Steven6282

I'm surprised there isn't a quadrajet tuning sticky!

Anyway, sorry if this is answered elsewhere I could not find it in a search. My quadrajet is running lean and I'm trying to figure out how to tune that out. I did a search on google and the only thing I can immediately find talks about changing jet sizes. Is that really the only way for me to tune it is to change jets?

That sounds complicated! I don't even know where to get different jets, and how to tell which ones I have (much less where they even are on the carb lol).

Steven6282

Well, just watched a youtube video so I figured out where the jets, primary, and secondary rods are from the video.

Doesn't look to difficult to get to them, but the second half of my problem remains. Where to get new ones? Called advance and they don't stock them. Does anyone stock them or is it something that I just have to order a few sizes so that I can figure out which ones I need?

I still have the problem though of having no way to figure out what my mixture is (don't have a meter or anything and not spending a lot of money to buy one). So it seems even if I do get some jets I'm going to be simply guess at how it's effecting the mixture. But, I found this article here:
http://answers.yahoo.com/question/in...9093318AA7bB3K
that has a very nice write up on how to tune the stuff.

If I'm reading and understanding it correctly, and my assumption that my leanness is coming in during WOT is correct, I need to increase my jet size in order to allow more fuel in during WOT. I think I'm running a little rich at cruising speeds, so I would need to increase my primary rod size to cut how much fuel gets in during cruising to account for that... correct? This is where I really need a meter of some sort to be able to figure out where I'm running lean or rich lol...

The secondary rods are for fine tuning if I understand it correctly, and I can probably work out most of my tuning through just the primary rods and jets, correct?



One last question before I get all wrench happy on it. Is it possible that my air valve flap being to loose and opening to easily might be the entire reason it's running lean, and not a problem with the jet sizes at all?

I have a slight bog / stutter on initial WOT, and I think I know what I need to do to work that out (tighten the spring adjustment). I've played with that adjustment some already but was worried I was going to tight on it, however after reading that yahoo article and understanding a little better it's purpose I think I can go tighter on it.

EDIT: Was just playing with it some and I'm not so sure it's simply not getting enough gas. Sitting under the hood reving it up and watching it, if I do a WOT it lags almost a full second before the engine reacts and starts reving up and the back flap starts to open.

Could I possibly need a bigger fuel pump to deliver the fuel quicker under WOT?

I'm guessing simply not getting fuel to the carb fast enough could cause a lean mixture just as much as the carb tuning itself?

TTOP350

iTrader: (8)

Before you get to tuning the carb, make sure your base plate to main body screws are tight. You will have to remove the carb to get to them. Also make sure your fuel pump is working properly and your fuel filter is new.

IROCtheRoad

Summit, the dealership, and Cliff's High Performance are the best places for parts.

Some Oreilley's have OBD1 readers that you can rent.

The secondary rods are easy enough to get too. The mains take a bit more work, but are doable. Also, the air flaps aren't your problem with the car running lean so you can rule that out.

Good luck and let us know how everything turns out.

Steven6282

Is there a way for me to determine if the fuel pump is not supplying enough fuel to the carb without just having to throw money at it on new parts? I mean I could see it being the fuel pump not delivering enough fuel, or it could be the jets are to small and not dumping fuel in fast enough on WOT. If I accelerate slowly to full throttle it doesn't have a problem. If I just go immediately to WOT is when it hesitates noticeably. Once it is past the initial hesitation, it's fine usually.

I don't think an OBD1 reader would do me any good. I don't have an ECM anymore. This is a non CC Q-jet.

Can you explain more as to why I can rule the flaps out as to why the car is running lean? I need to learn this stuff since it's apparently impossible to find anyone that knows how to tune these things.

I can record a video of the hesitation if anyone thinks that would help...

nate perron

try carbs unlimited.com they have all the parts you need small and kits check it out

nickyakker

iTrader: (1)

- When you secondaries are loose and you WOT it would bog
- I just tuned my mixture screws on my quadrajet two days ago for the first time. its easy though you need a Vaccuum gague to be precise. Hook up the vaccum gauge to the lowest vaccum line on the carb (below thottle plate) to get the best vaccuum reading from your intake manifold, now fiddle with both mixture screws until you get the highest vaccuum reading (my boss told me it should be around 18inchs of vaccuum but i almost got 20). turning the screws clockwise goes lean and turning them counter clockwise goes rich. Doing this woke up my quadrajet big time

Steven6282

I can say the hesitation on WOT is not due to the secondary being to loose. I actually tightened all the way down today and it still exhibited the problem. (I of course tried back it back off and the problem still remained). I've already adjusted the idle mixture screws previously. I don't know enough about these carbs yet, but do they even play a role in WOT? Seems like being named idle mixture screws they would only effect idle mixture hehe Unless of course, I'm just misremembering their name as idle mixture screws.

The more I'm reading the more I think my fuel pump may not be delivering enough fuel. I'm running a stock fuel pump that is rated at 7.5 psi and only 40 GPH free flow. I read a post from someone else in another forum that had something that sounded exactly like my situation and they ended up determining that their fuel pump was inadequate.

So I'm thinking about swapping the fuel pump with something that has better flow. The qjet carb I'm running calls for a max fuel psi of 5, but I can't find anything that low. Closest I can find is this thing:

http://www.summitracing.com/parts/CRT-M6626/

But I don't know if I trust that one to be any good. It's really cheap for such a high flowing fuel pump.

The other two I'm looking at and considering are:

http://www.summitracing.com/parts/HLY-12-327-11/
and
http://www.summitracing.com/parts/EDL-1721/

I don't know which one would be best? The edelbrock has a nice low 6 psi that closely matches what my carb wants. But it's also the most expensive =/


Also, I'm wondering what I would do about the outlet size. The outlet on the stock pump is 5/8, the carter claims to have a "stock" outlet size, so I assume it is 5/8. But both the Holley and Edelbrock have 3/8" outlet sizes. Can I just pick up an adapter to connect it to my hose? I'm assuming my hose has a 5/8" connector on it. The inlet is 3/8" on all of them.

I was even thinking about if I needed to replace fuel lines and such, but I don't think I'm going to go that far yet. I think my fuel lines are fine really. I'll leave replacing them for when I get around to replacing my fuel tank at some point in the future (plan to do that simply because I'm sure that 26 year old tank has plenty of trash in it).

EDIT:
Also as far as jets and rods go, would this kit of jets work on a quadrajet? http://www.summitracing.com/parts/SUM-210230/ The picture shows the case saying "Holley jet assortment", I don't know if they are the same for quadrajets or not. I don't see any that say specifically quadrajet on summit though. I really don't think I need an entire kit, but I guess it would be better than guessing and buying a few sizes to end up not getting the correct ones. I don't see any metering rod kits though, so looks like I'd have to end up guessing with those

Steven6282

Another question I have about fuel pumps. Just got off the phone with my local race parts shop and they have a holley 80 gph in stock there. I'm pretty sure it's this one:

http://www.summitracing.com/parts/HLY-12-834/

The only thing I question on it is the inlet / outlet sizes. They are 1/4 inch instead of 3/8. The race shop said that wouldn't really cause any issues but I don't understand personally. If I have a 3/8 line going up to the pump and then it gets taken down 1/4, is that going to bottle neck it?

naf

iTrader: (7)

Fuel pump's not a problem unless it runs like hell then dies out while it's still under full throttle. The bowl holds enough full for a good few seconds of WOT.

If it's bogging no matter where the AV tension is set (try super loose, then increase an 1/8th turn at a time) it could be lack of adequate booster shot. You should be able to open the throttle by hand and verify that the fuel pump is shooting gas into the primaries. You'll see two streams going in while looking down as you move the throttle. Some booster arms have two holes to place the lever in (the lever/rod connects the arm to the throttle). The hole closest to the carb will increase the pump shot.

Another possible cause is a bad vacuum break. The vacuum canister on the front, right of the carb will keep the AV from opening under vacuum conditions (NOT WOT) and will slowly release the linkage as vacuum falls off. It works in concert with the AV tension. Test it by removing the short vacuum line, push it in and hold your finger over the vac nipple. It should stay in until you release your finger.

WOT tuning is all done by the secondary rods and hangers. If you're not having part throttle transition issues, stay away from the primary jets. See what hangers and rods you have now, but first check everything above.

Steven6282

Thanks naf, I'll check that out. But I thought WOT was determined by the jets? As I understood it, at WOT the rods are lifted all the way up and the jet size determines how much fuel gets in. I also read that the secondaries are just supplemental even under WOT? Trying to find coinciding and accurate information about this carb is a PITA lol. I'm so tempted to switch to a holley just because more people know them, and parts for them are easier to get. I got one person insisting that all the problems are in my intake (which I'm going to replace soon too), another says my problem is in fuel delivery either the pump or a clogged fuel line, another says it's all in carb tuning and changing jets and rods, and now your idea that it's something to do with the vacuum break. I'm not trying to say anything bad about the information you have given me, it may very well be the correct information and I appreciate it. It's is just nerve racking to have been told 4 completely different ideas of the problem and the solution lol. I think I know how illiterate computer users that ask me about a problem they are having on their computers feel now

I went ahead and picked up a fuel pump over at CPR at lunch. It might not be the problem but if not at least I know I'll have a good fuel pump on there in the future. It could even be that the current fuel pump is causing it to be flooded initially because the PSI is to high, and maybe that is what is causing the hesitation. Current fuel pump has a PSI of 7.5 and the carb says to use a max of 5, I didn't realize this until I started doing research on fuel pumps recently. I didn't want to just throw money at it, but it seems like that is the only way I'm going to learn for myself and fix it. By simply experimenting and seeing what happens. I ended up getting one a little bigger than I need so that if I do decide to upgrade the cam / heads on my engine down the road, I wont need to replace the pump again. I picked up a regulator and a gauge for it as well so that I'll be able to make sure no more than 5 psi is going into the carb.

At least by the time I get done I should have a firm understanding of this thing and not have any problems in the future working on it myself

naf

iTrader: (7)

WOT is when the throttle is opened as far as it will go.

Fuel through through the secondary jets is tuned by changing the secondary rods and hanger. The rods restrict fuel flow through the jets/thinner rods allow more fuel to flow. The hanger controls how far out of the jets the rods will be a different throttle positions. The rods are tapered, the fatter part is in the jets at lower throttle settings.

Fuel delivery issues won't cause a hesitation, where it acts as if it's going to stall, then take off.

Check your booster pump and vac break for proper operation. Make sure everything is working as it's supposed to. Make sure you're tightening the set screw (allen head) between adjustments on the AV tension.

Peruse:

https://www.thirdgen.org/quadrajet

The main parts still apply, just disregard the last few paras where it talks about rich stop and IAB. The secondary operation is the same for both type carbs.