Big block cutting out when you stomp it

[Myfirstbigblock]

I just bought this truck from a guy he said it only had 1000 miles on the rebuilt 454 bored 30 over and mild cam I asked for more but he didn't have his cam card any more so that's it. It was backfiring through the carb bad so I plugged some vacuum leaks replaced the 750 holly with a edlebrock 650 thunder ASV off-road no change. Then I swapped the distributed with an accel destibuter, cap, rotor, coil, wires, and E3.40 spark plugs . It stoped backfiring through the carb but now it cuts out under fast acceleration

 

[Myfirstbigblock]

Oh and I set the timing at 16* BTDC didn't check the total timing any suggestions

 

[Jims86]

I dont think 650 is enough for a big block...750 at least.
Set BASE timing back to 4BTDC, until you get this figured out.
I would venture to say that you naaed more accellerator pump, since you say it is cutting at hard accel.

 

[towjoe]

Float levels may be to low in carb, or the accelerator pump may be cracked. Might have a bad fuel filter to.

 

[Myfirstbigblock]

It's a brand new carb and as long as he didn't put too big of a cam in it it should be enough and if it was too small it would be just not building enough power and running lean at high RPM's this is cutting out at low RPM's when floored and it won't run at 4*BTDC

 

[towjoe]

A friend of mine had 3 bad eldbrocks from the auto zoo in a row. Just because there new doesn't mean there right. Your vacum advance working and the advance weights loose in distributer?

 

[Myfirstbigblock]

The vacuum advance is working and the weights are free the destributer is new as well every thing seems right I played with the carb today and got it running better its drivable now but it is still cutting out when you stomp it from an idle oh and I also replaced the fuel pump today

 

[Jims86]

The vacuum advance is working and the weights are free the destributer is new as well every thing seems right I played with the carb today and got it running better its drivable now but it is still cutting out when you stomp it from an idle oh and I also replaced the fuel pump today

Did you adjust the accellerator pump?

 

[Driver4r]

I always thought 850 was average for a 454 base model.

 

[Jims86]

I always thought 850 was average for a 454 base model.

Nahh....750.
There is no 850...The 800 Q-Jet was only on Hi performance Buicks and Pontiacs.

 

[Driver4r]

im talking Holley 850 Double pumpers......

didnt relize you were talking about q-jets, or q-jets looka-likes

If you put on a doublepumper, Mech. Secondaries holley on there, it will be flying down the highway with little pressure on the peddle (but will suck gas like a ****) Also wont worry about vacume like a q-jet.

 

[woodsrider250]

I dont think 650 is enough for a big block...750 at least.

Agreed, but still shouldn't cause issues described....You have a lean condition somewhere, I'd think. I've run a bunch of BOP qjets on 455s et al and even if they don't get vac secondaries at all they won't just plain hickup like this...The 450ish primary WILL run the motor. Please continue to run the Qjet we'll help you figure it out. 850 Holley DP...LMFAO, that's for a 800hp BB...an d a Qjet will still feed that

 

[HotRodPC]

I'm with woods on this one. The carb being a bit to small isn't going to cause this problem. Only thing that might do is keep a few hp hidden from use but it should run fine. And again, there isn't much that needs a 850 Cfm Carb. I'd say you're getting into high 10's low 11's vehicles to need that much carb.
I never like to be the bad guy and make off the wall suggestions, but you're saying 1000 miles on this motor? Do you see signs of it being rebuilt? Like is it clean, what do gasket edges look like? How about the freeze plugs? There's ways to tell. And was this rebuild a true Reman with a new bore and new pistons or just a rering and valve lapping job? Always need to find this out. I've heard some people say, it's rebuilt with a paint job and that's exactly what they mean. They painted it and called it rebuilt. Where I'm going with this is either a bad valve is somewhat possible, but I'm really thinking you need to take a look at the valve timing. Did he try to advance or retard the cam to move the power band range? Something isn't right here if it won't run at 4BTDC but it will at 16BTDC. At 16BTDC, you should be at about 2200-2600rpm by then. You're idling at 50% of full advance. Not right !!! What rpm is it idling at or does it idle?

 

[crazy4offroad]

Hook the vac advance to full vacuum, and put the accelerator pump rod in the hole closest to the pivot point. You may have to cut 2-4 degrees of advance out of it running full vac.

 

[Jims86]

My post albout 650 being too small was not meant to say that the cfm was the issue, it was just the first thing that popped in my mind...BBC and 650...lil red flag. Probably run fine up to 3500 rpm.
I think he needs more on his accel pump.