new carb hesitating a bit

[v8s10kid]

i just put a new holley 570 cfm street avenger on my s10. it seams to hesitate till about 2700 2800 rpms then takes off. are the secondarys opening too late?

a little info:
1984 chevy s10
305 small block
edelbrock performer intake
shorty headers
2.5 inch custom exhaust with flowmaster mufflers
pertronics electronic egnition conversion
muncie m20
3.08 rear
weights about 3240 with me in it (thank you scrap yard)

altho my old edelbrock carb ran a little rough, it never hesitated like this. also, i didnt change anything else. timing is still the same, and i havnt put new plugs in yet. the vacume advance line should go to the port on the side of the metering block right? or to the port at the base plate?

[v8s10kid]

new msd wires, put in the lighter long yellow spring. still hesitates.

fouled plug?

come on guys this is my daily driver, i need to get it running good yesterday.

[ivmotor]

Did you check float levels yet? Do you have any way of knowing rich or lean? How much vacuum does it pull at idle? You should set your power valve just below that number so it opens under acceleration. You could install bigger jets and try the drive again and see if it improves. Your accelerator pump circuit could be plugged, or the wrong cam/nozzle combo. Watch the nozzles and crank the throttle, you should see a pretty healthy "squirt". Do you have a timing light to verify the timing hasn't changed?

[Vegas69]

Is this during normal driving or full throttle?

[GregWeld]

I just put a brand new out of the box Holley 650 on my buddies '32 Ford... got it running fine but not "perfect". I thought it was pig fat cause it felt a bit lazy in the bottom end... and it had a bog if you jumped in it.

Bottom line was -- we took it to the dyno -- it wasn't pig fat -- it was LEAN -- and needed the squirters resized (drilled out) and two jet sizes bigger in the primaries...

Here's what I'm trying to say:

Some of this stuff takes a pro and takes equipment (tail pipe sniffer etc) to sort out even if you're real familiar with carbs and timing etc. You could spend days trying to sort out all the advice and tips you're going to get in forums like this.

[v8s10kid]

i have no way of telling if its rich or lean. i dont have a timing light or a vacume gauge.

it does it in both normal and full throttle driving.

i got new plugs ill change em tomorrow and check a few more things but if i cant find it one of my dads friends builds and races modifieds at the local circle track, hopefully he can sort it out.

normal driving it has a lack of power and seams to bog a bit. full throttle it hesitates till about a quarter up the rpm band then it suddenly has this massive release of power. when i let off the gas it does pop and sometimes backfires.

[Ron in SoCal]

Here's what I'm trying to say:

Some of this stuff takes a pro and takes equipment (tail pipe sniffer etc) to sort out even if you're real familiar with carbs and timing etc. You could spend days trying to sort out all the advice and tips you're going to get in forums like this.

What Greg said. I had a new Holley 750 do the same thing you're describing. I spent hours trying to get it right, with help from so called 'carb tuner' friends. Took it to a tuner, ran great right after that. Good luck...

[chr2002ca]

I had the same trouble with 3 new Holley carbs. Two 750 Vac Sec models and one 770 Aluminum Street Avenger model. All 3 had a bog and WOT on a new engine. I had to bump up the squirter size 2 or 3 sizes, change the accelerator pump cam, install a larger CC accelerator pump, and change the vac sec spring. I also bumped up the primary jets one size. After that, the bog disappeared for the most part, but then it ran rich only on idle. I had to do some other tinkering to get the idle to not run rich(was fouling out my plugs), but those are unrelated to the bog issue discussed here. In summary, it took a lot of work to get the carb running right. I could not have done it without installing a FAST dual A/F metering system. I wish you good luck with yours.

[exwestracer]

X2 on the lean condition. You will almost never see a bog from being rich. We were chasing the same thing on a Camaro here at the school.

Are you running an adaptor on the manifold? We found some serious vacuum leaks under the carb with the el cheapo adaptor the student had on the car.

[v8s10kid]

yah, ill ahve to have my dads buddy tune it.

no, no adaptor.

did have a misshap. sence it is my daily i had to drive it to work today. i wasnt beating on in or anything. it backfired on the ighway and blew out the exhaust flange gasket i just fixed.

it sucks trying to do this crap when i have to drive it at least an hour of highway miles the next day.

[v8s10kid]

changed plugs, better still doing it tho. hopefully the mechanic will let me stick around so i can learn some $#!%

[v8s10kid]

cant get it to the mechanic so i did some more checking. also adjusted the idle mixture screws a bit.

-20 inches of vacume at idle (was 18 before adjustment)
-the accelerator pump nozzle is spraying a pritty thick stream of fuel
-changed vacume secondarys from silver to long yellow spring (lighter)

still need to check the floats and borrow a timing light from someone to check the timing. but i have to go to work :( , hope its at least better now.

[v8s10kid]

new msn cap and rotor, better but still there.

float levals are good, and as i said i got 19.5 inches of vacume on idle.

gona see if i can steal *ahem* i mean borrow someones timing light.
what do you guys think timing should be?
1983 305 H.O.
edelbrock performer intake
holley 570cfm street avenger
stock hei with:
-msd coil
-msd cap and rotor
msd wires
shorty headers
2.5 inch flowmaster exhaust

also, idk if this matters but the timing tab is straight above the balancer behind the water pump

[GregWeld]

Okay -- so tuning an engines timing is a function of MANY MANY things and a guy could write a book trying to explain all of that on a forum like this.

Timing is "what the motor wants" ----- and there's MANY things that affect what the motor wants.

Timing is not just @ idle.... it's timing at IDLE and the CURVE and TOTAL timing... and messing with the timing at idle will affect the TOTAL and vice versa....

Gasoline quality and the distributor CURVE and the Tranny/rear gears/tire diameter ALL affect what the motor "wants". Toss in a cam - the cylinder pressures (people call this COMPRESSION RATIO - but that is the WRONG thing to call it) all will affect the timing a motor wants to see.

Having said all of this.... which is why NOBODY can tell you want to set your timing at..... You should look for 10 to 12* at idle... and no more than 36* at 2400 or 2500 rpms with the vacuum line to the vacuum advance disconnected and plugged. Reconnect it when you're done.

Go out for a nice road test -- listen to the motor - for "pinging" under "load" --- so drive it UP a hill and try to lug the motor down. The minute you hear pinging STOP LUGGING IT by selecting a different gear or whatever you have to do. YOU CAN HURT THE MOTOR running with pre-ignition (pinging). Go cruise on the highway -- light throttle pressure - hold steady - try to see if there's any "bucking" or "surging"..... and then just do "seat of the pants" driving if you don't have pinging and you're not surging then just see how it runs and drives.

Remember as your timing is advanced your idle rpms go up - so you'll need to reset that and then check your timing again etc. Also -- as the rpms change - you may need to tweak the idle adjustment screws on the carb.

Best idle adjustment will give you the most rpms and the most VACUUM as read on a gauge... I use a timing light that gives me rpms and I always adjust a carb idle with a vacuum gauge and the timing light (for rpms).

[v8s10kid]

thanks alot for the info

[GregWeld]

You're welcome.

I'm not trying to make it seem "insurmountable" either -- but I always feel that people that are "informed" can usually do a better job....

Forgot that you mentioned your timing tab. There is only one way to ABSOLUTELY KNOW if your timing marks line up correctly.

Get a piston stop.... they can be bought from summit etc or borrow one.

Pull ALL the plugs out.

Open the throttle to wide open.

Put the piston stop in number one plug hole.

crank the motor over MANUALLY with a wrench on the balancer bolt -- DO NOT ATTEMPT TO TURN IT OVER WITH THE STARTER MOTOR!

This exercise is taken EASY -- don't attempt to JAM the piston into the piston stop... your pistons are aluminum - the piston stop will bend etc... so be gentle - turn it over nicely until you feel it bump up against the stop.

When it stops = make a mark on your balancer with a grease pencil or chalk etc where the ZERO is on the pointer. Rotate the motor the OTHER direction. When it stops make a mark on the balancer wherever the ZERO is on the pointer.

EXACTLY HALF WAY BETWEEN THESE TWO MARKS IS TOP DEAD CENTER.

So if you rotate the engine to line up the zero on the balancer and the zero on the pointer -- and they line up exactly half way in between your two marks you're good to go.... if not.... Then either the balancer is wrong or the pointer has been bent or is the wrong one etc. At least now you know your timing is either spot on or it's a mess that needs fixing and you can't trust it.

[v8s10kid]

good to know. now i just need a timing light and a piston stop.

actually, summit gave me a $20 credit when i ordered my carb and stuff :D .

[v8s10kid]

its a bit cold out but i finally decided to suck it up and check a few more things before i go spending $ all crazy like. holleytv.com gave me a few starting points

fuel filter - good
air filter - looks good but will run it without it to double check
egr valve - dont have one
alt voltage - good (at battery:12.9 volts when off, 14.8 volts when at idle)

as i was checking the alternater to see if maybe the ignition system wasnt getting enough voltage i could hear a metallic sound coming from the passanger side valve cover. not a constante noise but you could hear it every now and then. oil level is a bit low, im hoping its just a rocker not getting enough oil or that has too much lash.

ill have to check the valvetrain when i get home later