460 not running right.

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Jun 10, 2010 | 11:00 AM

460-f250

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From: st.peters, mo.

460 not running right.

i thought i had this fixed but i guess not. my 87 f250 has a carbed 460 and im having a hard time getting it to run right.

timing is 8*btdc and at 8* it spits and spudders and just doesn't run good. i have to bring it up to 18*btdc to get it to run decent but it backfires out the exhaust when driven hard . its so bad i thought i blew up a muffler.

also no matter what the timing is when i hit the gas from a stop it will hickup then take off.

does this sound like a vacuum leak? or do i need a carb rebuild? any help would be great.

thanks.

Jun 10, 2010 | 01:25 PM

460-f250

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From: st.peters, mo.

i found one vacuum leak, someone didnt tighten down the carb all the way and it was leaking from the gasket.

i have the timing at 12* (i read somewhere that is best for performance.) and it runs great now, no hiccup when accelerating but it still backfires. im starting to think its just my exhaust setup.

factory duals, no cats, with thrush mufflers and turn downs before the axle.

Jun 10, 2010 | 05:28 PM

ArdWrknTrk

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From: EXTREME southwest CT

leaking exhaust manifolds or the harmonic balancer may have slipped giving you a false timing indication.

Jun 10, 2010 | 07:00 PM

460-f250

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From: st.peters, mo.

i know i have a exhaust leak somewhere in the manifold area. would that advance or retard the timing?

Jun 11, 2010 | 05:46 AM

ArdWrknTrk

pedant

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From: EXTREME southwest CT

Your truck backfired through the carb.
The first thing is to check for a blown power valve in the carb.
The exhaust will be VERY rich.

I just meant to suggest that you check that TDC #1 is in fact correct if you seem to have issues timing it.
If the rubber of the harmonic balancer is no longer bonded, the collar with the timing marks could move anywhere.

You can pull the #1 spark plug and feel the piston rise to the top or you could bolt up a degree wheel, use a piston stop and halve the difference of where it indicates.

I didn't know that my 460's harmonic damper/balancer had slipped until I went to install a recurved distributor and I found that the rotor was no where near the #1 post when I set it up to remove the old one.
(after many years of checking ignition timing w/ every tuneup I don't bother)

Jun 13, 2010 | 12:36 PM

460-f250

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From: st.peters, mo.

well i finally checked the balancer and it has shifted. here is a picture of the balancer with #1 at TDC so im guessing i should have my timing set to 26-28* BTDC ? the white mark is 10*btdc