new carb hesitating a bit - Lateral-g Forums

v8s10kid · #1 11-20-2010, 07:45 PM

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 · #2 11-21-2010, 08:39 AM

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 · #3 11-21-2010, 09:27 AM

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 · #4 11-21-2010, 09:42 AM

Is this during normal driving or full throttle?

**GregWeld** · #5 11-21-2010, 02:58 PM

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 · #6 11-21-2010, 07:20 PM

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 · #7 11-22-2010, 07:28 AM

Quote:

Originally Posted by GregWeld

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 · #8 11-22-2010, 08:27 AM

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 · #9 11-22-2010, 09:09 AM

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 · #10 11-22-2010, 03:48 PM

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.