Holley pump cam help

[78Delta88]

Someone that don't know carbs.

You are part way in transition with not enough signal to get good distribution from the booster. And possible need to open air bleeds slightly.

650 runs good idles good ... Leave that there. Figure out cause of bog/stumble.

Try RV 10.5 power valve, check float level, try 2 steps up in primary jets. Make sure secondaries are shut. Make sure O rings on transfer tube are good. Check secondary boosters that they are not dripping.

 

[Ernest]

Does anyone know at what rpm you are out of the idle circuit? I first had it at 650rpm and that is where I got the smoothest idle with the best vacuum [20"]. They raised the idle thinking that would cover up the lag, but then it idled very rough. I know if the throttle plates are open too much you get the off-idle ports starting to drool gas, causing rough erratic idle. Now that the right cam is in place I can go back and play around with the idle. I am so used to a gentle Q-jet idle that this is annoying to me.

You're lQQking at a good 2400rpm as the idle circuit quits and the mains start to kick in through the boosters.

Honestly, without installing a wideband 02 sensor gauge. its a continuous guessing/tuning game, going by sound, feel(road manners) and reading of spark plugs... even with a WB02, i'd still check the spark plugs as its just another tool, its not absolute.

 

[1320chevy]

A friend put a 600 cfm Holley Quick Fuel vacuum secondary carb on his mostly stock Chevy 350 engine. This is in a very stock 1978 Malibu, auto trans. It does have headers. We got the idle nice and smooth, at around 650 rpm, with 20" idle vacuum. The vacuum advance is hooked to ported vacuum. But there is a hesitation off idle. WOT is fine. I know dick about Holleys, and he knows even less. I suspect the accelerator pump. I read up on the pump adjustments. I get the .010" gap at idle, and the .015" gap at WOT. It is the accelerator cam that I don't understand. What color would work best for this set up? My reading indicates the blue cam, in the #2 hole, would give the most volume fastest. I don't know what color is on it right now. I need to check that. If this was your car, what color would you use?

Holley carbs are very good but largely misunderstood. I'd get a few different size squirters and swap them to see if there's a difference. Larger isn't always better. A smaller # will deliver the same amount of fuel as a larger one, but over a longer duration. Going smaller will clean up your launch. You can also play with timing. Use only manifold vacuum. Make sure fuel bowl level has been correctly set. The linkage eccentric determines when the fuel shot begins and ends. generally just using the two different adjustment holes will give you all they can unless you actually modify the ramp. I set them up so just tapping on the linkage arm will cause a small amount of fuel to drip from the squirter at idle and then just backing off a tiny bit. A 600 is a bit small for a 350 but better than over carbing. 650 would be better but stay under 700.

 

[Bonnewagon]

I went back today with my handheld digital tachometer. I wanted to see what rpm the engine was running at, change timing, and test vacuum. They said it was 'running great' but as soon as I held the tach near #1 I saw it was idling at 1250rpm. Out of the idle circuit, past the off idle even, and running on the primaries. No wonder it 'ran great'. I idled it down and then the problems started. It would die, stumble, shake, all sorts of stuff. We tried changing the crank timing to 12,10, 8, nope. The vacuum came up with the 12°. But on the street it ran worse. It wants to be at 6° and that was where it had been for decades. The original old timer knew best. So I kept playing with the idle and discovered that if the idle was up high, out of the idle circuit, it ran rough, and seemed rich. If I kept the idle at 600- 700, it idled great, but would stall after coming to a stop. It feels like it is choking on gas. So, idle is fine, off idle is rich, deceleration is rich, feels like it is all around pig rich. The owner is not happy with me. Now that I think of it, all his cars idled real high, and all had Holleys. Not a coincidence?

I recovered the original carb that was tossed because it was 'dirty'. It is a Holley 3310-4 made on 1155. I am thinking that is 1995. Research indicates it is a 750cfm 4160 series. #72 primary jets. That seems OK for a 350, yes? 6.5 power valve. .031 nozzle. I have no idea what is in the current 600 but I will check the numbers next week. I am considering taking this old one apart and seeing for myself how these work.

 

[78Delta88]

You need to a a wet and dry compression test on it. Write down the numbers and post.

Depending on year, most emission 305s and similar late seventies and eighties start at or around 14 if running unleaded gas.

 

[78Delta88]

Tape a piece of printer paper across the exhaust pipe. Let it run about three minutes. Carefully light it. If it burns normal you are ok. If "pig rich" it will quickly incinerate because paper loaded up with unburned gas.

Rich usually hits the back of my throat, lean back of nose... But that's just me. Rich will run cooler, lean will run hotter.

 

[Bonnewagon]

most emission 305s and similar late seventies and eighties

It is a GM Targetmaster 350. Year unknown. I'm thinking mid 90's.

Rich will run cooler, lean will run hotter

I am amazed that it will sit there and idle all day at 180° while we play with it. The radiator is an OEM 6 cyl model and I can see blue-ish green corrosion all along the bottom. Amazing, or cool running from richness?

 

[melloelky]

I went back today with my handheld digital tachometer. I wanted to see what rpm the engine was running at, change timing, and test vacuum. They said it was 'running great' but as soon as I held the tach near #1 I saw it was idling at 1250rpm. Out of the idle circuit, past the off idle even, and running on the primaries. No wonder it 'ran great'. I idled it down and then the problems started. It would die, stumble, shake, all sorts of stuff. We tried changing the crank timing to 12,10, 8, nope. The vacuum came up with the 12°. But on the street it ran worse. It wants to be at 6° and that was where it had been for decades. The original old timer knew best. So I kept playing with the idle and discovered that if the idle was up high, out of the idle circuit, it ran rough, and seemed rich. If I kept the idle at 600- 700, it idled great, but would stall after coming to a stop. It feels like it is choking on gas. So, idle is fine, off idle is rich, deceleration is rich, feels like it is all around pig rich. The owner is not happy with me. Now that I think of it, all his cars idled real high, and all had Holleys. Not a coincidence?

I recovered the original carb that was tossed because it was 'dirty'. It is a Holley 3310-4 made on 1155. I am thinking that is 1995. Research indicates it is a 750cfm 4160 series. #72 primary jets. That seems OK for a 350, yes? 6.5 power valve. .031 nozzle. I have no idea what is in the current 600 but I will check the numbers next week. I am considering taking this old one apart and seeing for myself how these work.

an "average" 350 a 600 cfm is fine(a lot of variables to be had but for the scope of this..),most folks over carb everything for some reason.that 750 that came off it is a vac secondary model so it's gonna give it what it wants when needed and not just because you've got your foot in it like a double pumper would. but is on the larger side.a smaller carb equals a quicker throttle response and lower RPM acceleration vs it's larger counter part. this is just my .02

 

[Bonnewagon]

a smaller carb equals a quicker throttle response and lower RPM acceleration

That is why I am so confused. The small 600 should be running 'CRISP'. It is anything but that.

 

[Bonnewagon]

So after some online reading I have learned something. You CANNOT just take a Holley carb out of the box and just plop it on an engine and expect it to run perfect. Buy I kind of knew that. The Quick Fuel series is known to be pig rich out of the box. This is where tuning the idle air bleeds and idle restrictions comes in. Unfortunately I know very little about this and the owner doesn't even want to know. I still need to get the carb part number so I can see what came in it from the factory, then I can make an educated guess what is going on.