new carb hesitating a bit - Lateral-g Forums

chr2002ca · #1 11-22-2010, 09:27 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 · #2 11-22-2010, 10:09 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 · #3 11-22-2010, 04:48 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.

v8s10kid · #4 11-23-2010, 10:20 AM

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

v8s10kid · #5 11-29-2010, 07:12 AM

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 · #6 12-02-2010, 11:17 AM

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** · #7 12-02-2010, 12:25 PM

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 · #8 12-02-2010, 01:08 PM

thanks alot for the info

v8s10kid · #9 12-08-2010, 11:20 AM

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