi User InAccordance's Avatar
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    Re: Idle Circuit Running Rich

    Talking carb I assume... if the egr starts acting up, dump it. Easy to do on carb ones... not so much on FI but doable.
    Originally posted by ShiRen:
    Nice car or not, nobody likes losing a race to an old 4 door Honda.

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    LX User Fixedit's Avatar
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    Re: Idle Circuit Running Rich

    I thought about it...Iíve done the EGR delete on the LXi, but with the way I planned on romping on the DX after a Weber 38 and a 272 cam swap, I figured leaving the EGR would help the 200K+ piston rings and cylinder walls. Though with the plugs out I can see a very healthy cross-hatch on the walls still so maybe I shouldnít worry about cylinder temps so bad.

    Whatís easier about the EGR delete on the carb models? My only knowledge has been to weld the nut at the manifold shut (unless thereís a plug with that thread pitch I donít know about) and make a block off plate for the EGR valve. What I donít know about is the other box & valve in front of the carb right along the valve cover. I see it just bolts to the intake, does it come right out without a hole needing a block off plate?

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    LX User Fixedit's Avatar
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    Re: Idle Circuit Running Rich

    Also, quick thought..

    Shouldnít carbed models have a vented gas cap? This one has a solid metal one like my lxi, and on hot days or with a low tank, opening the cap releases a bunch of pressure. In fact, when I had streams of fuel coming out of every hole down into both barrels (engine both running and shut off), I released fuel tank pressure by opening the cap and the fuel stopped pouring into the barrels. Every carbureted vehicle Iíve owned or worked on had a vented cap to either release pressure or prevent tank-vacuum. Donít know, just a thought. Whoís got an LX or DX, what kind of gas cap do you have?

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    Re: Idle Circuit Running Rich

    Quote Originally Posted by Fixedit View Post
    Also, quick thought..

    Shouldnít carbed models have a vented gas cap? This one has a solid metal one like my lxi, and on hot days or with a low tank, opening the cap releases a bunch of pressure. In fact, when I had streams of fuel coming out of every hole down into both barrels (engine both running and shut off), I released fuel tank pressure by opening the cap and the fuel stopped pouring into the barrels. Every carbureted vehicle Iíve owned or worked on had a vented cap to either release pressure or prevent tank-vacuum. Donít know, just a thought. Whoís got an LX or DX, what kind of gas cap do you have?
    Leave it loose or drill a hole in it.
    1988 Lxi owner since August 1995
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    LXi User InAccordance's Avatar
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    Re: Idle Circuit Running Rich

    Easier because if you remove it off an fi model, itll throw an ecu code. Carb wont.
    Mine has a solid metal cap, far as I know it's the original one. If you look at the backside of it, it has vent holes.
    I do get pressure though but isn't too crazy. Mine is so heavily modified though I cant compare it to stock anymore. Like I dont have a return line anymore, etc etc
    Originally posted by ShiRen:
    Nice car or not, nobody likes losing a race to an old 4 door Honda.

  14. #14
    LX User Fixedit's Avatar
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    Re: Idle Circuit Running Rich

    Ah okay well if they are vented then I wonít mess with mine. And shit I forgot about the code thing on the lxis, what does throw the light on for carbed models? I was surprised to see no blinking light on this car when I got it. Yeah man I like your build, if I could afford it Iíd go that route. A Weber will have to do though haha.

    Still just an intermittent problem. If it starts up rough, I can keep it alive and once itís driven around for a bit the idle will be fine. But the opposite happens too, Iíll start up fine and idle smooth but a little driving and the idle with get rich and try to die and all that. Making a trip north to get some parts this month and Iíll just save for a Weber 38.

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    LXi User InAccordance's Avatar
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    Re: Idle Circuit Running Rich

    Carb wont throw a light on the dash, they do have a quasi ecu thing under the seat but all it does is control emissions functions, itll still run without it.

    38/38 is a nice route. Good power gains and will give you room to add more. I was going to do it but I've always wanted side drafts so just had to go for it lol.

    Have you pulled the carb apart? I'd wonder if the float or needle are sticking.
    Originally posted by ShiRen:
    Nice car or not, nobody likes losing a race to an old 4 door Honda.

  16. #16
    LX User Fixedit's Avatar
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    Re: Idle Circuit Running Rich

    Yeah I just meant the ecu under the seat. Itís nice not having a blinking light for a change. Iíd love side drafts too but a 38 and a delta 272 cam should be plenty for me haha. Yeah itís a long mess of a paragraph but in the first post I mention pulling the top hat off. Everything was normal in there, no sticking. Finally getting to set the float today, will be interesting if a lower level will help prevent a rich idle. Anyone know which direction the screw goes for up and down for the float? Iíll figure it out on my own but it could save me a few minutes knowing before I dig in lol

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    LX User Fixedit's Avatar
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    Re: Idle Circuit Running Rich

    Okay counterclockwise for up, clockwise for down (referring to the level of fuel). Again when I first opened things up today and checked the level in the sight glass, it filled up way past normal. Opened the gas cap to release a bunch of pressure and the level went back to its regular spot. Upon adjusting the float level though it of course began to leak from the screw, luckily I got the level lowered enough to my liking with the screw in a spot that doesnít leak. Still covered the edges of the screw with some sealant to be safe though.

    With the float level adjusted I went for a long drive and couldnít get it to act up. Weíll see what it does tonight when I go into work. Itís gotta be something sticking. Probably a combination of the pressure and something sticking that makes this all intermittent. Though I would like to conquer this problem and learn all that I can from it, Iím satisfied with the car still running for now and will just look forward to the carb and cam swap.

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    LXi User InAccordance's Avatar
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    Re: Idle Circuit Running Rich

    Sounds like that pressure buildup is causing the float to stick open.

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    Re: Idle Circuit Running Rich

    That's what what I'm thinking. Just have no idea why there's a problem with pressure at all though. Or is that kind of pressure normal, and it's just the old float/carb that can't handle it? Dunno. If I have the same issue after a carb swap, I guess we'll know lol

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    Re: Idle Circuit Running Rich

    Quote Originally Posted by Fixedit View Post
    Okay, what are your thoughts behind it? Just a sticking needle whenever it decides to stick, and leaks a little extra in from time to time? I could see that
    Just not sealing well. Depending on how they fail, they can allow more fuel to enter the bowl than they should or not enough or both depending on the situation.

    Quote Originally Posted by Fixedit View Post
    Shouldnít carbed models have a vented gas cap? This one has a solid metal one like my lxi, and on hot days or with a low tank, opening the cap releases a bunch of pressure. In fact, when I had streams of fuel coming out of every hole down into both barrels (engine both running and shut off), I released fuel tank pressure by opening the cap and the fuel stopped pouring into the barrels. Every carbureted vehicle Iíve owned or worked on had a vented cap to either release pressure or prevent tank-vacuum. Donít know, just a thought. Whoís got an LX or DX, what kind of gas cap do you have?
    Vented gas caps went the way of the Dodo starting in the '70s when stringent smog standards were implemented across the country. Instead of venting through the cap, emissions controlled tanks vent through the charcoal canister via the evaporative emission control system (EVAP). That's a fancy way of describing a vent tube that connects to a cylinder full of charcoal. The system works well but does sometimes have trouble. When it fails, it can clog and cause excessive tank pressure or simply stop filtering altogether which will make your garage smell like fresh gas all the time. Some tank pressure is normal, but if it's causing problems, you should fix it. You can read up on the system online (there isn't much to it) and then follow the troubleshooting chart on p. 12-84 of the manual to fix it. You can also bypass it, but expect the car to smell like gas all the time if you do.

    The alternative is that the EVAP system is working perfectly well, but your needle valves are no longer sealing sufficiently to overcome normal tank pressure. In that case, you need to replace them. Traditionally, that is done in the context of a complete carb overhaul because you have to remove so much stuff to get to them that it makes sense to refresh everything else at the same time. That's normal carbs, but these are the legendary Keihin carbs that strike fear into the hearts of mortal men. I've done battle with 2 other Keihin carbs (1 win and 1 horrible, horrible loss), but not a 3g carb, so I can't really say what your best strategy is. I would do an overhaul, but if you don't feel confident, don't have the time, can't find the parts, etc. and you can open the float bowl without disturbing a lot of other stuff, then a simple needle valve replacement may be your best option. I'd try to replace the seats as well (the big brass screws you turn to adjust the fuel level), because they could be damaged, which would make short work of your new valves. It is a good idea to replace any carb gaskets you open too.

    https://itstillruns.com/causes-build...s-6899381.html

    I know a lot of people can't wait to remove every smog control device on their cars, but those systems have a lot of usefulness beyond keeping the air clean. EVAP systems, for instance, keep your car from stinking. EGR, as another example, prevents pinging, which is good if you plan to advance your timing. It's worth learning about the various systems and how to repair them. Almost all of them have positive benefits for the engine.



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    Last edited by Dr_Snooz; 06-29-2019 at 09:53 PM.
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  21. #21
    LX User Fixedit's Avatar
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    Re: Idle Circuit Running Rich

    I had thoughts about the EVAP charcoal canister clogging and causing excess pressure, but as I typed it out I though ďnah, thatíd be too easy, sounds too good to be true,Ē and promptly deleted all that I typed hahah. Itís been on my to-do list to refresh my memory of the entire system so I can do some testing. Easy to forget to do that though when it decides not to act up for a couple days! And yeah see I really like the idea of the EGR taking care of cylinder temps if Iím going to lead-foot it the way I know I will after a Weber and cam swap. It seems to not be causing any issues but itís making noise, which may or may not be normal Iím just not familiar with everything about carbed models yet.

    Iíll test the EVAP to look for a difference in tank pressure and/or any improvement, then needle valves and deeper carb maintenance if I need to drive it longer before any swaps are done. If it can stay exactly the way it is right now for a while though I should be okay

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    Re: Idle Circuit Running Rich

    I'll cross my fingers for you. LOL
    Dr_Snooz

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  23. #23
    LXi User InAccordance's Avatar
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    Re: Idle Circuit Running Rich

    Guess that's why I get pressure buildup, evap system is gone lol
    Originally posted by ShiRen:
    Nice car or not, nobody likes losing a race to an old 4 door Honda.

  24. #24
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    Re: Idle Circuit Running Rich

    I may be jinxing it but I thought I'd update. No issues since I adjusted the float...I'm thinking the non-ethanol just got the dirt-nasties through the system and had a hiccup along the way. I've been kind of helping it by releasing tank pressure at the fill cap before and after driving on warm days. Probably helps but I don't know for sure at this point. Saving up for that Weber 38...got a 272 cam coming for it and after the carb I'll go for a DC header. Wishful thinking lol...

  25. #25
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    Re: Idle Circuit Running Rich

    Quote Originally Posted by InAccordance View Post
    Guess that's why I get pressure buildup, evap system is gone lol

    This thread has me thinking... is your vent line (where the evap plugged into on the tank) plugged? I deleted the evap and plugged the vent on a mercury cougar I had and the plastic tank imploded and crushed the fuel sender. if the evap clogging up is a possibility for pressure creep and a rich idle then it needs to vent. I get some crazy tank pressure in the summer and this never dawned on me, but Im kinda scared to vent it because I need all the fuel I can get to idle right lol, but Ive also never seen the afrs change after opening the tank or anything

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