Motor sputtering and bogging down
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Mountain Pass
Joined: Feb 2015
Posts: 118
Likes: 2
From: Floresville, Tx
Motor sputtering and bogging down
I have a 68 f100 with 302, 3 speed manual. Has brand new carb, intake, timing set (all 3 edelbrock carb is 600 cfm), fuel pump, distributor and coil. Also the fuel system has been completely re done also pulled motor and replaced all seals. The timing is perfect, compression test reads great on all 8 cylinders. The motor will fire up and run strong and is getting plenty of fuel, it idles great but when I try to hit the gas it sputters out. It's hard to get the thing passed 2-2500 rpms in any gear. Any input is much appreciated pulling my hair out over this one.
Fleet Mechanic
Joined: Jul 2006
Posts: 1,346
Likes: 4
From: Rapid City, SoDak
Did it run well before the engine was pulled and seals replaced?
Also, I just went through a heck of a time with my carb doing something similar to me and it was old rubber fuel line getting into the needle and seat even hundreds of miles after I replaced all the rubber lines and blew the metal ones out a few times. How are you sure it's getting plenty of fuel?
Also, I just went through a heck of a time with my carb doing something similar to me and it was old rubber fuel line getting into the needle and seat even hundreds of miles after I replaced all the rubber lines and blew the metal ones out a few times. How are you sure it's getting plenty of fuel?
Thread Starter
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Mountain Pass
Joined: Feb 2015
Posts: 118
Likes: 2
From: Floresville, Tx
Ran the same before I pulled it, figured it was vacuum leak from the old intake. When I pulled it the aluminum was corroded and rough so I figured it wasn't sealing properly. I replaced all the lines before installing the new carb. Seems like it's getting plenty of fuel, strong shot into the carb when I hit the throttle, maybe it's not getting enough under load? Fuel is running about 7-9 psi.
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Mountain Pass
Joined: Feb 2015
Posts: 118
Likes: 2
From: Floresville, Tx
I'll check on that after work maybe even take the pipes off and just run it with the headers. Would it run bad if the cats are out? They definitely rattle, maybe they're clogged up?
Posting Guru
Joined: Mar 2016
Posts: 1,412
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From: Barre Mass
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Post Fiend
Joined: Apr 2002
Posts: 19,311
Likes: 97
From: Waterloo, Iowa
Running points and condenser? Replace with NOS if that's the case. If ignition is good... (check spark at plug)
Put a vacuum gauge on manifold and see what it pulls at factory idle RPM. Should be at least 18" steady at sea level. Tune carburetor idle mixture screws for highest vacuum, this makes a big difference in off idle acceleration. Make sure accelerator pump shot is working correctly, the big gulp of air when hitting throttle means a healthy squirt of extra fuel is required or it will bog.
Put a vacuum gauge on manifold and see what it pulls at factory idle RPM. Should be at least 18" steady at sea level. Tune carburetor idle mixture screws for highest vacuum, this makes a big difference in off idle acceleration. Make sure accelerator pump shot is working correctly, the big gulp of air when hitting throttle means a healthy squirt of extra fuel is required or it will bog.
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Hotshot
Joined: Mar 2013
Posts: 14,255
Likes: 199
From: Phoenix, Az.
Ya gotta fix what you know is broke first. Whatever is rattling replace them. What is causing the rattle could be plugging them at higher RPM. Especially if your PO did indeed install Cats for some unkown reason.
Cargo Master
Joined: Sep 2012
Posts: 3,064
Likes: 39
From: Laramie, WY
Easiest way to see how the carb is working is to install an O2 sensor and readout kit. The carb straight out of the box may not be jetted properly for every possible engine it might get installed on. The idle screws will set the idle mixture but once you open the throttle the jet and needle sizes come into play.
This is the latest version of what I use.
https://www.bmotorsports.com/shop/in...bj3qk3lpd17096
This is the latest version of what I use.
https://www.bmotorsports.com/shop/in...bj3qk3lpd17096
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