84oldsDelta88

So now i'm having a new problem. It used to only do this when cold but now its doing it all the time.

When i accelerate from a dead stop the car has a horrible hesitation that wont go away unless i punch the gas and open up the secondaries. Also i notice a huge lack in power through all rpm ranges even at WOT.

I think its running lean judging by the plugs. I'm not sure though. I placed my hand over the primary side of the carb and noticed rpms went up slightly. (Which from what i read online means its running too lean).

I tried adjusting both the APT screw and the idle mixture screws but it seems that no adjustments i've done have fixed the problem. Right now i got both idle mixture screws turned 8 turns out and its still running like crap.

I also noticed that my vacuum advance unit wont hold vacuum too well, could that cause my problem?

Lady72nRob71

Sounds like a vacuum leak to me.
This is possibly the problem! Use a new hose to the disty and suck a vacuum on it. If it will not hold, then replace it.
Check your other vac lines too while you are rottin around in there.

AZ455

The idle screws are 8 turns out? Not sure about your 84 carb, but on my 74 8 turns out would be extremely rich. You turn them in to lean the mixture. However, this wouldn't make a difference once you come off idle. The leaking vacuum advance could definitely hurt part throttle response. How is your accelerator pump working? Nice strong shot when your depress the plunger?

84oldsDelta88

Just tried a new piece of vacuum hose, it wont hold vacuum for more then a couple seconds so gonna try and get a new advance module this week.

Also i'm using ported vacuum for the advance, is that right or should i be using full manifold?

Would a bad vacuum advance cause the hesitation? And if not what else might cause it?

What can i do to richen it up some? The adjustment screws dont seem to be helping much. And i tried rejetting the carb again using 55 rods and 73 jets. Still running too lean according to the plugs that is.

84oldsDelta88

No longer using the 84 electronic carb. I'm using a late 70's quadrajet M4MC.

I though 8 turns was too much also but it still runs too lean (according to the plugs).

I'm guessing the APT screw controls part-throttle? Currently i have that screw set to 3 turns out from seated.

Its funny you mention the accel. pump cause i just replaced it this morning, the rubber cup was ripping on 1 side. Thats what i thought the problem was when i noticed the hesitation.

olds 307 and 403

Stock 403 carb on my 78 403 engine came with 48K rods and 73 jets. The Holley reman 350/403 carb came with 48K and 71 jets, read lean on my 403. Switching to the 73 jets reads a nice medium brown. The track will really tell me how ideal it is.

Creativeindy

Accelerator pump could rarely cause hesitation from a dead stop. Mine used to do this and it turned out to be this. I followed alot of information on this link to help me diagnose my issues. Seems very helpful and informative. Covers dead stop hesitation(Surging) and accelerate hesitation, along with a bunch of other issues and topics. Gives you ways to troubleshoot so you can rule out one thing or another.

http://www.thecarburetorshop.com/Troubleshooting.htm

bdub217

I'd find out where the vacuum leak is first if indeed it is a vacuum leak. Also check every single piece of hosing for dry rot.

There's the Dist Vacuum Advance module which is a round looking deal , then the egr solenoid, .....evap canister purge....what else am i missing for the vacuum system.....i know the a/c and cruise stuffs....but that wouldnt be causing this. If it does fine at higher rpms while under load (driving at speed) then it's gotta be vacuum related... All the parts I listed would be game for fail correct?

ralsy

Thanks for the web site. What a great find

84oldsDelta88

Thanks for the help guys. I think i finally fixed it, unfortunately i don't know what the actual problem was.

Today I replaced the accelerator pump with the 1 from my e4mc it appears to be a tad bit longer then the m4mc accel. pump. I also changed out the jets again going back to the 71 jets. Set the APT screw to 3 turns out from seated. And didnt even bother touching the idle mixture screws but i think they're at 3.75 turns out from seated.

So far it seems to be running great now. so well see what happens.

84oldsDelta88

Well the problems back again. I get the hesitation on acceleration. I've noticed the problem comes random, 1 day its running great no hesitation, smooth acceleration, and then out of no where the next time i drive it its hesitating.

What could be causing this? I've tried everything to richen up the mixture but nothing works. I tried installing the richest rod and jet combo i have, and even turning the APT screw all the way out so it would be running full time rich and nothings working!!! It still has a hesitation and feels really lean. Checked all vacuums lines and theres no leaks

BILL DEMMER

a longer accelerator pump stem will give you a shorter(leaner) pump shot. the m4m and e4m carbs. have restrictors in the passages so you can't over-richen the idle mixture, there's a limit to how much fuel can pass through them. adjusting beyond that restriction you could take the idle needles out of the carb. without any effect.


bill

84oldsDelta88

So i'm still having problems with this off idle stumble. I've tried almost everything i can think of, Rebuilt the carb atleast 3 times now within the last month, Tried different jet/rod combos, Tried adjusting the idle mixture and APT, I've read about 50-100 online forum posts covering off idle stumbles, and nothing is working.

What do i do?

I'm stumped. And no one in my area knows anything about carburetors, they all do fuel injection which of course olds motors dont have (1 reason I wish I would of went with a chevy motor, i could have fuel injection right now and not have to deal with this) but i wanted to keep it all olds which is biting me in the *** now.

And at the moment i'm flat broke so i cant afford to send the carb off to be professionally overhauled or have a garage fix the problem. So i need some ideas guys?

BILL DEMMER

a shorter/leaner pump shot can cause a stumble.


bill

84oldsDelta88

I reinstalled the original acel. pump (with new pump cup and spring) the other day no change.

Also i noticed that my idle mixture screws have little to no effect except when their turned all the way in.

I tried a couple tests the results are below

1. Closed choke partially/ covered primaries with hand:
engine speed increased slightly for a few seconds then calmed down, which would indicite a lean condition.

2. Disconnected accel pump level and gave the throttle a couple jabs:
it reved fine which would indicate a rich condition
(i was even able to drive it with the accel pump disconnected, but it still had the hesitation from off idle acceleration)

3. Sprayed carb cleaner around the carb and vacuum lines:
the only place i found had an increase in rpm was when i sprayed the back of the carb between the carb and intake near the brake booster vac. line.
(it wont do it right away but if i keep spraying there for a sec. the rpms will start to pick up)

Does that mean my throttle plate/base plate is warped? or possibly even the bowl section.
Could I use rtv sealant to try to fill in the area?

Getting horrible gas mileage, and my spark plugs are all white. So i'm wondering is it too rich or too lean? It seems to be giving the symptoms of both and im so confused right now as to what to do.

84oldsDelta88

Well i decided to try something. i took my carb apart and used red rtv silicone sealer on the intake gasket and carb base gaskets to help cure air leaks, it did work somewhat my air/fuel ratio gauge now rides in the lower section of "ideal" at idle (before, it was all the way lean).
Throttle response is a little better but the hesitation is still there when you accelerate from a stop.
Also now if i put my hand over the carb the rpms don't increase, it will stay normal for a sec. and then idle down.

So i went to the junkyard this morning and picked up another carb to try. its a M4MC off a 1977-1980 olds delta 88 with a 350 sbo. I figured this would be a perfect match for my setup.

I got my work cut out for me on the carb rebuild. According to the inspection sticker it hasn't been driven since 03, and the carb definitely shows, the carb bowl has some nasty white/yellow flaky looking crap in it. Although the good thing is it has never been rebuilt and still has the idle mixture screw caps in place so its a good find and it was only 28 bucks. and so far from what i could see isn't warped