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Discussion Starter #1
i just put a 268 comp cam in my 350 in my blazer, and it pulles real good until the secondarys open. then it will hesitate and take off slow. like its going lean.

i was looking at some metering rods but what do i need?
or what is causeing this?

it has headers and a stock q-jet that has been rebuild several months ago.
 

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Sounds like it`s either running out of gas due to low fuel pressure, plugged filter or low float level. Before I richened the secondary side, I would do a plug chop, kick it to the floor and hold it until the bog appears, then turn the key one click back so the steering wheel doesn`t lock, and roll to the side of the road and yank a few plugs to see what they look like, if it`s white it`s too lean. There are many sites online that list Quadrajet secondary metering rods, it shows how to know them by the letters stamped on them, but it most cases you can just look at the size. I have quite a collection amassed myself. You also may want to check the secondary upper butterflies to make sure there not too tight and not opening far enough resulting in not enough air.
 

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Inbetween the back upper butterflies, there`s a hanger with one small screw holding it on, on the hanger is the metering rods, there size dictates how much fuel the engine gets.
The hanger also plays a role, you`ll see on the hanger a letter, in alphabetical order they run, Example, a hanger labeled "B" will be richer than one labeled "R"
As for metering rods they are stamped with letters as I said in my before post, this site:
http://www.hioutput.com/tech/qjetrod.html
Should tell you all you need to know.
Why I suspect it isn`t too lean is because usually when the secondary side of a Q-jet is too lean, it`ll back fire through the carb, although it could be borderline lean and no backfire will occur. if you change the hanger and the metering rods to richer ones and the problem still exists, it`s time to look elsewhere.
 

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Q jet

This may seem crazy but...Check to make sure that the metering rods are lifting when the air valve opens. There is a plastic cam that raises them and I had the same problem and it was the plastic cam was broken. The flap would open but the rods stayed down. I found a cam out of an old Q jet and installed it and the problem was gone!
Good Luck
 

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Discussion Starter #6 (Edited)
there wasnt any problem before the cam change.
i did not change anything but the chain, cam, and lifters.

and i adjusted the idle mixture, and timing. thats all.

what do i need to order? cause i have no idea.
i know i need a bigger one, but what size?

and i will get a float and maybe a performance hanger.

i plan on getting new valve springs and 1.6 or 1.7 rockers, so compensate for that.
 

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Cam in the carb

I was talking about the plastic cam that lifts the metering rods in the carb. Just push the air flap open with your finger and see if the metering rods raise up. If they do then this isn't your problem.
 

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Try adjusting the spring that controls how quickly the secondarys open.I'd lessen the tension so they open quicker.Did wonders for a 305 and E-Performer cam.
 

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Discussion Starter #10
does anybody know what size metering rods i need? or how much bigger than stock? or is it smaller?
i dont know.

ill get the biggest ones i can if nobody tells me.
 

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Discussion Starter #11
do i get bigger or smaller diameter rods?

i put my engine together and now it doesnt pull good at all.
any ideas? it doesnt seem like ignition. its carb probly, like its going way lean all through the rpm range.
 

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If it's going "way lean", then you need to go to a smaller secondary rod. I wouldn't order anything unless you have to. Go to a junkyard or comparable, and ask if you can dig out or buy for a negligible amount some rods out of some old q-jets. I'd print off that page that DoubleVision posted a link for, figure out which rods you have in there now, and see what you can find as far as richer (smaller) rods. Then, it's really a game of playing around to see what gives you the best results. In addition to rods, get a few hangers if possible. Even if it's just an extra one to bend (be careful that if you do bend these that you bend each side evenly, so as to keep metering the same for each barrel), and play with that as well. It takes some time to get Q-jets worked out, but once you do, you'll be happy you did.

Here's a few links that may help you understand a bit more as far as Q-Jet tuning is concerned. (Note the tuning of the secondary air valve doors, this is also valuable)

Q-Jet Tips
My Q-Jet Tips
Welcome to Dorian's Quadrajet/Carb page!
 

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Might want to double check whether they're going lean or rich when the secondary barrels open. Most of the times (not 100%, but most) I've seen engines stumble when secs open, it's been due to a rich mixture, rather than lean, especially in Holley carbs. Which brings to mind another point: I really never think of the words "Q-jet" and "Performance" in the same context;)

If you want better performance and more ease of adjustment, buy a Holley 650 vacuum secondary. If you're constantly sticking your foot into the bell housing you're not going to get decent mileage anyway (another two words I never think of together....350 chevy, and mileage), and the Holley will give you great WOT performance, and is far easier (and faster) to work on.
 

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Discussion Starter #14
it was working perfectly before i changed the cam out.

then it would only pull good at partial throttle and when i floored it for a few seconds, and then it would get weak until i got off of it again.

and now i changed out my intake gaskets(dont ask), and water pump, so now it is weak constantly.

there is no stumble or hesitate and it runs real good. but it starts hard like it leaks gas in the engine just sitting.

it would not start last time i tried and the starter when out. i got a new starter and 2 gauge wires, and a rear main seal, and a high volume oil pump.

should i start looking for a new edlebrock q-jet?
 

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I'm confused after your last post...but did you change springs when you changed the cam? is the power loss more throttle or RPM dependent?
 

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Lean usually will start, it's the flooding that makes a hard start.

Somebody suggested the plug check and a compression test at this time would be good too(if you don't have a gauge just put your finger in(over tightly) the plug hole and have your buddy crank it over. If your finger doesn't pop off....

If it does blow your finger of you've got compression. (Cams timed correct and rings/pistons are good)

You are convinced it's the secondary side of the carb. On a Q-jet this is hard to do b/c of the linkage not having much slack from the primary side but...

Start your engine, hold the secondary flappers open and only using the rear throttle bores(try not to let the primaries open) see if the engine will rev.(BE VERY CAREFUL>>>IF IT IS LEAN IT COULD SHOOT A NASTY FIREBALL OUT!) It should rev smooth, if it doesn't there is your problem. Jets usually won't be far enough off after a small cam change like that to cause those probs.
 

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Sounds to me like your lifters are too tight. I assume you've pulled the dist cap, inspected all those parts and checked fire at the plug .

Did you change plugs?Too wide of gap can cause this also.

I'm still going back to lifters pumping up/ too tight.
 

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Discussion Starter #20
ok, i think my lifters are too tight and my gaps are to wide.

i adjusted the lash out and then another full turn. so i will do 1/2 of a turn instead?

and the gaps are .055 or .060, i dont remember. but it worked good before the cam change.

do you need less gap for more pressure and rpm?
 
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