I know the carb on my truck needs rebuilt, however just the other day a new problem came up and i dont know if the problem is the carb or the engine.

The engine on my truck is a '71 302 and the carb is a holley 4bbl.

When i hit 45 the truck completely loses all power and almost sounds like its back firing then the truck will completely die if you come to a complete stop but if i just slow down and dont let it get back to an idle it will keep running. Does anyone have any idea what is causing this?

 

Its a holley. if it isnt tuned almost perfect your gonna have issues with either running rich or idle issues. on the other hand you might want to check your fuel filter to see if its plugged at all. i had a similar issue with my 352 and it turned out that my fuel filter was plugged and at high speed i wasnt getting enough fuel in the carb and it would start to spit and cough like the ignition was cutting out. but your best bet would be to check the smallest things first like the fuel filter and if that doesnt fix it buy a used 600 cfm edlebrock put it on tune it once and never have another issue with it.

 

Not an authority, have a 65 F100 with 302 and manual trans. Not sure if auto trans would have additional bells and whistles effecting trottle operation. Before tearing into the carb suggest start with a quick tune up to ensure problem is not related to timing or points, etc. I purchased a cheap inline spark plug tester; don't need to remove plug, and a remote start button; connects to start relay, and batt., thus able to perform quick check from under the hood, takes about 3-4 minutes. Usually get u in the ball park and can fine tune later.

Recently completed a first timer 'do it myself' rebuild of couple Holley 4V 1850's, (4160), with the vacuum secondary. With my limited experience, found the Holley 1850 basic, and not too complicated to rebuild. However, suggest before rebuilding start engine and have someone operate throttle while inspecting under the hood to determine if anything obvious with linkage, vac. leak, etc. Primarily see if the auto, or manual choke is operating properly. There's also a secondary diaphram, check and make sure the linkage, or diaphram is operating correctly. Check the float level by removing the screws on the sides of the bowls, fuel should be level with the bottom of the screw hole with truck on level ground. Next check the mixture adjustment by screwing them all the way in; lightly don't want to damage the seats, then back them out about 1 1/2 turns, this should be in ball park and fine tune later. I use a vac gauge to see if there's any vac. leaks, and to adjust fuel mixture. Also, check the vac advance, on the 1850 Holley 4V the vac. for distributor advance is taken off the secondary vacuum. Anyhow, rambled on enough, had an urge to chime in.

 

check the power valv on the carb if it has one. it very likely has ben damaged if the carb is backfiring out of the carb or is it backfiring out of the exhaust? need a little more info