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Old 07-21-2012, 09:39 PM
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400 sbc

hello, I have a sbc 400 that i had rebuild 2 years ago it sat in a project now that I'm building a 468bbc for. I took the motor out and put it in my 73 c-10. This motor had 0 miles on it. far as i took it was around the block Since it been in my truck. I started to drive it to iron out all the bugs one day it backfired through the carb. then started sputtering upon acceleration idling it does fine but runs rich. I cant seem to get idel dialed in without it shutting off. 1100 rpm its where its comfortable at in gear 400rpm something weird there. Looked over my build sheet from the engine shop i was given the wrong piston for one. I thought i had the flat tops for 10.1 compression instead i was given dished piston for 8.75:1 factory compression im running an elgin 1015p cam thats asking for 10.3:1 or less compression. could it be the problem causing ideling issues. It run like a champ driving it in traffic seem to want to die out with out keeping my foot on the gas. I'm looking in cranes 274 h06 cam how is it. I'll give you my parts list could you tell me what need to be fixed.

400 sbc
600 summitt carb
performer intake
stock factory heads for a 400 from a 1975 caprice
Elgin 1015p cam 224/234dur. @50 468/488 on 110 adv dur 290/300 10.3:1 compression 2,000-5500 rpm stock stall ok. Remember Im running 8.75:1 compression Flowtech headders 1 3/4 2 1/2 exhaust into flow 40 dumped. gear drive. forgot to mention 2500 stall conveter.

help me please solve my idling issue and sputtering while driving. Already purchased the crane cam and will replace all wires cap rotor and spark plugs any advice will help. thank much fellow hotrodders.

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Old 07-21-2012, 09:48 PM
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more info please? how long did the truck sit? did you check the carb,pull a valve cover,check for vacuum leaks,old fuel?what kind of ignition? hei/points?
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Old 07-21-2012, 10:24 PM
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400 sbc

@vinniekq2 the motor sat in my in another project for about 1 1/2 years. I started it up twice a week maybe drive it around the block just to move the fluids around. I did check the carb it leak up under the 1inch spacer replaced the gasket no leak problem solved on that one. but it still run rich. I check the spark plugs for gap it was alright just black from it running rich and those plugs are new. I'am running and hei unit. The cap and rotor appears to be in good shape. I tried installing a new fuel filter changed to 91 octane with a little additives still nothing. The motor sat in my truck for 4 months. before i actually started to drive it. all was well to well i thought. every time i would go around a corner i couldnt keep the rear tires from spinning even on lite throttle. this is even with a heavy 20 inch wheel. even nailing this @2000 rpm even worse i would lay rubber with no problem. All fun ended with the backfire through the carburetor. If it was my guess i would probably say it was a power valve along with jetting for carb issue. Now ideling in stop and go traffic the just going from park to drive without the car dying or the hard bump from park to drive i just dont know. everything from the motor to the transmission is fully rebuild. I would love to drive it, its just i spend more time tooling than enjoy this truck. I ready to replace the cam, to carb. and hopefully that will fix it right up. But if you have any suggestions on what to do then i will jump to it readilly. Thanks once again for the rapid reply and sorry for writing a book.
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Old 07-21-2012, 10:32 PM
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first thing I suspected was the power valve too.I dont know anything about the summit carb and was trying to get more info posted for obvious reasons.did you pull the valve covers,did the distributor move,( is it loose)
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Old 07-21-2012, 10:48 PM
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@vinniekq2, we did check valves everything is inline there. I checked timing everything is still spot on from rebuild to break in. We even moved timing around to see what we get for vacum less than 5hg. Something is really wrong there. Was at 15 inch of vacum before the carb. Backfired. I was told that I didn't have enough compression to support the cam also. It would idel comfortable at 1000 rpm brought it down to 9. Put it in gear it would barely stay on. Moved to 1100 then in gear it would idel at 900. In traffic a complete nightmare I would have tree the stop.light to keep it from dying off and the only way to solve would be to have the idel set way above normal I consume more gas than alittle bit.
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Old 07-21-2012, 11:42 PM
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400 sbc

@ fbird88 I have a stock hei distributor would a pro bullet or msd sreet fire hei work better. With the timing set up as you laid out. 2500 stall is that not enough for this cam. Now the elgin 1015p cam asked for 10.3:1 compression or less I'm at 8.5:1 will this be a issue. It ran really well. Just having trouble with the idel and running rich.
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Old 07-21-2012, 11:50 PM
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400 sbc

@fbird88
These are factory 400 heads from a 1975 caprice classic. When I acquired this motor I had limited knowledge. I was given all the wrong info on how to build this motor. In building my 468bbc right now so tearing the heads off at this time is not a option, but a future upgrade that I will be sure to take using your format. So I have to use what I have since I'm knee deep in this big block using the info you gave. This is a set back. This truck is my toy and da.ily driver
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Old 07-21-2012, 11:58 PM
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still need to repair the car or carb back to when it ran well.Can you borrow a working carb for testing?I have a few but Im a little ways away I bet
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Old 07-22-2012, 12:15 AM
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just looked up your cam.107 intake angle/117 exhaust, extra 10 degrees exhaust. That 400 can use all of that cam.If its not damaged and the carb is the problem I wouldnt rush out to buy a new one yet.dial in what you have before pulling the grille on your truck.You could advance it 2 degrees if bottom end is low out put.I cant see it though
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Old 07-22-2012, 12:20 AM
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400 sbc

@ vinnikq2 yes I am far away. I'm here in California, central valley. Yes I do have a carb for testing.
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Old 07-22-2012, 12:32 AM
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400 sbc

@fbird88 I will use the hei set and use your formula for the correct setup. The heads I will check and see what I have from the casting.number and foe.from there after I get the carb to function properly. Yeah I thought I could use a rpm air gap myself.
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Old 07-22-2012, 12:37 AM
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test your car with the borrowed and hopefully known carb.You can power time your car for testing,by plugging vacuum advance,set max timing around 34- 36 total timing.This usually happens by 3k rpm.make sure the weights are free in the distributor of course. I built a low compression 400 for a friend before,it ran 14.1s and got over 20 to the gallon. with 2.7 gears and stock stall,stock 400 heads,,,78 monte carlo
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Old 07-22-2012, 02:34 AM
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feuling gone arye

Quote:
Originally Posted by hotboy454 View Post
I started to drive it to iron out all the bugs one day it backfired through the carb. then started sputtering upon acceleration idling it does fine but runs rich. I cant seem to get idel dialed in without it shutting off. 1100 rpm its where its comfortable at in gear 400rpm something weird there. It run like a champ driving it in traffic seem to want to die out with out keeping my foot on the gas. 600 summitt carb
Is the 600 a holley? you may have blowen the power valves when she back fired, now shes loading up on you and thats not tunable, replace the power valves.
Keeping your foot on the gas to feed it more air is another indecation shes loading up.
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Old 07-22-2012, 10:57 AM
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400 sbc

@ cridder the 600 carb is a summit brand. I believe its a clone of holley 4150 or 4160 old style carbs. It's real easy to change the jets and power.valves.
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Old 07-22-2012, 11:25 AM
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400 sbc

Now is the power valves causing it to run rich and making the spark plugs black. Also you can smell the gas coming through. Is the a indication of it running rich and needing to be netted to or just power valves and adjusting the idel mixture screws. Also the description for the cam said Cai idile with lope can't hardly tell. Elgin1015p cam. Or crane 274 h06.
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