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01-20-2025, 10:40 PM | #1 |
Registered User
Join Date: Nov 2022
Location: Willits, CA
Posts: 27
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Engine troubles (carb)
I have a 70' K20 with a Blueprint 383 stroker and Holley 750 carb. Truck was running fine, and then recently, i can't keep it running. I pump the gas pedal twice, crank it over and she fires right up, i then keep the RPM's at 1500 or 2000 to let it warm up. If i let the RPMs drop below 1500 she'll start to stall out and i can't catch it, or stop it by giving more throttle. Then once she's stalled, she won't start again. Just cranks. I've tried keeping it floored, pumping the gas, you name it, won't start back up. First thought was a plugged needle thing thats below the float bowl adjustment screw, so i pulled that, blew it out and reinstalled. No luck. Then i thought maybe a vacuum leak, so i checked all my vacuum hoses, and they all look good. If the truck would stay running i'd try spraying starter fluid around the base of the carb or near vacuum lines to double confirm no leaks, but i can't keep her running. Fuel filter is full of fuel. Both sight windows for the front and rear float bowls have fuel. I'm kinda baffled. Thoughts?
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01-20-2025, 11:09 PM | #2 |
Post Whore
Join Date: Feb 2016
Location: Portland Oregon
Posts: 11,475
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Re: Engine troubles (carb)
What is the choke doing?
There is a test that can be done but it has a dangerous element to it. Put some good leather gloves on and when truck is running hold your hands over the carburetor. Your trying to slowly choke the air off to the engine. If you can block air off and get the engine to run better then the engine is running lean or getting too much air. Could be a vacuum leak or a bad gasket in the carburetor or other internal carburetor issue. If the problem gets worse then the engine is getting too much fuel. Could be stuck/sunken float, bad gasket in the carburetor, too much fuel pressure or several other things. If this only makes the engine mildly worse then I would dive into the ignition system. As they say 90% of all carburetor problems are electrical. DO THIS AT YOUR OWN RISK! Carburetor backfires can cause burns. Good luck and keep us posted.
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Thanks to Bob and Jeanie and everyone else at Superior Performance for all their great help. RIP Bob Parks. 1967 Burban (the WMB),1988 S10 Blazer (the Stink10 II),1969 GTO (the Goat), 1970 Javelin, 1952 F2 Ford OHC six 4X4, 29 Model A, 72 Firebird (the DBP Bird). 85 Alfa Romeo If it breaks I didn't want it in the first place The WMB repair thread http://67-72chevytrucks.com/vboard/s...d.php?t=698377 |
01-20-2025, 11:28 PM | #3 | |
Registered User
Join Date: Nov 2022
Location: Willits, CA
Posts: 27
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Re: Engine troubles (carb)
Quote:
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01-20-2025, 11:54 PM | #4 | |
Senior Member
Join Date: Jun 2022
Location: San Ramon,CA
Posts: 638
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Re: Engine troubles (carb)
Cliff's "tip-in" test is a less flame-worthy version of the above procedure
I'm not sure from your description whether that's where the problem lies, but it might help to rule some things out. Mine(which isn't a Holley) runs as you describe on a cold day because I currently have no choke, BUT it will restart Quote:
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1970 C10 Custom longbed 350/350 Code:
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01-20-2025, 11:56 PM | #5 |
Senior Member
Join Date: Jun 2022
Location: San Ramon,CA
Posts: 638
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Re: Engine troubles (carb)
Maybe get a mirror over the carb and see if your accelerator pump is doing its thing
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1970 C10 Custom longbed 350/350 Code:
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01-21-2025, 09:58 AM | #6 |
State of Confusion!
Join Date: Jul 2002
Location: Gulfport, MS USA
Posts: 47,324
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Re: Engine troubles (carb)
First thing I normally do with something like you describe is check/change the fuel filter. If it is a see thru one, see if any trash is in your filter that may indicate something got thru and clogged something.. I also spray carb cleaner down breather to see if it clears up everything. IF it starts and still sounds bad I look and spray carb cleaner to check for vacuum leaks. If that didn't clear me up I start going deeper into carb and/or ignition.
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Bill 1970 Chevy Custom/10 LWB Fleetside 2010 Toyota Tacoma PreRunner SR5 Double Cab - DD Member of Louisiana Classic Truck Club (LCTC) Bill's Gallery Life isn't tied with a bow, but it's still a gift. Live simply. Love generously. Care deeply. Speak kindly. Leave the rest to God! |
01-21-2025, 11:23 AM | #7 |
Registered User
Join Date: Apr 2022
Location: Medina, Ohio
Posts: 232
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Re: Engine troubles (carb)
Choke settings or Vacuum Leaks, most common. Did UT occur, when Temps drop.
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01-21-2025, 11:51 AM | #8 |
The Older Generation
Join Date: Aug 2006
Location: Montezuma, Iowa
Posts: 25,896
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Re: Engine troubles (carb)
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If you have never replaced the sock filter on the fuel pickup tube, in the tank, That would be one of my first suspected problems. They do disintegrate and plug up the tube or filter. https://americanclassic.com/1967-87-...3-8-sku-23-598 They just slip on the end of the fuel pickup tube in the tank. Any parts vendor should have them. If you think it might be flooding hold the accelerator pedal all theway to the floor when you are trying to re-start it.
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Leon Locksmith, Specializing In Antique Trucks, Automobiles, & Motorcycles (My Dually Pickup Project Thread) http://67-72chevytrucks.com/vboard/s...d.php?t=829820 - Last edited by LockDoc; 01-21-2025 at 04:22 PM. |
01-21-2025, 01:15 PM | #9 |
Registered User
Join Date: Apr 2010
Location: So Cal
Posts: 1,472
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Re: Engine troubles (carb)
If it's a Holley and running rich, did you check the power valve. Power valve could be blown, loose or bad gasket.
A power valve problem can happen without warning.
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'67 GMC 2500, 292, 4spd, AC |
01-22-2025, 11:15 PM | #10 |
Registered User
Join Date: May 2016
Location: Waverly, NE
Posts: 408
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Re: Engine troubles (carb)
Yep, blown power valve would be the first thing I'd be checking.
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1965 Malibu SS L79 Restoration Page 1965 Two-Door Wagon Project Progress Page 2006 Pontiac GTO Preservation Project Rich Cummings |
Yesterday, 05:11 PM | #11 |
Registered User
Join Date: Nov 2022
Location: Willits, CA
Posts: 27
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Re: Engine troubles (carb)
I am carb stupid and really don’t know anything about carbs, but i will look into the power valve. Unrelated new issue, i just noticed that my distributor is touching the fire wall. I have never noticed my distributor touching my firewall before and I even recently adjusted my timing, and i would have surely noticed it being that tight then. Also recently put a new Tremec 4050 Trans in, and would have noticed my dist. touching after we buttoned it all back up. So now thats my new issue. I checked motor mounts, trans mounts, bolts that bolt the trans to the bell housing, and the bell housing to the engine, all look fine. I’m really baffled as to while i’m tight at the rear of the engine there now…?!?!!?! FML.
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Yesterday, 09:29 PM | #12 |
Post Whore
Join Date: Feb 2016
Location: Portland Oregon
Posts: 11,475
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Re: Engine troubles (carb)
I would do a complete inspection of the motor mounts and the transmission mount. Some of the motor mounts that are available new are junk! See photos at the bottom of the link.
If the engine shifted and forced the distributor cap into the firewall it may have forced out of position on the distributor causing the rotor to hit the cap which may explain your issues. Pull the distributor cap and inspect it too. http://67-72chevytrucks.com/vboard/s...d.php?t=773824
__________________
Thanks to Bob and Jeanie and everyone else at Superior Performance for all their great help. RIP Bob Parks. 1967 Burban (the WMB),1988 S10 Blazer (the Stink10 II),1969 GTO (the Goat), 1970 Javelin, 1952 F2 Ford OHC six 4X4, 29 Model A, 72 Firebird (the DBP Bird). 85 Alfa Romeo If it breaks I didn't want it in the first place The WMB repair thread http://67-72chevytrucks.com/vboard/s...d.php?t=698377 |
Yesterday, 09:37 PM | #13 | |
Registered User
Join Date: Nov 2022
Location: Willits, CA
Posts: 27
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Re: Engine troubles (carb)
Quote:
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Yesterday, 09:38 PM | #14 |
Registered User
Join Date: Nov 2022
Location: Willits, CA
Posts: 27
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Re: Engine troubles (carb)
oh and the trans mounts are brand new. My brother and i put a new tremec 4050 in just last Nov., and those mounts all are new and looked fine.
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Yesterday, 09:41 PM | #15 |
Registered User
Join Date: Nov 2022
Location: Willits, CA
Posts: 27
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Re: Engine troubles (carb)
Maybe next weekend i’ll try pulling the motor mounts out to give them a look. They seem fine from what i’m able to see….?
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