I've never had a 1920 run correctly, even after rebuilding them and such. Heard the power valve or some plastic piece inside goes bad after awhile and there's nothing you can do. Supersix that Chally and never look back. I don't miss the 1920
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| 225 falls flat if I go WOT https://slantsix.org/forum/viewtopic.php?t=56737 |
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| Author: | 67Charger [ Wed Dec 17, 2014 10:55 am ] |
| Post subject: | 225 falls flat if I go WOT |
I have the stock 225 in my '71 Challenger and it has an annoying habit. If I increase the throttle too far past the cruising throttle position for any given RPM/LOAD, the engine falls flat and stays there. If I roll the throttle as the RPMs increase, it will keep pulling. Holley 1920, very clean, new needle/seat twice, wet fuel level correct, #55 jet, choke open, 8° initial/29° total plus vacuum advance (unknown pod, believe it said 11X), new fuel filter, 3 psi fuel pressure. Example: 45 MPH at 25% throttle, mash the gas, it will pull for a split second then sputter and misfire. It will continue to run this way until I back off the throttle to say 50%, then it will start pulling. I can continue to stay just ahead of the rpm and with will pull through 90MPH , but only to about 80% throttle. 100% is just no go.. 75 MPH, sitting at 50% throttle, If I pass about 75% it falls flat and cannot accellerate. If I back off and keep it 10% ahead of cruise position, it will pull fine through top end, 90 MPH and 80% throttle. It almost seems like it wants more ignition advance and backing off the throttle pulls higher vacuum and adds some from the pod. Also, it could be starving for fuel using the higher vacuum to pull more fuel through the booster. Looking for direction. |
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| Author: | wjajr [ Wed Dec 17, 2014 6:39 pm ] |
| Post subject: | |
Accelerator pump shot may not be correct duration or volume for whatever reason; bad pump, wrong squitter, crap stuck in internal passages... Take a look-see down the carb with air cleaner removed, choke butterfly wide open, with engine not running then rotate throttle wide open, and see how the fuel flow from accelerator pump acts. Example: Does flow start strong, than piddle or stop just after opening throttle? Is weak throughout entire throttle opening? |
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| Author: | DusterIdiot [ Wed Dec 17, 2014 7:29 pm ] |
| Post subject: | And... |
I would also check for vacc. leaks or a blown vacc adv. pod that will lean things out.... Are you running an EI set up? (it kind of sounds like it since the points distributors only go up to a 9.5x on the vacc. adv. pod arms...) Once you see if the acc. pump is the culprit or a vacc. leak...next up would be to increase your jet, a #55 is a bit lean for a 225 and a heavier car like the E-body...bump it up to #56 or #57 if you are doing a rebuild. |
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| Author: | Overbored [ Wed Dec 17, 2014 9:32 pm ] |
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I had the same problem, check your fuel pump,to much demand at WOT,worked if accelerating slowly. I also had a old rubber fuel line collapse at WOT on my` race car, couldn't make it happen in the shop, drove me crazy. |
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| Author: | 67Charger [ Wed Dec 17, 2014 11:54 pm ] |
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Just checked, vacuum advance is not leaking. Yes, it is EI using an orange box. Will check acc pump tomorrow. Have to drive it to work, it is late, and I get up really early. |
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| Author: | cpslntdchrg [ Thu Dec 18, 2014 6:39 am ] |
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3 psi fuel pressure is the lower side of the 1969 service manual reccomended fuel pressure (Fuel pump pressure range: 3.5 to 5 psi, at 650 RPM, just mentioned in a recent thread). Check the easy stuff first, but it might be the pump (check with a different fuel pressure gauge if possible, just to be sure). |
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| Author: | nm9stheham [ Thu Dec 18, 2014 7:16 am ] |
| Post subject: | |
I would be checking the economizer valve for being stuck, or the spring loaded jet and tube from it to the main jet area being clogged/blocked. The conditions you describe are that the carb won't deliver fuel above a certain level of flow as you push the throttle down and the manifold vacuum drops; that is when the economizer valve (power valve) should open and add fuel to the main well. When you roll onto the throttle as RPM's increase the vacuum is staying higher (and the airflow limited) and the economizer never would have to open. When you get to near WOT, the flow wil be high and vacuum will be low regardless of RPM and the economizer (power) valve always needs to be open. This does not sound like the accel pump; you would be having issues just coming off idle, etc. And agreed, 3 psi fuel seems to be too low. It is hard to say what it is doing when not at idle; did you increase engine RPM's whiel testing pressure to see if it went up at all? |
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| Author: | Jester [ Sun Dec 28, 2014 10:54 am ] |
| Post subject: | |
I've never had a 1920 run correctly, even after rebuilding them and such. Heard the power valve or some plastic piece inside goes bad after awhile and there's nothing you can do. Supersix that Chally and never look back. I don't miss the 1920
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| Author: | 67Charger [ Sun Dec 28, 2014 12:13 pm ] |
| Post subject: | |
Picked up a super 6 setup. Working on putting together a good BBD for it. I am still looking at the 1920 in the meantine. |
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| Author: | nm9stheham [ Sun Dec 28, 2014 4:28 pm ] |
| Post subject: | |
No problems with my 1920..... even after a rebuild. Older model, list 24xx range. Some good tips are available for rebuilding them on the 2 video's for the 1920 at the Mike's Carburetors site. Did you ever check the fuel pressure again? If it is still on the car, have you tried taking vacuum readings at idle and also when it is acting good versus acting up? |
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| Author: | SlantSixDan [ Sun Dec 28, 2014 5:23 pm ] |
| Post subject: | |
Your problem is almost certainly not being caused by "insufficient" fuel pressure; 3 pounds is plenty (much higher makes problems), so don't chase your tail on that. As others have said, the problem is probably in the carburetor, probably in the "Economizer" (power valve) system. You may or may not be able to get this carb working well; the 1920s eventually hit (hard) the end of their useful life with problems like this that defy all attempts at remediation. The videos at Mikes Carb are about half a notch above useless. Carburetor operation and repair manuals and links to training movies and carb repair/modification threads are posted here for free download. |
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