Holley carb issues

[pkonopasky]

The UMP one is bigger, could be bigger still.....

Yeah that one looks close to the same size as my ump one... Maybe I can just cut it and on another inlet and make it a dual myself?

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[12LaPaz]

I have never had good luck with vacuum secondary carbs on a race car or pre runner. We currently have a 383 with a Braswell 850 with mechanical secondary, ( we have also ran the same carb on our 410 & 415 small blocks) some times a out of the box carb just doesnt do it, get with a carb specialist like braswell, its money well spent. Send your carb back and get a holley hp series carb, it would be a much better starting point & the standard needle and seat will work fine dont waste your time or money on the spring loaded needle & seat. Run a - 8 line to the carb and plumb your pressure gauge off the fuel log that you will need to buy for the double pump HP series carb (summit has them)

[Zambo]

Unless its super convenient for you guys to test, I'd beg borrow or steal a big air cleaner before heading out just so you have it. I'm still betting that hat is the problem. A big air cleaner will tell you if its the problem, regardless of whether you use it permanently. If airflow does in fact wind up being the problem, THEN you can go thru the effort and spend the money to modify the hat or get a new one.

[clogking]

I am using the MSD offroad ignition system, brand new wires and plugs, and we have the timing around 20 advanced

I would start looking at the Timming. Is that 20 total? 20 initial? Do you use any vacume advance? Does the mechanical advance work and how much advance is there?Those carbs should work pretty good out of the box new. you need to look at the whole picture timing,fuel and Air supply. I am not sure how much total timing you should have but 20 total is not enough.

[scottm]

Yeah good point. With a big cam, I suggest 10 to 12° initial timing, with 22 to 24° of mechanical advance, for 34 to 36 total. WIth iron heads and/or pump gas, limit total advance to 33-34 max. On a street legal truck, run an additional 10° of vacuum advance, connected to the 'timed' vacuum port on the carb. Race carbs like the holley HP series do not have a vac advance port.

[dezerts10]

man this stuff has me totally scared to dump money into a truck avenger for my motor.

[pkonopasky]

I have never had good luck with vacuum secondary carbs on a race car or pre runner. We currently have a 383 with a Braswell 850 with mechanical secondary, ( we have also ran the same carb on our 410 & 415 small blocks) some times a out of the box carb just doesnt do it, get with a carb specialist like braswell, its money well spent. Send your carb back and get a holley hp series carb, it would be a much better starting point & the standard needle and seat will work fine dont waste your time or money on the spring loaded needle & seat. Run a - 8 line to the carb and plumb your pressure gauge off the fuel log that you will need to buy for the double pump HP series carb (summit has them)

Sounds good! Thank you!

[pkonopasky]

Unless its super convenient for you guys to test, I'd beg borrow or steal a big air cleaner before heading out just so you have it. I'm still betting that hat is the problem. A big air cleaner will tell you if its the problem, regardless of whether you use it permanently. If airflow does in fact wind up being the problem, THEN you can go thru the effort and spend the money to modify the hat or get a new one.

Will do.. Usually we head out to ocotillo, which is about an hour and a half away, but we are going to try and handle this carb issue at a buddies property about 20 minutes away so it's pretty convenient! But I'll try and bring another air cleaner setup!

[pkonopasky]

I would start looking at the Timming. Is that 20 total? 20 initial? Do you use any vacume advance? Does the mechanical advance work and how much advance is there?Those carbs should work pretty good out of the box new. you need to look at the whole picture timing,fuel and Air supply. I am not sure how much total timing you should have but 20 total is not enough.

It's at about 20 at idle, with no
Vacuum advance.... Does increase with Rpm though... I don't recall exactly what it gets to though, I can check this weekend when I go work on the truck

[pkonopasky]

Yeah good point. With a big cam, I suggest 10 to 12° initial timing, with 22 to 24° of mechanical advance, for 34 to 36 total. WIth iron heads and/or pump gas, limit total advance to 33-34 max. On a street legal truck, run an additional 10° of vacuum advance, connected to the 'timed' vacuum port on the carb. Race carbs like the holley HP series do not have a vac advance port.

It is a pretty decent sized cam.... Comp cams 12-450-8, Duration 286/286, Lift .560/.560, it has aluminum AFR Heads, and with about 10.5:1 compression, running 91 octane (not street legal)... I'll maybe back down a little on the advance and give that a shot