Hard starting, cold misfiring
Thread Starter
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Tuned
Joined: Sep 2018
Posts: 364
Likes: 22
From: Eagar, az
Hard starting, cold misfiring
Howdy all. So I have a quick question to bounce off everyone.
Trucks a 1973 2wd f100 with fe390, manual choke, auto trans.
With the change in the weather has come a change in starting/warmup procedure, and I just cant get it dialed in. Over winter I installed a manual choke, as there was none, and truck would not start at any temp under say 50°f. Dialed in carb so I could just give one pump, full choke, turn key, and would always start right up. Let her idle 1 minute, and as idle started to bounce, remove choke and tap throttle to bring speed down, and just let be as it warmed up for 5 or 10 mins in morning.
Well now that temps are up a bit it just ain't liking to wake up anymore. If I choke at all it will NOT even fire. I have to pimp a few times, start, run for mabey 10 seconds and start over again. Do that like 6 times before she stays running. If i hit gas at all before she is running a few minutes it instantly dies. If i drive it before say 10 mins warm up it misfires, and runs like chit. HOWEVER. Any other time other than early morning, say afternoon, no pumping needed. Just get in, turn key(but still need warm up before drive). Has new fuel filter, but don't know where else to look. It's a motorcraft 2100 also
Trucks a 1973 2wd f100 with fe390, manual choke, auto trans.
With the change in the weather has come a change in starting/warmup procedure, and I just cant get it dialed in. Over winter I installed a manual choke, as there was none, and truck would not start at any temp under say 50°f. Dialed in carb so I could just give one pump, full choke, turn key, and would always start right up. Let her idle 1 minute, and as idle started to bounce, remove choke and tap throttle to bring speed down, and just let be as it warmed up for 5 or 10 mins in morning.
Well now that temps are up a bit it just ain't liking to wake up anymore. If I choke at all it will NOT even fire. I have to pimp a few times, start, run for mabey 10 seconds and start over again. Do that like 6 times before she stays running. If i hit gas at all before she is running a few minutes it instantly dies. If i drive it before say 10 mins warm up it misfires, and runs like chit. HOWEVER. Any other time other than early morning, say afternoon, no pumping needed. Just get in, turn key(but still need warm up before drive). Has new fuel filter, but don't know where else to look. It's a motorcraft 2100 also
Post Fiend
Joined: Feb 2008
Posts: 5,831
Likes: 121
From: St Albert, Alberta
Howdy all. So I have a quick question to bounce off everyone.
Trucks a 1973 2wd f100 with fe390, manual choke, auto trans.
With the change in the weather has come a change in starting/warmup procedure, and I just cant get it dialed in. Over winter I installed a manual choke, as there was none, and truck would not start at any temp under say 50°f. Dialed in carb so I could just give one pump, full choke, turn key, and would always start right up. Let her idle 1 minute, and as idle started to bounce, remove choke and tap throttle to bring speed down, and just let be as it warmed up for 5 or 10 mins in morning.
Well now that temps are up a bit it just ain't liking to wake up anymore. If I choke at all it will NOT even fire. I have to pimp a few times, start, run for mabey 10 seconds and start over again. Do that like 6 times before she stays running. If i hit gas at all before she is running a few minutes it instantly dies. If i drive it before say 10 mins warm up it misfires, and runs like chit. HOWEVER. Any other time other than early morning, say afternoon, no pumping needed. Just get in, turn key(but still need warm up before drive). Has new fuel filter, but don't know where else to look. It's a motorcraft 2100 also
Trucks a 1973 2wd f100 with fe390, manual choke, auto trans.
With the change in the weather has come a change in starting/warmup procedure, and I just cant get it dialed in. Over winter I installed a manual choke, as there was none, and truck would not start at any temp under say 50°f. Dialed in carb so I could just give one pump, full choke, turn key, and would always start right up. Let her idle 1 minute, and as idle started to bounce, remove choke and tap throttle to bring speed down, and just let be as it warmed up for 5 or 10 mins in morning.
Well now that temps are up a bit it just ain't liking to wake up anymore. If I choke at all it will NOT even fire. I have to pimp a few times, start, run for mabey 10 seconds and start over again. Do that like 6 times before she stays running. If i hit gas at all before she is running a few minutes it instantly dies. If i drive it before say 10 mins warm up it misfires, and runs like chit. HOWEVER. Any other time other than early morning, say afternoon, no pumping needed. Just get in, turn key(but still need warm up before drive). Has new fuel filter, but don't know where else to look. It's a motorcraft 2100 also
Grumpy goat
Joined: May 2017
Posts: 3,059
Likes: 597
We need more info. But with what you've stated, I'd say the carburetor is too rich. As ambient temps rise, air density decreases. Installing an Air/Fuel Ratio gauge will take all the guess work out of carburetor tuning. Check your timing too.
Thread Starter
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Tuned
Joined: Sep 2018
Posts: 364
Likes: 22
From: Eagar, az
Yeah timing is an issue I am sure. Never learned how to time an engine, but have a light, and played with it and turning distributor until it ran best, but light showed past the end of the Mark's when it was smothest(like around 35-40 btc) that was 6 months ago, and I have been really happy with how it ran, so let it be. Tried figuring out the distributor advance adjustments but got spooked that I was gonna mess it all up. I had the carb like 6.5 turns out on both sides when it was at it's best and I am definitely gonna get a new carb due to p.o. failed attempt at fixing a fuel inlet leak with some sorta red clear gloop. Same dab of red gloop on two parts either side of accelerator pump outlets also, and loose,and I imagine air leaking throttle linkage. Will take some pics in a minute
Thread Starter
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Tuned
Joined: Sep 2018
Posts: 364
Likes: 22
From: Eagar, az
Perhaps. I have replaced everything that I know would leak. All but the transmission valve line. The rubber parts of it are pretty weak, I am starting to think just the opposite. Replaced pcv spacer, and carb mount gaskets a few weeks ago due to cracking and overall bad shape and mabey the intake was relying on that extra air mixing in. Gonna zero everything out and start over when I get home today. Haven't ran a vacuum gauge on it since last summer before all lines and gaskets were replaced. Don't remember the number, but I know it was way low
Posting Guru
Joined: Nov 2011
Posts: 1,302
Likes: 5
From: Burlington, WI
For starters, it sounds to me like that engine isn't tuned well at all.
First is the timing is way off. I suspect your distributor is in a tooth off, or you have a vacuum/internal engine leak and need that much timing to dummy it up and work through it. You should have anywhere from 8-14* initial timing at curb idle. I would start at 12* and tune the engine from there.
Second is your carb. 6.5 turns out is ridiculously high. Yes it is very rich at that point, which tells me you likely have a vacuum leak. It sounds like the carb is also worn out, so I'd start with replacing that first.
When you attach your vacuum gauge to the motor, you want manifold vacuum. That means any port on the intake. You want to see 18-22" of vacuum with a steady needle on a stock healthy engine.
First is the timing is way off. I suspect your distributor is in a tooth off, or you have a vacuum/internal engine leak and need that much timing to dummy it up and work through it. You should have anywhere from 8-14* initial timing at curb idle. I would start at 12* and tune the engine from there.
Second is your carb. 6.5 turns out is ridiculously high. Yes it is very rich at that point, which tells me you likely have a vacuum leak. It sounds like the carb is also worn out, so I'd start with replacing that first.
When you attach your vacuum gauge to the motor, you want manifold vacuum. That means any port on the intake. You want to see 18-22" of vacuum with a steady needle on a stock healthy engine.
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Thread Starter
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Tuned
Joined: Sep 2018
Posts: 364
Likes: 22
From: Eagar, az
Okay, so I now have the carb mixture 3.5 out from bottom, and timing is down to 11 btc. Tried lower( 8 to 10,) but was stumbling on acceleration. 11 was just where that stopped happening. Vacuum is a steady 16 hg, but could not get it any higher. I am at 7500 feet elevation for what it matters. Its amazing how much better I can hear the engine since removing the glass packs and installing headers/new exhaust. It was much better for doing this
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Joined: Apr 2019
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Adjust your idle to 1800 -2000 rpms and adjust your A/F mixture on each bank by turning "out" til the engine stumbles , then turn "in" counting the revolutions til the engine stumbles and turn it back in between the two. Then adjust the idle back down. That's a great starting point for the A/F mixture. I know most of you know this , but I'm new to this site so I'm going out on a limb. Love this site by the way
Posting Guru
Joined: Nov 2011
Posts: 1,302
Likes: 5
From: Burlington, WI
No. Set the truck to curb idle (hot in park). Idle should be 800 rpm. Turn both screws all the way in. Engine should stall. Back the screws out 2.5 turns. Start engine. Will likely run like crap. Use vacuum gauge to go from there. You want to achieve the highest vacuum reading you can. Turn both screws evenly in and out to keep it balanced. You want 18-22" of vacuum with a steady needle. If you find the vacuum gauge doesn't work out well for if you don't have one, turn the screws till you hear the RPM's stop increasing. Then readjust your idle down and away you go.
I don't know where the bologna came from about adjusting your idle mixture at 1500+ rooms came from, but at that speed you are no longer on the idle circuit and have the throttle blades open so you aren't generating much vacuum anyway. Do not use that method.
I don't know where the bologna came from about adjusting your idle mixture at 1500+ rooms came from, but at that speed you are no longer on the idle circuit and have the throttle blades open so you aren't generating much vacuum anyway. Do not use that method.
More Turbo
Joined: Feb 2018
Posts: 710
Likes: 3
From: Oregon
OP you said you were at 16hg. That's does seem low but I am not sure what it should be at 7500 feet.
My truck (1979 F350 with a 460 / C6) pulls 22 inches Hg steady, I am supposedly only 154feet elevation where I live though.
If we read this article: https://www.gregsengine.com/using-a-vacuum-gauge.html
it says:
From sea level to 2,000 feet elevation all normal engines should show a vacuum reading between 17 to 21 inches. Above 2,000 feet elevation the vacuum reading will be about one (1) inch lower per each 1,000 feet rise in elevation.
Well, you are what, about 5 more "inches" above 2000 feet, so in theory your vacuum will be 5 inches lower than someone at my elevation. Seems about right then at 16ish.
My truck (1979 F350 with a 460 / C6) pulls 22 inches Hg steady, I am supposedly only 154feet elevation where I live though.
If we read this article: https://www.gregsengine.com/using-a-vacuum-gauge.html
it says:
From sea level to 2,000 feet elevation all normal engines should show a vacuum reading between 17 to 21 inches. Above 2,000 feet elevation the vacuum reading will be about one (1) inch lower per each 1,000 feet rise in elevation.
Well, you are what, about 5 more "inches" above 2000 feet, so in theory your vacuum will be 5 inches lower than someone at my elevation. Seems about right then at 16ish.