How do I lean out the mixture on a Rochester Quadrajet?

[ClydesdaleKevin]

Here's the big question.  Who knows how long the fuel pump was dangling in the tank...probably before we had the carb rebuilt in AZ last year.  So, when they did the final adjustments on the carb, they set the mixture to the fuel flow provided by the mechanical pump.

Well, now its getting too much fuel.  It sounds like the fan clutch is running constantly...VERY similar to the sound it made when we were pulling into the Carolina renfaire when the key chain pulled the manual choke out, and I thought for sure we had a defective fan clutch that was constantly running...until I noticed the choke was out, pushed it in, and all was well again.

So since I just installed the in tank fuel pump, not only did a similar sound appear...sounding just like the choke was pulled out (I checked and its working perfectly and is adjusted properly), but also my fuel economy went from the high 8s down to 5mpg.

Also suddenly have a flat spot right at idle, when you are stopped and have to hit the gas to accelerate.  Like a bunch of fuel getting dumped all at once, and then off we go, engine loud as if the fan clutch were engaged...just like when I drove it with the choke pulled out.

My guess is that the mixture needs to be leaned out.  How do I do that?  Since the carb is rebuilt, there are no plugs over the adjustment screws. 

Which on is which?  How do I preset them, or only the one, and how many turns out do I turn it until I know its right before testing it?

Can someone put the mixture adjustment into laymans terms, step by step?  I'm not very carb savy.

Thanks!

Kev

[Elandan2]

The screws are the idle mixture screws.  They only are active at idle.  By turning them "in" you can lean out the idle mixture.  Turn each one equally, about a quarter turn at a time then try it with a road test.  That may get rid of the flat spot when coming off idle.  The mixture while running is regulated by the metering rods.  To change the mixture, the rods, metering jets or both need to be changed to get the right mixture.  Generally speaking, it is not a backyard mechanic job without a lot of trial and error.  Shops use an oxygen sensor to calculate the correct combination and even then it requires alot of patience.  Rick

[Elandan2]

Oh yes, the flat spot at idle could also be caused because of too little fuel.  If the accelerator pump is not working correctly, you can get that hesitation.  To check this, look down the throat of the carburetor and open the throttle.  There should be two solid streams of fuel coming out of the centre section of the primarys.  (the small bores).  Rick

[Sprdtyf350]

You sure the electric pump has not raised fuel pressure enough to be pushing past the needle and seat?? If it ran good before the electric pump that may be what's happening.

[DaveVA78Chieftain]

My understanding is you replaced the electric fuel pump and then this excess gas problem started.  My first guess is the float level adjustment is off or the increased pump pressure is pushing the needle off of it's seat.   First thing I would do is install an aftermarket fuel pressure gauge at the carb.
http://shop.advanceautoparts.com/webapp/wcs/stores/servlet/product_x_22906125-P_x_x?cm_mmc=ACQ-_-Google-_-enhancedRM-_-22906125&ci_src=17588969&ci_sku=22906125&ci_gpa=pla&ci_kw={keyword}&gclid=CPGHlMOS67MCFcuZ4AodICMAvg#utm_source=acq&utm_medium=google&utm_campaign=enhancedrm&utm_content=22906125

Fuel pressure at the carb should be between 5 to 7 lbs.  Anything greater than 8 will force the float needle off it's seat (flooding, excessive gas).  Most electric fuel pumps are designed to put out 13 or more pounds of pressure.  If pressure is to high at the carb, you will need to install a regulator.

Dave

[ClydesdaleKevin]

There is a fuel pressure regulator on the RV frame near the fuel tank...got the Holley part number saved just in case. 

But before the in tank pump slipped its mooring, this RV ran like a dream, so I doubt its the pressure regulator. 

I have the whole Rochester manual downloaded and read it cover to cover, and it seems that with all the special tools needed to do this job, I'd either have to invest a fortune in all kinds of specialized angle and measuring tools and do a complete carb rebuild, or else have it rebuilt AGAIN by mechanics that know what they are doing...and I am in unfamiliar territory, St Marys, GA, and know of no good mechanics in the area.  Also from reading the manual, I can make no heads or tails about how to adjust the screws.  It just says to refer to X document, which isn't included with manual, and apparently is a specific document to each individual application.

I was hoping this would be an easy answer, like old VW Solex carbs.  You turn the mixture screw all the way in, back it out 1.5 turns, then start the engine and adjust it on the fly while driving to dial it in.  Apparently not.

Looks like I'm getting an Edlebrock 1411 after all!  I can stay 3 days in my sister's paved flat driveway before her homeowners association sends her a letter, so it looks like its new carburetor time, unless someone has an easy answer.

Ah well...he next door neighbor was kind enough to lend me a sliding floor jack and 2 more heavy duty jack stands, so while I'm waiting for the carburetor I'll adjust the rear tag axle height myself.  The money I'll save doing it myself...and I pretty much know what I'm doing with the rear tag axle now...will pay for the carburetor.  Still money out of the till, but at least all will be well before heading out on the longest leg of the journey.

Never mind the extreme change if fuel economy.  I mean, I was getting 8 before the fuel pump slipped its moorings.  I was getting similar fuel economy but poor performance afterwards.  The rebuild brought most of the performance back, but I had to use a manual choke, and still didn't have all my power on hills, and then would go "empty" at half a tank.  The new in tank fuel pump restored most of my  power on hills...although significantly less than when we first got the rig and she would charge up the hills at 65...but now the carburetor is dumping way too much fuel...5.5 mpg is unacceptable.  That is a HUGE difference in out of pocket travel expense!

Yep...I'm off to check out Summit Racing, Jeggs, and Napa for Edelbrock 1411 carb prices, including the spring tuning kit, linkage adapter, and intake manifold adapter.  I'll let you all know what I find out.

The Rochester is just too complicated for me, has been tampered with by incompetents, and I'm just not qualified to fix it, nor do I have the proper specialized tools.  I can handle an Edlebrock.

Unless someone has an easier answer?

Kev

[ClydesdaleKevin]

Prices range from 415.00 to 460.00 bucks for complete installation kits, depending on if I need the calibration kit, or if it will fit and run well right out of the box.  Things definitely needed are the carb itself...329.95 from Summit, same price as Jegs.  Edlebrock themselves are unclear on the website...I may or may not need a linkage adapter, 12.95 from Summit.  Manifold adaptors range from 21 to 27 bucks.  Don't know if the stock Chevy air cleaner will fit on the Edlebrock...will find out when I call tech support at Summit tomorrow morning, since they are of course closed on Sunday.  Calibration kit, if I need it, is 47 bucks from Jegs or Summit.  So the price all depends on how many parts I need to make it work. 

Even at the max cost of 460.00, I would have spent 400 bucks to have some shop raise the rear suspension, so since I'm doing it myself, its an additional 60 bucks for a new Edlebrock by my twisted and convoluted calculations. 

And hey, I'll have an electric choke again!...lol!  Don't know what I'll do with the hole I drilled for the manual choke.

Worst case scenario and I'm delivering too much fuel pressure...which I highly doubt...I can replace the pressure regulator which is cheap and available at Napa next day.

Guess vacation is on hold another day or so while I get these mechanicals seen too by the only mechanic I trust...ME!!!

Kev

[DonD]

Kev, is your FP reg adjustable? Mine is.

[ClydesdaleKevin]

I checked out the inline pressure gauge, Dave, and the problem with it is that with the quadrajet, its a steel line that threads into the carburetor, so without adding all kinds of fitting and hoses, I can't check the fuel pressure at the carb with this unit.  I could check the fuel pressure coming to the mechanical pump, which has hoses coming to it, but it appears the steel line exits the mechanical pump and is steel all the way to the carb, so again, fittings and adapters and hoses...

My sister knows a trustworthy mechanic in town, so if he's willing to look at the RV and check the fuel pressure and maybe FIX the carburetor issue and dial it in, maybe I'll have him do it instead of botching the job myself, or ordering a new carburetor only to have it give me the same symptoms from overpressure.  Can't figure out why I'd have overpressure though, unless the fuel pressure regulator went bad from not being used for the year the in tank pump wasn't pumping. 

This carburetor crap is giving me a headache.  I'm this far {} from getting a bloody aftermarket throttle body injection for it...grrrrrrrrrrrrrrrrrrrrrr...

Jet Performance makes a carb specifically for RV applications, Summit part number Jet 35002, for 389.99, and Jet 35003 for 409.99, for big block applications.  Both start out as spread bore Quadrajets, then are modified for specific applications.  Not sure which would be ideal, if either, of if I'm just opening up yet another can of worms and wasting money.  The nice thing about either of them is that they are direct fit with no adapters required.

Have to wait until 9am to talk to a Summit rep...Jegs reps are open 24/7 and also carry the Jet Performance carbs, but their rep recommended I do the fuel pressure checks or have them done by a shop, and then try to adjust the carb first....or have the shop do it...before spending the money.  I'd just really hate to drop 300 bucks at a garage, only to have them tell me I now have to spend another 400 bucks on a carb that still has to be dialed in.  I'll get the number from my sis for her mechanic when she's up and about this morning and see if he can take us in today...seems like its the wisest course of action, and it might make the difference, especially if they can fix it on the spot.  Its not like we can leave our whole house with them for very long!

I'm really REALLY starting to despise Quadrajets for their complexity!

Kev

[ClydesdaleKevin]

I'm not sure Don.  I haven't actually physically SEEN it yet...I just know its supposedly on the frame rail somewhere near the fuel tank.

Kev

[ClydesdaleKevin]

So after rereading everyone's replies, let me hazard a guess as to what is going on.  Before adding the new in tank fuel pump, the rig was running okay after the rebuild with comparable fuel economy, just not as powerful up hills.  I'm 99% sure now that the fuel pump had slipped its moorings BEFORE the rebuild, thus all the vapor locking and loss of power, and the mechanic in AZ rebuilt the carb and dialed it in as best he could with the lower fuel pressure, and I recall him saying that he had to mess with the float level to get to run as good as he could get it.  So keeping in mind that no matter what he did with the adjustments, we couldn't get the choke to work and still have the high idle kickdown functional, and then we went with a manual choke.

Is it possible that he didn't adjust the float level correctly, but with a lower fuel pressure it was at least functional and the float needle was fully seating, but now that the fuel pressure is where its supposed to be, the fuel pressure is unseating the float needle and too much fuel is pushing past it?

That makes sense to me if that is the case. 

Rick, when the mechanic did the rebuild he didn't change the metering rods or jets, so they should have remained a constant...so logically I should be able to eliminate them from the equation, since this is the same carb that used to run so well on the RV.

Dave, I'm thinking you may have hit the nail on the head, although I don't think I'm running too high a pressure...again, its the same regulator that was functioning just fine when the rig was running perfect, before the in tank fuel pump slipped its moorings, so I think we can logically eliminate the fuel pressure regulator from the equation, at least for now.

But in keeping with this logical train of thought, if the mechanic adjusted the float level to a lower than stock fuel pressure, and it was running okay but with a loss of power on hills, and if by fixing the in tank fuel pump brought the fuel pressure back up to stock psi, then it stands to reason that the fuel IS pushing past the float valve, causing the major bog down flat spot at idle when going from a standstill and then accelerating (a symptom of a misadjusted float), and then causing the symptoms of too much fuel being dumped into the intake (with similar symptoms to when I drove it with the choke accidently pulled out), with the added symptom of a HUGE drop in fuel economy and a loss of power due to over fueling, which would have a similar effect to having the choke on...too much fuel compared to the air coming into the carburetor.

Does it sound like I'm on the right track here?

All this being said, even though I have the carburetor manual downloaded, can I adjust the float level myself?  Can I do it with the carburetor in place on the engine, and just remove the top body bolts to access the float assembly?  Logic would dictate that the float would have to be lowered so that when the fuel level came up it would close the needle valve sooner and more firmly.  Do I have that right? 

When I remove the top body, is the crap going to hit the fan with all kinds of small parts falling out and springs flying everywhere, or will everything pretty much stay where it is in the lower body?

Is there a special tool needed to measure the float level adjustment, or can I just eyeball it and lower it a millimeter or two?  Am I correct in assuming you bend the metal float arms to adjust its level?

Finally, do I need to buy a gasket kit and put in a new top body gasket if I attempt this myself today?

Thanks guys!

Kev

[gadgetman]

Might need a top gasket, nothing will fall away, just remove the top. Now as far as your problem goes if it is a float level problem you will see fuel dripping on the throttle plates at a normal idle speed. If you do the float level is too high or the fuel pressure is too high. If you dont see fuel dripping its not a high float level problem.

[DaveVA78Chieftain]

Theoritically, the fuel bowl level adjustment should not change whether the pressure is 2lbs or 7lbs.  As the bowl fills, the float raises pushing the needle against the seat to close off incoming fuel flow.  If the fuel pressure is to high, it will push the gas past the needle.  Just like the tank filling valve in household toilet.   My hunch is when the tank pumped slipped it's mooring it was not outputting anywhere near it's rated pressure.  The regulator may have taken a "set" due to age and might be stuck because of the previously reduced pressure (not regulating).  No way of knowing this without taking pressure measurements.  To bad you are not close to me as I have all the "tools" to do this stuff (even if it is near freezing outside!).

Manual says 85-89 chassis used intank pump with regulator on right rear frame rail (I have read it can be a bugger to get to)
90-93 used in tank pump no regulator however, that might be due to TBI fuel injection which requires around 15psi (way to high for a carburator)

Dave

[DonD]

My regulator is near the filler pipe in the frame.

[ClydesdaleKevin]

Thanks for all your replies guys!  So let me update you one what I did and discovered today. 

First, I found out what carburetor number I had...17085212...manufacture date 1985.

Reading the carb manual, I discovered that the proper float level is supposed to be 13/32.

Next I went to every local auto parts store, including a Chevy dealer, to find the gasket kit, and finally found one at an Advanced Automotive, so I could at least take the top plate off and measure the float level and adjust if necessary, and have a new gasket on hand.  30 bucks for the whole gasket and rebuild kit, since of course you can't get just the one gasket, or even just the gaskets kit, anymore.

So back home I went.  And first pressed in the accelerator pedal to rule out the accelerator pump...two strong streams of fuel, so all was well with that and it was ruled out.  And then I took the carburetor top body off.  NOT so simple as that sentence makes it seem.  A very long careful process, had to remove the choke, the air filter attachment rod, the dashpot, and twist the top body when all the bolts were out to get the linkage rod for the accelerator pump off.   Then of course remove the gasket, which had already glued itself to the carburetor since last March.  And yep, there are metering rods in the top body, but at least they stayed put. 

I did this with the carburetor in place, only having to remove the 2 front manifold mounting bolts...and of course the plethora of little torx head screws around the top of the top body, and even down in the primary bore.  Glad I didn't drop those!

Once the gasket was removed, the real fun began...scraping off the old gasket very carefully, and making sure not a spec of it went into the carburetor. 

To even see the float, you have to remove another set of metering rods and a plastic filler cover.  Did that, and the accelerator pump decided to launch itself across the living room...at least the spring stayed in place!

All the bolts layed out in the exact order removed, all parts layed out on clean paper in the approximate location of where they go, so now its time to check the float level according to the manual.  Had to make my own gauge with my engineering ruler!  Cheap bastages!  I remember getting rebuild kits and at least they gave you a cheap paper gauge....not anymore!

The float level was almost a 1/4 inch too high!  Geesh!  I bent it down and set it to exactly 13/32.

Then I had to put everything back together again with a new gasket.  Not an easy task when the accelerator pump still wanted to relaunch itself, and you have to set the first set of metering rods in their respective seats by feel and luck, since you sure can't see them with the plastic filler cover in the way!

Finally had that seated, then installed the gasket, then got the top metering rods to go all the way down, of course linking the linkage for the accelerator pump first, and then installed all the bolts and tightened them down.

Then my most hated task...getting the little loose connector, hanging off the end of the butterfly valve rod on the primaries, to line up with the rod on the choke body...DANG I hate that part...its sheer luck and LOTS of trying to get it to all line up and connect!  Got it finally.

Then it was reinstall the manual choke and then the dashpot, test the clearance of everything, then fire it up.

Started right up, great idle...and a great big looming flat spot, just like before, kicking in right between 850 rpm and 1000 rpm.  BOG---ZOOM!  Nice through the upper end, but not right for sure!

And that was it!  I was at the end of my skillset for Rochester Quadrajets, and definitely the end of my patience with them! 

O'Reilly's to the rescue!

They quoted me a brand new Edlebrock 1411, the Edlebrock adapter plate, the throttle cable adaptor, the linkage bracket adaptor since you can't use the stock one, the fuel line adaptor kit with filter, everything complete for the install, for less than 400 bucks...SOLD!  They had most of it for me by 4:30.  Only things we are waiting on are the linkage bracket and fuel line adaptor kit, which will be here at 7:30 am tomorrow morning.

Sure is a pretty carburetor!

I read all the documentation and then watched the DVD video on the installation and adjustment of this thing, and WOW its SO much easier than the Quadrajet!  I even went so far as to start the engine again and pull each vacuum line to determine which ones were full time, and which ones were timed (vacuum at higher idle), as per the instructions.

Yep ya gotta buy adapters to make it easier to install, or else get creative and make your own adapters, but adjusting this thing is way easier, to the point of being almost dummy proof.

And even if I end up having to buy the calibration kit, which comes with all the metering rods and jets and springs, changing them out is a breeze!  The metering rods come out of the top of the carb without disassembling the carb.  You do have to take the top body off for the jets and springs, but there aren't any complicated parts and springs and linkages in the way.

And it has an electric choke...Woohoo! 

Now if I still have a flooding or overfueling issue, an inline fuel pressure gauge will be easy to use...although I seriously doubt we will.  If we do, then its replace the regulator...and if its too hard to get to, just install an adjustable one up front where I can get to it.  Ideal fuel pressure for the Edlebrock 1411 is 6.5 psi, although the documentation said it will handle up to 10 before flooding issues occur.

We'll how it goes.  Sure is a pretty carburetor!  Shiny!!!

Kev

I'll see how she runs and what kind of fuel economy we get on the way to Louisiana.  If I'm satisfied with it, I'm done.  If not, I'll get the calibration kit and tinker with it all the way out west since its that easy!

[DonD]

"Sure is a pretty carburetor!"

Ahem...how would we know that?   Hm?

[joanfenn]

Gee Don............You can't see the pictures???  Kevin always takes and posts pictures.......... :)rotflmao

[DaveVA78Chieftain]

Glad to hear that is working out Kevin.  You seem to be acquiring a very wide variety of RV related knowledge stuff!   

[ClydesdaleKevin]

Thanks Dave!

And for all you picture lovin' folks, here's the Edlebrock all installed and ALMOST ready...using the stock air cleaner was a challenge though, so the complete install process with pictures is going to under its own heading in the Projects section.



Ain't it pretty?

Notice the very heavily modified Edelbrock "universal" Chevy big block throttle cable mounting bracket in the lower left corner...another challenge that was overcome with a lot of creativity and my Porter Cable grinder...lol!

Right out of the box this carburetor was nearly perfectly adjusted, except for the high speed idle being too high at 2K rpm.  I lowered it to 1200...a simple adjustment of one screw behind the throttle linkage.  Once it kicked down after warm up, low speed idle was already perfect at 700 rpm.  Idle mixture was perfect, so I didn't have to adjust the easily accessible screws.  Right out of the box, throttle response is even and smooth all the way up to 3000 rpm, and drops right down to a smooth idle when released...instantly.  No flat spots, no rough spots, just perfect!  I'll let you all know how she performs on the road tomorrow, but in the driveway, its the best this engine has ever run!

Okay, off to the Projects board!

Kev