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Holley DP Accelerator Pump |
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ccowx 
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Joined: Nov/03/2010 Location: Yukon Status: Offline Points: 3510 |
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 Posted: Aug/07/2017 at 7:41pm |
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Go 34 and 37. If it stumbles when you floor it, you still need a bigger shot right off. Once you get crisp response, then see how it is at part throttle driving. My guess is you may find that most or all of any stumble is gone there too. If not, then you can play with the cam profiles.
The size of the squirter will make the difference at first stab, but also what happens is that as squirters get bigger, the duration of the shot will go down because you are emptying the accelerator pump through a bigger hole. Get that first stab at the throttle right and then see if you need to increase the volume of the shot to keep it from running out too soon. That is where the cam lift comes in. Once that is done, then if you still have an issue with part throttle stumble, start looking at a fatter cam profile. I think you will find that once the squirter and cam lift is fixed, the part throttle will be fine. Remember, one thing at a time! Chris |
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Bandana
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Joined: Jul/26/2016 Location: NC Status: Offline Points: 473 |
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Posted: Aug/07/2017 at 8:04pm |
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I think I want to get it out for a drive before going up again on the squirters - if this damn rain ever stops.....
 Sometimes the seat of the pants feel is a better barometer of things. I have the 35/37s and the cam kit now so just need the weather window to give it a try.. One thing I learned, its definitely best to pull the carb to change that front squirt at least. The choke horn on this DP makes it near impossible to do on the car. |
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spiritdude
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Joined: Feb/21/2017 Location: Cocoa, FL Status: Offline Points: 70 |
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Posted: Aug/07/2017 at 9:33pm |
Either that or you could reverse the 35 and 31. When you go to the 37 you may want to get the high-flow screws. If you go bigger than a 37 you will definitely want the high-flow screws and possibly a 50cc pump. |
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spiritdude
1982 Spirit-10.865 @123.16mph |
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ccowx
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Joined: Nov/03/2010 Location: Yukon Status: Offline Points: 3510 |
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Posted: Aug/07/2017 at 9:55pm |
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Seat of the pants is the only way to go. There is not all that much point to just revving it in the garage, since the engine is not under load and will not really react the same. I think you just need to outwait mother nature!
Thanks! Chris |
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one bad rambler
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Joined: Jan/09/2008 Location: On The Island Status: Offline Points: 2007 |
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Posted: Aug/08/2017 at 7:22pm |
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 68 AMX 390 4 Speed,68 American,64 American 2 Door Wagon Altered Wheelbase,78 Concord Build 360,727,8.8
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Bandana
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Joined: Jul/26/2016 Location: NC Status: Offline Points: 473 |
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Posted: Aug/19/2017 at 7:35pm |
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Latest update - been awhile since I had the car out to see how it drives. Initial performance seemed better. Had pretty good acceleration without stumbles, good power. Drove it into town and the few times I punched it it pulled nice and smooth. Drove around for about 45 minutes then as I was making a turn in town with a slight acceleration the damn thing stumbled bad - bad to the point it stalled out. Restarted it while still rolling and she was quite unsteady for a minute or so until it finally stabilized. Did it a couple more times before I got on the highway and eased it back home..... Really frustrating!!! The work on the accelerator pump / squirts seemed to improve my off idle performance but I'm beginning to think the problem may be something that manifests itself after the engine gets good and warmed up as this seems to be a pattern. I looked at my fuel filter bowel (clear) when I got home and did not notice any fuel boiling where I might be getting vapor lock. Fuel line run does not put it near the exhaust or where it would really get hot. It does feel like I'm getting starved of fuel when it happens. I'm beginning to wonder if there is an issue with the fuel delivery system someplace from the tank pickup up to the pressure regulator??? I do note that the fuel tank builds a fair amount of pressure after being driven like this - really pisses off some air when it cracked open.
The fuel pump is a 110gpm Mallory which should be plenty of flow for this motor (435 hp with no return line) - unless the pump is not putting out as it should. The fuel line is the OEM 5/16" rubber line from the tank to the pump and up to the carb. I'd like to see something bigger - especially from the tank to the pump but not sure if this is causing a starvation problem. The pump inlet is an inch or so above the bottom of the fuel tank. While I know it would be better to be a few inches below the tank it doesn't seem that bad? No idea what the pickup / filter look like inside the tanks. Not sure where to go right now. I'm beginning to think the bigger issue is fuel delivery and not carb adjustments - although the adjustments did help. Over this winter I am definitely going to make some changes to the fuel delivery system. I have a new fuel tank that I wanted to install last year but didn't get around to it. Obviously I can check and replace as needed, the pickup and sock filter at that time. I would like to increase the size of the outlet from the tank to 3/8" at that point and also see if I can relocate that fuel pump to get it a bit lower. Might even consider changing out the entire fuel line to 3/8" up to the regulator. Anyone have any thoughts or ideas for the interim??? |
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ccowx
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Joined: Nov/03/2010 Location: Yukon Status: Offline Points: 3510 |
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Posted: Aug/19/2017 at 8:31pm |
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I am not hearing a fuel delivery problem. The fact that it seems to be having issues long after it is warmed up would indicate to me that there may be either a choke issue or something obscure like a fuel pump diaphragm that is getting too soft and not working when hot. That is assuming it is fuel related at all, see below.
If it was an issue of fuel delivery then it would do it after an extended period of high rpm running. This sounds like it did it with mild acceleration after a period of mid range driving. You have mentioned fuel delivery several times and I have to say that unless I am missing something, your description does not sound like it at all to me. In a car with a carb there is float bowls that hold enough fuel to run for a few second to a minute with no fuel pump whatsoever. Delivery issues like that don't show up instantly but after a few minutes of running at high demand. Your pump and other equipment should be able to support the power and set up you have, unless something is wrong with them. Another thought to consider is that most fuel issues are electrical. That is a tongue in cheek way of saying that people always want to blame the fuel system for things that more often than not end up being electrical/ignition. This is the voice of personal experience here! Your issue after extended warm up could well be a coil, which tends to malfunction when hot but work better cold. Similar issues can effect condensors, ballast resistors, wires and other electrical components. Quite seriously, 75% of misdiagnosed fuel issues turn out to be electrical. I would check that asap. In short, if you have the car warmed up for ten minutes and she is running well with good throttle response and all that, you have nailed the accelerator pumps and related stuff. If it gets really warm and THEN craps out, I would suggest choke first, fuel pump second, mostly because you are already there and they are easy, and then I would move onto the rest of the electrical system. Swapping coils might be just the ticket, for example. Chris |
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68-73 amx
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Joined: Jun/14/2012 Location: Pa. Status: Offline Points: 532 |
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Posted: Aug/19/2017 at 8:54pm |
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Extended float tubes in top of bowl ? You mentioned stalling around turn , how is it after a sudden stop ?
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Bandana
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Joined: Jul/26/2016 Location: NC Status: Offline Points: 473 |
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Posted: Aug/20/2017 at 11:42am |
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I don't think cornering is related. It just happened after I made a turn yesterday. I'm struggling on the electrical thoughts. This is a full MSD ignition - 6AL, distributor, coil and wires. While the components were all installed way back in 2003, they have very low miles on them. I recently ohmed the plug wires and they all were very close to each other. I guess its possible that there is something going on with the coil but I don't know...
I think one night this week I need to get up under the rear and take a look at the fuel pump and lines to see if there is anything obvious there. I do smell gas all the time.. BTW, I think these Mallory pumps are gear pumps so no diaphragm. Wonder if it could be the needle & seat in the carb sticking?? |
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Bandana
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Joined: Jul/26/2016 Location: NC Status: Offline Points: 473 |
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Posted: Aug/20/2017 at 11:59am |
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Interesting, I had the date on the MSD components from receipts I got with the car. Just went back and looked and I have a 6A box not an 6AL, pre digital? Also note the box was bought in 2008 while all the other items are from 2003.
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Bandana wrote: