Running Rich?

[Bruce Wingate]

I think my truck is running rich. I'm just starting to track down this problem, so I don't have too many hard facts yet (or - I'm starting to think about fixing this now). Truck is an 84 K10 with a replacement 350 running a Quadrajet style carb.

What I know:
1) Starts like a champ - quick pop of the key and it starts every time (unless it has been sitting a few days, then the clear fuel filter is empty and I have to pump some fuel up to the carb).
2) Idles well without blipping the throttle to keep it going.
3) Warms up what I consider slowly - just sitting idling takes at least 15 minutes for the e-fans to kick on
4) Mileage is around 8 mpg - not accurately measured yet - I'm not expecting miracles, but I was hoping for 10-12 mpg
5) Exhaust smells like it is rich and leaves sooty marks on the pavement when idling for a while

My plan:
1) Check and change the plugs - look for black/sooty plugs
2) Time the engine (HEI distributor)
3) Check fuel pressure (currently have a mechanical pump)
4) Learn to live with lousy mileage - but by the exhaust smell I can tell something is off

Last thing will be to identify then clean/rebuild the carb. Externally, the choke and carb linkages looks like they are functioning correctly. I can't for the life of me figure out how you guys look into a carb on a running engine to see if fuel is leaking into the secondaries.

Is this a decent game plan - any suggestions or anything I missed?

 

[SirRobyn0]

Bruce, If you have started working on this problem an update would be good. But I'll add this. 15 minutes idling for E-fans to come on is fine, but there are lots of variables, such as temp fans are set to come on at and outside temps. Sometimes at the shop we struggle to get fans to come on in factory equipped cars in cooler whether in 30mins of idling but those fans don't kick until 220F So would need to know T-stat temp and fan set temp and outside to even take a stab at whether that normal.

If this is a mostly stock drive train with 4.10 higher gear ratio ie 4.10, 3.73 or 3.41 and your not a lead foot then 8 is probably low.

Soot marks on the pavement is not normal. I expect your plugs will look similar but check to know for sure.

Look for vacuum leaks, a choke that does not open or does not open all the way. Check of tune up, timing and vac leaks all good ideas. Also Q-jets have welch plugs that can drop fuel from float bowl directly to manifold so if you decide that a rebuild is in order don't forget to look at those.

 

[Bruce Wingate]

Thanks @SirRobyn0 . I have not progressed much except to connect the torque converter lock up vacuum switch but I haven't driven enough to see if this helps. My first measured MPG was 7.6, but that was with a lot of idling and short shake down trips around the block.

Right now, since it starts and runs well I am focusing on other little projects with the truck, like wrapping up all the final bits with wiring, installing a temp sensor and replacing the oil pressure sensor. I'll keep updating this thread as things change.

Carb Issues: I knew about the leaky plugs - just don't know if mine are leaking or not. Another thought I have is that the mechanical fuel pump is a little too strong and overfilling the float bowl. There are no obvious vacuum leaks (all ports are plugged and hoses are new) but I don't know if there could be a leak around the base of the carb (starter fluid check was negative)

Tune up: I know that the British Top Gear show is 99.9% entertainment BS, but one episode they did was improving horsepower on basic Japanese hatchbacks. All the tuner cr@p got 1-2 HP, most horsepower came from a tune up.

 

[SirRobyn0]

Something is most definitely up with the black soot thing. That's definitely not normal. Keep in mind long term that running rich isn't good for the motor. I wouldn't be to worried in the short term but it is something you should get to the bottom off it.

 

[Bruce Wingate]

Connecting the torque converter lock up vacuum switch and less idling in the driveway brought mileage up to 9.3 mpg. This weekend I will change the plugs and try to adjust the timing (assuming I can get to the distributor lockdown nut)

 

[SirRobyn0]

Connecting the torque converter lock up vacuum switch and less idling in the driveway brought mileage up to 9.3 mpg. This weekend I will change the plugs and try to adjust the timing (assuming I can get to the distributor lockdown nut)

Lock down bolt typically isn't to hard to get loose. 9.3 is better for sure, but I still think there is a reason for that black soot.

 

[Bruce Wingate]

Last tank was down to 7.6 again but there was a lot of local driving and a breakdown so that might have had an affect. Breakdown was from a loose power feed into the distributor which I have fixed along with replacing the cap and rotor

When I re-did the plug wires, I started from scratch instead of just transferring them over from the old cap, and now the engine runs much smoother. The exhaust smells better too. Next up is new plugs and timing

 

[Red Rex]

Spark plug gap can affect the mileage and the black sooty thing.

You might try increasing gaps in increments if you are on the low side or decreasing if you are on the low side. Also plug mfg., composition and heat range could be the culprit(s).

My 84 350 also liked 12 degrees advance @800 rpm best found it by adjusting timing for best manifold vacuum

 

[Bruce Wingate]

Slow progress: I tried timing the engine, and I could not see the timing mark at all. Tried again today and never saw a timing mark - I started to suspect that (1) I had no idea what the timing mark looked like (I didn't - I expected a notch) or (2) there was no timing mark. Spent a lot of time feeling around for the mark and finally found it. Tried marking it with a piece of painter's tape but that would not stick. Gave up for now because it was cold and drove the truck.

Tomorrow I will clean the harmonic balancer some brake cleaner and steal some of my wife's nail polish.
Probably will replace the plugs too.

 

[SirRobyn0]

@Bruce Wingate I have a white metal marking pen that I like to use on timing marks, white out will work to as will the nail polish, just wanted to throw a couple other ideas your way.

 

[Bruce Wingate]

Slow progress: I tried timing the engine, and I could not see the timing mark at all. Tried again today and never saw a timing mark - I started to suspect that (1) I had no idea what the timing mark looked like (I didn't - I expected a notch) or (2) there was no timing mark. Spent a lot of time feeling around for the mark and finally found it. Tried marking it with a piece of painter's tape but that would not stick. Gave up for now because it was cold and drove the truck.

Tomorrow I will clean the harmonic balancer some brake cleaner and steal some of my wife's nail polish.
Probably will replace the plugs too.

It got cold and I got impatient, so I gave a trusted mechanic my truck and a list of things to do, including timing setting the idle. He said some things that were odd: First, he said that the timing mark on the harmonic balance was way off - like 50 degrees off so he estimated where TDC was and set it at 4*. He also said that no matter what he did to the idle adjustment screws, there was no effect. I was a little miffed by this, but he otherwise has done good by me for years, so I guess I'll just have to redo this my self. Right now, the engine idles very low and will stall out if you don't goose it a little bit for the first couple of minutes. After it is warmed up, the idle is fine, maybe a little low, and an occasional miss. Gas mileage is now at 8.5 mpg. The exhaust also smells better.

So, next step is to determine exactly where TDC is and mark the balancer with a timing tape and retime the engine. Along with that, it is new plugs and a fuel pressure check.

Like I said, this is not a top priority for me because the truck runs well otherwise. I'll post updates when I get to it.

Thanks for your input and reading along.

 

[Dutch Rutter]

@Bruce Wingate
Sounds like your harmonic balancer either spun (happens) or someone put on a different and wrong balancer (also happens)

The idle adjustment screws not having any effect is a red flag to something not being right with the carb. Too much fuel pressure is where I'd start looking.

 

[Bruce Wingate]

@Bruce Wingate
Sounds like your harmonic balancer either spun (happens) or someone put on a different and wrong balancer (also happens)

The idle adjustment screws not having any effect is a red flag to something not being right with the carb. Too much fuel pressure is where I'd start looking.

Thanks. Fuel pressure or wonky timing have been my suspected culprits. Just trying to do one change at a time so I can see the effects.

 

[SquareRoot]

If the idle air screws make little or no difference, there's a vacuum leak. Could be anywhere- manifold, egr, pcv, vac advance cannister, trans modulator, heater/ac control, cruise control, valve seals... It's getting air from somewhere. And of course, the carb circuits/gaskets could be the culprit as well. Is it a vac secondary carb?

 

[Bruce Wingate]

If the idle air screws make little or no difference, there's a vacuum leak. Could be anywhere- manifold, egr, pcv, vac advance cannister, trans modulator, heater/ac control, cruise control, valve seals... It's getting air from somewhere. And of course, the carb circuits/gaskets could be the culprit as well. Is it a vac secondary carb?

I think it's mechanical secondary. There's no egr or cruise control hooked up. Heater/AC is after market and the vacuum ports were plugged. I'm going to have to track down any other possible leaks