carb problem???

[kelseydum]

Not sure if it's my carb but here is my scenario. When diving my rat rod up a steep hill it acts like it has no horse power. On a straight away I can gun it and haul some ass, but when I REALLY punch it it kinda stalls out or something. I'm thinking this may be a vacuum issue on my carb... I don't know much about motors and carbs but trying too learn.

I was looking at my carb the other day and I noticed some of the lines I put rubber plugs on had cracked (I guess the plugs were too small). I replaced the plugs with one size bigger and they seem to be okay... however I noticed one of the lines was not plugged at all. Not knowing much about motors I didn't know if this originally didn't need a plug or the this plug ccracked as well and fell completely off.

Does every line need to be plugged on the carb except the distributor vacuum and the other vacuum hose that comes out of the carb and goes back in the carb (I'm guessing some sort of fuel vacuum). In other words, all lines plugged except 2 hoses??????

I hope this makes sense. I'm going to buy a new Edelbrock 500 cfm carb soon but for now I just have the stock Quadrajet.

 

[BigIrish]

Yes they should all have a hose on them or a cap - other wise you're likely sucking in extra air, running lean. You would really need to search online for a vacuum diagram for whatever car that came out of. Emissions related outlets should be capped with little rubber caps you can get at the auto parts store.

 

[kelseydum]

Thanks, I'll get pics up in a minute of the actual outlet on the carb I'm talking about.

 

[kelseydum]

Here you go. You can see the two plugs... and the third inlet/oulet that has no pug. Should it be plugged?

 

[rustybeercan]

I plug all those. It's just another vacuum leak but I doubt that would cause your car to have a hard time going up hills but what do I know! [S

Beercan

 

[shakey56]

Carbs

A Quadrajet runs about 750 cfm. If you replace it with a 500 cfm Edelbrock, you will notice a loss of power. I just replaced my 500 Edlebrock with a Quadrajet. I like 'em.

 

[kelseydum]

A Quadrajet runs about 750 cfm. If you replace it with a 500 cfm Edelbrock, you will notice a loss of power. I just replaced my 500 Edlebrock with a Quadrajet. I like 'em.

I'm no expert but going from a 750 cfm to a 500 cfm carb might mean less power but to what application. On a mild street motor a 750 cfm carb would run rich... one would think. If the carb is flooding out on a hill when I gun it then there is a problem... no? I'm not saying it's flooding but would that be an option here?

The carb is old and used and I plan on getting a new carb anyways... I just wonder if this will fix the problem.

 

[Tripper]

The carb is old and used and I plan on getting a new carb anyways... I just wonder if this will fix the problem.

I always like to have a new carb or one rebuilt by someone who knows what they're do'n. I've tried many times to rebuild them myself & I suck @ it!!!

BoB

 

[Willowbilly3]

That port should be plugged if not in use, but I think it might be the one that you use for the dist. vac. advance. Quadrajets came in sizes from around 400 cfm to well over 800, depends on what it came on. The numbers run up and down on the drivers side and you can find out what it is from that.The number should start out with a 7 or a 17. Quadrajets are much maligned because people don't know how to fix them but IMHO, they are great carbs and easy to work on. But if they have been jacked with by a previous owner they can be a mess to straighten out. Try this, take off the air cleaner and look for a tube about 1/2 inch in diameter that sticks up out of the front but inside where the air cleaner goes on. Take a small screwdriver and gently push down inside that tube. You should feel the power valve and it should push down agains light spring pressure. If it's stuck, it might cause your problem. Also the butterflys in the secondary air horn open when air goes by them and pull metering rods out of thier orifices to let in more gas. Maybe there is a problen there. The metering rods hang off a Y shaped thing that is connected to the air butterfly arem with one little screw. If they aren't connected right then it might not be getting enough fuel when the secondarys open. Or if someone put the wrong needles in they might be too fat or the wrong profile to let in enough fuel. Also if the choke doesn't open completely, the secondarys are locked out.

 

[Willowbilly3]

I don't know if this will show up big enough to see but here is a diagram

You can see the Y shaped thing (13) connects to the secondary metering rods . Also you can see the power valve, 33, and the primary metering rods that connect to it, 31. The power valve is pulled down by manifold vacuum and has a spring to lift it when the vacuum signal is less, like when you push the loud pedal. The secondary rods raise off the seat when air goes by the butterflys and opens them as they are connected to the secondary metering rods via the Y shaped thing.
These are the 2 things that control how much fuel gets in. I hope that helps some.

 

[Sniper]

When diving my rat rod up a steep hill it acts like it has no horse power. On a straight away I can gun it and haul some ass, but when I REALLY punch it it kinda stalls out or something.

Sounds like a bad, or stuck accelerator pump. The alcohol in todays gas is really causing a lot of trouble with the rubber parts and seals, can make them soft, goopy, and swell up. If it is the case, the umbrella seal may be causing the plunger to stick in the bore. You can check it out by looking down the carb while opening the carb linkage by hand, just the same as if you were flooring it. No need for the engine to be running when you do this, you should see two solid streams of fuel directed down the carb bores. (You will only get 2 or 3 tries at this before the fuel bowl goes dry.) This quick riching up of the fuel action (by the accelerator pump) is what covers the 'momentary vaccuum loss' the carb experiences when the butterflys are whacked wide open. If it's not working, you will get the classic 'bog' you mention. Willowbilly is right about the open vac port, that is the 'ported vaccuum' for the distributor advance/retard. The large port tube 5/16th or 3/8ths in size should be the vent port for the fuel bowl. That would have been vented to a charcoal canister and outside atmosphere pressure. Block it off and the bowl won't breath, and can cause a vaccuum that will stop fuel flow through the jets at the most inopportune times. I've have in the past, made up an adapter so a short pleated paper fuel filter can be used as an air filter, then the bowl can breath while keeping out the dirt and dust.

 

[kelseydum]

Thanks guys. That's some good info. I've only rebuilt 1 carb before and sucked at it. The first one I did by myself. I'm thinking a good rebuild with some experienced supervision. I actually found a recorded episode of Powerblock TV on rebuilding a Q-jet.

It seems like the Q-jet is better for gas mileage with the way the primaries and secondaries work... maybe that's why they came stock.

I found a new in box Edelbrock 600 in the paper and he wants $175 for it. I was wanting a 500cfm but for the price I may just grab that if he still has it.

What do you guys think?..... rebuild or buy new? If I rebuild I can at least learn more.

 

[kelseydum]

Also, can a bad carb effect downshifts? When slowing down it seems like it will go back and forth from 1st and second until I hit the gas again and it chooses a gear.

 

[Willowbilly3]

There are a couple tricks you need to know to get a Q-jet apart. First is the choke rod, dissconnect it from the butterfly arm and jiggle it around while rotating it 90 degrees. Do not be tempted to remove the screw and choke linkage from the outside, it is a real pita to get that little arm back down inside that hole and get the screw through it.
Then there is the accelerator pump pivit arm. Use a small pin punch and drive the pivot pin back, but just far enough to get the arm out. You don't want to drive it all the way to the airhorn or it is hard to get back, leave enough roon to get a flat blade screwdriver between the pin and the airhorn and you can pry it back in for re-assembly. Use the same pin pumch to align the hole while prying it back.

 

[porkchop4464]

Maybe the float?

Hey Kelsey, I was thinking maybe it's metering valve, they have two rods in the bottom that can get gummed up, was the carb sitting?