770 Holley TA too big? Can I modify it to work? (1 Viewer)

[oldracerguy]

I have a 383 sbc in my FJ40. The folks that built the motor also installed a 770 Holley Truck Avenger. I like the tuneability of the carb, however I can't get it to rev or stop the bog when the secondaries open up past around 4,500 rpm. I have a 600 Holley that revs right to 6,000 rpm, but it is not made for off road. Can I lean out the jetting on the secondary circuit on the 770 to make it work? Or should I just sell it and get the 670? Thanks!

 

[Downey]

I'm not convinced any of Holleys "off road" carb choices are properly set up for off road use, considering what we have to do to in fact set them up for off road use. I also can't see how anybody (daily driver/off roader) would be tickled pink with 770 cfm??? Possibly the best choice of all time (in a non-baffled choice) is a vacuum secondaries Quadrajet.

 

[oldracerguy]

The Truck Avenger actually works awesome for me in off camber and uphill situation. I also run in the dunes with it, works great. Very responsiive. This is not a daily driver. However I just got off the phone with Holley Tech, since I still have the receipt they are sending me a 670. They said the 770 Truck Avenger just flows way too much for anything less than a built big block! The Holley Tech line came through for me, great service! Not sure if there is a tech line for quadrajets?? This was however my third call and the first guy I talked to was not helpful, the second guy actually tried to solve my issue and sent me a different metering block which improved the issue greatly but did not solve it. The guy I talked to today got right to the point and flat out said that carb will not work on a small block. Boy was I glad to hear I have a solution as I have been playing with this setup for weeks. I have also been told to run a quadrajet by everyone else. Going to give this Holley a chance, I like the design, features, and the tech line support. I'll keep you posted on my results with the new 670 when I get it.

 

[oldracerguy]

I would also be curious to what it is that is done to a Holley to prep them for off road. I assume the Truck Avenger does give you a better platform to start with? Thanks for the help. I was very clos eto buying a quadrajet, but the manifold would need to be swapped, money already invested in Holley, new carb price for a good one, etc.

 

[sixty]

you shouldn't be getting a big bog on the opening of the secondaries. It is probably going way lean or rich. A wideband O2 would help imensly in tuning the carb.

A 770cfm on a stroker should not be too oversized, I have a 750 cfm TBI and its not oversized.

not sure on the answers to your other questions... I HATE carbs!

 

[oldracerguy]

I have changed the secondary springs numerous times, changed jetting, adjusted fuel pressure, changed float heights, installed new ignition that was run on a distributor machine to set up the timing curve, etc. If Holley is telling me it is too big, and the motor is telly me it won't work, I have to go with it. The simple number of a 750 CFM does not tell you the hole story. There are vacuum secondary carbs that are 750cfm that will run fine on this, just not the 770 TA. I'll trust Holley on this one..................

 

[Downey]

I would also be curious to what it is that is done to a Holley to prep them for off road.

Go to Downeys website
Click onto Engine Components
Click onto Carburetion
Scroll down to Sealed Baffle Kit
Click onto Tech Talk
www.downeyoff-road.com

 

[oldracerguy]

Great information on off road Holley tricks!

Thanks for the detail on some of the tricks that can be done to a holley for off road. I did receive a new 670 truck avenger carb from Holley and have it back on. It runs good, pulls hard, and now revs as high as I dare with the 383. I cannot however get it to idle as low as I could with the little 600. Also my truck runs really nice with the 600 on it. It's good with the 670, however the idle and the throotle just seem to be very smooth with the 600.

Your mods may be something I could do to the 600 Holley that I have and make it off road worthy. My little test comparison for both the 600 Holley and the 670 TA is to let the FJ idle up the face of one of my kids tabletop jumps in the backyard.

The results for the 600 are a very nice smooth running idle at maybe 500rpm with no stalling. It just sits there and idles up and just chugs away with no input from me.

The out of the box 670 TA would stall if I could get the idle down below 1,000rpm. Just doesn't seem to want to run as clean down low. I did set the idle mixture also with a vacuum gauge before I did my little test, this seemed to help a bit.

HHMMM, maybe I can convert this little 600cfm with vacuum secondaries to work off road.....with your baffle and spring loaded needles??

Thanks!!!

 

[mminter1973]

I have 2 built 454 motors (500hp) and the 770 TA from the factory was dumping way too much fuel for the motor to use. Shocked the hell out of me, but some jet changing and float adjustments got them where they need to be. The 770 TA has got 76 jets in the primary and 99 jets in the secondary, this is more jetting than what folks run in their dirt track cars around here. I went to 72s and 94s and all is good.

 

[oldracerguy]

I have 2 built 454 motors (500hp) and the 770 TA from the factory was dumping way too much fuel for the motor to use. Shocked the hell out of me, but some jet changing and float adjustments got them where they need to be. The 770 TA has got 76 jets in the primary and 99 jets in the secondary, this is more jetting than what folks run in their dirt track cars around here. I went to 72s and 94s and all is good.

The jetting on the secondary for the 770 TA with the 99's in there must be to compensate for the lack of a powervalve in the secondary metering block. Supposedly the powervalve is equivalent to around 10 jet sizes. With the 670 now on the 383 I might still drop the jets to try and clean it up a bit, but it does run strong.

My hats off to Holley for taking the time to fix the problem and provide a solution! Wow, that seems to be harder to come by in todays business.