dixie wrecked

iTrader: (6)

Howdy y'all..ive had an issue for a while where no matter what I do, I just cannot get rid of this damn off idle stumble!
Motor is 305 from a 2000 van, weiand intake, accel hei, stock cam and vortec heads, headers, quick fuel 600vs.

Everything to convert to carb, including the dizzy, is new 4000 mi ago.

T5 car.
Motor runs just fine. 170k miles and still 45psi oil pressure.
Its not timing, I can set it to both extremes (retarded and advanced, everywhere in between ) and no difference in stumble.
Come winter, I threw in an orange accel pump cam, it helped some. Now that it's summer, the stumble is back off idle. I've kept upping pump cams all the way to blue, no change. Wouldn't figure a granny geared 305 would need that much pump shot anyway .
Upped to a 35 accel pump shot, no change. Dropped a size..no change.
Accel pump is indeed working fine and not leaking. Exhaust smells lightly rich, but barely.
Otherwise runs like a champ, pulls 18mpg avg actually .

Any ideas, or "quit being a Dumbass, its X" tips?

redneckjoe

have you tried changing springs in the seconarys, or getting an adjustable one?

you may want to try a 50cc accelerator pump? also try different shooter/squirter size. and dont forget the hollow screw if your needing more pump shot.

dixie wrecked

iTrader: (6)

Quick fuels don't use springs, they're adjustable with a screw. Regardless..an off idle stumble is not my secondaries. If they're opening at 800rpm, something is wrong. I don't think the answer is more gas either. It's a granny geared 305.

krisner89

Would it be possible that throttle blades are not closed enough at idle. Not allowing idle circuits to work. Therefore making idle actually running on primary side of carb and not utilizing the idle circuits. Just a idea. I am not familiar with holley type carbs yet just edelbrocks. What rpm is it at idle?

crazynights

iTrader: (3)

Did you try the Sticky from Sofa on how to adjust Holleys?

brettr81

What is the fuel pressure at?

dixie wrecked

iTrader: (6)

Idle is at 7-800, I'm definitely on the idle circuit. Should also mention I have the stock IFR's, stock air bleeds, though I did go up 3 sizes in winter.

dixie wrecked

iTrader: (6)

4psi, pretty steady, although I could probably use a new higher flow pump.

I don't get a stumble if I let the clutch out reaaaly slow whilst holding rpm around 1500. Like 3-4 secs from full disengage to full engage.

sootie007

Read up on squaring the idle transfer slot ....FWIW.

dixie wrecked

iTrader: (6)

They're both set right. Rear set at .017. this is only while on the idle circuit while taking off from a stop. Othereise I have it right on the money.

brettr81

Have you tried running it at different fuel pressures to see if that would help? I know, with mine, there is a big difference with how it runs at startup at 4 psi compared 4.5 psi. I'm not too familiar with the Holley or similar carbs, but I thought they usually liked the fuel pressure to be in the 5-6 psi range.

dixie wrecked

iTrader: (6)

Now that, I haven't done/can't do with this pump, I've considered it as well but cant know for sure until I get another one.

brettr81

You're using a mechanical pump? You can put on an adjustable fuel pressure regulator and see if that makes a difference. Which fuel pump are you using?

dixie wrecked

iTrader: (6)

No, electric. A shitcase Orileys mr gasket one, haven't found a need to up to a holley yet.

skinny z

What do you mean the rear is set at .017?
Let's deal with the primary throttle blade position at idle.
With the carb flipped upside down, how much of the transfer slot is visible with the throttle blades closed? The classis Holley stumble is often caused by the throttle blades being adjusted in a too open position. This results in a shortage of fuel (and a flat spot) when accelerating from an idle.

sootie007

X2

MSgt Luttrell

It's also possible that you don't have your vacuum advance hooked to ported vacuum source, which should have no vacuum at idle and an increase of vacuum when the throttle is opened. Make sure your initial timing is correct and the vacuum advance is hooked to a ported source.

dixie wrecked

iTrader: (6)

"Squaring" it off, I found it was lightly too open and I couldn't the primariesc closed enough to bring my idle under 1000. I think..it's been a bit since I tuned it.

I'll check this weekend, I ate a pothole and now have a very nicely bent header and exhaust leak to deal with. Yay..

skinny z

Tough luck about the pothole. Been there and wrecked a tire not too long ago.
You sound like you know your way around a carb so there's not much sense in giving a lesson on what to do.
That said, If the idle is staying too high, no matter what your timing is (as an example I have my initial set at 16 and have my vacuum advance on full manifold vacuum. That adds another 16 for a total of 32 at idle) you should still be able to get your RPMs down to 600 easily. I'd not then either: the primaries are opened too far, the secondaries are opened too far, there's a vacuum leak somewhere or a combination of the above. Or maybe the carb needs a good going over. You may want to check that you're not getting hung up on the choke fast idle cam.
Keep us posted.

dixie wrecked

iTrader: (6)

I think this crap can knows that as soon as my other 92 bird is up and going, its going to get turned into a bunch of coke cans, just so I have to spend more $$ on it.

I have it at ported, what with the stocker cam and such, but yeah I can adjust timing to both extremes and everywhere in between, but I'm set
at 16° base if I remember correct, which half the time I don't.

This weekend, I'll pop the carb off and re-check how I have the throttle blades set. There's no vacuum leak (externally), only other issue with this motor is worn valve guides. 1/3 qt every 2000 miles kind of worn, not bad for 178k miles.

Carb was brand new as of February. Jackass buddy broke the vac port off my primary metering block, so QF sent me one of the red ones, so I'm also rockin one of those. Reminds me, need a bigger Pv..WHY can holley or QF not make a 9.5..

dixie wrecked

iTrader: (6)

Just yoinked my carb off, not a clue what the hell happened, but secondary side is way off. Secondary transfer slot showing? .005.


Primary side is about .2

dixie wrecked

iTrader: (6)

Just bumped my secondaries up to .2, closed my primaries as much as they will go..which still leaves about .002 showing. Now I remember why I set my secondaries so low. With that setting, it won't idle under 1100 without turning my mixture screws all the way in.

Going back to primaries set at .017, secondaries closed, back to idling fine. Stays at 800, screws have excellent response. Can't back the idle speed screw out anymore, however the secondaries seemed to still be ever so slightly open. I manually fully closed em by rotating the arm on drivers side. Looks like I might have left larger IFR's/smaller idle air bleeds in and just forgot..what with playing musical carburetors between a few motors.



Edit: went on test drive, everything felt fine. Stop, go grab a sandwich, come out and restart her and suddenly back to 1200 idle. Seeing as it as raining and I didn't want to get my sandwich wet, I didn't check if the fast idle was engaged or not.

skinny z

My original post to this somehow evaporated. Sort of a recap: you've adjusted the primary throttle blades so that the transfer slot is "square", about .020" (or .017" as you stated). Secondaries are as closed as you can get them. Idle mixture screws adjusted to provide the highest vacuum/ rpm. Is that about right?
So, after your test drive, was there still an off-idle stumble?
How was your sandwich?

dixie wrecked

iTrader: (6)

Mine have been doing that too, odd.. The primaries aren't quite square, but close, yes.
I can't really use a vacuum gauge on the mixture screws- my valve guides are worn, ergo vac gauge flutters some. However, how I adjusted them was start at 2 turns out, then turn either direction until rpm drops (using a timing light), then richening by 1/6 turn). The stumble was slightly present, however much, much less prevalent. If I had to rate it, when I started the thread, the sumble was about a 7/10, now it's about a 2.5-3/10.

However my idle was staying at 1200, fast idle off. Im thinking I might have torn my carb gasket and not realized it, ima throw a new one on tomorrow. Possibly going down to a 76 IAB and double checking that it's the stock IFR.
She definitely has her ***** back (for a 308 geared 305)!
Also, it was delicious! Left over corned beef with crisp kraut- best sandwich of summer!

skinny z

Starting to sound good all around. Tuning-wise and sandwich-wise.
Keep us posted.