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  • Rough or no idle.....

    304 v8, HEI ignition, edlebrock intake, 4 barrel 600 cfm one size fits all holley carb with a 125-50 pwr valve, dual exhaust, no cats, flowmasters. Last month I called holley and they had me change the pwr valve because the exhaust smelled really rich. I timed it (by ear, without the advance), I started from scratch on the mixture (both sides all the way in and started with a turn and a quarter), set the idler screw, verified (don't know what its called, but primes the bowl) could fit a piece of paper underneath the adjustment and it ran great for a month. I drove it everywhere and had zero trouble. It's the best it's ever run. Took it to Uwharrie today and when I started it this morning it idled rough, but I thought I didn't let it warm up enough. Drove 45 mins to Uwharrie, no problems, but idle was a bit low, and started on the trail. I could not keep the thing runing all day. It drove fine going up hills, but if I went down one it choked off. Low power between 800 and 2300 RPM. Like no pwr and it sounded horrible. On the way home I couldn't keep it running on the road if the RPM's were between 1500 and 2000 so everytime I hit a 35 zone I could hear it quit and fire over and over, and it choked off at every light. I checked the position of the dizzy and verified it didn't move, checked the vacuum (14 to 16 inch hg, about what it was, but if fluxuated about 2 to 3 hg). I checked my mixture and it's right where I left it. Any ideas? Brand new fuel filter too. Less that a month old. Also, I have a hand throttle, and if I set idle with that and keep it where it will run, it idles rough....then smooth, then rough, almost chokes, and smooth again. Sorry about the long explaination, but it seemed important to give you all the symptoms.

  • #2
    Have you checked to see if any bolts loosened? I would look at that first, check intake manifold(lower vac). Also how close does your exhaust come to your fuel lines?

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    • #3
      Penguin,
      Your talking about the bolts that hold the carb on the intake right? That was the first thing that I checked, all were tight. I also fueled up a rag and went around the bottom of the carb to see if there was a leak but I noticed no difference. The fuel line runs close to the header, I'd say a couple of inches, as do the brake lines. Is that good or bad? Can you explain it to me? I have run the Jeep in this configuration for several years. Whatever the problem it, I feel that I "vibrated" it loose.

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      • #4
        you've done a little more to your 304 then i have mine, but your positive you have zero vac leaks? checked all fitting connections? correct me if im wrong but i believe the choke on that carb is manual not electric, if it is electric, tried running it with the choke unplugged?

        if anything the rough/smooth idle at the same time is what gets me

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        • #5
          Your fuel line could be too close to your header. I had problems with that before on different rigs: the fuel gets too hot and begins to vaporize causing fuel startvation.

          Another thought: I understand on some carbs, the adjustment screws can get damaged if they are screwed in all the way. I dunno much more, but just a thought.

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          • #6
            Originally posted by Gryphon
            Your fuel line could be too close to your header. I had problems with that before on different rigs: the fuel gets too hot and begins to vaporize causing fuel startvation.

            Another thought: I understand on some carbs, the adjustment screws can get damaged if they are screwed in all the way. I dunno much more, but just a thought.
            OK I see what you mean about the fuel but this is happening at start up now. This is screaming vac leak to me too, but I can't figure where. When I replaced the pwr valve last month, I replaced all the vacuum caps and lines.

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            • #7
              Is the EGR valve stuck open? While it is running rough try spraying some carb cleaner around the suspect area and see if the motor smooths out. Sometimes a tap on the EGR valve with a small hammer will do the trick, although it will most likely stick again.

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              • #8
                Originally posted by xlr8n
                Is the EGR valve stuck open? While it is running rough try spraying some carb cleaner around the suspect area and see if the motor smooths out. Sometimes a tap on the EGR valve with a small hammer will do the trick, although it will most likely stick again.
                I'm equiped with zero emissions. All I have attached to the carb or intake is brakes (to the manifold), advance (to the correct port on the carb), PCV to the brake/pcv port on the carb. All else is capped.

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                • #9
                  gummed up

                  Wierd how it works going up hill and not down. Is the float possibly sticking? You probably already tried this but, maybe some carb cleaner will clean out the carb. you checked the vac line for any leaks...Hum. New filter- so Only other thing I can think of causing it is the fuel pump. I had some problems once with my electric choke once but that doesn't sound like your problem. Good luck hope you get it figured out
                  Last edited by rippin YJ; 07-09-2007, 11:07 AM.

                  Comment


                  • #10
                    Try to determine if you are running too rich or lean, as this sounds like a fuel related problem to me. Do you notice black smoke from the exhaust?

                    What happens when you restrict the amount of air into the carb, either using a rag or the choke flap? If it smooths out it is a lean condition. If it dies right away without running any better it most likely is running rich.

                    Lean;
                    Try capping all ports off since you don't have many to begin with. I am suspecting a possible brake booster diaphragm.

                    Rich;
                    You might have some trash stuck between the needle and seat. Try this technique to suck the trash through without carb disassembly for cleaning. I have had about a 50% success rate using this method.

                    Rev the motor up to about 2500 rpm. Fully restrict the air into the carb so that the motor falls on its face. While the motor is falling open the throttle wide open. Just before it dies remove your air restriction and release the throttle so that it will go back to idle. You might have to try this 3 or 4 times before success.

                    Hope this helps.

                    Comment


                    • #11
                      Originally posted by xlr8n
                      Try to determine if you are running too rich or lean, as this sounds like a fuel related problem to me. Do you notice black smoke from the exhaust?

                      What happens when you restrict the amount of air into the carb, either using a rag or the choke flap? If it smooths out it is a lean condition. If it dies right away without running any better it most likely is running rich.

                      Lean;
                      Try capping all ports off since you don't have many to begin with. I am suspecting a possible brake booster diaphragm.

                      Rich;
                      You might have some trash stuck between the needle and seat. Try this technique to suck the trash through without carb disassembly for cleaning. I have had about a 50% success rate using this method.

                      Rev the motor up to about 2500 rpm. Fully restrict the air into the carb so that the motor falls on its face. While the motor is falling open the throttle wide open. Just before it dies remove your air restriction and release the throttle so that it will go back to idle. You might have to try this 3 or 4 times before success.

                      Hope this helps.
                      Yesterday I covered the front barrels with my hand and it smoothed out. I got black smoke at 3000 to 3500 RPM's on the trail, but I didn't notice it at low RPM at idle on level ground in the driveway. I pulled the booster check valve from the diaphram yesterday and caped it with my finger, but I didn't notice a change in performance. What I did notice: I felt fluttering in the check valve with the vacuum. In other words, it sucked my finger to it, but it felt like air may be getting by. I'll go to the other side of the check valve tonight, to make sure I didn't crack the valve. I thought this was normal for a check valve, am I mistaken? The exhaust smells rich to me, but the exhaust pipe shows so carbon buildup (which would suggest black smoke or a lean condition) on the chrome ends that looks recent since it's last bath. I'll cap it all tonight and let you know.

                      Comment


                      • #12
                        this is something i did to mine to "clean it out" persay

                        they sell a bottle of all use carbon cleaner for fuel tanks and as an additive to your oil.

                        but if your careful and have a buddy around to hold the RPM's at about 1500-2000, you can pour it straight down the carb as its running and it will clean all the needle heads, valves, and possible carbon buildup.

                        its called seafoam. its a liquid metal can at advance.

                        i poured the whole can slowly down the carb, just enough to keep it almost alive, while my brother held the gas at 1500-2000RPM.

                        for carbon and or junk, just shut the engine off after you dump the whole can, let it sit for 5 minutes, let it foam up everywhere, and crank it back up. give it a good gunning to jet out all the junk, or drive it to a gas station and back.

                        you'd be surprised most likely.

                        hope this helps

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                        • #13
                          Didn't get to it tonight fella's. I'll try again tomorrow.

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                          • #14
                            Originally posted by xlr8n
                            Try to determine if you are running too rich or lean, as this sounds like a fuel related problem to me. Do you notice black smoke from the exhaust?

                            What happens when you restrict the amount of air into the carb, either using a rag or the choke flap? If it smooths out it is a lean condition. If it dies right away without running any better it most likely is running rich.

                            Lean;
                            Try capping all ports off since you don't have many to begin with. I am suspecting a possible brake booster diaphragm.

                            Rich;
                            You might have some trash stuck between the needle and seat. Try this technique to suck the trash through without carb disassembly for cleaning. I have had about a 50% success rate using this method.

                            Rev the motor up to about 2500 rpm. Fully restrict the air into the carb so that the motor falls on its face. While the motor is falling open the throttle wide open. Just before it dies remove your air restriction and release the throttle so that it will go back to idle. You might have to try this 3 or 4 times before success.

                            Hope this helps.

                            just bumping a thread, i went to crank up the beast earlier, and after warming up shes putting black exhaust, expecially when reving above 1500.

                            new carb about a month ago, and its had fuel stabilizer in her for a while, as she isnt my daily driver.

                            carb setting or fuel?

                            im thinking its more of a carb setting of too lean or too rich. pretty sure the needles need to be adjusted.

                            btw, runs fine. no putting, choking, stalling, kicking, anything. just lots of unwanted black smoke

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                            • #15
                              ok, i restricted the air-flow using the choke flap and it just about kills the motor after it sets for 2 seconds

                              the black smoke cures if i run the needles in, you cant see it idling

                              gets worse as i run them out half turns

                              and just for reference, my dads not a carb guy so i never learned, in - more fuel out - less

                              thanks,

                              -matt

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