Well I was reading this article http://www.hotrod.com/how-to/engine/mopp-1303-c-body-383-bolt-on-and-go/ I am running a 650cfm on it currently, I used the same cam and have the rpm intake and have headers on it. They said they used a Edelbrock 750 cfm Performer Series being it will need the extra airflow. The car has good power while going but when I stomp on it it feels like it is lacking. No vacuum leaks either. Oil pressure is great 60 at idle. They did it to a newport with a 383 just like mine.
68 Newport Carb Question
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66Newyorker
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If you do the math with a cfm calculator your 650 carb is big enough through 5500 rpm with a mildly built engine. A couple of things you might want to try before going to a bigger carb. Are you getting a total of about 36 deg of timing at about 2500 rpm. Are you using an electronic dist? Is your coil putting out enough voltage? After you know that your issue is not something with the ignition. You can re-jet your carb. In the mid 60's from the factory even the 440 only can with a 625 cfm carb. If you do the work you will have better throttle response with the 650 carb.
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If you haven't already, make sure your fuel pump pushrod hasn't been warn down. Have you been using additives in your fuel? If you're not you should be.
Well I have a Pertronix kit in my distributor along with the flamethrower 2 coil. I currently have stabilizer in the gas because it is in my garage for the winter I still start it up every 3 or 4 days. As far as additives I usually use dry gas. I did also notice one thing the other day, I had my foot on the brake and pressed on the gas a little and felt the brake pedal go down a little bit, I thought maybe not enough air is getting to the booster from the carb being too small, no brake line leaks and brand new master and booster. I am probably wrong but I just am thinking of other things, the timing is good at 2500.
70bigblockdodge
Old Man with a Hat
The carb is lagging or slow due to the performers counterweighted secondary upper butterflies. They are set up that way to keep the customer service dept. from getting overrun with complaints about bogging carbs. Most people will not complain if it performs OK just slowly. The fix is to lighten the counterweights so it chases the rpm, the catch is the top of the carb has to come off remove the weight over and over and don't remove too much or you will have a bog. This is why I promote the thunderseries , it has a spring loaded air vavle that can be adjusted right on the side of the road and if you go too far just tighten it back up, easy. The simple fix is live with it and be glad you don't have a bog, or sell it and buy a thunder series.
70bigblockdodge
Old Man with a Hat
That's because I have this similar problem on my brother in laws Challenger, he has a 750 performer series on a 440 with a M.P. 509 cam it really needs to "come on sooner" but I hate to mess with the weights because the engine is all extra or currently unused pieces thrown together. I have messed with it a bit and still have more to do and I know the combo will change again.
It still bogs with the 650 Thunder?
It feels like its lacking something. I only brought up the article because of the 750 carb they used. But I like the secondary air valve on the thunder series. The article said because of the performer intake it would need a higher than 650 cfm which was stock on the hi performance 383s that came with stock afb carbs. I am not doubting anyone's experience on here, I feel the power difference in the car but it is just slow to get there.
A 650 is more than enough for a 383. With 2 different carbs having the same bog problem I would suspect a vacuum leak somewhere. Maybe the intake manifold gasket or a vacuum hose or even the power brake booster if the car has one.
I haven't tried another carb, I think I need to mess with the secondary air valve more, it might need to be looser. I loosened already and noticed a slight difference. I used the comp cam kit http://www.amazon.com/COMP-Cams-K21-223-4-Camshaft-Kit/dp/B000R9VLHU, could the springs be to heavy, they are single with damper, also the 906 heads where changed with 346 heads with the hardened seats. I am exploring all different types of things now.
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Do you ever have any starting issues, hot or otherwise?
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I was having all kinds of fuel delivery issues that were worse than yours and it turned out to be a fuel pump pushrod being worn down. It was caused by years of modern oil that's not sufficient for these old engines. You may not be having the same issue but should take it out of the equation.
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