Let's try another one!!

[jtl_77]

I posted a while back about getting a 770 truck avenger carb. It had a off idle bog and I posted about it and got alot of good responses. Well the tech dept. at Holley said I needed a 670 on my mostly stock 454 (mild cam, edelbrock intake and dynomax headers). I got a 670 in and bolted it up. It ran good and seemed ok until about 3 days after I put it on and finally got a chance to really hammer on the truck. 2500 to 3500 it spit and sputterd and did not pull good. After 3500 rpm it pulled like a rocket. So I call Holley back and tech. says maybe something wrong with carb,we will send you another. Got it a week later and the same thing!!!
So I just got off the phone with tech again and now the think maybe I need a 770 cfm on the 454???
So now I will try some of the original sugg. I got from my first post and see what happens.

Rant off.

 

[southernspeed]

If it's pulling good after 3500 rpm you don't need a bigger carb! A carb too small would give you good low down response and torque but would fizzle out at higher rpm. Sounds like it just needs the needles/jets sorting out.

 

[GM Man]

I'm having almost the same problem, but mine bogs right off the line. Since Holley sent me a brand new carb thats "Ready to run out of the box" I jetted it and tried to run it. Checked the float levels and the front bowl had almost no gas in it at all, while the rear bowl was completely full. So much for ready to run. After I adjusted the float levels, it helped. Your rear bowl might be completly empty like my front was and could be why it runs bad in the upper RPMs..

 

[supersize75]

I have had the 670 off road truck advenger for just over a year now, I have had it on a couple small blocks and big blocks as well,

the factory jet that the 670 comes with is a .065, I bumped mine a couple sizes and it made a world of difference, I had the same problems that you stated.

also I loved the 670 on my .30 over 454, nice low end throttle responce

-shawn

 

[jtl_77]

So which carb should I keep? I currently have 2 670cfm, and one 770 on the way .
I always check the float height and idle screws before I even drive it. Then drive it and double check those settings.
I mostly trail ride with lots of loose hills , but I also mud bog sometimes to. So I need it to rev clean but I like to idle around as much as possible.
Which ever carb I keep I'am going to keep for good because I'm tired of waiting 5 days for them to ship it 100 miles.

 

[rcurrier44]

Don't stick that 770 on, you know the 670 is pulling good above 3500rpm so why in the world would you think you need the 770 (witch wasn't working before). Do you have an O2 sensor and guage hooked up to it so you can actualy see what it is doing? It sounds prety obvious that the secondarys are eather kicking on to early or to late. You need to figure out witch one and figure out if it goes lean or ritch on you at that point you are having problems.

It is very rare that any carb will work on every engine streight out of the box (however the floats should have been closer than what GM MAN had). If that was true then there would be no need for carb adjustments...there are just to many variables between engins that affect how a carb works.

Here is a good article about holley tuning. There is also alot of good info on the holley website.

http://www.fordmuscle.com/archives/1999/12/holley/index2.shtml

 

[jtl_77]

I tried the silver spring (opens secondarys sooner) and it runs worse. So I am assuming that the secondarys are opening to fast with the black spring installed. The tech dept. at holley is stumped (or does'nt want to try to much) because they say they have no clue,thats why they keep sending me carbs to try.
When I had the 770 on it pulled great all the thru it just had the off idle bog.
I'm looking for any and all help!! I will be getting the 770 by Friday or Monday but it will be my choice as to which one I keep.

So should it be the 770 with the off idle bog but run good the rest of the way thru or

the 670 which runs good except 2500-3500 and try to fix that???

thanks for any help.