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| Trying to diagnose a rough idle issue https://www.slantsix.org/forum/viewtopic.php?t=65185 |
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| Author: | briwill [ Tue Aug 04, 2020 12:58 pm ] |
| Post subject: | Trying to diagnose a rough idle issue |
Just got my newly built engine running. Compression is roughly 8.5:1. New electronic ignition, tested wires, NGK ZFR5N plugs, Weber 38 adjusted to best lean idle and timing at initial +15 degrees. Also snugged down all intake bolts and does not appear to have any vacuum leaks. Runs and accelerates great but stumbles a bit when idling. Really bad in gear. Has an Oregon 2106 cam, adjusted lash to .015 IN/EX per cam card while on the stand. Maybe too tight? Other thoughts? |
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| Author: | matv91 [ Tue Aug 04, 2020 1:25 pm ] |
| Post subject: | Re: Trying to diagnose a rough idle issue |
http://www.redlineweber.com/html/Tech/3 ... unning.htm |
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| Author: | briwill [ Tue Aug 04, 2020 1:31 pm ] |
| Post subject: | Re: Trying to diagnose a rough idle issue |
Quote: http://www.redlineweber.com/html/Tech/38_dgas_tunning.htm
Thanks but I already went through that procedure.
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| Author: | matv91 [ Tue Aug 04, 2020 1:54 pm ] |
| Post subject: | Re: Other thoughts |
Next up is valve adjustment. With face shield looking down carb venturi any fuel dripping? Hand over top of carb to reduce air flow any change? Vacuum advance ported or manifold or try disconnected. |
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| Author: | briwill [ Tue Aug 04, 2020 2:36 pm ] |
| Post subject: | Re: Other thoughts |
Quote: Next up is valve adjustment. With face shield looking down carb venturi any fuel dripping? Hand over top of carb to reduce air flow any change? Vacuum advance ported or manifold or try disconnected.
Yeah, Plan to check plugs, compression check and valve adjustment tonight to rule out any mechanical issues. Runs good otherwise, just really rough idle. Also verified that the timing mark is correct when building the engine. Still idles rough at 10, 15 and 20 degrees advance. Pulls harder at 20 but currently 10-15 seems to idle best.
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| Author: | Joshie225 [ Tue Aug 04, 2020 3:24 pm ] |
| Post subject: | Re: Trying to diagnose a rough idle issue |
Check thoroughly that the carburetor adapter is not leaking air. |
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| Author: | matv91 [ Tue Aug 04, 2020 4:53 pm ] |
| Post subject: | Re: Trying to diagnose a rough idle issue |
Hope it some thing easy, read some of your old posts. GM module wires to distributor pick-up coil might need to be swapped at module. |
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| Author: | SlantSixDan [ Tue Aug 04, 2020 7:14 pm ] |
| Post subject: | Re: Trying to diagnose a rough idle issue |
You might try backing off your valve adjustments to 0.020"/0.020" (hot and running per valve adjustment procedure) and see if it does anything for your rough idle. If not, it's easy enough to change back. But I suspect your problem is in the carburetion department. 15° BTDC is a lot of initial timing—could easily be too much. Some time and effort or money invested in dialling-in your advance curves so everything's happy at 5° to 7° BTDC will pay back handsomely. Talk to DusterIdiot on here if you're not up for recurving you distributor on your own. |
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| Author: | briwill [ Wed Aug 05, 2020 7:33 am ] |
| Post subject: | Re: Trying to diagnose a rough idle issue |
Quote: Check thoroughly that the carburetor adapter is not leaking air.
Thanks. Don't think it's a vacuum leak. I was very careful putting everything together and tightening. Sprayed water around seams and didn't hear or see any sucking. Adjusted valves again and is a bit better.
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| Author: | Joshie225 [ Wed Aug 05, 2020 8:04 am ] |
| Post subject: | Re: Trying to diagnose a rough idle issue |
Quote: Quote: Check thoroughly that the carburetor adapter is not leaking air.
Thanks. Don't think it's a vacuum leak. I was very careful putting everything together and tightening. Sprayed water around seams and didn't hear or see any sucking. Adjusted valves again and is a bit better. |
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| Author: | briwill [ Sat Aug 08, 2020 10:39 am ] |
| Post subject: | Re: Trying to diagnose a rough idle issue |
Set timing around 10 degrees and Double checked adapter plates and all seems good. Discovered some moisture around the super six egr block off plate so I removed. Fuel dribbled out of this hole. Has anyone had this issue? Is it common to block off this hole inside the intake? Never saw a mention of this when researching the intake. Installed a new gasket and car still idles rough but otherwise runs good. |
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| Author: | briwill [ Mon Aug 10, 2020 9:15 am ] |
| Post subject: | Re: Trying to diagnose a rough idle issue |
Really surprised no one has any feedback about gas pooling in the super six EGR area. |
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| Author: | volaredon [ Mon Aug 10, 2020 9:57 am ] |
| Post subject: | Re: Trying to diagnose a rough idle issue |
I have a super 6 intake that I have painted and am getting ready to put into my kids truck, I tapped out the hole below the carb and put in a pipe plug with plenty of red loctite. Planning to do the same thing with the other one I have sitting here for my truck. On the 1st one I discovered that it appears to have been already tapped but I had a little difficulty getting the tap started because of carbon built up within those threads. |
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| Author: | SlantSixDan [ Mon Aug 10, 2020 11:04 am ] |
| Post subject: | Re: Trying to diagnose a rough idle issue |
Quote: Really surprised no one has any feedback about gas pooling in the super six EGR area.
There were gazillions of '73-up Slant-6 intake manifolds in service with those EGR passages—both with and without functional EGR systems, both from the factory and as modified. If fuel pooling were practically a problem, it would be a known thing. It's not. Keep in mind the inside of that hole area you're worrying about is the hottest part of the intake plenum; any liquid fuel that might find its way in there would be flash-vapourised immediately by the heat. And unless the carburetor is literally raining liquid gasoline into the intake (in which case there are problems to fix), not much fuel is going to find its way into that hole/pocket area—think about the flowpath through the plenum; you've got a dead-end hole there.A small amount of liquid fuel might collect in the hole under certain conditions after engine shutdown. Don't get sidetracked. Look elsewhere for your rough-idle issue. |
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| Author: | briwill [ Mon Aug 10, 2020 11:40 am ] |
| Post subject: | Re: Trying to diagnose a rough idle issue |
Thanks. Didn't think that was the rough idle cause but wanted to confirm that was a non-issue. Double checking the float level and looking at the plugs later this week. |
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