When adjusting a holley carb, what does "stumbling" mean?

Hi Scoop. Ok.. here goes.

I found these 3 SBF builds and another AMC 304 in a Rebel(don't ask.. lol) with many similarities to your build. I also looked at the 2 carbs on my shelf to see what they were running but didn't pull the bowls off the 650 to compare because I'm near positive that it's also similar. I'll also list my 310CID/289 Hi-Po headed/600VS tuning spec's at the very end as I think it has some interesting similarities to your combo and could be used as a decent "optimized tune" for your combo.

All engines were between about 9.0 - 9.7-1 CR(except mine at the end of all this which was 10.5-1). All had 600 or 650cfm Holley's and 3 of them had the choke horn removed. All has headers and medium sized camshafts(between 215 and 228 @.050. All were using dual-planes and spacers between 1" - 1.5"(not sure which had open or 4-hole designs though). Two of the SBF motors(a 302 and 351w) had my ported heads on them but there was minimal chamber work aside from light valve deshrouding due to oversize intake valves and would not affect timing or fuel requirements enough to exclude them from this comparison. ALL used premium fuel to achieve more aggressive tunes, although I'm not sure what the RM/2 spec's of the fuel used would have been at the time and in 2 different states. Maybe just average it to 92 octane.

Main jets were between 68-72. As expected.. the 351w used the larger 72's.

Rear jets were between 72-76. Keep in mind that your rear jet sizes will probably end up about 6 sizes larger than the primaries due to not having a rear power valve.

I only deciphered bleed sizing on two of the builds and they were between .016 and .028 for both front and rear LSB and HSB but that will probably be irrelevant to your setup because the IFR sizing was/is likely much different on those carb's compared to your HP. Didn't check all the spec's and I'm only assuming that's the case though.

PV rating were between 4.5 - 6.5 on all.

Weights and gear ratio's varied between around 3,200 - 3,800lbs and 3.25 - 3.70 ratio. ALL were automatics and with all of them, except the 351w powered Ranchero, having mild stalls. Wide variations I know.. but wanted to eliminate any more questions later on so I just threw that in here too.

Initial timing was between 16 and 24 for all. Mechanical sweeps were fairly aggressive and "all in" around 2,400 to 2,800 for every combo(as expected, the lighter cars came in quicker). All ran manifold based vacuum advance pot ranging between 8* and 14*. Total timing numbers varied between 38 and 44*.

Here are the last logged tuning spec's I wrote down for my 310 inch(+.060) motor before I pulled it and sold the car off. Cam was a custom ground 218/224 @.050 with .500'ish lift. Ford DS disty with an advance sweep mod(welded) to achieve more limited travel of around 16-17* mechanical sweep. 600VS carb with choke horn removed and short style K&N stubstack. Plus slabbed throttle shafts and a few other tricks to help improve throttle response and airflow.

* Front jets = 72 and rears = 76
* 6.5 PV
* LSB(low speed bleed) = approximately .016 and HSB(high speed bleed) = .022
* Yellow secondary spring
* Timing = 25 initial + 17 centrifugal("all in" at 2,700 rpm) = 42 total advance + another 10*.. or so(because I didn't record it) of manifold vacuum advance under light load.

About all I really have for time for right now but I'll check back later on to see if you have any more questions. Hopefully you get time to fiddle with those pump cams see if we're on the right track with pump shot volume and duration changes.

 

Cool! I will try to mess with that this weekend. Not sure if the weather is going to cooperate, though. Beautiful today, but they say it will start thundering tomorrow.

 

You surely have much more patience than I do because I'd be out in the garage tuning away if I had the parts in hand to fix an issue I was having.

So, I have a somewhat unrelated question for you. Is that a hydro cam.. and how high have you revved it before power noses over? You reach 7,000 rpm with it?

Reason I ask is that I have a similar custom solid cam(224/230) with about the same lift(using 1.8 rockers) that was ordered to take the place of the above mentioned slightly milder 218/224 grind. I'm still on the fence on whether I should just use it to get my junk slapped together quicker?.. or sell it in unused condition(so it's actually worth anything at all to someone) and bite the bullet for a custom solid roller setup right off the bat.

My other "little cam" was supposed to fall off after around 6,400 or so according to the grinder I worked with on it.. but I easily shifted at around 7,100 and pushed it a bit higher.. to around 7,300'ish.. through the lights. If I did keep it.. I'd be looking at upgrading the lifters to the pressure fed "face oiler" type.. "EDM" or whatever they're calling it these days. I just hate to throw any more cash at making that stick work on my combo since it would just be a starter grind anyways. Was just curious about how much you like yours.

 

Hydraulic roller.

I have shifted as high at 7200, but 6500 is my typical "getting on it" shift point. If I am just screwing around with a passenger, 6000. It pulls good to 6500 but starts to fall off after that.

It gets to 6500 pretty quickly, but from 6500 to 7000 is much slower than 6000 to 6500.

 

ok.. got it. Thanks much.

PS. Once you get it to the track.. I'm sure it will be like mine in the respect that you'll likely find lower ET's with a slight over-rev because it will counteract the rpm drop associated with gear changes. That's really the biggest problem with smaller/shorter stroke motors.. just not enough torque production to help with gear change rpm drops. At least until we get into really short gears and close ratio transmissions, anyways. Heavier flex-plates and larger diameter stall convertors help some too.

 

The main problem is the weather. Beautiful today, but supposed to rain all weekend. So....

I had several things I had to get done today while weather was good.

While it is raining this weekend, I can work on my carbs and drivetrain noise. Won't be able to test drive until it dries up, but I will have two days of thunderstorms where I HAVE TO be inside, so I am budgeting that time for working on the car.

 

One more question, What size squirters are recommended?

Way back before you looked, you were estimating .032 and .035. Still your recommendation?

Those are $20 each, so I don't want to be buying a bunch of them. And I will have to order from summit

 

I would install the more aggressive pump cams before going any further with ordering any parts.

Then.. if the holes start to clear up but don't go away completely?.. and I doubt that they will with the severity of the stumbles you're indicating.. swap the 31 from the back over to the front and install the new 35 onto the back. Then.. if those shooters turn out to be slightly too aggressive?.. just pull back on the pump cams lobe size to provide less fueling.

 

OK...Cant wait for good weather...

 

Finally got around to doing this. Brown cam in back, green in front, .035 squirters in the back.

As soon as the engine warms up gonna go give it a try...

 

Oh well...if it isn't one thing, its another.

After shimming up the transmission to get better driveshaft angle, I feel something lightly scrubbing/bumping the trans tunnel when the car is in motion. I thing it is a u-joint or the oil flinger.

It DID back up and go forward without hiccups, so THAT is promising.

When engine cools, I will pull out one of those transmission shims and try it again.

 

I really don't know how you do it, Scoop. I'm extremely patient.. but I would'a been tuning that carb in a thunderstorm just so I knew where I was going to end up right away. Steer.. pedal.. steer.. pedal.. shift.. and repeat.

 

Well, with the weather around here changing every 20 minutes, and all the other activities of daily life, I have found that I am trying to beat the clock and get things done before it gets too hot and i cannot work outside for 6 months.

Spent last weekend cutting dead branches out of a huge tree that hovers over our house, and thinning it out so the summer storms don't blow it over on us. Then two garden/planters that needed to be re-done, cleaning out the pool and preparing it for the summer, etc.

We are getting a couple of late cool fronts, but when they stop, I will not be able to work outside until October.

So, next things I NEED to do. Lower transmission, confirm carb is responsive, get car aligned better with more caster and LEAVE IT ALONE until after the MCCI Meet in July.

My boat needs all new rubber and it is all on order (fuel lines, cooling lines, impeller, belts, etc). Luckily that stuff did not come in on Thursday as expected so I can finish the car up instead. Got to have both the boat and the car lined up in the next few weeks or they will set up for a summer. Unless I can find an air conditioned location to haul them to work on them.

 

Well, found the problem. I had the tailshaft pointing up enough that the oil flinger was lightly rubbing on one of the bolts that mount my floor shifter to the floor.

Simple fix, but labor intensive, as I had to remove the exhaust, disassemble and remove the floor shifter to get to the mounting bolts, cut the long bolt, and reverse to reassemble.

Still reassembling...

 

Alright!!!

I got two of my long-standing major problems fixed in one day1

No more drone, and no more carb hiccups!!!

It transitions from idle to primaries, and then to secondaries without any stumbles, and idles better, starts easier, and pulls harder than it ever has!

Thanks a bunch to groberts!!!