Sounds like that Qjet might be leaking out those pesky bottom plugs. I haven't done a Qjet in very long time. If that's what it is just put a tomco plug in it and all will be cured. Those Qjets are good carbs for street use, don't let anyone talk you into a Holly unless you don't mind replacing power valves, gaskets etc every time you come home.

 

Qjet leaks

I haven't done a Qjet in many years. They were however prone to leaking around the small expansion plugs on the bottom of main body. Common fix used to be to install a Tomco Plug. It's a dense foam pad that goes under those expansion plugs. Sounds like that could be the problem. It's worth a look. Don't let anyone tell you to replace Qjet with a Holly unless you don't mind keeping an extra power valve, float bowl gaskets etc in your glove box. Qjets are a great carb especially for street use.

 

Whoops

Looks like I posted twice. Sorry but still can't emphasize enough on not using a Holly.

 

nothing wrong with a Holley or an eddy for that matter.
Learn how to run them. They all have their little quirks!
The wells on a quadrajet don’t leak enough to show up on the gaskets. If they leak and likely aren’t.
You might have a high float level, or stuck needle/seat causing flooding.
You need your float level set lower at elevation too.
And you need more initial timing too.
Find and fix the flooding first.

 

I don’t think it’s the well plugs. Did the J-B weld thing. Plus it starts right up. I did not take in account 2500’ elevation when setting float level though. Only starts acting up after carb gets warm.

 

Did you rebuild the carb yourself?

 

I did rebuild it myself. I can check the float level later today.

 

While you’re in there check your needle clip is installed right.
Info in here.
http://www.crankshaftcoalition.com/wiki/How_to_rebuild_a_Rochester_Quadrajet_4MV_carburetor

 

Sounds like a heat problem. Did you install the heat riser block off plates in the intake manifold gaskets? Are you running ported or manifold vacuum advance? You say 14° timing, but what about the advance curve. Timing can also have a lot to do with temperature. As an aside, I really don't understand why you would go to all the trouble of building the basic 383 correctly/carefully and even get a boutique cam - then use a spread-bore to square adapter and a QJet on a square Performer RPM manifold? Carb adapters are one of my pet peeves.

With Brodix heads, a serious boutique roller cam, and a dual plane manifold on a 383, I would slap a 750-850cfm Holley or Quick Fuel on there. DP if you are light weight. Vacuum secondaries if you are heavy or lower stall converter. Don't forget the rest of the fuel system necessary to feed such a beast. Best strategy is 14 psi pump / 6an line - then regulate it down to 6.5 psi right at the carb.

 

Something like this. A return line regulator would be even better, but I haven't found the need on my vehicle.

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What is your fuel pump mounted on? And what is the mount mounted to? Looks nice.

 

If you want to evaluate temps easily, get an IR thermometer from Amazon.

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Runs crappy when hot. In my experience it was two things, well three. The fuel boiling in the carb and/or boiling/partial vapor lock in the mechanical fuel pump. Or the brand new MSD distributor. Took me so long to find out it was the distributor that it was out of warranty. The MSD ready to quit, I really don't know what was wrong with it. It didn't stumble or miss, not much anyway but it felt like it lost 75-100HP when hot.


You already have the spacer, that's good to insulate, (hollow side up) but did you block off the exhaust crossover in the intake manifold? (if you do, don't use the cheap aluminum things that often come with the gaskets. Cut some sheet metal and make your own. (I had a backfire that blew out the thin aluminum ones.)



That fuel leak is really odd back there, I'm guessing you tightened the screws a little more? Get it good and hot till it acts up then pull the air cleaner to see if any fuel is bubbling out the carb vent. I didn't want to pull the manifold to add the block off plates so I did the spacer first and it only helped. Blocking the crossover made it much better. If your studs are long enough, or buy some all thread and make new ones and add the 1/4" gasket above the spacer.



What is in your ignition system? Could be a bad coil also, they most definitely can get weak when hot. What is the saying? "Most carburetor problems are in the ignition". Also when it's actiing up, measure the voltage going to the + side of the coil. I also had a bad ignition switch that gave me low voltage to the coil, but only at higher rpms. So you may have to rev it a bit while checking the voltage.


Edit: Why do my single spaces between lines above show up as two or sometimes 3 spaces???

 

I just looked up the Brodix IK heads. They don't have the heat riser crossover passage, so can't be a problem there.

 

I had the Q Jet and spacer so no $$. Re Manufactured stock HEI I also had on the shelf that I added a Per Tronix PNK-7200 flame thrower module. Yup no exhaust crossover. Ill check the needle and seat for leaks with vacuum. its not really getting all that hot. weather is in the 60s, no hood and new aluminum radiator. Stock fuel pump.

 

Well it looks like my bad. float level should be 15/32 for#7045229 Q Jet not 3/8 as I had it set. I recall having trouble using that little paper scale that comes in the kit. That is the excuse in going to use.

There is no info on adjusting float level above sea level. I thought that was just jets .
Ill run it tomorrow and see how it does.

 

So you raised the floats 3/32.
No gain there.
I always set my floats lower due to reduced air pressure.
Right or wrong that worked for me.

 

What does air pressure have to do with float height?

 

Well the float adjustment didn't help. I did set it a hair lower than called for.
I had an extra HEI with cap @ coil so I swapped it out. I got it to idle at 850 It ran for a few minutes. Initial timing at 14.Even adjusted it to peak vacuum 10LB until the idle would drop off and try to die. Kept it running, it will stabilize for a minute then try to die again. even Ideling at 1100 for a minute it will drop idle and try to die.
Guess its time for a new carb but with budget im not sure which way to go.
Its about 2800lb with me in it. 4l60 with 2600 stall. Probably change to 4l80 with higher stall. 343s but have 373 limited slip.
Summits 750 for $320 sure looks good in the add but is it really. I hear Holly's quality isn't what it use to be. Quick fuel sure has a lot of models

 

Summit's 750 house brand carb is a good carb, it is the latest generation of the Ford Autolite 4100 type design, rehashed by Holley in the mid 1980's as their 4010/4011 models(4010 squarebore/4011 spreadbore) and then dropped from production in the mid to late 1990's when it didn't catch on with hotrodders and sell in the numbers Holley was looking for.

Summit had the Holley rendition redesigned a bit so that it takes regular dual feed lines(Holley version took a special dual feed line) and has fully adjustable booster clusters with replaceable bleeds and pump nozzle orifices(Holley version had to replace whole booster cluster to get different pump nozzle sizes) thus making the Summit version a big improvement. Jets, powervalves, pump diaphragms, vacuum secondary pod diaphragms, needle and seat are interchangeable with all common Holley tuning parts
Another plus s that is has annular boosters, which give a stronger mixture signal than other booster designs.. Has no gaskets below the fuel line to leak.

If looking at QuickFuel, look at the Slayer series. Every easy tuning feature most street and street/strip guys could ever need at a good price.

 

I can't see the carb acting up as the motor warms up or like you describe later. After it quits, I'd pull a few spark plugs to take a look. See if they are wet and dark or dry and white.


Is the motor completely warmed up when it quits? Such as after a drive for 15 minutes, or doesn't it run well enough for a drive? Will it quit just at idle or at say 2000 rpm?

 

When I re set the float checked the air horn for flat. .018 warped. Just ordered a Quick Fuel Slayer.

 

Good choice! 750?? Vacuum Secondaries?

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If you get a new carb look at the holley store on ebay as they sell refurbished carbs that you can get for some good prices that are less then $300 depending on the model and its original price. They are as good as new and normally are ones that people have bought and adjusted and did not know what they was doing and sent them back and said something was wrong with them etc.

I have bought a boat load of the refurbished ones and checked the over when I got them and they was always good but I will say if your going to get a holley style carb go with a quick fuel brand one as they are way better with more adjustments and changes you can make to them compared to a equal price holley brand one for example the 3310 750 vacuum secondary vs a quick fuel 750 slayer vacuum secondary carb. The slayer has way more areas you can change and recalibrate with out having to modify metering blocks etc.

Also the last two years that I have gotten some brand new and refurbished holley brand carbs and a few towers of the older classic ones like the 1850 vacuum secondary and 4777 double pumper holley has been having some of there boosters in the towers be kind of on the loose side to where you can wiggle it with your finger and I have to rip all of those boosters out and i installed down leg boosters to fix them and make them have better flowing boosters anyways but the quick fuel carbs i have gotten i have not had to do any of that as there boosters have been as tight as can be.

Holley owns quick fuel but they quick fuel carbs seem to have better quality control for the time being. There is also the quick fuel brawler series which are very nice as well.

 

Good choice with the slayer carb as they are very nice and really perform nice once dialed in. Let us know how it goes once you got it hooked up.

 

I did the same thing on my 383 with forgetting the gauge. Yes just get one.
It's needed.
Then the next time you can find some dollars get an air fuel gauge. Best tuning money you will spend.

 

Its running with the slayer carb. sl 750 vs. Had it idling fairly well around 850 rpm. Wants to die when put in gear so feathered the gas to drive it. Comes with a 6.5 power valve. I need to check vacuum in gear but ran out of time. Need to read up on tuning the carb. Plugs are Autolite 3924 @ .035 timing at 16

 

On the idle speed drop and trying to die when placed in gear, richen the mixture screws a bit, 1/16 to1/4 turn out from highest vacuum/best idle speed settings. See if that helps you out.

Performance engines rarely like being idled at best lean/highest vacuum settings, they like to be a little rich compared to more stock type engines due to camshaft duration and overlap being larger.

 

On the idle speed drop and trying to die when placed in gear, richen the mixture screws a bit, 1/16 to1/4 turn out from highest vacuum/best idle speed settings. See if that helps you out.

Performance engines rarely like being idled at best lean/highest vacuum settings, they like to be a little rich compared to more stock type engines due to camshaft duration and overlap being larger.

Agreed!! I'm also curious how the timing is set up and if ported vacuum is being used. Previous posts indicate rebuilt HEI with a Pertronix Module installed - but we really don't know if its a stock rebuilt distributor from NAPA or a performance distributor with performance advance curves. But generally speaking, if he is using ported vacuum and he has no vacuum advance until he is off of idle, then 16° is not much timing to idle very well on. Getting the timing advance curves set up right could also help improve things - but as you say, getting the idle mix right is the first thing to do.

Goneagain, I'm curious what are your cam specs? Please include LCA (lobe center angle) and intake centerline. Did you degree the cam? How much vacuum do you have at the 850 RPM? When you adjust the carb, remember to adjust all 4 idle screws just a touch in or out at a time (instead of trying to get best idle while adjusting on one idle mix screw). Start with them all out exactly the same distance out from lightly closed. Need to keep them even. Just a little nudge open or closed on all four will make quite a difference once you get close. I think most of the 4 corner idle mix QF carbs fall within about 1/2 to 3/4 of a turn out in the end, but there could be exceptions.

 

16 degrees at idle is a lot of timing. You should not need that much low rpm timing unless the engine has an aggressive cam and higher compression. If you back down the timing and then reset your idle fuel mix I bet you'll get a smoother idle in gear.
When you reduce the timing the idle will go lower too. So be ready to open the throttle a bit.
I have my marine 750 Quickfuel idling around 725 and it falls to 650 in gear. The engine is a 10:1 383 Chevrolet.
I love the exhaust sound when I can get it way down on rpms. My pipes are effectively open, they just run through a mixing chamber where they get some water added.