New turn key crate motor backfires through carb

[Gigem]

Brand new GMPP 350 HO crate motor. "Turn key", came with Holley 650.

Doesn't happen all the time, but every once in a while it backfires through the carb on acceleration. Sounds like a sneeze. Seems to happen more when I am driving the car easy. Otherwise seems to run great.

Timing was way off out of the crate, but is right now.

Any guesses? Or ditch the Holley and get an Edelbrock carb, as a buddy suggested...
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[wraprail]

For what it must have cost ($$$$$$$$$$$$$!!!!) I would expect it run perfectly!
Get on the phone with whoever sold it to you.
Demand they make it right...Or else!

[BurnoutNova]

Originally Posted by wraprail

For what it must have cost ($$$$$$$$$$$$$!!!!) I would expect it run perfectly!
Get on the phone with whoever sold it to you.
Demand they make it right...Or else!

You have to be able to tune the carb and make sure the timing is right. I know there are alot of carbs out there that say they should be good to go out of the box, but if you expect it to run perfect you need to tune it to some degree..

There are to many variables to make a carbureted engine run perfect in every situation. Altitude, humidity, vehicle weight, etc all come in to play.

[79Betty]

I agree. If i'm going to spend that kind of money IT WILL BE RIGHT OUTTA THE BOX.
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[jon75]

I doubt there is anything wrong with the engine at all. It's funny you say you have a Holley carb on there. My buddy has a '67 Nova with the same exact setup and his hickups when trying to accelerate heavily. I can almost guarantee you that if your timing is set correctly, that your jetting or mixture is off. Sure, you might get good acceleration or power with a rich mixture, but when the engine can't burn all the fuel that Holley is trying to stuff in there, it will come back and burn right up through the intake manifold.

Solution? Take it to someone who knows how to adjust the carburetor for you or learn how to do it yourself. I went with Edelbrock simply for the ease of adjustment and have always had great luck with their products. Good luck.

[V10farmboysdream]

My 383 did the same thing with my eldo 600. Another notch down on my excelerator linkage and the cough was gone. Can't comment on a holly. To touchy for this shade tree phd
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[Vader85]

I had the same problem on my Camaro. Turned out to be the accelerator pump adjustment. I looked down the carb and slowly opened the throttle, I noticed that the throttle would open a good bit before fuel would start to come out of the squirter. I adjusted it until I would see fuel come out of the squirter as soon as the throttle started to open and had good steady stream.

[tony58]

Lean condition causing the backfire. Can be either mixture or accel pump, probably accel pump. Wouldn't hurt to triple check that it has enough timing also.

[Blackpony]

Sounds like the carb needs to be dialed in. Even though its a turn key crate motor, it will always need to be fine tuned.
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[88Jimmy4x4]

take the truck to www.bumberas.com in katy and tell them your problems and that you need a tune. They work on classics everyday and are very familiar with carbs.

[Gigem]

Problem solved. Power valve. Ended up replacing Holley with Edelbrock 650 anyways. Runs awesome now!