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

[blazer74]

From my experience you don't want pressure maintained in the lines between the pump and carb.
Hot start problems can be created by pressure build up in the lines due to heat.
After hot shutdown pressure builds and overcomes needle and seat causing flooding requiring pedal to the floor for start after about 15 minutes. I had this issue.
I have the holly reg in my closet, yet to be installed would remedy the pressure build up I would think.
I had this problem with my stock pump, remedied by a EDL pump , 5-6 psi and drops off pressure within a few minutes of shutdown.
Be cautious of over the counter pumps. Many put out to much pressure, as much as 9 psi and cause flooding issues.

 

[dyeager535]

I may have mentioned this somewhere in the previous 221 posts (lol), and I'm not sure it's applicable, but with my TPI setup, when I was running such low fuel pressure, about half of spec, the fuel rail was about the temperature of the intake manifold. Too hot to touch while running, and it's aluminum. At that fuel pressure, nothing should have been returned to the tank, so essentially a returnless system, soaking up whatever heat is conducted to the rails.

With the pressure issue fixed, the rail is cold enough to touch under the same conditions.

Looking at it another way, a return line doubles the length that heat can be radiated from the fuel.

 

[my kids took the truck]

there is real experience - the fuel reaches engine temperature without return line

in an early post you had the idea that the return line will eventually heat the fuel in the gas tank - have you had a problem with this or heard of it? If the fuel in the tank warms then the evaporation will increase and the fuel temperature will be intake temp (header temp?) no matter what.

to be honest - I just now fully got onboard with the return line theory and why it is so important, and can now see why the Chevy engineers added the money to put in two fuel lines (I am slow - it only took 200+ posts to get that across to me)

a question - a '74 K5 has a single line, my '72 1500 had a single line and I assume every chevy back to the first V8 had a single line, why did it take them a decade (return introduced in '76?) to figure out they needed a return line?

I don't think a return line is in the works for me (this hotrodders thread talks about adding it to an earlier system) but I can see that if I ever change the OEM fuel tank (ethanol fuel makes this likely) then I should seriously consider a return line at that time.

blazer74 - I agree, my carter replacement pump is supposed to be 5psi max output not the 8psi I measured (and that was after a 90 deg fitting, a few feet of rubber hose and a filter - it must have been 9psi or 10 psi at the pump).

 

[dyeager535]

I'm sure it increases tank temp somewhat, but I never did measure it...you'd need to know how much based on ambient. And controlling for all the variables would be pretty hard to do.

I suspect GM made that change for the same reasons they went to Vortec heads, fuel injection, one piece rear mains, redesigned valve covers, etc....people expected more of their vehicles/competition, and emissions regulations forced them to.

Engines lasting under 100,000 miles was the norm, way back when, if they even got drive that much. Times changed.

 

[my kids took the truck]

• I ordered a 4psi to 12 psi fuel pressure regulator and the AN to 3/8" hose barb fittings - will let you know the results; I expect the fuel economy should improve a bit.
  
• Fuel return line - I have seen adapters that add the return line to the fuel filler neck, but also saw that this is not a good fix since the fuel continuously drains down the filler and adds air bubbles to the tank. Someday my steel fuel tank will suffer from the ethanol and will need a plastic replacement, return line will go in then from a donor truck.
  
• On the timing side, as suggested in this thread, I have the CRANE timing kit. I will change to the light springs and the adjustable canister. Not sure why the GM performance HEI did not have these as features. My wife said that from the stop light getting going in 2nd gear (3.08 gears) she has to think to not stall it with the clutch. I have it tuned lean and if the idle is richened or idle speed is higher you can dump the clutch and it goes. Maybe if the ignition advance comes in sooner that will be the happy balance between lean and go. EDIT - new thread for HEI tuning.

Probably a few weeks until I get these parts in and re-tune.

 

[dyeager535]

Will be watching. I enjoy your dedication to this.

 

[my kids took the truck]

Will be watching. I enjoy your dedication to this.

appreciate your dedication to stick with this thread

On the timing side the Crane yellow springs (lightest) seem to have worked - the stop sign off idle feels much better and less need to pay attention to the clutch throttle - my wife will be happy. I will create another post https://ck5.com/forums/threads/tuning-hei-for-4spd-350.323538/ but now I want to know what OEM springs are in the GM Perf HEI.

The fuel pressure regulator has AN fittings inlet and outlet. Just in case anyone else goes that same route; I bought the same pressure regulator that is pictured in that clean engine bay I put in post #9 Mostly my logic is if that pressure regulator is good enough for that guy and he seems happy with it, then good enough for me, I don't need to go explore some other regulator and take my chances.

In that setup he used AN fittings and hose - I don't want to change my hoses to AN so that required finding some AN to 3/8" barb fuel fittings - they were not as easy to find as they seemed; Sweet Performance has them through his ebay store http://www.ebay.com/usr/sweet_performance

• -6 O Ring Boss 3/8" Hose Barb Adapter AN Fitting ORB
• -10 O Ring Boss 3/8" Hose Barb Adapter AN Fitting ORB
• -6 O Ring Boss Port Plug

 

[dyeager535]

I will create another post, but now I want to know what OEM springs are in the GM Perf HEI.

I should break out the parts manual and see how many spring/weight combinations GM used on the trucks. I assume they did a ton of tweaking with them (same as needle/seats in the carbs) so having a "one size fits all" performance setup would seem a bit counter-productive.

The amount of effort GM took doing what we would consider miniscule changes, that we could probably never feel, are pretty amazing IMO. Obviously most of it this vintage was all for trying to get emissions where they needed to be, but still a ton of research, development, and testing to accomplish each model year.

 

[my kids took the truck]

I should break out the parts manual and see how many spring/weight combinations GM used on the trucks. I assume they did a ton of tweaking with them (same as needle/seats in the carbs) so having a "one size fits all" performance setup would seem a bit counter-productive.

That is a really good point.

 

[dyeager535]

If you have the time and desire, download the parts manual(s) at the link in my sig. You'll probably need the non-illustrated portion, as the springs/weights if they were different will just be listed as a group number instead of PN anyway. They have a pretty good selection, so you could choose which years you wanted to compare. I'm sure the weights/spring difference between a 305 with 3.08's and a 454 with 4.56's would be quite noticeable if swapped out one for the other, but if they used a different setup for a 305 with 3.08 and 3.42, probably not nearly as noticeable.

 

[my kids took the truck]

The big news - the weather has cooled a bit and for the first time after four days, the blazer started without having to prime the fuel bowl. I think when I started all this it was two or three days and I had to prime the bowls. So, four days seems reasonable - a week would be better.

dyeager535 - I downloaded your parts manuals awhile back and looked at the list of vacuum canisters and springs - quite a list. I just have the OEM Perf GM Dist mech advance springs (1,400 to 5,500 rpm) and the sets of springs that come with the Crane kit.

I have been playing around with the Crane timing kit https://ck5.com/forums/threads/tuning-hei-for-4spd-350.323538/

 

[my kids took the truck]

This morning I installed a 4psi to 12 psi fuel pressure regulator - I will post photos in bit.

There were not a lot of options for where to attach the pressure regulator - under the wireloom next to the carb there are no bolt bungs only the manifold bolts. The options seen in the following images A) hole in the frame near the fuel pump, B) bolt on firewall near heater hose, C) intake manifold thermostat housing or alternator bracket bolts, D) attach to alternator bracket, E) fab bracket to mount to carb bolts

The fuel economy over to the inlaws was 12.2 mpg and on the way back after adding the pressure regulator is 14.5 mpg. On the way there I'd occasionally get a boggy feel from the blazer and then it would clean up an run. On the way home that boggy feel has gone away and now it drives noticeably better.

 

[my kids took the truck]

To wrap up this thread, back in post #1 I could see my fuel backflowing after shutdown and I suspected this was causing a hard start condition a few days later.

During the resolving of this problem I have found a few things

• Hard start due to no fuel in fuel bowl and in-turn the accelerator pump
  • Fuel now (2005+) has ethanol - ethanol evaporates easier than gasoline and back in 1966 when they designed the q-jet "The Design Evolution of the Quadrajet" the fuel bowl was barely adequate to hold enough gasoline so that after evaporation there was enough to restart.
  • The '75 and earlier chevy trucks and blazers do not have fuel return lines (as noted by @dyeager535 in post #21) and this means the fuel is hot - up to 150 degrees F (fuel boils at 160 degrees F) around the headers and over 100 deg F before entering the carburetor. After shutdown that fuel evaporates and creates a dry fuel bowl as well as the hot fuel hurting performance (maybe contributing to detonation too). I need to add a fuel return line (I added insulating screens on header tubes near fuel line and on muffler near fuel line - reduced carb temp 60 deg - with changes, comparison to temp graphic in post #76 with fuel temp after insulation is in post #174; note #76 is a 50 deg night and #174 is a 75 deg F day).
  • The carburetor has a hot spot under it - it is 200 degrees F and the carburetor is 190 deg F. That means that the fuel will evaporate after shutdown and cause a dry fuel bowl as well as the hot carburetor hurting performance. You need to add a 4-hole phenolic spacer under the carburetor (carb baseplate temp reduced from 200 deg F to 100 deg F).
  • The quadrajet carburetor has a hook that connects the fuel float to the fuel needle and seat - when the hot carb and hot fuel cause evaporation that lowers the fuel level the then the float pulls the needle off the seat letting fuel drain back - further aggregating a dry fuel bowl. You need to remove the hook from the float (no more backflow).
  • The quadrajet accelerator pump does not have a backflow check valve like a Holley does and the accelerator pump on the qjet is parallel to the fuel bowl rather than under the fuel bowl like the Holley, so when the fuel bowl level drops so does the accelerator pump shot
  • The sum of the previous five problems means that after 48 hours there will be insufficient fuel in the fuel bowl and the accelerator pump shot will be insufficient to start. Resolving the previous five problems (except for return line) means that the fuel shot will be extended from 48 hours to between 72 and 96 hours. After that, you need to turn over the engine to fill the fuel bow (suggested solution is to add an electric in-line pump to prime the bowl but I did not try this).
• Additional problem with fuel and quadrajet
  • The quadrajet needle and seat is not good with fuel pressure over 5 psi.
  • Many of the (maybe all) fuel pumps while specified for the quadrajet put out too much pressure (>6psi).
  • The result is a boggy feel when the fuel overflows the fuel bowl and leaks into the throttle bores - while this does not contribute to a dry fuel bowl it is still not cool.
  • The solution is you need to add a pressure regulator (seems somewhat mandatory).

After that, in addition to a functioning choke you have the tuning - from what I can tell, tuning requires a wideband sensor (advisable) and an HEI timing kit (somewhat mandatory); there are lots of threads covering these two topic so I won't contribute anything though through this thread both topics came up and were relevant.

Lots of thanks to the guys that helped walk me through resolving these problems.

The solution for the pressure regulator is to mount it to the alternator bracket with a sandwich bracket; the firewall required nearly six feet of fuel line passing near the headers, the intake manifold did not have anyplace to easily bolt and heat would transfer from manifold to regulator, and the frame location was too close to the fuel pump to get a filter between pump and regulator. Removed the insulating sleeve I had added to the fuel hose - the idea is to let heat radiate from the hose. From regulator to carb I kept the insulating sleeve and for the first section after the fuel pump where the fuel hose is near the block I kept the sleeve. I added teflon washers and the regulator mount has rubber washers to reduce vibration. The fuel in the filter is cool to the touch but this is before driving for a couple hours - I will check with the heat gun and edit this post.

 

[dyeager535]

Nice wrap up! It helps to see all the high points summarized.

Another thing we never talked about....did you ever try a "sealed" (factory) air cleaner? I don't know as it would really help with evaporation, but with all you've done to it, I just wonder if the open element doesn't help encourage the heated fuel to evaporate faster with the potential for unrestricted airflow?

Seems somewhat unlikely, but GM did install a carbon element on the air cleaner assembly for just that purpose in the 80's, so there must have been enough to worry about.

 

[my kids took the truck]

It probably would help slow the evaporation though how much is debatable. The carbon filter they used certainly shows there is still evaporation even with the enclosed filter. All things equal I'd rather have a closed air cleaner with a cold air intake but I don't think it will ever get high enough on my list to actually happen.

 

[dyeager535]

I have never had a closed air cleaner (for smog check I used to borrow one from my '72) it probably would help slow the evaporation though how much is debatable. The carbon filter they used certainly shows there is still evaporation even with the enclosed filter. All things equal I'd rather have a closed air cleaner with a cold air intake but I don't think it will ever get high enough on my list to actually happen.

Yeah, the temperature increase underhood is really not that much to make but about 5HP difference from what I figured, if you can't get to it you can't.

Now that I think about it though, as a holistic approach, if the air coming in was cooler up until engine shutdown, that would also tend to keep the carb cooler, eh?

 

[my kids took the truck]

A short update:

• Still have the dry fuel bowl sequence pump, wrrr, pump, vroom after three days - at best any changes will get me to four days
• The pressure regulator made all the difference (just feels different) - still haven't used more than a 1/4 tank so don't know the new fuel economy yet - on the Christmas run to the the in-laws I will go through a full tank.
• As far as cold air intake: we dug through that back in post #164, a short recap, there is a 20 degree F increase in incoming air temp from underhood heat - my carb was 190 deg F, after adding a carb spacer and fuel line shielding it is now down 60 deg to 130 deg F (in post #158 I talk about measuring a 70 deg F carb but not sure how) - maybe it is time to think cold air again, instead of a 10% change in temp from cold air, I'd now get a 15% drop and that would result in a cooler carburetor (I'd have to do the calc to figure out by how much). The big hangup is the '74 does not have a hole in the radiator support for an air duct and I don't want to cut one. My target is a 50 deg F carb operating temp, so cold air alone is not going to get me there. This ck5 thread looks at adding a cold air intake to a '74 K5 https://ck5.com/forums/threads/cold-air-intake-routing.233447/
• Something new - a source of heat is my fuel since the fuel line runs parallel to the exhaust from fuel pump to fuel tank with hot spots at the muffler and the header. In post #158 I gave the fuel temp as 127 deg F and earlier a measurement on a cold day was 100 deg F fuel. I don't have a fuel return so when the fuel dwells while the float needle is closed the fuel temp rises fast. Over in the "Second truck, first 4x4..." thread he has an innovative solution to the clearance problem created by the single exhaust crossover with the front driveshaft under the oilpan. He wrapped the exhaust pipe in front of the oil pan and then ran a single exhaust down the side without the fuel line. If I have a new exhaust (including ditching my full tube tri-y headers) in the cards then this might be my approach. See pic #1 in "Second truck, first 4x4..." post # 152. If my fuel stayed 60 deg F to 85 deg F or whatever it is in the tank then a 45 deg F drop in fuel temp should make a big difference (more than a 20 deg drop in air temp), both would be nice and then I'd be comparable to a post '78 blazer starting point (first year for return line is '76 and cold air duct is '79).

As far as a fuel return and cold air intake swap from a post '78 K5 (sounds like the fuel tank and pump from a post 87' is the ticket). I wish I understood the importance of air/fuel temp when I was 16 and A) had time, B) had energy, C) had money, D) thought laying in mud/oil for an hour at a junk yard was cool, and E) parts were still plentiful for K5s.

Next step:
Thinking: On a warm day the fuel is 127 deg F and the carb (with thick phenolic insulating spacer) is 130 deg F. Without the insulating spacer the carb is 190 deg F and the intake is 200 deg F. I don't think that is a coincidence that with an insulating spacer the fuel and the carb are the same temperature. Also, the air entering the air cleaner is 10 deg colder than the air in the air cleaner, meaning the carb is heating the air rather than the air is heating the carb. That means my #1 source of heat is the fuel.

Test: If I insulate the exhaust pipe that runs along the fuel line then the fuel should not pickup heat (insulated good so the frame rail is also not heated, that then heats the fuel line clamped to it). With the fuel insulated from the exhaust heat I should see the carb temp drop 50 deg F from 130 deg to 80 deg F. A few clamp-on 3' pipe shields (not good for mud) and a muffler shield should do it (maybe some pipe wrap to really get it).

Action: If that works then I don't need a return line or a cold air intake - what I need is a single exhaust on the non-fuel line side or I need to get really aggressive with pipe wrap.

 

[dyeager535]

For your air intake. Do the 70's rigs have pretty big openings in the fenders? The later trucks ('88+ C/K's IIRC) took air out of the passenger fender, and at least for testing, I would think temporary routing to there would be the easiest. I don't like hacking up sheetmetal. here is a pic of something along the lines of what I'm thinking of. http://67-72chevytrucks.com/vboard/attachment.php?attachmentid=867914&d=1328536023 Can't find a pic of the stock '88+ intake. At least the air cleaner portion should be easy to find.

The hedman 69830 will allow the exhaust to be run between the bellhousing and trans pan. I'd have to look closely to see if their routing would affect the fuel lines. If I can get a good pic or 4 I will. Weather has been terrible so it may take some time.

You don't need a post-'87 fuel pump, most were injected at that point. There were still carbed rigs at that point, but it's so uncommon it's better to stick with earlier, where there can be no mistake. (anything R/V '87-91 is terrible trying to work with auto parts stores for, you invariably get '88+ C/K parts) GM was running pumps with return lines at LEAST in the early 80's, pretty much any passenger car or light GVWR truck should have it. I know my '83 K5 with 305 had a return line on it.

Not sure if all or not, but the trucks with cats I've dealt with have a tin-type shield that bolts to the frame above them. Since GM used this for heat shielding, I would expect that it would be ideal material. I'm not sold on steel or AL, both absorb and radiate heat, I think there are so many variables along those lines that it would be hard to figure out what would work best without some serious temp measuring, and a lot of trial runs. Based on how GM shielded the floor from the converter heat, I think a thin plate (perhaps reflective, the factory piece is...whether that is just to prevent rust or help reflect heat, not sure) between the exhaust and the fuel lines is better than trying to insulate other ways, like reflective wrap on the fuel lines.

Another piece of the puzzle to note is that GM used double wall tubing for the exhaust from the manifolds, but I don't know where they ended that. What I cut off the truck a few feet from the manifolds was still double wall, only reasons I can think that they would have used that was for either sound or heat.

 

[my kids took the truck]

• The later trucks ('88+ C/K's IIRC) took air out of the passenger fender, routing to there would be the easiest.
• The hedman 69830 will allow the exhaust to be run between the bellhousing and trans pan.
• You don't need a post-'87 fuel pump for the return line, most were injected at that point (anything R/V '87-91 is terrible trying to work with auto parts stores for, you invariably get '88+ C/K parts) GM was running pumps with return lines at LEAST in the early 80's.
• The trucks with cats have a tin-type shield that bolts to the frame above them. Based on how GM shielded the floor from the converter heat, I think a thin plate (reflective like the factory piece) between the exhaust and the fuel lines is better than trying to insulate other ways.
• GM used double wall tubing for the exhaust from the manifolds. What I cut off the truck a few feet from the manifolds was still double wall, they would have used that for either sound or heat.

Nice comments - if time and $$$ was no issue, all five of your suggestions would get done

• The air duct from the fender is too tempting to pass up - I will add that to my test list, probably a year-out since the dual snorkel air cleaners are difficult/$$$ to find or build.
• I have a SM465 so the clearance for the crossover is a little tighter - new exhaust is on the 'probably not going to happen soon' list anyways.
• Good call on the post '87 blazer parts mixup with truck parts at the store - I was thinking more about a baffled tank and immersed electric pump with return line; this is also on the ''won't be done unless current fuel tank fails' list.
• Getting some cat heat shields from the local pickem' yard sounds like something doable - a shield on the muffler will cut down on a lot of the heat, cost less (though requires half day yard run time that is equally/more valuable) than other options, and if done right won't form a starting point for a mud rock.
• Double wall exhaust pipe - I like that idea too. If I have new exhaust installed (and the crossover single exhaust just won't work - see bullet #2) then I think some form of double wall tube will be in the works. I am considering heat wrap products for the near term. I need to look around and see how heat wrap does in offroad with heat, dirt, and moisture (no salt), as far as longer term rust problems.

Merry Christmas - heading out to the in-laws with the family

 

[my kids took the truck]

@dyeager535

back to your advice about air temp reduction versus fuel temp reduction - you are correct; my father-in-law had the same ideas as you and so I had to dig around the web and find some real numbers.

I found some key info in David Vizard's How to Super Tune and Modify Holley Carburetors

• every 5 deg reduction in fuel temp is equal to 1 deg reduction in charge temp (inferred from fig 11.10 in Vizard's; 120 deg F inlet air temp and 40 deg F fuel (reduced from 120 deg F) results in 18 deg F reduced charge temp - the baseline is comparable to my current temps).
• this seems to mean that each 5 deg reduction in air temp is equal to a 4 deg reduction is charge temp (air rules and the cold air intake should take precedence over efforts to cool the fuel).
• the result of reduced air/fuel charge temp is found in both power and timing

1. 1% power increase for every 10 deg F reduction in charge temp due to air contraction
2. every 8 deg F decrease in charge temp is equivalent to 1 octane increase (hotrod.com shows that nobody knows what this translates to since there are too many variables), regardless it means in my case more low end torque while staying out of detonation on grades at highway speed

interesting side note from Vizard's - he found a 5 ft-lb increase with the heat crossover removed (maybe includes 16 HP but Vizard does not say the HP change, 5% anyways and comparable to a 50 deg F reduction is intake charge temp - so regardless of what I do with air and fuel temp I would find just as much improvement by simply blocking my intake manifolds heat crossover)

Lets assume I A) get the fuel temp down 20 deg F and the air temp down 40 deg F for a combined (20/5 = 4 deg F and 40 * 4/5 = 32 deg F) 36 deg F reduction in charge temp, and then I B) block my intake manifold crossover for an additional 50 deg F reduction in charge temp, for a combined (50 deg F + 36 deg F) 86 deg F reduction in charge temp. On an 80 deg F day that reduction is equivalent to

• 86/10 = 8.6% horsepower increase (300HP * .086 = 26 HP)
• 86/8 = 10 octane points, so my 87 octane is now equivalent to 97 octane, and that would provide real benefits in either a more aggressive timing curve or larger safety buffer to stay out of detonation on hot days.