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400 problems...

LEB Ben

Arrogant A-hole At-Large
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...and my girl ain't one of 'em. Seriously though, trying to do a little trouble shooting and have a few questions, mainly fuel delivery/carb related I believe.


1) The biggest problem of all is, there seems to be a backfiring issue. It's not a consistent problem, but it seems to happen most often when I let off the gas to coast or slow down, then when I go to get back on the throttle I get pop/backfire and then it'll accelerate. It also seems to happen at shift changes as well. It's worse when the vehicle is cold, but as I said...the problem is not consistent at all.


2) When traveling at sub 35mph speeds, and I go to give it a little bit of gas, it will sputter/stutter a little bit and then resume properly...not that big of a deal...just more of an annoyance.


3) There have been 5 times now in about 500 miles of driving where I will start the vehicle and start driving and after a few hundred feet the vehicle will die. It's almost like it's using whatever fuel is in the bowl, and then like there was no fuel in the outlet line from the fuel pump.


4) I've noticed a new vibration...or wobble rather...that wasn't there with the old engine between 60-70mph. Not sure if this is engine related, but it wasn't there until the swap.


5) Now I know these things aren't gas sippers, and I'm not complaining...I just made an observation, that could possibly be attributed to any of the above problems. The old, tired, worn out 351M would get 10mpg city and 14mpg hwy...the new 400 get's about 7 and 9.5. I just really didn't expect such a big drop in mpg's going from a bad engine to a good one.



All that said, this was all tried with a Holley Mechanical fuel pump, an O'Reilly's house brand mech. pump, and an AutoZone chinese piece of crap mech pump. The problems seemed to get better with the Holley pump, but was still there...and that pump was trashed when it was accidentally ran over.


I also tried an electric fuel pump rated at 4-7psi and problems 1,2 and 5 were worse. Problem 3 was eliminated. And problem 4 maintained.


Again, thanks for any info.
 

LEB Ben

Arrogant A-hole At-Large
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Its the carb Ben it needs a rebuild. Its probly all gummed up inside.


I've got no problem rebuilding the carb, and not even ruling it out as a fix...just wanna see if there are any other thoughts/suggestions.
 

1985 Ford F-150

Country Boys Can Survive
7,816
307
Tooele, Utah
Thats the only thing I can think of thatll cause the kind of problems your talkin about I had em give me all kinds of little bugs when I had a carb that needed to get rebuilt. It might just need to get set back to what it was when it came out of the box then just start over and re tune it from there changin mixtures and jets as it needs it.
 

UNRULEE

^LARGE carbon footprint^
I agree with Dan, start with the carb. Should take care of most of your troubles.
 

DNFXDLI

The Token Canadian
Staff member
Sounds like the float could be not working right.
 

LEB Ben

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Alright...will do. And god almighty, it's been a while since I rebuilt a carb...just looked on Summit, and a rebuild is gonna run $35-40. Last carb I rebuilt was probably 3 years ago and the kit was $25, and I thought that was high at the time.
 

LEB Ben

Arrogant A-hole At-Large
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Sounds like the float could be not working right.


As far as I can tell it's working fine, but how can you really test it? The float levels were fine on the 351, swapped it over, and they were way high...dropped them down and they were fine again.
 

LEB Ben

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Edelbrock rebuild kits are 50 bucks. Might also check the timing and see if its ok.


Yeah...I saw some as high as $55 and some as low as $25...but not for my carb.
 

DNFXDLI

The Token Canadian
Staff member
As far as I can tell it's working fine, but how can you really test it? The float levels were fine on the 351, swapped it over, and they were way high...dropped them down and they were fine again.

Is it the carb that came on the engine?...or one that you put on?
 

UNRULEE

^LARGE carbon footprint^
eBay my friend, if you can wait for the shipping. Most things seem cheaper on there.
 

LEB Ben

Arrogant A-hole At-Large
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Is it the carb that came on the engine?...or one that you put on?

It's the one I swapped on Holley 4150 650cfm PN 80783-C

eBay my friend, if you can wait for the shipping. Most things seem cheaper on there.

Good call...I just always worry that I'll order a rebuild kit and I'll get a peg legged midget or something.

They aint got one at a parts store?

I'm sure they do, or can order one. But I don't have a parts store at my disposal at 1am...haha.
 

UNRULEE

^LARGE carbon footprint^
I've boughten a ton of truck accessories off of the 'bay. Just do the reseach for what you need and go with a seller with a good rating.
 

DNFXDLI

The Token Canadian
Staff member
So it was one that you already had installed and running?...hmmm...have you checked your vacuum readings with a gauge?
 

LEB Ben

Arrogant A-hole At-Large
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I've boughten a ton of truck accessories off of the 'bay. Just do the reseach for what you need and go with a seller with a good rating.

Will do

So it was one that you already had installed and running?...hmmm...have you checked your vacuum readings with a gauge?

Yes it was a previous carb that was running. But as I said somewhere else, it was tuned as a bandaid to cover up the other inefficiencies. And no I haven't tested vacuum.
 

LEB Ben

Arrogant A-hole At-Large
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Is it possible the vacuum advance is crap?


Doubtful...but keep the ideas coming, just what I'm looking for. I mean hell I'm essentially starting over and getting to know the rig again, so I'll check out everything you guys throw at me. I mean the thing runs pretty well, just not as fine tuned as I'd like...and it sounds like a rebuild kit is the leader so far. So keep the ideas coming.
 

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