When I try to accelerate, my truck will make a popping noise from the carburetor and lose a lot of power, if I'm at a higher speed like 40mph+, or almost die if I'm at low speed like a stop sign or turning a corner. I know it's from the carburetor because we took the filter off and it coughs some smoke on the rare times it does it idling.

Sounds like the EGR problem that is so common. However....

I cleaned my EGR valve and stuck my fingers in the holes it sits on to make sure they weren't full of carbon. I've changed my plugs and wires 2x, and distributor cap 2x, and a new Carburetor. I used almost 2 cans of Seafoam today in the Carb, Gas, oil, but mostly in the brake booster line. The booster line was the only one that caused any discoloration in exhaust so I used more there.

I've been told it's probably the timing. It used to have discolored smoke, but we changed the timing to about where it should be (best we can tell), and now its clear exhaust.

Thanks


(sorry this is at night, phone cam)
10 and 27 seconds
http://www.youtube.com/watch?v=6bPkUlVeDrc

 

My truck would behave similarly when the carb's idle mixture adjustment was too lean
(combined with an intentional vacuum leak). I would say to check the basics - no vacuum
leaks, the EGR valve isn't stuck open (I know you said you cleaned it, but, does it work?),
set the timing with a timing light. What have you ever done to the carb?

 

I made sure to check a few of the vacuum lines, primarily the one that goes to the vacuum advance. There is what people keep telling me is an "exhaust leak" behind the engine facing the cab I think. When I was letting the brake booster line suck in the Seafoam, some blue smoke was coming out back there. I couldn't track it down with before the smoke stopped. All of the settings were out of the box when I installed the new carburetor and it was doing this same thing with the old one, I'll check the mixture setting The EGR valve works as best I can tell, the diaphragm opens and closes it when I push it. We set the timing with a light and it was within a degree or 2. It's hard to see the way the engine is set up because you have to shine it down from above all the way to the bottom. I don't know if that's standard, just hard to be 100% from that distance.

 

A brand-new, out-of-the-box carb should be set pretty decently, do the instructions say
anything about that? My Holley's instructions said everything should already be set pretty
well. If your situation is similar, I wouldn't mess with the idle mixture adjustment but would
focus elsewhere. Have you checked the fuel pressure & output flow rate? What engine is
this? My 1981 F350 400 4X4 doesn't have a computer, I'd imagine yours doesn't, either?

 

It's the custom 400 6.6L 4x4, same engine?

I've changed the fuel pump twice too, I think the second one wasn't necessary.

Changed the fuel filter once, and had to bypass the front/back tank switch because it was stuck in the wrong position. Now the good tank goes straight to the fuel pump.

I'll check for vacuum leaks and the fuel filter tomorrow. I haven't checked the filter since I bypassed it.

I did mess with the Idle speed, but I'm sure that was set right when the timing was done, will look into it.

no, not sure how, will look into it.

TY btw

 

Quote:

Originally Posted by Skrilla

It's the custom 400 6.6L 4x4, same engine?

Yeah, I have that same engine, it was Summer '08's project to rebuild it.
There are some pics in my gallery if you're interested, I also had one or two
threads in the 335 forum.

If you've replaced the fuel pump twice, I really doubt that's causing your
problem. If it's a fuel delivery problem, I'd be suspicious of crud in the tank,
dry-rotted rubber connecting lines underneath (especially connecting the steel
line & sending unit together, mine had crumbled), a sticking tank selector valve
(which you removed from the equation).

A fuel/vacuum tester will tell you output pressure, I'd disconnect the fuel line
from the carb, probably add an extra length of rubber tubing onto the fuel line
and route it to a plastic jug or whatever's handy; disconnect the coil wire and
turn the key for a few seconds and look for healthy streams being pumped out
such that you have a warm fuzzy feeling that the flow rate is good.

Once you're past all this stuff, then you get into things like the distributor
pickup (electrical part underneath the rotor) and burnt or sticking valves,
neither of which I know how to test for off the top of my head. I *think* I've
seen it talked about here and you *might* be able to find something by
searching the archives but it might be hard (it's easy to get spoiled by google).

This is why I hope it's something easy but it sounds like you've done a fair
amount of work to rule out a lot of the obvious things, hopefully others will
chime in with help, too.

You might also ask this in the 335 forum; there are some GOOD people there
sometimes but you'd have to be lucky and hope one of 'em stops by.

 

Quote:

Originally Posted by Skrilla

When I try to accelerate, my truck will make a popping noise from the carburetor and lose a lot of power, if I'm at a higher speed like 40mph+, or almost die if I'm at low speed like a stop sign or turning a corner.

Want to be sure I understand... are you saying the popping noise from the carb
happens 1) on acceleration (presumably from a dead stop) and 2) as well as
when running at a continuous speed/RPM?

It sounds like you're describing slight backfiring through the carb, which is
generally an indication of misadjusted ignition timing which could be caused by
several things.

I wonder if it jumped time... When you replaced the fuel pump, did you stick
your finger in that hole and feel how much slack there is in the timing chain?
IIRC there should be no more than 1/2" inch.

I don't know how to check for a slipped timing chain (other than lining up the
marks on the gears and checking the orientation of the #1 cylinder's valves)
but I'm sure there must be a way...

Also, are you sure your plug wires are connected on the cap in the correct
order? I think the firing order is 13726548 but I'd need to look it up to verify it
(it's also cast into the factory intake manifold).

Hopefully, your "exhaust leak" is just that and not a leaking intake manifold
gasket....

 

Does this problem exist at all operating temperatures, or does it, say, go away as the engine
warms up?

When did this problem first appear? Is it a result of replacing all those parts, or was
replacing them an attempt to fix the problem?

Do/did you have any indication of soot building up in the carb's air horn?

 

1.yes
2.yes

I've been told this and I was thinking this (describe below). I took it to a mechanic and they said I had to put a new carb on it before they could check the timing. They may have just been wanting me to give them $500 though.... New carb acts the same as the old one. I'm only out $250 though.

Me either, the mechanic above said that a chain can jump but doesn't need to be changed (sounded dumber than that). Another mechanic said that the chains can stretch. I dunno.



Didn't know to do that. If the easier things left to check all work out I'll pull the pump and check.

Yes checked many times. I put numbers on the wires.

The other day my father in law thought it was all working fine, and it started out great, but after driving it around town for about 3 hours it got to the point that if I turned a corner or came to a stop sign it would almost die. At this point if I put any gas on it untill the RPM went back up it would die. At the same time, it popped occasionally while driving if I removed my foot and then reapplied gas, this was random though. The exhaust is clear as well.


No idea, will look into it.

I asked to have the idle lowered and just before I left we checked the timing, it was close, but the distributor was stuck, so we WD40'd it but it still wouldn't move. Next morning these problems started. My truck died and I saw the WD40 worked finally and the distributor was free moving. I tried to tighten it down but it kept acting up. I wanted to make sure that it wasn't anything else. I'm gonna try the other things you mentioned before I have anyone take the front of my engine off. We've re-timed it about 5 times since then.

Funny thing is I told the mechanic I wanted them to change the timing chain and the water pump while he was in there(it's fine atm) but he wanted to do the pump and argued about the chain. This was when I had extra money lol. Gonna check some stuff in a bit. Thanks again.