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| RPM Drop / Poor Acceleration https://www.slantsix.org/forum/viewtopic.php?t=62413 |
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| Author: | Reicher [ Tue May 29, 2018 7:25 am ] |
| Post subject: | RPM Drop / Poor Acceleration |
Hi, I'm new to the forum but used resources here to trouble shoot and research parts and specs here for a while now but I'm having issues with bogging acceleration and the rpm dropping when put in gear to the point the oil light flickers on. Car is a 71 Scamp. Up to this point this is what I've done from what I read online: -disassemble and clean carb -check valve lash while running and adjust. This help my idle quality but valves click louder. -pertronix unit added to remove points and replaced coil. This improved idle quality as well and my radio stopped singing unbearably. -checked vacuum, manifold pulls over 20 at idle. -vacuum advance pulls over 20 when accelerating engine -replaced fuel pump and filter, tank and sending unit aren't old. -new plugs recommended made by NGK What happens and things I've tried to trouble shoot: -black soot comes out of exhaust, was really bad with points and it looks black compared to white snow when I started it this winter -spraying carb cleaner around the ports, throttle and intake and there's no change. -pulling plug boots off does cause engine to shutter -spraying carb cleaner in manifold vacuum port causes rpm to rise, but spraying on snorkle boggs it out. - fuel level is about 28/32 in bowl -turning in idle screw until it bottoms out increases rpm. The screw I removed and replaced was severely tapered from screwing it in too tight. Not sure what else to look at. What do you think it is? I'm at a loss. |
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| Author: | Joshie225 [ Tue May 29, 2018 12:19 pm ] |
| Post subject: | Re: RPM Drop / Poor Acceleration |
Black soot is too much fuel. And turning in the idle mixture screw increasing the engine RPM supports this. I was going to ask if fuel is dribbling from the booster venturi, but this appears to be an idle circuit issue rather than a float/fuel level problem. It's likely that the carburetor is damaged and unrepairable. The construction of the Holley 1920 lends itself to disintegrating within the metering block once the protective plating is compromised. There is no fix for this aside from a good metering block. And your carburetor may also have damage in the idle passage. The Carter BBS doesn't have the same metering block issues as it has brass where the Holley has pot metal. I've also had better luck with the Holley 1945 than the 1920, but not everyone does. |
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| Author: | Reicher [ Tue May 29, 2018 12:29 pm ] |
| Post subject: | Re: RPM Drop / Poor Acceleration |
Does the holley 1945 have the same linkage hookups? I do know this carb was a replacement because the original was in the trunk corroded like crazy. And would that support the drop in RPM when going into gear? I'm wondering if the wire is corroded enough to prevent voltage to flow nicely so I'm going to hook up a gauge to it to see if the pressure is still in spec or not. |
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| Author: | Joshie225 [ Tue May 29, 2018 3:49 pm ] |
| Post subject: | Re: RPM Drop / Poor Acceleration |
Yes, a Holley 1945 will bolt on to your '71. The fuel inlet is on the front instead of the side of the carburetor however. Usually a severe loss of RPM when shifting into gear is a sign of being too lean, but if you can close the needle valve completely then it's not too lean. If the mixture is much too rich from an internal leak slowing the engine down could make it richer still, but this is not a common failure mode. I do not understand your last sentence. |
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| Author: | Reicher [ Tue May 29, 2018 4:00 pm ] |
| Post subject: | Re: RPM Drop / Poor Acceleration |
Last sentence reworded: Im wondering if the oil pressure doesn't actually drop that much and it's partly caused by insufficient voltage travelling through the wire. I bought a oil pressure gauge for it, what range should it be in? |
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| Author: | Reicher [ Tue May 29, 2018 4:06 pm ] |
| Post subject: | Re: RPM Drop / Poor Acceleration |
Update : Drove the car for the first time since the new pertronix , coil, and fuel pump install. Accelerated not bad!!! Oil pressure was ok until the engine started getting hot. Then the light started flickering. Wasn't fully lit though. In park it was ok. When standing being the car you could hear the exhaust pffft a bit but I'm wondering if the car is try to burn off the excess build up. I tried playing with playing with the curb idle and idle mixture screw to see of I could get something working. Was very surprised that the car accelerates not bad now |
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| Author: | Joshie225 [ Wed May 30, 2018 11:12 am ] |
| Post subject: | Re: RPM Drop / Poor Acceleration |
The oil pressure switch is a ground switch. The oil light is provided power whenever the key is on, but it only illuminates when the ground circuit is completed through the oil pressure switch. Ground the wire and the light will come on. Disconnect the wire and the light will not come on. You've been dumping a lot of fuel in the oil so it will be thinner than it should and the idle oil pressure will drop as a result. It's possible the oil pump or bearings are worn, but try an oil change first. And get a healthy carburetor on there or you're going to wipe out the rings and cylinders. |
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| Author: | Reicher [ Wed May 30, 2018 1:52 pm ] |
| Post subject: | Re: RPM Drop / Poor Acceleration |
I never thought about changing the oil. Thanks for the idea. I will for sure do that. |
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