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

Biggest and common mistake is over-tightening front mount bolts. Can ruin the air horn. Or using wrong gaskets will throw you for a loop.

I like to just snug them up and resist temptation to tighten further.
 
I just tighten the flange and front bolts finger tight and then give them a half turn with the wrench - I think I read that on a post here in CK5, then spray some brake cleaner or chem-tool to check for vacuum leaks (EDIT: I now use a propane bottle (no fire) to check for leaks).

this was my brother-in-law's carb back when he was in high-school, odds are he torqued it, I found it in the back of the garage; my holley carb flange was bent - so I did it too
 
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after sitting a few days I tried starting the blazer and it did not start without turning over for awhile - removing the clip from the float and needle did not work, so I guess the fuel is not back siphoning, or at least it was not prevented by removing the clip

I will try dyeager535 idea and directly measure the fuel float level each day and see how much fuel is gone. I have a chopstick that looks about the right size to fit through the vent.
 
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I will tell you that when it's cold out like 40's or less if I start my cold blazer for a minute or so and shut it off with the choke still set after a few days it will still start right up within a few seconds and that's with out touching the gas.

Put it away heat soaked and I'm good for about a day, in the summer/longer in the winter but after that crank and pump.
 
we notice fuel evap issues in the boats big time with the ethanol.. all standard quads pretty much.. tho they are going the way of the dodo, I still have about a 1/2 dozen mills in the yard with em...

it's not like the old days of reg gas, sit a couple months, pump twice, light right off... with the ethanol after a couple months you can get in and wap the throttle a couple times and you get nothing... wrrrr, wrrrr, wrrrr, wrrrr, pump, pump, fire...
 
it's not like the old days of reg gas, sit a couple months, pump twice, light right off... with the ethanol after a couple months you can get in and wap the throttle a couple times and you get nothing... wrrrr, wrrrr, wrrrr, wrrrr, pump, pump, fire...




I remember those days, and in the k5
 
yup, reg gas had it's varnishing issues, but I'll take that over the probs we see with ethanol on a daily basis, phase separation, effects on rubber and filters, white deposits, etc....
 
I'm to the point anymore that ethanol is probably evil. At least 94% so.

Filled up a spare fuel tank (about 30-40 gallons) with the stuff about 3 weeks prior to using it a month back. Tank is vented at a fairly low pressure, but not open to atmosphere. After just 3 weeks, putting it in an OBD2 car (10.5:1CR on 87 octane) I actually got a "stop driving the car something seriously bad is happening" flashing engine light immediately upon refill and trying to drive out of the driveway at idle speed. Car consistently (as in last 40,000 miles, so 100 fillups?) knocks down 40+ MPG every fillup. Since I couldn't measure how much I was putting in, couldn't calculate mileage exactly, but it was very, very clear after the first fillup that I was getting way under that.

And ethanol that has sat for 6 months? Could not use the pedal more than 1/4 of the way before I got a cylinder misfire flashing CEL, which took two nearly full tanks to dilute enough to not cause issues. Same vintage gas in the ~9.5:1 350 had some audible knock under heavy throttle which of course it doesn't with "fresh" gas.

Not sure if it can be attributed to picking up water or losing detonation resistance very quickly, or both, but this never happened pre-ethanol. Even though I'll feed my lawnmower 1:1 gas/oil (don't ask) I have second thoughts about leaving gas in cans over the winter for it.

I'll not be surprised to find that vaporization is worse. Coupled with it's propensity to pick up water, you are likely to end up with a worse air/water mix than you would with "pure" gas. I try not to leave any of my vehicles with more than 1/4 tank if they are going to sit anymore, as I'd rather not have these problems again.
 
it has been a bit since my last post - anymore I have to get to my father-in-laws for shop space

I have not checked to float level yet after shutting down, but I plan too

Just to wall-off the possibility I have a hard-starting issue and it is not a dry fuel bowl, I pulled the plugs and checked the compression. All eight are between 150 and 165psi after three strokes, with a strong 120psi on the first stroke. That was a cold test and I forgot to wedge the throttle plates open. I think those numbers are good. When I find my notebook I can compare with the compression test when the engine was fresh.

I put some new sparkplugs, it had a set of autolite 145 short tips that I must have put in sometime in the late '90s (until recently I haven't drove the K5 since 2002) and replaced them with some AC R44TS (long tip), the gap was .035 now .045 - seemed to idle a bit better, already good so no big difference. After a few weeks I will see if starting changes.

I asked Cliff about the power valve spring he sent with his rebuild kit - he included the spring he figured was best for my setup. I didn't install it, so I need to open the q-jet and add his spring (EDIT: got added at some point).
 
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Update as you get time...will be interesting if nothing else, to see what you find!
 
well i read most of this thread.. sounds like you might have a few problems going on here. I really think you need to stick a wideband on this bad boy to really see whats happening to the mixture, you might be surprised in your findings.
My k5 has the return style mech pump and I always had a cranking issue. I messed with my idle mixture and that helped a bit, seems though my engine likes 12:1 afr and no leaner. Switching to an Air-gap manifold and holley's has erased even my need for a choke! it will idle in 20+ degree weather no problem. I think your issue might be the sum of a few things. you might have an issue with your idle bleed circuit?? mybee you are getting air from somewhere else making the issue worse.. my first k20 was a 400 sbc with a qjet and it was a single bump start.. from my experimentation with the holley's its really finick with timing and idle mixture for that to occur.. Its obviosly going to be different for every engine. good luck I hope you figure this out.. If you really believe the fuel is evaporating id try raising the rear portion of the hoof to allow radiated air to escape and see if that helps.. Also if you painted the carb black it will radiate the heat quicker also..
 
Thank you sreidmx, that all sounds like good advice.

My holley always started right up on this blazer, not even a slight hesitation to start. I switched to a q-jet to get better 600rpm and 500rpm lugging in first gear in parking lots. The idea was so my wife could drive the kids, she has yet to drive even once after 6 months (EDIT: make that 12 months). In all reality, she probably thought the truck did not run and I was full of bs when I said it would start right up and I could just put small tires on and takeoff the lift for her. I'd planned to do it anyways, it was just a matter of finding some motivation.

The K5 started right up, and then my father-in-law tells me I really need to take off the holly to make it drive better and fuel mileage and all that. So, I find my brother-in-law's old q-jet sitting in the back of the garage and rebuild it. It gets worse gas milage than the holley, starts like crap, makes a lot of noise but not much else, but it does idle lower. Plus you can drive a q-jet sideways without flooding it. Everything I remember about q-jet back in high school and my original reason for putting a holley on my K5.

I filed the q-jet surfaces flat, but it is possible there is some air leaking. A suggestion given in an earlier post was to take measurements on the float level every so often for a few days after shutdown. That is on my list of things to do. I only drive the K5 twice a week so it is easy to let this fall off the radar.
 
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I bought a temp gun and measured the fuel line and exhaust temperatures. The setup before measuring was a couple hour drive on a cold night (above freezing but less than 55 deg F). As soon as we parked at home I crawled under with pen and paper and took these measurements - the truck was idling. One thing I noticed is when the fuel float must have been closed the fuel temp rose and when it must have opened it dropped. Around the headers I was getting inconsistent readings from 80 degrees F to 110 deg F, that is all I can figure was going on.

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K5_temp.jpg
 
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Something I have overlooked in diagnosis. I have not checked my voltage at the coil. Super simple check that could be the source of some problems. In shop class at the community college I recall air-fuel-spark. I better check my spark.

Back in 1994 when I built the K5 I did not fully understand electrical wiring and the importance of preventing voltage drop. Plus my high school evening job at the local clays range did not pay for much in the way of parts. After a few university classes having to calculate voltage drop in electrical wiring, I am little more sensitive to the topic. All my wiring was done dry, no solder, just crimping those little colored connectors you get at the parts store. I'd bet they have corroded a bit over the years. Plus, my wire sizes could be off, I used to just eyeball something as 12ga, 10ga, or 14ga. Neverminding the length of the wire run.

Next weekend I think I can get up to the in-laws place and do some electrical checks, father-in-law should be handy since he 1) is an electrician and 2) works for a brewery that gives him free beer.
 
This is a returnless setup, right?

Pretty easy to see why GM went with them if so, those temps get close to boiling pretty quick.
 
Yea heat soak could be the issue I just don't see how even with a phenolic spacer it could reduce it 60 degrees. The other consideration might also be your timing not being perfect enough to start it quickly.. There is so many factors at play here it's not even funny.
Also if you really need that low of rpm you need a modified holley that can have adjustable air bleeds to operate at the lower rpm and it will but it won't out of the box..
 
Man, this is a long thread, and a long time of not having a solution yet. I too, only got to page 3. :whistle:

Here's my humble opinion: These trucks ran great new/stock.
Heat shielding lines- no.
phenolic spacers- no.

Stock parts, quality stock parts, set to factory specs.

I think it'd be great to email cliff and give him the link to this thread.

There's a couple regulars in this thread. Maybe, if they're lazy like me, make a recap post. Summarize what has happened, what you've done, what your original goal is, and where you sit right now. I know you wanted to lower your idling/slow speed rpms, but why? How much lower than factory? Hard starts? List ALL of your specs. Qjets are more complex, but they should run PERFECT when tuned properly.

Oh, and if you don't have 'em, I suggest getting All three books, the Haynes Qjet book, Cliff's, and Doug Roe's. I don't think I'll be using mine anymore, so you're welcome to them if you'd like.

And I agree with sreidmx, there's so many non-carb related things that could be masquerading as a carb issue.
 
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