Hi-I just bought a rebuilt Holley 780 vac sec to replace a newer Holley 850 Ultra XP double pumper; beautiful carb, but too big for my application, shouldn’t have bought it, but it’s done. I found a very nice looking rebuild mentioned above, and put it on the car this afternoon. This past weekend, plugs were changed, timing set, all good. Car ran as good as I could get it with the 850. Anyhow, bolted on the 780, cranked it up with coil wire removed to get fuel in, float level check, and gave it a couple squirts. Car fired up instantly, ran for a couple seconds, then stalled. Expected it, cold start no choke. I then turned key to crank it and gave a little pump of the accelerator pedal, when I heard a small pop, and saw small fire, flame coming out of carb, which I snuffed out in couple seconds. I didn’t try again, as I was pressed for time. Before trying tomorrow, is there anything I should do first, or just give it another try. Don’t want to do damage to the carb. Any thoughts would be appreciated. Thanks!
Holley 3310 780 CFM rebuilt vac sec first try starting
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65-440
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Sure you got the timing right?
Backfire + Holley = blown power valve.
65-440
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Not necessarily, pretty sure most have that blow out protection. Still a possibility though I guess.
New ones yes, I bet he has a old 3310
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3310 780?
We got our own little chat going on here! Haha
Timing was set 12 initial 32 full advance. It’s an old rebuild, not sure if the guy did the mod for power valve protection when rebuilt. I asked him but waiting for reply. Just wondering if I should try again tomorrow. Not sure if it was a backfire-just a small pop sound but I guess same thing. If I blew the power valve, what happens if I try starting again?
So I guess I missed something? Im not a carb expert. Please Enlighten me. Here’s the exact description for the item.I didn't notice it in the title.
I understood some early 3310's were actually rated at 780 cfm. Later versions and those with a secondary metering plate were rated at 750 cfm. There was a way to visually confirm by looking at the inside of the carb, but I can't recall now what it was. Anyway, I do have a very old 3310 with secondary metering block and at the time confirmed it was one of the 780 versions.
The ad you posted suggests 2 metering blocks and changeable jets for the secondary side, so it could well be a 780.
The small pop and flames I'd attribute to a lean out condition because of the choke not being involved. In my experience a 50/50 chance the power valve was damaged. You should be able to still try and start the engine, but if the power valve is damaged it'll run richer than normal. I've run them with a blown valve for weeks until I could get to going through the carb. Idle would stink pretty good and sometimes the rich condition made it necessary to crank more than normal for restarting, but didn't do any real harm to anything.
The ad you posted suggests 2 metering blocks and changeable jets for the secondary side, so it could well be a 780.
The small pop and flames I'd attribute to a lean out condition because of the choke not being involved. In my experience a 50/50 chance the power valve was damaged. You should be able to still try and start the engine, but if the power valve is damaged it'll run richer than normal. I've run them with a blown valve for weeks until I could get to going through the carb. Idle would stink pretty good and sometimes the rich condition made it necessary to crank more than normal for restarting, but didn't do any real harm to anything.
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I don't think you stated what your engine setup was. I've run 750's on lots of small block Chevy's over the years. You can over carb an engine to a point. They tend to like to run real good when you've got your foot in it, but can be difficult to get through things like idle, off idle transition, sometimes bogging, chugging, etc. There are lots of tech articles on line that can help you determine the right carb size for your needs.
I'd recommend you read up on Holley power valves. With a vacuum gauge (and assuming you can get your engine to idle ok) you can quickly determine what power valve you should be running, based on the vacuum readings you get. It's not as difficult as it sounds.
Personally, I've always had good luck with the 3310's. I like the vacuum secondary, jet changes are intuitive especially when compared to the jet/step up rod routine on Carter/Edelbrock. Getting the right power valves in place really makes them run well.
I'd recommend you read up on Holley power valves. With a vacuum gauge (and assuming you can get your engine to idle ok) you can quickly determine what power valve you should be running, based on the vacuum readings you get. It's not as difficult as it sounds.
Personally, I've always had good luck with the 3310's. I like the vacuum secondary, jet changes are intuitive especially when compared to the jet/step up rod routine on Carter/Edelbrock. Getting the right power valves in place really makes them run well.
kramer
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I believe the only 3310's that were 780 cfm were the first 3310-1 carbs (which I regret selling the one I had). 3310-2's and later as said before had different boosters and had a rear jet plate and no rear metering block.
The carb looks to be very nicely finished. The vacuum canister has been changed to a later model unit. I wouldn't be afraid of it. The secondary metering block gives you more flexibility in fine tuning things.
I'd try starting the engine again and see what happens. There's lots of smarter people than me on this forum that can chime in.
I'd try starting the engine again and see what happens. There's lots of smarter people than me on this forum that can chime in.
I can only go by what the seller advertised and described. I should have never gotten rid of my Holley 780 that I bought new for the car in 1977, and was on it until minor engine refresh in 2017, at which time I bought the XP Ultra 850 which I regret. If I can get this mystery 3310 to run decent for now, the XP will be up for sale. Thanks for weighing in
Thanks. Your comments have been helpful and I really appreciate your thoughts and ideas. I’ll definitely try your suggestions. Thanks
383HP original to the car; pulled in 1979 for rebuilding to get car to high 11’s. Bored .030 os, cam and converter matched for 4.56 rear- cam dynamics cam, Fairbanks 3800 stall converter, edelbrock TM6 intake, with the Holley 780VS carb bought new for the rebuild. Car ran great in that configuration. Wish I never got rid of the 780. The 850 XP isn’t working for me, but no racing. Street only, limited to maybe 200 miles a year if that. Thanks for your input
If your carb doesn't have of these buy one. Youtube video for install. not mine.
https://www.summitracing.com/search...lve-savers?SortBy=Default&SortOrder=Ascending
https://www.summitracing.com/search...lve-savers?SortBy=Default&SortOrder=Ascending
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