I Need Help 400 not working
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New User
Joined: Mar 2011
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From: Hopkinsville
I Need Help 400 not working
I rebuild my 400 sb and now it has an off idle bog and high end sputter along with, what feels to be huge loss in power. I have done everything that I can think and I just cant figure it out anything helps.
Engine is bored out 30, heads port/polish, edelbrock performer 400, holley 770 truck avenger, 7 PSI 98 GPM electric fuel pump, Crane Cams RV cam and lifters, blueprinted and balanced crank, flat top pistons, MSD ignition (except distributor, have the cap and button) high volume oil pump, high volume water pump, exhaust headers and more
Checked the Accelerator cam and tried 4 other ones
checked conconnection to the Accelerator pump= no play and right tolerance.
Cam degree is good.
engine gets fuel
vacuum is like 10
Ive tried different timing degrees from 8-20 advance, no change just harder to start
have not checked my compression yet but it should be good everything is new.
everything on the engine has been grounded.
Air fuel screws are 1-1/4 out equal both sides. For the highest vacuum.
Summit racing said it might be like 25 things starting with transition valve or something.
Engine is also running really weak for all I have in it. I need help
Engine is bored out 30, heads port/polish, edelbrock performer 400, holley 770 truck avenger, 7 PSI 98 GPM electric fuel pump, Crane Cams RV cam and lifters, blueprinted and balanced crank, flat top pistons, MSD ignition (except distributor, have the cap and button) high volume oil pump, high volume water pump, exhaust headers and more
Checked the Accelerator cam and tried 4 other ones
checked conconnection to the Accelerator pump= no play and right tolerance.
Cam degree is good.
engine gets fuel
vacuum is like 10
Ive tried different timing degrees from 8-20 advance, no change just harder to start
have not checked my compression yet but it should be good everything is new.
everything on the engine has been grounded.
Air fuel screws are 1-1/4 out equal both sides. For the highest vacuum.
Summit racing said it might be like 25 things starting with transition valve or something.
Engine is also running really weak for all I have in it. I need help
Moderator
Joined: Jan 2001
Posts: 56,984
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From: Virginia
I would check compression. It may not be good. How much have to ran it? Does it smoke any that you notice? Sometimes it takes a little bit for it to break-in, especially if the correct cylinder finish was not done.
How much of this did you do yourself?
How much of this did you do yourself?
Fleet Mechanic
Joined: Jul 2011
Posts: 1,916
Likes: 4
Have you checked for all the obvious things first? No vacuum leaks? Intake manifold and carb/carb spacer, etc. all tight?
Where is your idle set at? What size power-valve? What size jets? Are the floats set correctly? Etc.
Have you tried timing it with a vacuum gauge? Is the vacuum advance hooked to the right port?
There's no reason why you're having a stumble and low vacuum. Either too much fuel or not enough, and it sounds like too much fuel.
Do you have a 600 or 650 CFM carburetor you could put on and try? The 770 CFM might be wrong for the 400.
Is your cam timing right as well?
Where is your idle set at? What size power-valve? What size jets? Are the floats set correctly? Etc.
Have you tried timing it with a vacuum gauge? Is the vacuum advance hooked to the right port?
There's no reason why you're having a stumble and low vacuum. Either too much fuel or not enough, and it sounds like too much fuel.
Do you have a 600 or 650 CFM carburetor you could put on and try? The 770 CFM might be wrong for the 400.
Is your cam timing right as well?
Senior User
Joined: May 2011
Posts: 184
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From: Garden City
Look down the carb while the engine is idling. If you see fuel coming out of the venturis, then you might have to adjust the float level. If that doesn't fix it, then the fuel pressure might be too high, try backing it down to 4-5 psi.
If the cam of the engine is big enough to have a lope at idle, then get a power valve that is rated for a lower vacuum application.
If the cam of the engine is big enough to have a lope at idle, then get a power valve that is rated for a lower vacuum application.
Moderator
Joined: Jan 2001
Posts: 56,984
Likes: 2,738
From: Virginia
I would put the carb being too big down on the list. It should adjust itself somewhat if it's a vacuum secondary carb. The vacuum being that low is a sign, you just have to figure out what's causing it. Many things could cause it.
Thread Starter
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New User
Joined: Mar 2011
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From: Hopkinsville
I think i found my problem. I checked the compression and Im down at 50 on #7and 98 on #3 so then i looked at my valvetrain and it seems to be fine so i put a little oil in the hole and she jumped to 125 like the rest of them. So i found a guy to put in new rings hopefully that will fix it
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Fleet Mechanic
Joined: Jul 2011
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If your engine was bored 0.030 over, then it should have 30 over pistons with a new set of fresh rings.
Something is wrong with the rebuild. I'd pull the whole thing apart and re-check it ALL.
Is it possible your rings weren't put on right or haven't seated correctly?
Something is wrong with the rebuild. I'd pull the whole thing apart and re-check it ALL.
Is it possible your rings weren't put on right or haven't seated correctly?
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