FE Power Forums
FE Power Forums => FE Technical Forum => Topic started by: Hotrodjohn71 on October 26, 2026, 07:27:51 PM
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I'm going to be breaking in my 390 with new solid lifter flat tappet cam and I have a good 4 barrel carb on a 4barrel manifold on another engine that I can pull that's ready to go. No worries about it running well.
The motor I am breaking in is going to use my Ford low riser 2x4 manifold but the carbs aren't dialed in enough to be sure it will run well for that first 20 mins.
I can remove my 4 barrel manifold from my other motor and swap it on for break-in, but my question is: can I expect the motor to run well If I take my known good 4 barrel carb and bolt it on the 2x4 manifold, then blank plate the other carb pad?
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If all you'll be using it for is the 2500 RPM break-in, you'll probably be okay. The factory progressive linkage only uses the main carbs primaries for idling and lower RPMs with no load. You should be able to get the desired RPM with just that initial step on the linkage, under no load, which means one carb should work. I would NOT try upping the RPM beyond break-in with just one carb. It would likely end up being very lean on several cylinders, which means lots of heat in those cylinders. Under no circumstances should it be driven that way.
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Defiantly will be lean on at least 4 cylinders. If it where mine id either fix the carbs i was using with the 2x4 manifold and use them , or use a single 4v intake and the single carb, then change it after break in. You didnt ask but i will add makes sure all your lifters are spinning freely in there bores. If double springs , take out the inners. Make sure its lights off and your not cracking on it over and over.
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When my 462 Stroker with a low riser 2 x 4 intake and Quick Fuel carbs was put together it was running very rich on the idle and transition circuits. I did exactly what you are describing just to see how it affected the air fuel gauge. Contrary to what Doug is saying I did take it out and drive it, I’m thinking I drove it less than10 mile. It was about 10 years ago and if I remember correctly it drove fine. I did not drive it hard or do any wide open throttle applications. Hope this helps.
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As having had that 8V intake as mounted to engines on our dyno, this with observation of the EGT's mounted for each cylinder, I couldn't advise that your plan is a good idea. ;)
Scott.