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Car Forum / Driving, Maintenance, Tuning / Maintenance and Repair / January 2006Carb Flat Spot
When I press the gas pedal slightly (1/2 inch or so) from a stop, the car lunges like the accelerator pump is working ok but it then boggs down. If you stomp it it goes just fine. I assume there is something wrong with the transfer from idle circuit to the run circuit of the carb. This is an Edelbrock 1406 on a 351c in a 1970 Cougar. Vacuum advance is plugged into the ported vacuum. A little history, the car had a Holly 600cmf on it and ran fine but was flooding easily and running ritch. Tried to adjust the float but turning the screws didn't make any difference in the level. Pulled the needle out and the orings were gone and just some black hard stuff was left. Put in a kit and had a terrible flat spot just off idle (first time rebuilding one) and gas mileage was like 9. Bought this Edelbrock no ebay so maybe it has a problem. Any suggestions appreciated. Bobby bbusselman at hotmail dot com >When I press the gas pedal slightly (1/2 inch or so) from a stop, the car >lunges like the accelerator pump is working ok but it then boggs down. If [quoted text clipped - 13 lines] >Bobby >bbusselman at hotmail dot com Is the distributor advance working? I have seen that problem where the vacuum advance was ok and it would respond seemingly as it should but, when the throttle was opened a bit more dropping the vacuum to the advancer, it would go flat. I would look for either a bad vacuum advance or a frozen mechanical advance if you have had a similar problem with 2 carbs. The 351C with 4V heads neads all the advance it can get off idle without knocking to avoid stumbling and falling flat on it's face. Lugnut > >When I press the gas pedal slightly (1/2 inch or so) from a stop, the car > >lunges like the accelerator pump is working ok but it then boggs down. If [quoted text clipped - 25 lines] > > Lugnut Lugnut, Thanks for the advice. I was thinking about playing with base timing this weekend so this adds motivation. I know the vacuum advance is working at least somewhat as I did move the hose to the fulltime vacuum port and idle jumps. I reset idle and drove it like that for a couple of days and I think it made it worse so I put it back on ported vacuum. Also, the heads are 2v so it has the smaller ports. > When I press the gas pedal slightly (1/2 inch or so) from a stop, the car > lunges like the accelerator pump is working ok but it then boggs down. [quoted text clipped - 17 lines] > Bobby > bbusselman at hotmail dot com Is it for sale? If so how much and where is it? Bob > > When I press the gas pedal slightly (1/2 inch or so) from a stop, the car > > lunges like the accelerator pump is working ok but it then boggs down. [quoted text clipped - 20 lines] > Is it for sale? If so how much and where is it? > Bob It might be... Long story but I was looking for a Cutlass convertible when I bought this Cougar. I found one a couple of years ago and never did anything with either and wife wants driveway/garage space back so need to get rid of one. Both are 1970 convertibles. Cutlass needs more work and haven't had time to work on it so put both up for sale and sell whichever got the best offer. Almost sold the Cougar and wife says "but I like that one better" so now trying to pick one and put the other up for sale. Neither is offically for sale right now but details and pictures can be seen at http://mysite.verizon.net/blondechick/for_sale.htm Located in Rowlett Texas (a Dallas suburb to the East, just east of Arland... I mean Garland) Thanks for asking. >> > When I press the gas pedal slightly (1/2 inch or so) from a stop, the >car [quoted text clipped - 40 lines] > >Thanks for asking. I was just looking at yuor info on the Cougar a/c overpressure problem. My Torino had the same problem. I destroyed several compressors and never got it to cool right for more than a few minutes at a time. I removed the condenser and found a small dent in one of the tubes near the bottom - probably a stone. I used air in the reverse flow direction and blew out a huge quantity of sludge and trash that has accumulated at the restricted spot where it was dented. Since the dent was in a "U" bend in the tube, it could not be repaired. The condensor was replaced and no further problems. I would never have found the problem w/o pulling the condensor out of the car while I had the radiator out. Lugnut I get your symptoms when my EGR needs cleaning. It gets carboned up so it doesn't seal closed and then appears to open too fast with the acceleration. I don't know if that engine has an EGR, but my test is to unplug and block the line and then try. If the hesitation is gone, time to remove the EGR for a clean. Mike 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's Canadian Off Road Trips Photos: Non members can still view! Jan/06 http://www.imagestation.com/album/pictures.html?id=2115147590 (More Off Road album links at bottom of the view page) > When I press the gas pedal slightly (1/2 inch or so) from a stop, the car > lunges like the accelerator pump is working ok but it then boggs down. If [quoted text clipped - 13 lines] > Bobby > bbusselman at hotmail dot com Mike, thanks for the response but no EGR on this motor. Don't know if it used to be there but it is long gone... > I get your symptoms when my EGR needs cleaning. It gets carboned up so > it doesn't seal closed and then appears to open too fast with the [quoted text clipped - 28 lines] > > Bobby > > bbusselman at hotmail dot com Another sneaky one is a carbon tracked distributor cap. That can take a bright light or direct sun looking inside the cap to nail it. I look for fine, even clear spider web looking markings. Mike > Mike, thanks for the response but no EGR on this motor. Don't know if it > used to be there but it is long gone... [quoted text clipped - 38 lines] > > > Bobby > > > bbusselman at hotmail dot com > When I press the gas pedal slightly (1/2 inch or so) from a stop, the car > lunges like the accelerator pump is working ok but it then boggs down. If [quoted text clipped - 13 lines] > Bobby > bbusselman at hotmail dot com It sounds like you need one or two changes, or both. First, try getting metering rods with a richer "power" step which will even out the flat-spot by enriching the mixture on accelration until vacuum builds up. Second, you could try simply putting stiffer return springs on the metering rods so that they will stay on their "rich" step until the vacuum level comes up higher. You could also try adjusting the accelrator for a longer shot, or putting on a smaller squirter cluster to lengthen the pump shot a bit. The trade off there is that too small and you'll get a flat spot immediately on stepping on the gas. Thanks Steve, I've never opened up an Edelbrock yet but might do that soon so have to think about this some. Since it ran well for 10 years on the Holly, I'm pretty sure it has to do with the carb so I may either get a book on this carb or just buy a new one. The ebay one one could have a problem but it is an improvement over my kitted Holley. I did mess with the timing as I installed another distributor for awhile (electronic) but pulled it as it turned out to be part of the problem. I may just go back to the basics (I reinstalled the ponits/condensor disributor) and get it set up to the best spot. > > When I press the gas pedal slightly (1/2 inch or so) from a stop, the car > > lunges like the accelerator pump is working ok but it then boggs down. If [quoted text clipped - 28 lines] > The trade off there is that too small and you'll get a flat spot > immediately on stepping on the gas. > Thanks Steve, > > I've never opened up an Edelbrock yet but might do that soon so have to > think about this some. Since it ran well for 10 years on the Holly, I'm > pretty sure it has to do with the carb so I may either get a book on this > carb or just buy a new one. "Modifying and Super-Tuning Carter Carburetors" by Dave Emanuel is excellent. The Edelbrock is a re-branded Carter AFB. > The ebay one one could have a problem but it is > an improvement over my kitted Holley. I doubt that it has a "problem," it was probably tuned for an engine that has different characteristics than yours. |
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