At idle, you dont need to have the vacuum hooked up as long as everything on the carb and intake manifold is plugged it should idle fine. if the carb is new It sounds more like a timing problem to me... have you tried loosening the distributor hold down and slightly advancing/retarding the timing to see if that helps?

i`m in trouble with my quadrajet.i have a 76 coupe deville 500cui the only engine option anyway it has 800cfm M4ME 17056230 electric choke q jet.the old one needed to be replaced , i didn`t have enough time and suitable place to rebuild it so i decided to buy a remanufactured one.recently i`ve bougth same carb from CA and they shipped the item here Miami.i think i gave so detailed info so far

anyway after i mount my carb it didn`t work properly.especially at idle it was really rough and when i pump the gas pedal to rev the engine it backfired and stalled.

probably i`m the zillionth person who askes the same questions but i need your help cause this friday i`m gonna leave the country and my car has to work before i leave cause the building management will get the car(since april stays in same park slot) towed otherwise.

ok my questiones are

-is it possible to find a vacuum diagram of this carb?what happens if i plug the wrong ports with wrong vacuums?each vacuum port has its own particular function so i mean if i plug distributor vacuum advance hose to egr valve vacuum port does anything change?or should i plug each hose to the vacuum ports where they actually belong to?

-my former carb had two choke pulloffs.but the remanufactured one has only one.does it make any difference?what is the actual duty of the second choke pulloff other than ``provide a progressive choke``?what if i don`t use it?or should i buy a new sec. choke pull off and mount on the carb?

-i have no idea how to adjust choke pulloff and thermostat?how slack and how strick?how open should the choke plate be when engine cold and when engine warmed up?

-as i told you the engine idling was really rough.i didn`t tamper with the idle afr screws and rpm screw?should i change anything with them to solve the problem?

at first although it has rough idle and backfire when i hit the gas pedal,it was working but then i turned some screws on pull off and thermostat.now it doesn`t even ignite

please help me ...

 

vaccum leak

check your base gasket,I changed the carb on my truck last year and used a thinner gasket and the blockoff plate for the EGR was holding the carb up just enough for a nice vac. leak.it did the same thing. I put four different carbs that I had on before I figured it out.the bad thing was the orig. carb was fine,I just wanted to try one that I had rebuilt. It made for a very interesting afternoon,I was madderna mashed duck.

 

I bought a remanufactured qjet for my corvette in 2008, never got it running right. Even got it rebuild, but no luck, still ran like crap.

I ended up buying an old unmolested qjet, and after a rebuild, it runs really great

 

At idle, you dont need to have the vacuum hooked up as long as everything on the carb and intake manifold is plugged it should idle fine. if the carb is new It sounds more like a timing problem to me... have you tried loosening the distributor hold down and slightly advancing/retarding the timing to see if that helps?

i didn`t understand the first sentence at all??!?! could you explain more?

about timing i don`t think so.cause before i pulled out the old carb, timing was ok.and i`m sure i didn`t touch anything with ignition system.

after carb replacement could the ignition timing change by itself?

 

check your base gasket,I changed the carb on my truck last year and used a thinner gasket and the blockoff plate for the EGR was holding the carb up just enough for a nice vac. leak.it did the same thing. I put four different carbs that I had on before I figured it out.the bad thing was the orig. carb was fine,I just wanted to try one that I had rebuilt. It made for a very interesting afternoon,I was madderna mashed duck.

the new base gasket was thick enough compared to the old one.at least 3-4 times thicker.

 

I bought a remanufactured qjet for my corvette in 2008, never got it running right. Even got it rebuild, but no luck, still ran like crap.

I ended up buying an old unmolested qjet, and after a rebuild, it runs really great

damn i whish i had enough time.

anyway i asked the same questiones to the carb remanufacturer and i`m waiting for the answers.i think that`s the best way to tackle the adjustment problem.

 

ok i think i found the problem.

first,i notice that i connected the hose comes from egr to the port which is supposed to be connected to the evaporation can :drunk:

i changed it.however after backfiring, the engine persisted not to start and now i have a dead battery.

than i thought the engine might have flooded and replaced the spark plugs with new ones.before plug the spark plugs i cranked the engine to vent the combustion chambers and to take the excessive fuel out of chambers.to increase compression i injected some atf oil into the chambers that washed by fuel.i turned the idle mixture screws one and a half turn out form the bottom too,in order to prevent the engine get flooded again.i checked the ignition as well.it still ignites,nothing wrong with the ignition system.finally we jump my car`s dead battery with my friend`s car battery.

eventhough i did all these things the engine didn`t work.

what else should i do?what could the problem be?

last thing to try,on my old carburetor`s main body there was no apart seperated distributor vacuum hose port.

shown in this picture,my new carburetor has a different dist. vacuum port that i circle with yellow.but my old carb didn`t have this port,instead ,the dist. vacuum hose connected to the same port as the first choke pulloff connected to.should i change them like my old carb connections?does it change anything?

and the last question,backfiring could damage my carb or any part of the engine or cause to change any crucial adjustment?

 

"anyway after i mount my carb it didn`t work properly.especially at idle it was really rough and when i pump the gas pedal to rev the engine it backfired and stalled."

first things first:

set the motor to TDC #1 and make sure the dist. rotor points to #1 on the cap and the motor has not jumped time, which is what this sounds like :evil:

 

"anyway after i mount my carb it didn`t work properly.especially at idle it was really rough and when i pump the gas pedal to rev the engine it backfired and stalled."

first things first:

set the motor to TDC #1 and make sure the dist. rotor points to #1 on the cap and the motor has not jumped time, which is what this sounds like :evil:

you think the problem is ignition timing?but i haven`t touched anything with distributor before at all.

just make sure before touching dist. cause i don`t wanna mess dist adjustment either.

 

"just make sure before touching dist. cause i don`t wanna mess dist adjustment either."

back then GM would use a nylon coated cam gear and it may have worn down and jumped a tooth, sending all the engine's internal time off.

Just turn the engine over until the front timing marks line up and pop the dist. cap off and see IF the rotor is pointing to #1 or exactly opposite #1.

DO NOT turn the dist. like you are setting the timing.

 

"just make sure before touching dist. cause i don`t wanna mess dist adjustment either."

back then GM would use a nylon coated cam gear and it may have worn down and jumped a tooth, sending all the engine's internal time off.

Just turn the engine over until the front timing marks line up and pop the dist. cap off and see IF the rotor is pointing to #1 or exactly opposite #1.

DO NOT turn the dist. like you are setting the timing.

ok thanks oldBodyman i`m gonna check it as soon as possible.

but first i need to get the answer of my question

``shown in this picture,my new carburetor has a different dist. vacuum port that i circle with yellow.but my old carb didn`t have this port,instead ,the dist. vacuum hose connected to the same port as the first choke pulloff connected to.should i change them like my old carb connections?does it change anything?

and the last question,backfiring could damage my carb or any part of the engine or cause to change any crucial adjustment?``

nobody knows the answer?i just wonder if the different ports with different vacuum hoses change anything

 

As I was saying in my first post, you do not need to have any of the vacuum lines connected for the engine to start and idle as long as you have all vacuum lines plugged before you start it. The vacuum is for EGR, Secondaries, Distributor vacuum advance (not needed until engine revs) and Brakes none of which you need at idle while testing.

1. remove all the vacuum lines from the carb
2. plug all of the vacuum connections on the carb
3. plug each vacuum hose you removed from the carb going to the various engine components (use bolts or screws or duct tape if you dont have anything else)
4. Remove the #1 cylinder spark plug
5. Get the #1 piston at top dead center on the compression stroke either by turning the engine over by hand, or by disconnecting the coil wire (or HEI wire on the distributor) and cranking with the starter until you hear a "woosh" of air coming out of the #1
6. remove your distributor cap and see if the rotor is pointing at the #1 cylinder
7. If it's not, it may have jumped as mentioned earlier. If you are sure your at Top Dead Center on the compression stroke then adjust the distributor so that the rotor is pointing to #1
8. reinsert spark plug and reconnect coil or HEI
9. Start the car
10. if necessary rotate the distributor to adjust the timing advance/retard while the car is running to see if the idle quality improves. (dont forget to check with a timing light later)
11.Problem gone? or Problem Remains? let us know

Also, check to be 100% sure you havent missed any vacuum ports on the carb or on the engine. Especially that pesky "tree" connector usually found on the intake manifold behind the carb.

ok thanks oldBodyman i`m gonna check it as soon as possible.

but first i need to get the answer of my question

``shown in this picture,my new carburetor has a different dist. vacuum port that i circle with yellow.but my old carb didn`t have this port,instead ,the dist. vacuum hose connected to the same port as the first choke pulloff connected to.should i change them like my old carb connections?does it change anything?

and the last question,backfiring could damage my carb or any part of the engine or cause to change any crucial adjustment?``

nobody knows the answer?i just wonder if the different ports with different vacuum hoses change anything

 

-is it possible to find a vacuum diagram of this carb?what happens if i plug the wrong ports with wrong vacuums?each vacuum port has its own particular function so i mean if i plug distributor vacuum advance hose to egr valve vacuum port does anything change?or should i plug each hose to the vacuum ports where they actually belong to?

should be one on your radiator support or somewhere under the hood

-my former carb had two choke pulloffs.but the remanufactured one has only one.does it make any difference?what is the actual duty of the second choke pulloff other than ``provide a progressive choke``?what if i don`t use it?or should i buy a new sec. choke pull off and mount on the carb?

The second brake is actually there to slow the throttle from closing too quickly when you let off the pedal. It can be eliminated in 99% of the applications I've done.

-i have no idea how to adjust choke pulloff and thermostat?how slack and how strick?how open should the choke plate be when engine cold and when engine warmed up?

You can experiment a bit. Use a 3/16" drill bit in the choke horn. Adjust the choke housing until the plate just barely contacts it. That's a good starting point. With the engine fully warmed up, the choke plate will be straight up and down and should have some spring tension on it holding it wide open.

-as i told you the engine idling was really rough.i didn`t tamper with the idle afr screws and rpm screw?should i change anything with them to solve the problem?

With the engine off, turn them in to the seat counting how many turns it takes. Bench setting is typically about 2.5 turns out from seated. Always remember where it was so you can return to the original setting in case it wasn't the problem.

at first although it has rough idle and backfire when i hit the gas pedal,it was working but then i turned some screws on pull off and thermostat.now it doesn`t even ignite

The backfire could be one of several things, but since you just changed the carb and vacuum lines that narrows it down to three in my opinion: 1) the distributor is hooked up to the wrong port. If the vacuum is making the incorrect advance, it can make things backfire. 2) the configuration of the carb is incorrect for your engine. If it is not providing enough gas during pedal movement (either because the jets are too lean or the pump shot is too weak) it will go lean during accelleration and make a pop through the carb. 3) the secondary air doors are set too loose. The upper butterflies on the secondaries open by airflow and the shaft is on a spring that prevents them from slamming open and making a lean condition. On the one side of the upper door shaft will be a set screw that you loosen. Then underneath that there is an allen screw that sets the tension on the spring. Loosen the set screw and adjust the allen screw in 1/2 turn increments (again remembering where it was to start) and see if the problem goes away.

 

You have the tension on the secondary backwards. The allen screw holds the adjustment screw. Put a screwdriver on the adjustment screw on the side of the carb before you loosen the allen screw or you might loose the spring. It is easiest to make the adjustment with the carb off the car. If you have an automatic try starting with the screw turned at about 1/2 turn to 7/8 turn. Don't go over one turn.

 

@ SS66chevelle,curtis73,Mertz

thanks a lot guys.i wish you gave me these recommendations before.unfortunately this is my last day and tomorrow i`m gonna leave the country.so until i come back to miami car has to wait for me and i don`t have any chance to try what you suggested so far.but anyway at least i solved the garage problem

again i`m really grateful for your help and i`m gonna try it as soon as possible when i come back.and will share the results.

 

Big Al

From experience , having a carburetor that is jetted too lean for the engine will cause all of the problems stated . I bought a calibration kit for the Edelbrock on the engine in my T-bucket and went too lean at first and had all the problems described . Bigger jets solved the problem instantly .

 

From experience , having a carburetor that is jetted too lean for the engine will cause all of the problems stated . I bought a calibration kit for the Edelbrock on the engine in my T-bucket and went too lean at first and had all the problems described . Bigger jets solved the problem instantly .

ovv i'll keep it in my mind.after i check what other users suggested , if it doesn't start again i will try it for my last chance.

your carb was edelbrock so you might not know how to change fuel jets.does anyone know how to change fuel jets for quadrajet?i have more than 2 months to see my car though ,i asked just in case.

 

Rochester Q-jet

I am very familiar with Q-jets . I have rebuilt and rejetted several of them . This was my first Edelbrock . The are very similar in design , and the procedure is almost identical . With either one you have to remove the fuel bowl cover to replace the jets . The most touchy part is getting the metering rods in place and not destroying the fuel bowl gasket taking it apart . I always have a new gasket in hand anyway . I'd go with the largest primary jets you can find and see if it runs . If it does , then you can trial and error downsizing the jets until you get a flatspot and then go back up one size if you want gas mileage . Edelbrock sells a calibration kit for their carbs which has 6 different each of jets, metering rods and springs . I think you should be able to find the same for the Q-jet . Good luck.

 

how many miles on it?

Timing chain is bad

 

This is from www.autozone.com under repair guides. Hope it helps.

http://www.autozone.com/autozone/re.../autozone/repairinfo/repairguide/repairGuideContent.jsp?pageId=0900c152801c8479

 

I'd go with the largest primary jets you can find and see if it runs .

Instead of doing something like this, you should simply see that there is about a 30 number difference on the primary side, between the jet size (larger number) and the metering rod size (smaller number). Unless you are using the "M"-series rods (which use about a 20 number difference- an example is: Jets are 76, rods are 54M), this will put you very close to where you want to be.

You want the float level to be set about 1/4", measured at the mark on the toe of the float (or 3/32" in from the end if no make) to the float bowl, w/o a gasket present.

 

The 30 rule can be a good one but you need to start at the right point based on the air bleeds and the original carb jetting. You can find the correct jet and rod combination based on the carb number. Then fine tune from there. I have a very large air bleed carb and I can't get a jet big enough to make it run right. It will always be lean. Believe me I learned this the hard way. I had a modified carb and had to try a number of combinations to get it right. Your best bet is to get a carb that has never been messed with get the correct jets and rods and do a cleaning and rebuild. It also helps if you can find one originally for your application. The later ones are better because they have an APT to help fine tune the rod location in the jet. A half turn can make a big difference. These things will run great and give you more power and mileage when tuned in. I have mine dialed in with an LC-1 air fuel monitor and was able to record the A/F while driving under different conditions. I now have good power, a very smooth running engine and it gets 16mpg with a 3/4 ton 72 Chevy with 350 and 350 auto.

 

You can find the correct jet and rod combination based on the carb number. Then fine tune from there.

Where is this info- I need it.

 

Here is one site I used.

http://www.digitalcorvettes.com/forums/showthread.php?t=88376

You can also contact Cliff at http://www.cliffshighperformance.com/