Carb recommendations

[Henry]

Hi:
It is certainly possible that one variation of the M4ME did not have a front vac break diaphragm...maybe for cars...but I doubt it. That image from the Haynes manual I sent you should be exactly what was M4ME configurations for trucks....the Haynes guys know their stuff!

I think when you get your truck back you will see that the correct port for the front vac break is there on the front of the carb...you just have the wrong hose to it now.

Concerning the THERMAC hose connection, maybe I am confusing you with someone else who was wondering what the hose connection under the electric choke was for...anyway, look to see if it is there. If not, maybe it should be the plugged pipe on the  throttle plate (front, pass side, bottom) of carb. How many vac ports do you have on the back of your carb (not including the big one that goes to your brake vac can)?

Evap Emission Control (EEC) port: OK, if you dont have the charcoal cannister anymore you should leave the cap on this port on the carb. It was used to send a vacuum signal to a valve in the cannister. I do not believe it was actually a vent for the carb.

PCV: You really should have this...you can do a search the forum to see where someone asked whether this was needed or not and a couple of us commented on the function of the PCV system. It was a couple of weeks ago on the "engine" section I think. The oem Chevy valve covers tend to get bent up and overtightened over the years so they do not seal properly...you can straighten the attachment points with a hammer and drift and if they are in such bad shape you can buy originals or aftermarket with the PCV holes. The Chevy oem valve covers and gaskets require a lot of attention to detail when installing such that you dont get leaks.

Vacuum connection at back of intake manifold: Yes, that T-fitting is supposed to have a top nipple (big) and side nipple (small). Short hose is supposed to slide over top nipple and then trans tube is supposed to slide into the short hose...I think this short hose allows the arrangement to bend over to the rear to allow your air cleaner housing to fit.

Choke and linkage adjustment: I think that some of those paragraphs from the Haynes catalog I will send you should straighten this out.

Regards,
Henry

[Monkey Uncle]

Thanks, Henry.  I'll have to wait until I get the truck back to continue addressing most of these questions/issues. 

Regarding PCV: the driver's side valve cover has a vent that is connected via the OEM hose to the appropriate port on the front of the carburetor.  Is this sufficient, or should the passenger side be vented also?  If the passenger side also needs to be vented, I'm wondering if I can get a vented cap for the oil fill hole, which currently just has a rubber plug in it.

In light of all the issues that we've identified so far, I'm again beginning to wonder if it's worth trying to fix this carb vs. replacing it.  I could envision throwing several parts and a lot of work at it and potentially still having problems that can't be fixed.  Do you think it would be worthwhile to go through the full, step-by-step tuning procedure without replacing any of the missing and potentially defective parts first?  If that could mitigate the richness and fluttery idle issues, then I would feel more confident about replacing parts.

[Henry]

Hi:
PCV: sounds like you have half of the PCV system installed. On the pass side valve cover is where you are missing a hole for an air inlet to the system...the original design had a valve cover with a hole at the back for this...and to keep the air clean coming in it had a metal pipe connecting to a little filter on the side of your air cleaner...so all this is missing. You really need it and the quick solution as you say is if you can find a combo oil filler cap-filter...I have never seen this but maybe it exists. And yes, you would need to plug the hole in the air cleaner. If you cannot find this combo filter, you just need to bite the bullet and get the valve cover with hole at back and get the metal tube, grommet and filter for air cleaner attachment...or just a valve cover with hole that has a filter attached to hole.

Carb decisions: I cannot determine if there is still something wrong inside your carb that  buying choke parts and tuning up will not fix. My gut feel is that if the person that rebuilt your carb was the same person that installed the air cleaner stud, then I would not trust the rebuild...I would either rebuild it again myself or buy a rebuilt M4ME.

Regards,
Henry

[blazer74]

Do not over tighten the front 2 mounting bolts. Just snug. Will cause warping of the air horn.

Common for this to happen and can ruin the the sealing of the airhorn to the float bowl.

Can cause fuel to seep out around the top gasket.

If warped enough can cause air bleeds and fuel channels restrictions to be violated and destroy calibration and adjustability.

Too high a float level and or fuel pressure can also cause fuel to seep out around top gasket and accelerator pump shaft.
Would cause an over rich condition.

Front, Rear or both pull offs came on different applications, but you should not be missing any linkages as apparently you are.

Take the vertical 7 digit carb # from the drivers side of the float bowl and plug in google and see what comes up.

Can’t see your pics for some reason.

These remanufactured carbs can be very generic in calibration in an attempt to cover many applications which doesn’t always work. They can use a mix match of parts causing sealing issues also.

They were originally calibrated for specific applications.

You should be able to turn the mix Screws  in all the way and almost or kill the engine if the idle circuit is calibrated correctly.

If the idle screw is turned in too far to keep the engine idling this will uncover the idle slots in the throttle bores.
This can cause the main feed system to draw fuel from the booster rings. The result will be over rich and rough idle.
You can see this by using extreme caution and looking down the primary(fwd) Ventures. There should be no visible dripping of fuel with the engine at idle.

For all tests or Adj the engine must be at normal operating temp with the choke fully open unless you are adjusting the choke system itself.


No vac leaks are imperative as well as a vac tight distributor advance can along with a tuned engine.

[Monkey Uncle]

Henry - thanks.  I'll talk to the mechanic about the breather cap for the passenger side valve cover.  He mentioned that he was going to get a cap for that side when he put the new covers on.  I'll have to remind him.  If he doesn't have it, it looks like there is an abundance of options available from the auto parts stores.

Blazer - thanks for the info.  I have not attempted to tighten the mounting bolts, just the screws in the top of the air horn.  They were all noticeably loose, and I just snugged them down with a manual screwdriver.  But no telling whether someone else warped the carb castings over the course of the last 30-plus years.  That's my major concern right now - the possibility that I might throw a bunch of parts and effort at the carb, and it still might have problems I can't fix due to being warped or otherwise having non-replaceable parts messed up.

Google doesn't turn up anything specific on the model number, but I have looked up the number on a couple of carb ID web sites and determined that it came from a 1983 Chevrolet with an automatic transmission.  Can't really find anything more specific than that, so I don't know if it was originally calibrated for a truck application.  Who knows how many times it's been rebuilt and whether the calibration is original.  I don't know if the carb is a reman or not - it doesn't have a nameplate or anything that would identifying as coming from one of the big reman shops.

Prior to my adjustments, the idle mix screws were turned pretty far out (I forgot to count how many turns).  So it sounds like the issue you described with the idle screws being turned too far in was not the problem.  They are currently set at 3 1/2 turns out.

[bd]

There has been a lot of guessing and second-guessing in this thread, introducing some false data interspersed with accurate data.  Based on the casting number, 17083226, the existing M4ME carburetor on your truck was produced for 1983 2WD and 4WD, 1/2- and 3/4-ton, Chevrolet/GMC trucks with a 305H engine, automatic transmission, federal emissions, and air-conditioning.  The carburetor was manufactured without a primary choke pull-off (vacuum break).  Whether or not the secondary air valve is actually missing a link requires a schematic breakdown and part number call out that is specific to that carburetor.  Most such references are out of print.  Although the carburetor's configuration lends itself to supporting a link between the air valve and rear vacuum break, that in itself is no assurance it should have one.  An idle mixture screw adjustment of 3-1/2 turns out is typical and expected for this carburetor.  The float setting should be 13/32" (10 mm).  The accelerator pump rod in the inner hole of the lever is correct.  One of the most chronic problems with QJ carburetors is float saturation, exacerbated by the introduction of enriched fuels.  Bending of the fuel bowl cover is also a weakness in the design, but can be corrected.

OP, in a new unit of time, what are you wanting to accomplish - what symptoms are you trying to correct?

Edited for clarification.

[Monkey Uncle]

Thanks for that information, bd.  Here are the symptoms I'm trying to remedy:

Running rich.  I haven't had much run time with the truck since I made the mix screw adjustments and choke adjustments, so at this point I'm not certain how big of a problem I still have in this regard.  When I get it back from the mechanic, are there any indicators I should be looking for to determine whether it is still running richer than it should?

Rough/fluttery idle.  It is worst upon a cold start, but it is still noticeable when the engine is warm.

Not kicking down from fast idle.  Again, I haven't had enough run time with the truck since the choke adjustment to determine the extent to which this problem still exists.  I did get it to kick down after the adjustment, but I haven't tried enough to know if it works consistently.

Fuel seepage.  When I get the truck back, I need to assess whether my screw-tightening did anything to fix this.  I noticed it most around the accelerator pump shaft.

Beyond those symptoms, I'd also like to (1) figure out the best place to attach the vacuum hose for the air cleaner's Thermac system, (2) make sure distributor vacuum advance is hooked up to an appropriate port, (3) make sure the choke is adjusted appropriately, and (4) ensure proper routing and attachment of the transmission vacuum line to the manifold such that it doesn't interfere with the seating of the air cleaner.

Out of curiosity, where did you find the information on this carb model?  If it is available on line somewhere, I'd like to download it so I have as much info about the specs as possible.

Thanks again.

[blazer74]

First pic is your carb. The rear pull off is required do to the type of airhorn installed and the 2ndary flap linkage hole is on the lower side of the the shaft. This requires the rear pull off. The lower link goes to the choke mechanism. The upper slot on the pull of goes to the 2ndary flap link hole I mentioned and is missing and should BE there.

When this type of air horn is used the front pull off is not needed nor has the vac port for it as you see in the pics.I’ve added some pics of different variations for you to study and you can see the difference when a front pull off is used and not.

I’m not saying this carb is set up as it was new. Due to the silver color it is Probably a reman and could have a mix of parts.
You can see the diff variations in the pics added

The only way to check the correct assy is to get these books pictured below and check each part by #.
Vol 1 should do it.

Also the later carbs past 78/79 have thinner and finer pitch threads mix screws with smaller holes under them than the earlier carbs so it is NOT uncommon to require 5 or more turns out as compared 3 or so for earlier carbs.

Everyone here is trying to help. There will be comments that could be wrong, misinterpreted, or type O’s.

There is no reason no matter how knowledgeable one is and contributes to this site that they should be insulting or otherwise in a demeaning manner.
A simple correction is all that is needed for the benefit of all.

[bd]

Blazer, I was amidst amending my prior post when you responded.  And your comment surprised me.  No demeaning commentary or insult was/is intended, ever.  So, if my post reads that way to you or anyone else, I beg your pardon.  The point I was attempting to make, perhaps poorly, is that under the circumstances, to provide reliable 'help' to the OP requires a source reference that gives absolute and unrefutable information.  The books you imaged are the references that would settle conclusively all parts and adjustment questions.  Unfortunately, they are out of print.  I discarded my volumes 20 some years ago and have rued the day many times since.  I expended several hours today attempting to find them online, or a reasonable substitute, to no avail.  I found partial breakdowns of the carburetor peripherals but none illustrating sufficient detail to support an absolute claim.  Adjustment of QJ idle mixture screws can vary anywhere between 1-1/2 to 5 turns out.  However, 3 to 3-1/2 turns is by far the most common setting for all M4M and E4M carburetors.

Monkey Uncle, if you decide to keep the existing carburetor I recommend checking the float for fuel logging as well as float level adjustment.  Reiterating prior posts, a high fuel level can cause the fuel bowl gasket and accelerator pump plunger to seep as well as early fuel tip-in and dribbling from the main nozzles causing the engine to run rich.  An electric choke should open fully within 3-5 minutes of engine running.  If it doesn't, you will need to verify choke circuit integrity.  If you haven't already done so, recheck the ignition base timing and spray for vacuum leaks before attempting any more carburetor adjustments.

[Monkey Uncle]

Blazer, thanks for the comparative pics.  Those are very helpful in understanding the pull-off and secondary air flap linkage issues.

Bd, would fuel-logging be apparent by looking at the float?

[Stewart G Griffin]

i have an 83 carb (because my truck is an 83) sitting on the shelf.  i'm not sure what the casting # is, but i suspect it's in the same series because i was also originally equipped with the 305, AC, and automatic federal.

If anyone needs a picture of it, i can provide it, but not until the weekend.  It's all original, not reman.    And yes, it only has one choke pulloff.

[Stewart G Griffin]

P.S.

i can't believe the tech at national concerning the "new" quadrajets until i see a webpage or other documentation.  This is very bad business for a company representative to tell you that, i suspect.......

[Stewart G Griffin]

P.P.S.

i'm going to go out on a limb and say that all your 4 major symptoms can be solved by getting the jegs/summit #15805.


2) Something is funny about your fitting on the intake for the vacuum modulator line to the trans.  You may need a 90 degree fitting such as:
http://www.ebay.com/bhp/vacuum-intake-fitting

[Monkey Uncle]

Thanks for all that, Stewart.  I'm interested in seeing a picture of your '83 carb, when you have the time.

[bd]

Bd, would fuel-logging be apparent by looking at the float?

The factory float is manufactured from lightweight nitrophyl closed cell foam.  Give the float a gentle squeeze with your fingers and depress any blisters with a fingernail.  If the float has absorbed fuel, it will ooze from the applied pressure.