Stumble off idle -

[decooney]

Originally Posted by blykins

I have a little more personal contact than that. One of the former carb designers for Quick Fuel builds my carbs.

blykins,
Did your designer contact provide any follow-up recommendations for John to follow?

[blykins]

I'm not sure if John has got a hold of him yet. I gave him a couple of phone numbers to reach him with but I haven't heard if they've connected yet. If John is calling and can't connect, then he needs to let me know and I'll have Scott call him.

[Grubby]

SUCCESS

Drilled out IFR from .037 to .039. Test drove and things were very close. So I went up to .040 on both the primary and secondary.

The car drives fantastic. Crisp response at all speeds and no lean surges.

Everything else in the carb is as delivered from Quickfuel.

If someone is interested in the breakdown of parts in the carb, I will post it.

I am disappointed with expert advice from several sources. If I had listetened to them, I am not sure It would have gotten fixed. What does the average Joe do that doesn't know anything about cars?

Ultimately, I had to brush up on my Holley tuning experience and purchase many more jets and air bleeds than I wanted to get this fixed.

John

[decooney]

And there it is, IFRs once again! Once you said primary jetting did not help, this was the only other thing I could imagine it would be.

John,
great job sticking to it and for seeing it through.

Now are you able to cruise the car below say 1,800 rpms without issue?

[patrickt]

Originally Posted by Grubby

SUCCESS

If someone is interested in the breakdown of parts in the carb, I will post it.

CONGRATS! Yes, you should post the parts and any extra details (pics too, if you took them). Not for guys now, but the ones that will search this and read it years from now. I get PMs all the time about stuff I wrote years ago.

Good Job!

[blykins]

Excellent.

To answer your disapproval of the "experts", I will say that it's tough to give a prognosis of an issue that someone has not seen/heard/experienced in person. There are so many answers to one particular problem.

I will say that it wasn't the tune from QFT, but a tune from my carb builder, Scott. He coincidentally advises QFT on all of their metering block calibration updates. I think being a few sizes off on an IFR with everything else good as you say, is a pretty cool feat.

[Grubby]

Originally Posted by decooney

And there it is, IFRs once again! Once you said primary jetting did not help, this was the only other thing I could imagine it would be.

John,
great job sticking to it and for seeing it through.

Now are you able to cruise the car below say 1,800 rpms without issue?

Duane,

In 4th gear it actually pulled 1400rpms without complaint.

I was surprised how little idle mixture screw adjustment was needed after drilling the IFRs. About 1/4 turn from the existing setting.

John

[kgs365]

please post parts...grubby...what do you have for a transmission that you can go as low as 1,400 in 4th?...i looked up my specs and i have a 445 FE...780 Quickfuel...edelbrock heads..cam =HR112 230/233@.050 .544 /.553 lift 1.7 112 LSA...this is my second cam milder then the first.also second carb first was a holley 650 that was too small..the car is much more driveable especially with the cooler weather...I've been watching this tread because I think i'm fighting a similar problem

Kevin

[Grubby]

Car and carb specifics;

Engine specifics are posted much earlier in the thread. It is a pretty mild 428 bored and stroked to 447.

Quickfuel HR 850 mechanical secondary (air horn milled)
80 primary jets
86 secondary jets
65 power valve in the primary
No power valve in the secondary
Primary accel pump cam is pink in 1
Secondary accel pump cam is red in 1
IAB 70 both ends
HSAB 33 both ends
Idle Fuel Restrictors were .037 both ends - fixed by drilling to .040"

Trans is a TKO600 with .64OD
FInal drive is 3.54

The throttle response across all ranges is much better than the Holley 750. The power comes one at a lower rpm because the secondaries come open immediately. Tire spin is much easier; like that was a problem.

No report on gas mileage. Double pumpers are notorious for poor mileage.

John

[Grubby]

Originally Posted by Grubby

I spoke to Ultradyne today. My engine builder buys two cam grinds. I assume the first is mine and the second is used in 482s. The builder didn't remember. My cam is one of the following two with number one the most likely;
1. 235 int / 239 ex duration with 112 deg separation
2. 239 int / 244 ex duration with 112 deg separation

Bigger cam than I expected.

I spoke to my local carb tuner. He said he could put my 750 on his "dyno" and he could fix it. I am skeptical becaus he was a bit vague when I pushed for details. His shop is pretty close to my office so I plan to stop by this week and see if his "dyno" is a flow bench.

Not sure how a flow bench could be useful in finding or fixing a stumble.

I made contact with Quick Fuel for a suggestion and should get something soon.

John

kgs365 -
It looks like my cam is actually bigger than yours. Driveability around town was pretty good with the Holley 750 and really good with the Quickfuel.

John