Stumble under Acceleration

[Doppleganger]

Ok...new issue. I got my hard start thing all figured out (with the help of you fellas here)....now got another hiccup. It starts and runs stronger and smoother than ever. What I'm noticing now is, that under a hard throttle (no hole shots - just getting on it to pull out into traffic).....it will stumble and almost stall. Today, it did stall - first time ever even when it was mistimed. Started quick again but I had to be gentle on the pedal to get it home. It does get slightly better when it warms up, but still has this persistent 'dont push me' attitude.

Timing is around 12 advanced. This has a <500 mile Holly 650 the PO put on it. I loathe it - will be on CL as soon as possible. I've heard about them having issues with accelerator pumps but dont know anything about them. The Q-Jet is all fresh and rebuilt (by Mountainman FI in AR) - would put it on but think it has more street value NIB than soiled on my motor.....end goal is my iron block 6L sitting in the shed, so gotta raise $ for that.

I did hook up the vac advance to the vac port in the middle on the passenger side. Would that do anything?

Thanks in advance for any insight!

 

[Wumbo]

I'd check the fuel filter first. Not enough flow through the filter to keep the carb bowls full.

 

[Doppleganger]

Good idea. Will do.

 

[Backfoot100]

Could be a couple things...

First, Holleys like to have the idle adjustment screws set while loaded. A second person is the best for this to keep foot firmly planted on the brake. Set for highest idle or highest vacuum while warmed and in gear.
Second, the accelerator pump operates from an arm and spring setup off the throttle. Make sure that the gap between the throttle arm and the pump arm have zero gap. You adjust the spring to arm lash by a nut on the spring. A lot of times there is a very small gap there.
The idea is that even the slightest movement of the throttle will give you a pump shot. Any gap in that arm and you can get a stumble.

I love Holleys and I hope this helps.

 

[Doppleganger]

It does help - thanks much. A local mechanic told me he prefers the Hollys but when I asked him to tune it, he acted like he didn't know how - lol.

 

[Charlie]

I had a bad fuel pump that acted a little like your stalling. Replaced pump with AC Delco and no more issues. A possibility.

 

[Doppleganger]

The one on it looks very new - which as I've found with batteries, means very little. lol

I do have a couple spare Carter's NIB. The clown that put the Holly on just twisted and tweaked the heck out of the pre-bent fuel line to make it fit (then hose clamped it anyways). I always wondered about that too.

He put a lot of thought and design into his fk ups.

Geez....this truck is a mess.

 

[DirtyDYT]

Sounds like a fueling issue if it’s not a tuning issue. Clogged filter, dying pump, or clogged pickup sock on the sender are my top three guesses.

Does it sputter when it’s cold? If it only does it when hot then it may be a vapor lock issue related to the creative fuel line work you described.

 

[Matt69olds]

Make sure the accelerator pump squirts fuel as soon as the throttle moves. If that’s good, you may need to play around with the accelerator pump cams or squirters.

If all else fails, get a good Q-Jet, bolt it on and go. Holley carbs are great if you want to tinker with them, it’s hard to beat the economy, power, and reliability of a properly built Q-Jet.

 

[Doppleganger]

I have the original q-jet all rebuilt and ready to go. I've also got a 6.0LS to be built for the truck - was hoping to keep the q-jet's new virginity intact for street value when the LS time comes (and $$$ will be needed).

However, its looking more and more like thats the path if I want reliability. I had a Holly on my last square body 25 yrs ago....and all I did was adjust and mess with it (it had a manual choke to boot). Went back to the QJ and it was night-day power and runability. 406 SBC and a built 700R4 - miss that truck alot.

Plus.....I know nothing about the Hollys and cant find anyone locally who does either - otherwise I'd at least give it a shot. The carb thing is temporary - maybe another year if that.