Plug pvc hose, got power brakes?,plug that too. Tighten bowl cover screws,air leak into idle circuit. Block off air to idle air bleed.
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| RPM diagnosis https://www.slantsix.org/forum/viewtopic.php?t=64784 |
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| Author: | davidrad [ Mon Apr 20, 2020 9:28 pm ] |
| Post subject: | RPM diagnosis |
So my 70 dart with a 225 is driving me a bit nuts. My cold idle is fine, and I can set my normal idle speed with no load. If input it in gear it dies. Once warm the RPM continues to go up. If I go for a drive I'm riding the brakes to keep the speed below about 35. When I stop and put it in park it goes to around 3k RPM. RPM doesn't change when I spray around looking for vacuum leaks and when I cover the Holley 1945 carb it dies. I bought it out of a field a few years ago and have been working on rust repair. That's done so now I'm trying to get it running . Where should I look next. Sloppy timing chain, valve seats and seals. |
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| Author: | slantzilla [ Tue Apr 21, 2020 11:33 am ] |
| Post subject: | Re: RPM diagnosis |
Sounds to me like the choke linkage is out of adjustment and it is not coming off the fast idle cam. |
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| Author: | davidrad [ Tue Apr 21, 2020 1:55 pm ] |
| Post subject: | Re: RPM diagnosis |
Nope, the choke is wide open and the cam is sitting there free. |
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| Author: | cpslntdchrg [ Tue Apr 21, 2020 2:36 pm ] |
| Post subject: | Re: RPM diagnosis |
It sounded the same to me. I know you answered the question once, but can you do this (and my apologies if this bothers you): a) When car is cold, please press fully the accelerator once, without starting the car (you're setting the choke) b) Now, if you remove the lid of the air filter, can you see the choke closed (The choke flapper closed, blocking the carb entrance). That is the normal starting condition. c) You can start the engine, the choke is keeping the mixture rich. As the car warms up a thermostatic sensor located in the exhaust manifold heats, and pulls a lever that opens the choke. Is that thermostat there? Choke moving? d) You can dislodge the choke if you accelerate while warming up, if the thermostat is warm enough. I'll post pictures. PD: I added the pictures, check: https://1drv.ms/u/s!Av8-aQGlkBg2g2k_byd ... W?e=qzxHqh The one with the throat open is before setting the choke/normal operating condition, the other shows how the flapper should close when in a cold car you give one full press to the accelerator, car should start with the choke in that position. If you can see, there is a yellowish box over the exhaust multiple connected with a wire to the carb, that is the thermostat. By the way, that carburetor is a Holley 1920, from a 1969 slant. Not looking exactly like yours, but the idea is visible. |
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| Author: | slantzilla [ Tue Apr 21, 2020 2:43 pm ] |
| Post subject: | Re: RPM diagnosis |
Is the throttle cable too short? |
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| Author: | matv91 [ Tue Apr 21, 2020 3:42 pm ] |
| Post subject: | Re: RPM diagnosis |
https://www.slantsix.org/forum/viewtopi ... 7&start=30 Disconnect throttle, throttle spring may be broken. There are pictures half way down that page. |
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| Author: | davidrad [ Tue Apr 21, 2020 4:34 pm ] |
| Post subject: | Re: RPM diagnosis |
Thank you everyone for the time and effort. I have an electric choke, I can sit and watch the flap open over about 5 minutes during warm up. It comes off the cam and goes to still a high idle. If input the hot idle screw lower than about 1200 car isles for a second and dies. If I keep it above 1300 it runs great. After a short drive when I put it in park the idle goes to 3k. Throttle cable releases and return spring has done it's job and sitting on the hot idle screw. It's got to be vacuum. Everything plugged in the carb except the pcv and choke pull off. Can't detect an intake leak or can base leak and when I cover the airhorn the car dies. I kind of wondering if valve seats and seals are the culprit. Confused. |
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| Author: | drgonzo [ Tue Apr 21, 2020 4:50 pm ] |
| Post subject: | Re: RPM diagnosis |
Is the tach set for a 6 cylinder engine? |
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| Author: | Joshie225 [ Tue Apr 21, 2020 5:02 pm ] |
| Post subject: | Re: RPM diagnosis |
Sounds like you have a Holley 1920 with a dead idle circuit. |
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| Author: | matv91 [ Tue Apr 21, 2020 7:00 pm ] |
| Post subject: | Re: RPM diagnosis |
Plug pvc hose, got power brakes?,plug that too. Tighten bowl cover screws,air leak into idle circuit. Block off air to idle air bleed.
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| Author: | matv91 [ Tue Apr 21, 2020 7:01 pm ] |
| Post subject: | Re: RPM diagnosis |
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| Author: | matv91 [ Tue Apr 21, 2020 7:14 pm ] |
| Post subject: | Re: RPM diagnosis |
Blocking that hole will increase vacuum and make idle richer, good place for carb cleaner too. After hole is blocked see if it will idle slower then,may need mixture adjustment. |
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| Author: | matv91 [ Tue Apr 21, 2020 7:25 pm ] |
| Post subject: | Re: RPM diagnosis |
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| Author: | matv91 [ Tue Apr 21, 2020 7:34 pm ] |
| Post subject: | Re: RPM diagnosis |
To the left of yellow arrow is idle down channel, to the right is idle feed tube probably clogged up |
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| Author: | matv91 [ Tue Apr 21, 2020 7:36 pm ] |
| Post subject: | Re: RPM diagnosis |
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