Sounds lean for sure, I would bump up the jetting 2 sizes. If it has 71's I would try 73's.

Dave

 

Reading the plugs and the way it drives I think so too

the stock jet-rod combo for this carb from what I have been reading is a 74/43.I don't exactly know if that is a good combo for what I have or a bad one? I learn as I go

Hope to get some input

 

What Dave said. If you think it's running good at WOT now you might try 2 sizes smaller primary metering rods. For that carb you'll want the early "B" series. They're different from the more plentiful K series. The B series have a small power tip similar to the K series for the later model carbs.

74/43 is pretty rich, it may not actually have those in it. The carb may have large main air bleeds or it may have had brass restrictors in the bleeds that got lost during an earlier overhaul.

 

if you have the lid off the carb for any reason make sure the float level is right up there. 1/4 to 5/16" is where it's at. forget about the specs.

If you're going to be working with a Q much it'll be worth your while to buy a 3/16" pin punch for the roll pin in the pump lever.

 

Amazon.com: How to Rebuild and Modify Rochester Quadrajet Carburetors (S-a Design): Cliff Ruggles: Books

Printed by the damned Communists; but the info is WONDERFUL.

 

if you look at that amazon link there's also a book by Doug Roe, highly recommended. Careful reading of there books can save you many hours of time and trouble.

 

I forgot I bought Doug Roe's rochester carb book many years ago, I have it in front of me now

OK, well glad I looked closer at the carb, I pulled it off and got the numbers off of the rods and jets.

The rods are 36B and the jets are 70's.

I do have 2 other rods and jets, these are looks to be either a 71 or a 77 jet and number 43 rods. I can't see the second number on the jet itelf even after a light sanding, but visually the hole is larger than the one that came out of the carb.

the rear rods hace DA stamped in them.

 

It's likely running lean at part throttle cruise,but the 74/43(B?) jetting & rods is not that lean.

What may be happeing is when at part throttle cruise i think the spring in the power piston is too weak still being over come by intake vacuum even when applying some gas to accellorate not allowing the power piston spring to push power piston up some to pull prim rods out of the prim jets a little bit for a little more fuel at cruise or for when applying more throttle to accellorate some cauisng a lean condition.

For ex many 396/402 bbc street motors i have setup with perfcams work well with 72-73 jet/45b rod so the 74/43(B?) rod your running (which is a riched jet/rod combo) should be plenty rich enough with your setup as long as the correct power piston spring is used.

But 1st take a min to verify you have approx 16-18 deg bmase timing & 36-38 deg total with the perf cam your running,then move onto the carb tuning aftering verifiying thats correct.

Now back to your q-jet ,1st gat a hold of a vacuum gauge and hook to full intake vacuum & test the idle vac with auto trans in gear.

Then after you get that vacuum reading buy the edelbrock q-jet power piston spring kit with 3-4 springs in it from summit/jegs.(listed info below on that for you)

Then try a power piston spring thats rated at approx 1/2 idle vacuum in gear and hopefully that will get you squared away.

For ex,if you have 11" -12"idle vac in gear auto trans then go for the 6" Hg spring.

(SEE POWER SPRING INFO PASTED BELOW)

What secondary metering rods are you running.

Please also list the specs for the cam your running so we dont have to look for them.

BTW,with some senceable/patient tuning you can get it running very well without an 02 meter,it just takes some trial & error road testing along some plug readings but to get it perfect the 02 meter will get you there,thats for sure.

Scott

========================================================


EDL-1994
$8.39

Brand:
Edelbrock
Product*Line:
Edelbrock Q-Jet Power Piston Spring Kits
Part*Type:
Carburetor Stepup Springs
Step*Up*Spring*Material:
Steel
Quantity:
Sold as a set of 4.

Carburetor Step-Up Springs, Quadrajet, Set of 4
Check to make sure this part fits your application
Four springs for super-tuning your Quadrajet.
These Edelbrock Quadrajet Power Piston spring kits include four different color-coded springs that will help you fine-tune your Quadrajet carburetor for varying loads and conditions.

Kit contains:

* One 4 in. Hg gold spring
* One 5 in. Hg orange spring
* One 6 in. Hg black spring
* One 8 in. Hg yellow spring

==================================================================

 

Thank you Scott

I don't actually have the 74/43 setup like I originally said, it ended up being a 70/36B setup instead. I do however have a set of 43 rods out of another carb, but the largest jet I have right now looks to be a 71 so I will end up buying an assortment of jets and power piston springs here this week.

The secondary rods have DA stamped on them.

Asking around my friend network this afternoon, none of them have a O2 meter setup so unless I want to buy one (not yet, low on $$) I will have to trial and error this carb for now.

Tom, I will have to look at the air bleeds and post back.

The cam specs are:
Duration at 050 inch Lift:219 int./227 exh.
Advertised Duration:262 int./268 exh.
Valve Lift with Factory Rocker Arm Ratio:0.468 int./0.489 exh. liftLobe Separation (degrees):112

 

70/36b should still be rich enough,70-36b rod=34 fuel curve and for ex 73-43b rod=30 which is a leaner cruise fuel curve but richer WOT when prim rods are in full up position assuming correct power piston is being used.

The 70 jet is pretty lrg for 36b rod,GM used 66 prim jet with 36b rods,7036019 power piston,and BG secondary rods in the 7029207 q-jet that came stock on the sbc 350/350hp vette for an example of fuel calibration used in a q-jet for a farily hot sbc.

So you having 4 size larger jet on the same 36b rod that came from gm with 66 jet is more then is normally used before stepping up in rod size. Normally you move up in rod size 1 step for every 2 increase in prim jet to keep light load/part throttle fuel calibration reasonable/not too rich .

Your prim jet/rod setup can work with not the be best fuel mileage on prim side but dont go any larger on jet with the 36b rods.

If you find WOT is lean i would step up to 72 jet with 44B prim rods or 73 with 45b rods depending on which prim rods you can find.

But again i think you need to do the tuning work with the power piston to get your cruise/part throttle and light accelloration lean heasitaion corrected.

What base/total timing are you running?

Scott

 

Right now I have the timing set at 14* and 35* total. I also run a vacuum advance.

This morning I looked at the main airbleeds and they do not have brass restrictors in them, they are pretty large.

I was thinking of setting the carb up like the general had it from the get go (74/43) and start modifying from there. Doing just that might fix my problem, or get me that much closer. What do you think?

I still want to get the piston springs as well.

 

That 's about all the timing vortects like so go with that,follow the inst i gave for proper power piston tuning and that will get it corrected,its not the prim jetting thats causing the lean part throttle cruise when it comes to your case running the q-jet.

But i will say over jetting the prim side will bandaid the problem fattening up cruise fuel calibration a bit but that will result in an over rich cruise/low load/part throttle cruise rpm all the time.

But getting the correct power piston spring that will raise the prim rods out of the prim jets a little bit at part throttle cruise and or when applying some throttle to accellorate should fix yourproblem while retaining a more reasonable fuel calibration.

Scott

 

I called around and found a local speed shop that carries the Edelbrock tuning parts I need, so in the morning I will take a trip over there and pick up the springs and a couple of sizes in jets/rods.

But I will focus on the power piston spring first, like you said and that makes perfect sense.

I am use to Holleys, the q-jet is a different animal finally my brain is grasping the whole concept (ever so slowly) of how everything works together Not too difficult once you get understand it.

 

CRAIG,SOUNDS GOOD.

Also,you have email with great q-jet tuning thats easy to understand for your future refference.

Scott

 

Craig,fyi,your email address listed here in t/c dosent work so maybe you need to correct it or need to updatE to a new/current email address.

So send me a working email address so i can send you the q-jet tune info

scott

 

Scott, I sent you a PM with the right address and I will update the one that is listed on this site.

OK went out this morning, picked up an edelbrock power spring kit (not color coded or anything?) but I will be able to tell what spring is the next stiffer one from stock so I will go with that one first.

Also a couple of sets of jets, 74 and 76's just in case. I will give the power piston springs a shot then off to rods/jets. As I said before, I have a set of stock 43 rods for this carb.

I did take it for a 20 mile freeway drive, did much better with no other changes but still seems to be lacking primary cruise power. No stumbling but just lacking something. Plugs are still white as new.

 

BTW, i just checked the vacuum in gear and it's 12-13hg

 

OK, did some changes to the carb with very positive results.

Scott sent me something from Lars Grimsrud that was very good reading, thanks again Scott.

I put the 'black' power spring in there, woke is up low/mid throttle big time. I was able to smoothly accelerate in OD under throttle load with no sputtering or hesitations Still need smaller rear tires, those 31" meats with the 3.42 gear in OD lugs the engine too much.

I also did what Lars suggested and turned the carb back to it's stock setup, so I installed the original setup wich was the 74/43 for my 7042911 truck carb.

Better even yet, I am actually able to smell the exhaust now, before it smelled like warm air, not that was so bad but I know that was lean.

Smooth power now, I am happy :beers:

Plugs still read bright white, I may jump up a couple of jet/rod sizes and see where that gets me.

 

Craig,i am sure the power piston spring change i suggested was what made the biggest improvement in your flat/mid range lack of perf & stumble when moderately accellorating from a syteady cruise speed. It was not as much the going back to stock jet/rod that did most of the improvement. That because that didnt change the overall fuel calibration that much esp at cruise and or when under light/moderate accelloration like the different power piston spring did that raised the power piston/prim rods out of the jets for more fuel at those times/in that situation.

Your current 74/43 jet/rod setup should be plenty rich for your sbc,i run many bbc mild street perf motors with 72-73/45 rod setup thats leaner and its right on. So your mild smaller cubed sbc should be fine with the richer prim setup so dont make it any richer unless you see good evidence it needs to be fattened up more.

On the plugs,keep in mind the non leaded/ethenoled/lower octane/oxygenated fuels mfg today dont color the plugs as much or as fast esp when the motor is tuned well and there are no ring seal/oil issues vs fuels of 30-40 yrs ago that were leaded/had higher octane/no ethenol/werent oxygenated/etc & were a different formualtion in general.

Good job on the tuning.

Scott

 

Thank you all for the help too, I may have been poking around in the dark so to speak without it

I will leave the stock jetting/rods in there and put some miles on it before taking another plug out. Right now the engine has about 250 miles on it so it's young yet.

Now of to the rear tires, need some 275-60-15's here real soon.

 

Bringing this back up, hope you all don't mind 'cause I have another question

OK, before I installed this new 350 and 700 in the truck, I ran a stock 305 and the TH350. The only parts I carried over from this engine were the distributor and the q-jet.

What my question is, before I pulled the 305 for the final time it had developed a vibration bad enough to vibrate my mirrors and steering column that was coming from the engine, not the driveline. It would do this vibrating in neutral with the truck stopped in other words.

The new engine does this same thing.

I started troubleshooting this issue (drives me nuts) so the first to address was the ignition so I went nuts replacing the distributor with a good known unit, cap/rotor/wires and module. Still nothing, vibration still there.

Which leads me to the carb. What would cause this? Vacuum leak? I replaced the base gasket, and all of the vacuum ports are plugged.

Throttle shaft? This might be the issue, it does have some play in it.

Also, I noticed that when on the freeway on OD under some load the carb will whistle, let off and it will go away which I thought was kind of strange. Plus the vibration is worse when its cold outside, when it warms up it will not be as noticable.

Any help will be welcomed

 

have you checked the motor mounts?

are you sure it's hitting on all 8 at idle? Know how to do a cylinder drop test?

 

No, I am not sure but it idles smooth as stock (almost) but does stumble a little bit right off of it.

I forgot to mention that under full throttle it smooth as silk all the way up.

Motor mounts were almost new, I did not see any signs of cracking or anything.

No, never have done a drop test?

 

That wistle with motor loaded in OD at cruise could be an internal vacuum leak in the carb and or combines when stillsomewhat leat part throttle fuel calibration too which tou had improved some with recent tuning.

To test that theory out you could keep the same prim rods/45B(?) but go up 1 maybe 2 steps in prim jet max to see if that helps/stops the wistle when in OD & part throttle cruise with the motor somewhat loaded .

Scott

 

Thanks Scott,

The other day, I put a set of 76 jets in it, and I do run the 43 rods, and thar alone made a noticable improvement in power and response overall.

I have a set of 36B rods and 70/71/74 jets to chose from so somewhere in there I might find the sweet spot.

Internal vacum leak, bad body to top gasket maybe?