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quadrajet: the fuel pump, fuel bowl, and accelerator pump

Where I was going with that was simply for the cost vs. benefit I don't see it in the carbs case. Most people seem to be able to get a carb going "good enough" without anything other than their nose, their foot, and some time. As with EFI, that's not likely as good as it could/should be running, but good enough for most people running a carb.

There is no replacement for a WBO2 sensor, I won't argue that point. If I was going to the expense/hassle of getting a WBO2, I'd spend the money on TBI first lol. *BUT* I know plenty of people running carbs (such as racers) that probably should be using a wideband to dial it in better, who aren't. And if you are really techy, even with a carb the data you'd find out would be very beneficial.
 
Ill agree half on that mainly because good enough is usually so rich it covers up the bad stuff.. I don't think many people know the difference in smell or why your eyes water by the exhaust and if that's rich or lean.. There are obviously some traits people just know but when it comes down to this thread I believe the poster needs this additional data
 
Yes, I probably didn't word that quite right....good enough means it runs "ok". This is why people say that they swap something on TBI and it runs "fine" when reality, proven with a WBO2, would show something different than fine. It may run, it may feel like it's running good, but invariably you are leaving efficiency (economy and power) on the table by not utilizing a WBO2 to see what is REALLY going on.

The OP here certainly has the thought process and desire necessary to get information out of a WBO2 sensor. I suppose one way to look at it is that if it was used to get the carb dialed in, it's equally valuable when an EFI swap is completed. :)
 
Yes I agree completely regardless of the drawbacks of carbs a tuned carb beat efi on simplicity every time! Who doesn't love a clean engine bay!
 
I set my adjustable part throttle by 'nose.' I roll down the back window and adjust until my eyes stop watering. Right now it is clean - I don't smell anything. My kids are usually quick to point out if they smell something.

The bucking has smoothed out recently. Or I am just hitting those two corners with a little more speed or getting better at dropping into first (2nd) gear - I don't know. It could have been the 4-hole carb spacer that did it. I can make it buck if I try, but turning a no-stop-sign corner doesn't do it anymore. Based on your suggestion I gave the idle screws a half turn to richen it: probably all the above helped.

I just bought a few choke coils to test: I noticed some have five coils, others seven coils, and a few with nine coils. The prices are about the same.

Maybe next weekend I can get the new choke on, the fuel pressure gauge installed, and swap in the 1" phenolic spacer from the wood one in there now. Retune and see what happens. Fuel economy is basically a solid 13mpg.
 
dyeager535 said:
Yes, I probably didn't word that quite right....good enough means it runs "ok". This is why people say that they swap something on TBI and it runs "fine" when reality, proven with a WBO2, would show something different than fine.
Click to expand...

Actually, that's the "problem" with the WBO2. It's tuned right, runs good and hits the right AFRs all over the maps. But during transient conditions the AFR goes all over the place, so you have to mess with all these parameters trying to make the AFR do what you want at all times. Of course it's never perfect and without that sensor you would think it's perfect.
 
Results for fuel economy

The measurements

  • Mean (average) 12.7 mpg
  • Median 12.8 mpg
  • Mode 12.9 mpg
  • Min 12.1 mpg
  • Max 13.4 mpg
Data

  • I removed the outliers: 8mpg on half a tank when stuck in traffic for an entire afternoon and a 14.2 mpg run on what must have been a tailwind and that was a short 2/3 of a tank trip on a flat stretch of highway.
  • Interesting enough. My original (never been rebuilt in 20 years - sat for 12 years) smogger Holley with a goober'd secondary diaphragm and plugged 1.5 in-hg power valve (had a chunk of gasket stuck in it) was pulling consistently in the 13 mpg range.
  • The averages are only from the last 13 tanks - the first 11 tanks were tuning and figuring things out (the Q-jet after the rebuild and before tuning was in the 9 mpg range). I have only ran three full tanks on my current setup and tune - those three average 12.3 mpg.
  • Cooling the fuel and carb with insulators and spacers seems to have had no effect on mpg. Drivability certainly improved, particularly once warmed up and warmer days.
  • I found my notebook from highschool when I first built this truck. Has all the part numbers and specs for cam and all - nice find. I had 9 mpg with the Holley 4BBL out of the box, 30" tires, and before I really understood the timing spec in Chiltons is just a suggestion. Better gas back then too.

Comparison
I found a website with real averages for fuel economy http://www.truedelta.com/Chevrolet-Silverado-1500/mpg-58 too bad it is all newer trucks. The closest comparison I found is the average of four 2004 2Dr 4WD 1500 with the 5spd and 300HP V8. Those guys are getting 16.5 mpg a little over 30% better. The lowest of the four was 14.8 mpg (20% better) but close (7% better by 1mpg) to my 13.8 mpg from the 2-bbl (4bbl w/o secondary) Holley.

If fuel injection, computer control, a ton less steel (but weigh 400 lbs more?? 3,900lb versus 4,300lb), probably street tires and no lift, plus 30 years worth of aerodynamics, is good for 4 mpg, then for me that is a reason to just keep driving my '74 K5 how it is.

A few K5 mpg sources


Conclusion

Because the mean-median-mode are so close at 12.7-12.8-12.9 mpg it means the data is clustered with the average. I am for sure getting 12.7 mpg with the chance for slightly better on a good day.

It looks like if I dug out my old Rochester 2-bbl off the Buick v6 grandpa had in the blazer, then I would be right there with new trucks. Hows this for old man second guessing myself - if I'd just left that v6 in the blazer and fixed the flywheel balance problem, I'd have shown more intelligence. But the fun I'd have missed.

Maybe with a little more work on the adjustable power valve (maybe it wants more mid-range gas) and tighten up the secondaries, I could be right there with the Q-Jet. I havent been as light on the gas as I was earlier-on when I'd stare at the vacuum gauge and let it drift down to 50 mph on hills, and sneak behind a semi here and there when they passed me - so that could be worth a mpg or two.

In the last 30-days I bought one tank of gas so I wont be spending too much time on fuel economy. Driveability is key.

Hopefully in the next week or two I can work on the list of to-do stuff in an earlier post.
 
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Good writeup. :)

Since you are tracking all this, I took my solid 40MPG econobox out for a treat, and bought non-ethanol 87 octane gas for it. Was interested in finding out if the ethanol was harming my economy any. Was disappointed to find I got roughly +1MPG without ethanol. Needed about +4 to make it worth the cost difference, so in that car, it wasn't as much as some claims I've read, which is a 20% reduction in MPG due to ethanol.

I had an '83 K5 which I drove quite a bit. Q-jet/305/700/3.08/31's. Back in the day that thing netted me a 17-18MPG tank on a cool night on a super long flat road at 50MPH out in the middle of nowhere in Oregon.

Q-jet 350 with a 465 and 3.42's, 31's or 33's got me right around 17MPG on average if the roads weren't bad.

My current setup gets about the same. Pretty sad when you consider the amount of technology there is compared to the earlier setups, at least in the engine. It's a much stronger engine, and drivability is much better, but in terms of economy, it just didn't do what I had hoped.

I could be wrong, but it seems my off-highway MPG is a fair bit better with the newer motor though. I know I can get a solid 10MPG when I'm out hunting, and that is a LOT of hill climbing. Nothing flat about it, so a lot of throttle in lower gears. As I recall, I was in the 8's with prior variations of the truck(s) under the same conditions.

It would be interesting to drive one of the new trucks just to see what I could squeeze out of it. People drive differently, sometimes that matters, sometimes it does not.
 
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Re-tuned a bit, going to the coast over Highway 17 (lots of long duration steep incline and corners requires slowing and then acceleration on steep incline) on a hot day, my engine temps ran up over 200 deg F and I could hear slight pinging and had to let off the throttle. So I pulled over and did a quick retune on a wide pullout with shade.

Earlier in this thread one of you guys (or more) suggested I need to pay more attention to my distributor and tuning the advance curve. It is on the list of things to do.

Because on an earlier trip to the central valley with just plain flat cruising for two hours at 65 mph my temps rose up to 210 deg F (it was a little over 100 deg F outside - I turned on the heater as it nudged towards 215 deg so I don't know if it would have kept going - the heater brought it back down to 200 deg) I am thinking the current tune is a little lean for my more-or-less OEM cooling system (original 1974 radiator with a rod-out 20 years ago).

I gave the adjustable part throttle a full turn rich (it was bottomed out) and gave each idle screw a 3/8th turn rich. I don't smell fuel in the exhaust but I also haven't driven with the back window down to get the full smell test.

Temps came way down - 180 deg F steady and on downhill stretches dropped to 170 deg F. Pinging stopped - nothing I did could get it to ping again. Lower end is less temperamental too - clutches real easy now (again a suggestion earlier by one of you - same guy with the advance advice). I will post the new fuel economy after a few tanks.

It is summertime and at my father-in-law's driveway there is no shade - it is ridiculously hot where he lives - it must be 110 deg in the driveway. I think until it cools down I won't be doing the list of changes I gave in a previous post (changes to fuel inlet and adding a fuel pressure gauge).
 
I just took the kids to the movies and left the back window down to check the fumes - I can smell a little fuel while the engine was cold - my daughter said it is livable. On the freeway there was no fuel smell at all.
 
If you can stabilize the temp you'd probably be able to better tune it, especially in regards to pinging. That's way too much temperature swing IMO.

With a 195* t-stat I'm going from about 195-215 or so (fan on temp), your 45* difference is pretty excessive.
 
My cooling has always been marginal - it is drivable so it gets put on the back burner. Some workarounds that make it just enough of a nuisance to ignore:

  • Back in the 90s I'd drive on long trips through the central valley at night because of the temp.
  • Used to turn on the heater while driving in the hills in the summer.
  • Has the fan shroud and a decent fitting flexfan - pulleys are not underdrive or anything, high flow water pump.
  • Most of the time it is fine - just hills on hot days or really long drives on really hot days (low humidity out here).
  • Offroad it was ok just driving around slow.
  • I use a low coolant to water ratio and that helps.
  • 185 deg F thermostat to start things off colder - with better cooling I'd use a 195 deg thermostat
  • Now, richen the mix
  • Maybe with better cooling I could push the timing (and lean it out) - right now it is limited by that one really hot day a year (or every couple years) when there is traffic and I am having to give it part throttle to accelerate up a long grade and the heat starts climbing (maybe that tank of 87 gas is not so great too) - light ping, ping, ping: then I retune on the side of the road and just leave it at that tune since I know it works.
The rest of the time the temp is pegged at 185 deg to 195 deg F and never moves.


I will have to start a new thread for cooling gremlins.
 
Definitely a pain to try and deal with fueling/timing with that much variation in temp. I can tell with mine as the engine temp changes by a large margin.

I suppose my point was, in your case, that your temp swings are abnormal. I beat mine up pretty good this past weekend (90*+ climbing steep grades in second for long periods) and the temp never exceeded what my fan-on temp is.

As it relates to fuel, I wonder if your 215* upper temp limit is at least affecting your fueling somewhat? I have no idea at what temp the clutch fans come on, I would suspect under 215*.
 
I agree with you 100% - those temps are certainly doing something and fuel temp is part of it.

If I recall correctly the highest advance in timing is at part throttle (can't remember why - think I found this because tuning at WOT there was no ping but then cruising up the hill it pinged). Higher advance creates higher combustion chamber pressure resulting in high temperature - this starts working its way into the coolant. On a hot day the extra heat is more than the radiator can expel. If the acceleration at part throttle goes on long enough the coolant saturates with heat and overcomes the ability of the radiator to transfer heat. The higher temperature then creates a chain reaction - where detonation starts due to the higher temperature, this results in higher pressure and even more heat generation. The coolant is already saturated beyond the ability of the radiator to expel heat and at that point, the temps shoot up quick from 200 to 212 deg F. It seems like it does not take much light pinging to see it on the temp gauge. At that point they seem to rise more slowely but if I keep pushing it just below the point of pinging the temps will keep going up to 220 deg F. I have never pushed it more than that - I pull over (in this case and retune by backup off the timing or richen the idle) or usually the hill ends and I take it easy for awhile until the temps come back down.

Somewhere in all that the underhood temps must be climbing and the fuel temp must be getting hotter. I have my carb insulated with a 1" block of wood and the fuel line has a decent amount of insulation now so it is not affected as much as it used to or an OEM setup would be. In the box of parts I have more fuel line insulation and a phenolic spacer to help the carb temps more (phenolic relays 1/8th the heat of wood). If the carb heats up and the fuel heats up, then I'd suspect detonation will happen easier and the whole chain reaction cycle I gave above will be at a lower temp. Without detonation my temps usually won't go above 200 deg F unless it is well over 100 deg and I am driving for hours.

The air temp must be higher coming through that hot radiator - so across the board everything it hotter. Also, without fender wells I have noticed that the air flow through the radiator is not as good at 65 mph than at 35 mph. Years ago with the fenders, when it would heat up I'd take the exit and those temps would just keep going up. Without the fenders, I take the exit and slow down, the temps drop quick. It could be due to running lean but I suspect the fenders are like big scoops and are creating back pressure and reducing air flow through the radiator at highway speeds. I don't know. you'd think going faster would be better cooling. I can stop and idle at a light and the temps will drop. Used to be that was the absolute worst situation - pulling off highway marginally overheating then get stuck idling at a light and boom, it would be all I could do to keep it from over heating. My current problem is better - I'd rather it get hot at speed then pull over and have it calm right down in a few minutes.

Since insulating the fuel and the carburetor - I have noticed the engine temps are much more stable. I can drive on hotter days and have more freeboard for acceleration on those days than I used to. But there is still the limit where I can overcome my cooling system. That is not good - cooling should always be over capacity and then some.
 
put a fuel pressure gauge on:

  • 8psi cold at idle (pic 1) close to calculated 7.5 psi - that is higher than the 5psi I want, so I thought pressure regulator
  • 6 psi cold at 2000rpm
  • as the engine temps rose the fuel pressure dropped
  • at full temperature fuel pressure is down to 4psi (pic 2) - so, no fuel regulator needed
  • why does the fuel pressure drop with temperature? EDIT: pressure dropped because I have a liquid filled gauge and when the liquid expands it pushes the needle down and gives a false reading.
The pressure gauge was just to test - I took it back off. The glass filter is going soon - I bought a 5/16" plastic filter but then went with 3/8" hose so kept the old 3/8" glass filter.

I also swapped the 1" wood block under the carb for a 1" phenolic, I can't tell a difference, carb temps seemed comparable to before: 185 deg F intake manifold (200+ deg at crossover) and 125 deg F carb base (5 deg F temp drop over wood spacer, not the 60 deg drop I had guesstimated based on 8x better insulating properties). Maybe on longer drives the carb does not pickup as much heat. I insulated the fuel line from pump to carb with an insulating cover rather than just a heat reflective cover - the fuel temp went up 8 deg at the fuel inlet on the carb. I think the insulation is keeping heat in and from pump to carb, that section of hose must be radiating heat not absorbing heat (one for dyeager535 on that point).

I got Cliff's book in the mail - he signed it too - and used that to tune the AF. He said as a last step to pull an air hose and tune until there is no rpm change - that was good for the last 1/8th turn of the screws one way or another over my setpoint using the vacuum gauge. I will see what the fuel economy is - I did not notice much driving, if anything higher overall vacuum but I had to give more gas up the hills.

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Another mystery now has a plausible explanation: the accelerator pump goes dry (low enough the shot is weak) after a few days.

It seemed like even if the fuel bowl went dry the accelerator pump should retain the fuel shot since it is sealed. That presented a problem if my idea that the fuel is evaporating after two days and that is why I have to turn over a bit to get started after sitting. I measured the fuel in the bowl of the float and it showed the float dropping (removed float hook to needle so no more backflowing).

In Cliffs book I noticed that the accelerator pump has one check valve on the outlet side. My industrial process father-in-law notes that pumps have two valves to work. The holley has two valves on the accelerator pump (as well as the pump is on the bottom of the fuel bowl so it is the last to have fuel no matter what) with one valve on the inlet and one on the outlet. The q-jet has only a check ball on the outlet side to ensure the fuel passage from pump to nozzle has fuel so the accelerator response is quick (I had guessed it was the check ball was the inlet side but Cliff set it straight) and to prevent sucking air on the upstroke of the pump piston. All we can figure is the passage from fuel bowl to pump is small enough that not much fuel (pump is likely designed oversize to compensate for backflow to bowl) does not push back into the bowl when the accelerator piston pressurizes the pump chamber.

This means that as the fuel bowl dries, the fuel level in the accelerator pump also falls. So, when the fuel bowl is half dry, so is the pump. So that explains the weak shot. No start. Then I have to turn it over to fill the bowl (likely the line also dries out a bit, due to semi-previous fuel line - I changed all the '74 vintage OEM rubber line segments to low voc fuel injection line).

I think that is the explanation to the hard start I think this thread started with.

After a couple weeks I will relay back here what the phenolic spacer does for things as far as evaporation and how many days until there is no start.
 
correct - 10% blend

Where it is now
 Back in Oct last year post #30 I did the evaporation calc and in post #53 I got a good data log of fuel temps over time - with a 120 deg F fuel bowl, after shutdown in the first 2 hours a quarter of the fuel should evaporate (measured in post #95) and then over the next 24 hours another quarter evaporates. Checking with the gauge, after three days the fuel float was basically bottomed out (post #118). My fuel temps are now lower than what I estimated back in post #30 - that calc was what convinced me to try and lower my fuel bowl temp. I can let the truck sit for maybe a day longer than before without trouble starting. Blazer74 had the solution here in post #69 (posts #66 through #71 are on ethanol).

Here in post #141 I confess that it is just a challenge to get the mechanical pump and q-jet to work w E10 fuel.

At this point, I think I have verified the q-jet fuel bowl is too small for E10 fuel for fast starting if the vehicle is not started every three days. Back in post #1, the technical report I posted by the q-jet designers, said the fuel bowl was just barely adequate to accommodate 1965 fuel evaporation after shutdown so it should be expected that E10 fuel will evaporate. Placing the fuel bowl between the bores, the need to limit carb height to accommodate low hood lines, and sufficient fuel to start after evaporation became a major design problem for those guys. What I'd like to know is why they did not use a check valve on both the accelerator pump inlet and outlet to make the pump shot captive (post #216) - the fuel would probably stay in the plunger for months.

After the final on-the-fly tune in post #209 everything runs good, no low end bucking, starts right up hot or cold (assuming it has ran in the previous couple days and accel pump has fuel), and the 13mpg fuel economy is acceptable (post #207). At this point I have duplicated exactly what blazer74 relates as his experience in post #169 I think it is what it is with E10, mech pump, and no return lines (never have nailed down by how much return lines would reduce fuel temp - though it is clear this is what the return line is for - said best by dyeager in post #175).

Final issues
The last issues to resolve are my electric choke, the fuel pressure gauge, and checking the A/F on wideband:

I bought an electric choke that had more heat coils in the picture but they shipped me the cheap version, post #205. I will buy from some different vendors and see if I can get one. Alternative is return to the heat pipe - my coil for the heat pipe has a bunch of coils.

Check the fuel temp with the insulating sleeve, the radiant heat sleeve, and with no sleeve. Maybe I will buy a steel fuel line and check fuel temp for steel line versus rubber line.

Anyone know why the fuel pressure drops as the temperature rises (post #215)? I will search online too. Answer my own question -->
"The glycerin used to fill the gauge heats up and expands, and being inside a sealed container (the gauge case), the internal case pressure rises. Internal gauge case pressure can increase as much as 1-9 PSI above atmospheric pressure when hot. For every 1-PSI of pressure rise inside the case, the needle will fall 1-PSI." aeromotiveinc.com
Sounds like with 8psi cold a fuel pressure regulator is in my near future - that could change the fuel economy.

The wideband is still on the back of my mind. Probably first I will take it to the shop - they all have dinos for the smog check, we can check the tailpipe A/F.

Where to next

Timing
 Next, once the choke starts working like it should, I want to go back to sreidmx's recommendation to understand how my timing advance works and tune that. I confess - the advance curve is a huge mystery to me. I will start a new thread for timing and go at it.

Cooling
Also a new cooling setup is in the future (post #211) - the OEM '74 radiator was marginal when new. I'd like to use a dual electric fan and a redesigned radiator. What I have now works 98% of the time (cant beat a flex fan for simplicity) and even in the 2% of the time things are not nice it gets me by with some attention - so it is difficult to justify spending time on the cooling.
 
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Sorry for the long summaries in my last couple posts - I wanted to get everything together with links back to the various posts.

At this point I have done everything there is to prevent fuel bowl evaporation through moderating fuel temperature - without going to a return line (the return line as a solution is still a theory - I have not found a thread that documents fuel temperature in a system using the return line).

I am going to tackle the last three issues one at at time: first pressure regulator, then choke range of operation, and last, check the A/F on wideband (presumably it is good but this needs to be measured).

Pressure regulator

It looks like I am back to the pressure regulator. Back in post #1 I suspected a low fuel bowl level from backflow and siphoning, so I was going to either A) put in a backflow valve and/or B) replace the fuel pump if they had an internal backflow valve that had failed in my 30 year old fuel pump. Cliff suggested that I just remove the float hook from the needle - and backflow is no longer an issue. In post #2 I looked at the fuel pump specification for pressure and volume. By post #3 I realized I might have a fuel pressure issue outside of whatever was going on with startup.

Does anyone here have anything on fuel pressure regulators (Jegs should pay me for this)?

 
Sorry for the long summaries in my last couple posts - I wanted to get everything together with links back to the various posts.

At this point I have done everything there is to prevent fuel bowl evaporation through moderating fuel temperature - without going to a return line (the return line as a solution is still a theory - I have not found a thread that documents fuel temperature in a system using the return line).

I am going to tackle the last three issues one at at time: first pressure regulator, then choke range of operation, and last, check the A/F on wideband (presumably it is good but this needs to be measured).

Pressure regulator

It looks like I am back to the pressure regulator. Back in post #1 I suspected a low fuel bowl level from backflow and siphoning, so I was going to either A) put in a backflow valve and/or B) replace the fuel pump if they had an internal backflow valve that had failed in my 30 year old fuel pump. Cliff suggested that I just remove the float hook from the needle - and backflow is no longer an issue. In post #2 I looked at the fuel pump specification for pressure and volume in anticipation of replacing the fuel pump. By post #3 I realized my current Carter replacement fuel pump might have a fuel pressure issue outside of whatever was going on with startup.

Does anyone here have anything on fuel pressure regulators (Jegs should pay me for this)?

As a side note, in the reviews one guy said he gets his pressure regulator into the 2psi range using holley secondary springs - he said it works really well.
 
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