I'll start with I got --

Everything is new-

350 HO crate,performer intake,performer 1406 carb,mallory with adjustable vac advance dist,GM wires...
the only thing not new is the power steering pump and trans.

OK, at about 1500rpm I have a slight miss/vibration(while driving and park) I took it to the dealer just to make sure it wasn't a mechanical problem. They said all was good, Just needed to be "tuned".

So,I put a new O2 in to see whats going on. In park,as I open up to 1300-1500 area,the voltage drops way low .00x range(lean) right?

Next I ran a wire into the car to monitor the meter while driving,once I get to the same range ( cruising at 40ish 4th gear) I get a .7 to .9 reading,but still feel the miss/vibration whatever.

I'v changed springs,jets rods,timing 8* to 12*,right now the jets are 107-rods 65/47 pink springs. "Seems" better but not good enough.

I know most are gonna say ditch the carb and get a holley.

Any Ideas????

TIA

 

Have you checked for vacuum leaks?

If a cyl is too lean to fire, the unburned fuel entering the exh can cause a rich reading on the O2 sensor.

 

I sprayed starting fluid everywhere. Didn't find anything.

Could timing advance have anything to do with it?

i've got another set of rods on the way (.58/.42) might go to .113 on the jets.

After that ??????????? Maybe i'll go back to a Q-jet or try TBI.

maybe i should try the carb board. Don't wanna double post though.

 

With eng at 1500 rpm (or at what ever rpm it feels like it's missing), manually start moving the choke towards the closed position. If it smooths out, you're running lean..

 

Sorry,haven't had time to try your suggestion yet. Saturday i'll mess around with it. Good idea though.

thanks for the reply,any other ideas appreciated.

 

ZZ28ZZ, tried what you said,it did seem to disapear but not 100%.Wondering if I might have a vac leak under the intake,because I could not find one externally.Any way to check?

I also pulled plugs #1 and #2, both insulators were a dark brown color??? Also tried different advance springs in the distributor.

I've been wrestling with this problem for over a month and no matter what I do the problem is still there,same spot same condition.

The days are getting longer and my patience getting shorter.

HELP

 

To check for a vac leak under the intake:
Remove the PCV valve from one valve cover and the breather tube from the other valve cover. Using the palms of your hands plug up the holes (or you can tape up one side). Feel if a vacuum is building up in the crankcase. If you can feel vacuum building, there's a vacuum leak under the intake. You may need to remove the oil cap and tape over the hole for this test. Also, doing this test on a cold eng is MUCH more comfortable.

Do you have an EGR valve? If so, might wanna make a block-off plate for it to eliminate the possibility of it not closing all the way.

 

I had a similar problem when I put my engine in a few years ago, and as i turned out, my problem was the vacumm advance. It was pulling to much timing into engine, it was disconnected and plugged and now the advance is all mechanical that all comes in with 36 degrees total. No more miss, so check that you are not pulling to much advance, good luck..

 

zz28zz--checked like you said, definatly not sucking. Put my palm over the pcv hole and the duct tape on the other 2 holes start to push out.

I'm going to start from scratch,new plugs, wires, cap & rotor and stock jets/rods.

cc--Thanks for the reply, I've tried different springs/with advance and w/o advance hooked up.

I shouldn't have to check the valve lash on a new crate motor should I??

Could this have anything to do with.....??? Just wild guessing.

Thanks guys!!!!

 

OK,I'm done with playng with the carb. Pretty sure not the carb.

I've only got 100ish miles on the engine,could it be its not broken in yet??

I just been afraid to drive it like it is to avoid any possability of damage.

Like I said above,I have a miss or multiple misses at about 1500 to 2000ish.Any ideas??

 

I'm still leaning towards a vacuum leak or carb issue. Do you have a different carb to try?? The lean condition you saw with the O2 voltage and the fact it runs smoother with the choke partially closed are good clues.

 

I know, but i've sprayed and capped all vacuum sources.

And starting fluid near distributor=BAD!!!
Checked the floats Sat. and were in spec..sprayed carb cleaner through every hole I could find.

I guess what puzzles me is that its in the same spot no matter what I do.

The only other carb I have is the ccq-jet off the 305.I suppose i could try it. If anything it would run rich because the primary metering rods would up all the time,not cycling like they should.

Another thing I noticed is the miss/vibration is there on deceleration too,like if I slowly take it up through and past that point then let off.Changed the plugs again yesterday.Looked like there was some oil on the rim(the part surronding the center electrode) of some of the plugs.Thats why I said rings not seated.? I never flooded it,pump it once turn the key and fires right up.

Eventhough I'm getting a constant puff,puff,puff out of the valve cover,could there still be a vacuum leak???



I still have to take to emmisions test ,was due in march.



Thanks again!

 

another question. if i created a vacuum leak say by pulling the brake booster line while the car is running,should idle increase or decrease?

and what would that suggest if it increased/decreased?

I did just that and the idle increased atleast 500+ rpm.

 

Might try using propane to check for vacuum leaks. I perfer it over liquid spray. Just need to block the wind when using it.


Puff, puff, puff.....
Doesn't sound like the rings have seated yet. You'll need to drive it to seat them.

Pulling a vacuum line loose should make idle rpms rise a little.

Sounds like the carb is having trouble transitioning from the idle circuit to the main circuit. The ccq-jet might tell you something. I've never tried to run one w/o the ecm.

 

Not sure what to do now.I've capped all vacuum lines except pcv and vac. advance. No differance. I'm pulling 15 on the vacuum gauge at idle.

Might try to beg,barrow or steal a differant carb.

I tried the propane.Didn't seem to find anything.Even ran an extra ground wire from the neg. battery terminal to distributor base.Right now i'll try voodo,black magic,maybe I need a new FLUX CAPACITOR.

 

Make sure you cap the pcv hose too (while testing). If a pcv valve sticks open, that will be a huge vacuum leak.

You never replied abt the egr valve. If you have one, try making a blocking plate for it to rule out the possibility it may be leaking.

 

Sorry, no egr.

I really appreciate your help.I,ve built 3 engines,the last one about 2 years ago (350 roller motor),ran great until I was being stupid one morning 3am,this guy in a rustang was riding my a$$ for a couple miles.So I gave in and put the hammer down,he chaged lanes thinking he was gonna pass but I pulled away.Got it up to 130mph he was atleast 20 cars back by then so i let off. Anyway the next day I start it up and start off to work and start to hear a slight rap.turned out I scorched #1 rod bearing 2-3 were on there way.

So is not like I've never worked on a car before,but another set of "eyes" helps.

thanks