Rottenchester carb sticking/flooding (PICS!)

[Burgersquatch]

The model should be a Rochester Quadrajet.  I don't have any books right on hand at this moment, however according to http://www.recarbco.com/technical/rochester/qjet.html, http://www.cliffshighperformance.com/tech_carb_ID_2.html and http://www.carburetion.com/quadnumber.htm your carb is a 1973 Chevrolet Q-jet, 49-states emission (i.e., non-California) with an automatic transmission produced on the 306th day of 1972 (i.e., 3062). The QM should be a production code.

Yeah, I found this out recently looking up info about this carb. I kinda doubt it makes a difference, but I'm curious about the automatic transmission part. Like if it matters that my truck is manual.

Anyway, I'm taking it to a mechanic today to have it looked at. I cant really get it done myself and im having trouble finding help. I described what's going on over the phone and mentioned y'all helped me find out I'm missing parts to the choke. The dude said he could put a manual choke on it no problem. I'm gonna have him look over the rest of it to see if its got any other problems... the distributor is a little noisy/rattly/buzzy ... and there may be an exhaust leak or bad PCV valve - its like a flappy/tick sound on the passenger side. I hear it more from inside the cab and it increases with the acceleration. And while driving there's an oscillating hum, thinking it might just be the exhaust note.

[Burgersquatch]

Mechanic didn't touch much, I took off the air cleaner and you see where gas was spitting up through the pump rod hole and a couple other spots from starting it up this morning. He also mentioned a heat riser gasket or something like that. Said there should be a larger (gasket) space between the Carb and intake manifold. Bringing it back tomorrow morning.

[bake74]

Mechanic didn't touch much, I took off the air cleaner and you see where gas was spitting up through the pump rod hole and a couple other spots from starting it up this morning. He also mentioned a heat riser gasket or something like that. Said there should be a larger (gasket) space between the Carb and intake manifold. Bringing it back tomorrow morning.

      I thought you took it to him to do something with the choke ?

[Burgersquatch]

He saw other things that needed attention?

Brought it in this morning, actually ran OK after a cold cold start (tied the linkage to the flap). Called at 2:30 and parts still hadn't arrived. Whatever he's doing he says its under $100. But for taking 3 days I could have done that. I'm not excited about the situation but if gets it running good then ill be satisfied.

[Burgersquatch]

The fuel pump was over pressurizing and blew the needle off the valve, new pump, new needle valve, new fuel filter. Installed a 'heat riser' gasket thing that wasn't there (between the carb and manifold) and a manual choke cable. I'm not 100% on the choke cable, seems a bit finicky whether it actually pulls the flapper closed and operates the fast idle properly. I moved the throttle spring to a tighter position cuz the linkage seemed a bit sticky. Now the gas pedal seems a bit sticky, like it takes a little extra to move it and when I take my foot off the pedal, it returns kinda snappy. I'm going to move that spring back to it's original position and see if that helps but the linkage on the carb could use some lube/grease or something.

I kinda like the thermostat coil / auto / divorced choke seems like a better idea. I don't really notice a difference with how the manual choke is set up. It was a bit warmer this morning and I didn't use the choke to start, just sat in the cab and held the pedal until it warmed up to idle fine. It runs a lot better now (after it warms up). The choke cable does move the linkage but not as well as I would like / feel comfortable with. Maybe I just need to get accustomed to this setup.

It's pretty nasty out right now, wet, snowy and very windy, I'll post some pics when I can.

I also think the choke cable has some slack under the dash and when I pushed it in last night, the fuse for the tail/courtesy/dash popped. It blew Saturday night and I ended up leaving my truck at work and crashing with some friends who live nearby. Found the blown fuse yesterday, got a puller tool and replaced it. Then it popped again later when I went to leave. Luckily there was another spare in the glovebox, although it was a 30amp instead of a 20 that used to replace it the first time. I read somewhere that there are some grounds under the dash on that side (might have been a different year or GMC) but when I pushed the choke in, the tab it's mounted to flexed a little. Maybe it moved the connection and shorted a ground? The choke cable has a metal sleeve which is why I'm thinking with the pressure from pushing the choke in, the slack moved and touched the fuse box, which doesn't have a cover.

The directions the mechanic gave me to operate the choke are as follows:
Turn ignition on but don't start, push the gas pedal to release the flapper and pull choke.
Feather the gas while starting and it should fire up, then adjust the choke as it warms up.

With the linkage sticking (maybe the cold?) this process doesn't seem to really work. Maybe I'm not doing it right? I've had to take the air cleaner off and adjust things on the carb. That was the cold-cold morning the day after I got the truck back. My roommates were needing to leave in a hurry and rushing me to start my truck. We ended up pushing it to a point where they could move around me. After they left and a few more minutes of trying, it started and ran fine. Unfortunately, I do not have any covered parking and my truck is exposed to cold, snowy, icy elements of South Lake Tahoe.

I also have and aftermarket Barden bumper that one of the previous owners put on and the mechanic said to check the wiring there.

[thirsty]

The directions the mechanic gave me to operate the choke are as follows:
Turn ignition on but don't start, push the gas pedal to release the flapper and pull choke.
Feather the gas while starting and it should fire up, then adjust the choke as it warms up.

I've had quite a few manual chokes. The way I always start them is this:
Get in and pump the gas pedal 1 or 2 times.
The last time you pump the pedal hold it down to the floor and pull the choke cable.
Release your gas pedal and turn the key with your hand on the choke cable.
As soon as it starts push the cable in partially.
Let it run like that until the motor is comfortable with less choke.'
Let it run like that until the motor is comfortable with no choke.

You will get used to it and it will be second nature before you know it.

[Burgersquatch]

Ran fine for some time, then the choke linkage started sticking to where I had to pull the linkage to get the carb to fully open. Pretty sure there's some sediment in my tank(s) as well, when it gets low it'll act up and flood/stall when I come to a stop. Might only happen once then clear out but it still happens. Filled up the other day and it's behaved since.

Just put new plugs in, 3 looked good while the rest were a bit white and all gapped much larger than the .035 the sticker on my truck says to gap at (which is where they currently are). Then my friend adjusted the air/fuel screws and it's feeling a lot better. Throttle/power response is quicker and generally feels a bit better. I need to install secondary fuel filters, I'm thinking between the tanks and the tank selector valve.... but I'm pretty sure someone around here said to put it between the pump (which is on the motor) and the carb.

Truck's going to the mechanic Thursday afternoon to have him go over the steering and see what's going on there. In another thread I created on the topic, after I posted pics someone mentioned that it's likely needed to replace the ball joints.

[Engineer]

Question:

Why wouldn't you place the filter on the suction side of the pump?

[bd]

Most fuel pumps are more effective at pushing fuel than they are pulling fuel. 

Although, symptoms of filter placement don't generally appear until fuel filters begin to restrict, to prevent the fuel pump from starving for fuel, a filter installed in the suction line of the pump requires more frequent maintenance compared to a filter installed on the pressure side.  For electric pumps, it can actually mean death to the pump if starved of 'cooling' fuel flow.  Mechanical pumps are less susceptible to damage, but are still susceptible - especially the diaphragms.

The 'sock' on the fuel pickup in the tank functions as a coarse, self-rinsing pre-filter/water separator that has a significantly higher micron rating than the in-line filters routinely serviced during tune-ups, so 'socks' aren't generally a problem unless excessive sediment or rust accumulates in the tank.

[Engineer]

I figured that is what you would say, and it is not incorrect, but I prefer to put the fuel filter before the pump, and here is why. Actually I should state that I prefer to install the filter before the regulator.

Most mechanical pumps have the fuel pressure regulator built into them. I want nothing in between my regulator and the float valve. As a fuel filter becomes plugged the pump/regulator only sees a restriction. The regulator doesn't know if this is the float valve, or a chunk of dirt in the fuel line. With the filter between the regulator and the float you can see an inadequate supply of fuel as it starts to plug.

One other reason I like the filter on the tank side of the pump is simple physics. If your standard pump is regulated at 4 psi there will not be as much force available to push through a similarly restricted filter as there would be if you had 29.4" of vacuum drawing (14.7 psi pushing from the outside) through the filter on the suction side.

Ideally you would want tank>pump>filter>regulator>fuel distribution device in a similar fashion to the way GM has all fuel injection systems. GM's approach to putting the filter in the inlet of the q-jet carb was bad, just bad.

One other reason I like the filter on the tank side of the pump is because it traps any crud that may settle in the low parts of the pump.

[Burgersquatch]

My truck has a mechanical pump on the motor and a dinky little filter right at the carb.

To me, it makes sense to filter sediment before it goes through other parts. However, it also makes sense to put it on the push side of a pump with 'weak' suction. Added restriction on the weak side could/would cause the pump to wear or burn out. With the age of this truck, I'd be tempted to put filters everywhere. Like, high-flow/low-resistance filters off the tanks before the selector valve and better/regular filter after the pump. And probably toss a regulator in there somewhere to help keep things in check.

Pretty sure there's some sediment in the tanks, at least the default (pass side) tank that I've been using while the tank selector valve wasn't switching. I have one to replace it, just too dang busy. Since I have my bike now, I can afford to take my truck apart and work on stuff when I do have time, and can leave it apart longer than a day. So sometime this summer (if time/money allows) I would like to drop my tanks, clean them out and if they're not too trashed, seal them and put them back in.