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302c fueling issue??

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So im running a holley 600 vac secondary on a slightly worked 302. Noticed a big difference in pick up from the 465 holley it was running. But have noticed that once the secondarys open up, it boggs down, pops and farts and just turns to crap really. Only once has it ever picked up its skirt and got off it ass when they have opened. Gave it a go shortly after, and it turned to crap again. Was thinking along the lines of a inadequate fuel supply from the standard spec fuel pump? Anyone got any advice? 

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i'd be checking the secondary actually is opening... (on My gemini with original carby the diaphram was leaking and not opening.. = starving for fuel and backfiring etc)
@gerg would be the holley guru at the moment, 

 

could also be ign breaking down. it's like deja vu.. i'm sure this was just covered recently or very similar at least

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So im running a holley 600 vac secondary on a slightly worked 302. Noticed a big difference in pick up from the 465 holley it was running. But have noticed that once the secondarys open up, it boggs down, pops and farts and just turns to crap really. Only once has it ever picked up its skirt and got off it ass when they have opened. Gave it a go shortly after, and it turned to crap again. Was thinking along the lines of a inadequate fuel supply from the standard spec fuel pump? Anyone got any advice? 


Firstly, check that the secondary bowl is sitting at the right float level. If you have externally adjustable floats, do the usual sight plug procedure, if no sight plugs, adjust the level up until you see fuel dribbling out of the boosters and wind it back down a full turn. This is a good ballpark method to start from, then you fine-tune from there. You may have to drop it more if you get flooding under brakes.

Next, check what secondary spring you are running. The standard one is purple from memory. On a warm 302, it shouldn't be opening before around 3800 rpm, and if it does, the spring is too weak, which causes bogging due to insufficient airspeed through the venturi. Install the next stiffer one and run it again.

If running a secondary plate (not a block with jets and power valve) there's not much you can adjust for jetting except drill out the metering orifices in the bottom. You really shouldn't have to do this if everything else is working right on the carby.

Make sure your secondary float has free movement up and down and that the needle moves with it and the seat housing isn't blocked. You'll need to pull the secondary bowl off to check this.

I very recently did up a mate's 600 vac and when I pulled it down, found a whole bunch of things wrong. Secondary throttles were closed too much, secondary linkage not pushing them open slightly at WOT, but most importantly, this carby had sat with bad fuel for a long time and the secondary booster feeds were blocked. Had to scrape them out with a drill bit. Also, a secondary air bleed was blocked, which would cause flooding once that circuit came on. Another thing, one side of the squirter was blocked.

This carby looked quite shiny and new from the outside, but things were pretty ugly inside.

I'd start from there rather than automatically blame the fuel pump, which rarely give trouble.

Sent from my CPH1903 using Tapatalk

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Cheers guys, float levels are fine and its had a holley rebuild kit throwen at it. There is a possible chance of a definite maybe that the secondary diaphram hasnt been touched though. Will have a look at it at some stage. I thought it may of been the stock fuel pump wasnt enough to feed it, or possibly the fuel lines too small. Will check the diaphram first though. 

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Strong possibility it could be an ignition issue too. Its only got a crappy old 40amp alternator, which was ony thrown on to get it running after i rebuilt the engine 10+ years ago. Have got a 100amp unit to replace it but just havent got round to swapping it over haha.

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There's a saying in old hot rod circles: "carb issues are often ignition issues"

A hole in the secondary diaphragm will simply stop them from opening. Shouldn't cause popping and farting.

Sent from my CPH1903 using Tapatalk

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Its not running anything out of the ordinary. I do know that the headlights are dim and when the headlights are on, the alt light on the dash flashes on and off when i turn the indicators on. It was probably a 40 amp alt when it was new, think 39 of them escaped over the last 40 odd years. Noticed tonight when i had a look at it and found that one of the wires out of the back of the alt is pretty lunched so will be replacing that. 

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Im running a 750 holley on a warm 351 using a RP mechanical fuel pump and dont have any issues. I also run an ICE ignition sytem.

 

Only issue when  i put my foot down is the fuel needle follows suit and drops very quickly.

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Check the ignition system. Leads, cap, ignition module or points.... Sounds like the timing is going out at revs. 600cfm should be sweet on a 302. 

 

Check plug gaps, don't run leads 5 & 6 parallel to each other, cheap leads can crossfire. Tried running her on 98 PULP.?

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