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PostPosted: Mon Apr 08, 2019 7:44 pm 
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4 BBL ''Hyper-Pak''

Joined: Wed Mar 28, 2018 10:52 pm
Posts: 44
Car Model*: 1975 Plymouth Duster
So, after getting my donor slant 6 running seemingly decently, I decided to flush the trans today. Backed it out of the garage just fine, set the back end on jackstands, disconnected the trans cooler input line, started it up, and...

Won't stay running, barely idles at the best of times. At this point I have no idea what the hell is going on with this engine. It revs absolutely fine off the accelerator pump but the second it gets back on the idle circuit it's back to the land of sputtering and sadness. I took the carb off twice today, blew it out with air, took the bowl off, blew the passages out from there, no improvements. Had to push it back into the garage with the other car. Heard it might be the coil going out, so I tried another coil. No change. I know the gas is good, the fuel filter is new, the distributor cap and rotor are good, the spark plugs are all plugged in, etc. etc. ad infinitum. Idle mix screw on the carb (holley 1920) does basically nothing.


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PostPosted: Mon Apr 08, 2019 8:46 pm 
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Supercharged
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Joined: Sun Nov 03, 2002 9:20 pm
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Location: Fircrest, WA
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Vacuum leaks?


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PostPosted: Mon Apr 08, 2019 10:37 pm 
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4 BBL ''Hyper-Pak''

Joined: Wed Mar 28, 2018 10:52 pm
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Car Model*: 1975 Plymouth Duster
Reed wrote:
Vacuum leaks?


Don't think so, choking it just kills it faster.


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PostPosted: Tue Apr 09, 2019 8:04 am 
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Supercharged
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Location: Fircrest, WA
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Has the carburetor been rebuilt? Have you verified base timing and the operation of the mechanical and vacuum advance systems in the distributor? Does engine temperature make any difference in the symptoms? Is this a stock motor? Have you adjusted the valves?


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PostPosted: Wed Apr 10, 2019 12:35 pm 
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4 BBL ''Hyper-Pak''

Joined: Wed Mar 28, 2018 10:52 pm
Posts: 44
Car Model*: 1975 Plymouth Duster
Reed wrote:
Has the carburetor been rebuilt? Have you verified base timing and the operation of the mechanical and vacuum advance systems in the distributor? Does engine temperature make any difference in the symptoms? Is this a stock motor? Have you adjusted the valves?


Hasn't been rebuilt, but it was going fine last time I used it. It's a stock '76 slant, no difference regarding temp, and I haven't adjusted the valves because a month ago this engine drove twenty miles with zero ticking or other issues.


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PostPosted: Wed Apr 10, 2019 1:46 pm 
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Supercharged
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Location: Fircrest, WA
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How does it run with the car flat on the ground and the rear axle not on jack stands?


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PostPosted: Fri Apr 12, 2019 6:05 pm 
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4 BBL ''Hyper-Pak''

Joined: Sat Jan 03, 2015 7:17 pm
Posts: 30
Location: N. Alabama
Car Model*:
Those carburetors are awful unless you strike gold and find an NOS piece that has never been used or rebuilt. Good luck with that. Find a complete, relatively clean Carter BBS, overhaul it and move on with your life.

P.S.....don't "hear" things. Hearing, and thinking it could be will just waste your time and money.

_________________
1966 Chrysler 300 coupe
1968 Plymouth Valiant 100
1969 Dart Custom 273 V8


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PostPosted: Sat Apr 13, 2019 10:40 am 
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4 BBL ''Hyper-Pak''

Joined: Wed Mar 28, 2018 10:52 pm
Posts: 44
Car Model*: 1975 Plymouth Duster
Alright, think I've got it figured out. The line out of the filter is leaking, which is causing a change in fuel pressure, making the whole thing idle really lumpy. I have no idea how to fix this, though - this is the second filter I've tried and they've both leaked from the same spot. I've changed the position of the hose clamps and it did nothing. Neither engine ever had this problem before.


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PostPosted: Sat Apr 13, 2019 12:58 pm 
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Supercharged
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Location: Fircrest, WA
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Where is the leak coming from? The filter? The rubber line? The metal line? Is it a worn out fitting or a cracked hard line? It shouldn't be hard to trace the leak and repair it.


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PostPosted: Sat Apr 13, 2019 10:05 pm 
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4 BBL ''Hyper-Pak''

Joined: Wed Mar 28, 2018 10:52 pm
Posts: 44
Car Model*: 1975 Plymouth Duster
Reed wrote:
Where is the leak coming from? The filter? The rubber line? The metal line? Is it a worn out fitting or a cracked hard line? It shouldn't be hard to trace the leak and repair it.


Fixed the leak with screw-type hose clamps, rather than the spring clamps that came with the filter. That fixed the leak, but not the problem. Still idles rough and at around 1k RPM. Is it possible that I accidentally blew the jets out of the carb with compressed air?

The idle seems to only go up as the engine warms up.


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PostPosted: Sun Apr 14, 2019 9:34 am 
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Supercharged
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Location: Fircrest, WA
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Can you lower the idle via the idle speed screw, mixture screw, and timing? What is your vacuum at hot idle?


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PostPosted: Sun Apr 14, 2019 10:52 am 
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4 BBL ''Hyper-Pak''

Joined: Wed Mar 28, 2018 10:52 pm
Posts: 44
Car Model*: 1975 Plymouth Duster
Reed wrote:
Can you lower the idle via the idle speed screw, mixture screw, and timing? What is your vacuum at hot idle?


No idea. Hot idle keeps going up as the choke opens. I stopped the engine somewhere around 2k RPM I think? Idle screw does absolutely nothing still.


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PostPosted: Sun Apr 14, 2019 11:01 am 
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Turbo Slant 6
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Location: Houston, TX
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If your idle mixture screws do nothing, your idle circuit is probably clogged. If it was running fine before, you might have recently dislodged some crud that is now blocking a fuel passage. Try Dan's advice:

viewtopic.php?t=59692

_________________
Somehow I ended up owning three 1964 slant six A-bodies. I race one of them.
Escape Velocity Racing


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PostPosted: Sun Apr 14, 2019 10:09 pm 
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4 BBL ''Hyper-Pak''

Joined: Wed Mar 28, 2018 10:52 pm
Posts: 44
Car Model*: 1975 Plymouth Duster
SpaceFrank wrote:
If your idle mixture screws do nothing, your idle circuit is probably clogged. If it was running fine before, you might have recently dislodged some crud that is now blocking a fuel passage. Try Dan's advice:

http://www.slantsix.org/forum/viewtopic.php?t=59692


Will do that, but I have already taken the thing off the engine and blasted it with air three times to clean it out. Confirmed the idle circuit isn't clogged. However, I just noticed that the carb gasket that came on the engine is decently squishy and has molded to the 1920's gasket-facing fuel passages - which are significantly shallower than those on the 1945. I may try another gasket tomorrow if my instructor can't find anything wrong with the carb.


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PostPosted: Mon Apr 15, 2019 2:43 am 
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Turbo Slant 6

Joined: Sat Feb 18, 2006 2:19 pm
Posts: 761
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https://www.jalopyjournal.com/forum/thr ... t.1134518/ Got one of these


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