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Author Topic: Need some help with a 400RB  (Read 1836 times)
mosenji
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« on: May 02, 2009, 09:00:37 PM »

I have an 82 Miser. The engine is a 400 RB block im not sure on the bore,a mopar purple shaft 292 hyd. cam,Edlebrock performer intake, Hooker comp. headers w/ 3'' flowmaster,Edlebrock 750 cfm.performer carb, Crane cams dual high lift valve spings w/ high strength double groved retainers,high volume oil pump, and a mopar performance distributor curved for the cam to come in full advance @ around 34 degrees total timing @ 3200rpm. We installed a Lucas 8'' 3000rpm stall converter in front of a 727 trans. w/ larger clutch packs and the pressures were tweaked to firm the shifts,then installed a b& m mega shifter. The rear end is a 3:55 ratio out of a 1978 ford 4x4 pickup.

I am trying to increase my mileage as well as get rid of an irratating hesitation on take off. I have been told that going with an MSD distributor would do both for me.

Any comments, help, whatever will be greatly appreciated.

Thanks ....

MO-Truck or NO-Truck!
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Charlie1935
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« Reply #1 on: May 03, 2009, 08:40:48 AM »

The 400 is a B block. The RB blocks are 413, 426, and 440 except for some early 383's. May be a carb adjustment, accelerator pump adjustment, jetting and/or initial timing.
« Last Edit: May 03, 2009, 08:43:48 AM by Charlie1935 » Logged
mosenji
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« Reply #2 on: May 03, 2009, 12:02:54 PM »

The fella I got the motor from told me that it was a 400RB out of an Imperial. I'll give a look at your suggestions. The motor fires right up, is a bit cold natured but once she warms up she runs great, except that danged hesitation on take off.

Thanks ....

MO-Truck or NO-Truck!
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Griff in Fairbanks
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« Reply #3 on: May 03, 2009, 02:09:27 PM »

A quick search on the 'net for the block casting number should tell you whether it's a B or RB block.  (Unless I'm mistaken, the B and RB engines used different blocks and should have different casting numbers.)

To the best of everybody's knowledge, the 400 was a B block ... although, Mother Mopar and her five sons were known to do some strange things.  The engine serial number (not the casting number) stamped into the block should tell you what it was when it left the factory.  (I don't recall exactly where the engine serial number is on the B and RB blocks ... just where it is on the LA blocks.)  However, I wouldn't rule out the possibility someone converted another size into a 400 by changing the crank and rods.  (If they changed the crank without changing the rods ... )

Try advancing and/or retarding the timing a few degrees to see if that reduces or gets rid of the hesitation.  (Always start with the timing.)  If you can get your hands on a scope, it would help.  Especially, watch what happens to the hydrocarbon reading when you push on the accelerator.

You may need to recurve the distributor.  If so, going to an aftermarket distributor won't change your problem much.

Once you've got the timing adjusted to the optimum setting for your engine, check the accelerator pump.  It sounds like the engine may be temporarily flooding when you push on the gas pedal, which seems to indicate an overactive accelerator pump.

Next, make sure the idle screws are properly adjusted.  I once encountered a carb where a PO had opened up the idle jets in an effort to make the engine run smoother.  (The actual problem was an intake manifold leak that caused the engine to idle lean.  The PO's 'fix' caused the engine to flood when you opened the throttle.)
« Last Edit: May 03, 2009, 02:13:40 PM by Griff in Fairbanks » Logged

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Charlie1935
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« Reply #4 on: May 04, 2009, 04:58:07 PM »

The 'B' engine and can be identified by the cubic inches stamped on the right side of the block deck adjacent to the distributor. The RB engine has the engine size stamped on a pad at the left front of the engine adjacent to the front tappet rail. From Allpar.
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biggdog440
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« Reply #5 on: May 20, 2009, 10:23:04 PM »

400 is a b block, 350 361 383 400

rb  raised block, 413 426 wedge and 440

1st what do you do you the vehicle? its kinda to me mix matched, not a pulling but not street/strip but has componets going each way. would be easier if i knew what you used it for. just got done with a 78 cc with a 400 for towing and mud,and now working on a 70 chally r/t with a 383 that is for heavy street/strip so each is different app.

thanks tom
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