backfire through carb

[streetstang88]

i know this is windsor tech ,and a 400 in a 1977 pick up is not windsor tech
but its close enough ......
i have a old wore out (most likely my problem) 400 in my 4x4 and it keeps
back fireing trough the carb even when @ idle ,it is sporatic , i have checked timeing,and fuel to make shure its not a lean out problem(new carb) ...seem to be ok

the only other things that i can think of is weak valve springs or maybe
some carbon build up ???? i am thinking of running massive amounts of
seafom through the carb and fuel and in the oil ....

any ideas ????????? :banghead:

[Italian LX]

i am thinking of running massive amounts of
seafom through the carb and fuel and in the oil ....
That wouldn't be a bad idea.

[streetstang88]

much more of it and my holley will be toast

[Italian LX]

What condition is your timing chain in. Maybe it has enough slack to retard your cam timing a considerable amount. :shrug:

[coupe]

Carb could be shot or even bad EGR valve... But yea; most likely cam and/or ignition timing.

[streetstang88]

that will be my next step if this dont work ....along w/ whole new top end

but first prodigious amounts of seafoam

[Sendero]

Uhhh, isnt a 400 a 351 block with a Modifed crank? That would make it a Windsor.

Sorry :ot:

[QWKSNKE]

Uhhh, isnt a 400 a 351 block with a Modifed crank? That would make it a Windsor.

Sorry :ot:


No... 351-400 m's are not of the windsor family

[coupe]

It's a 351M-400 and it actually displaces 400"
It's a cleveland motor. My buddy's '78 T-bird had one with a 2-bbl.
Whatta pile of junk. :nono:

[1Quik85GT]

check the power valve..

[Wicked]

Burnt or leaky intake valve? I know its generally the exhaust valves that burn but I guess its a possibility.

[slvrbullit]

I am gonna go along the lines of stephen, check the power valve, usually one backfire will kill them.

[TheJeanyus]

It's a cleveland motor.
:werd: Taller deck height than a 351C. :yup:

[streetstang88]

i was thinking that it could have a large carbon buildup on top of an intake valve keeping it from closeing completely during power stroke.... i have checked timeing and fuel
and if one back fire can ruin a power valve then sounds like i have another problem to deal with ....guess i will have to rebuild the whole top end

i believe that 351c has a short deck ,351m has tall deck and 351c crank
385 series of big block

[QWKSNKE]

i believe that 351c has a short deck ,351m has tall deck and 351c crank
385 series of big block

yeah the M motors have a 10.2x deck height and 'big block' bell hosuing pattern. You can use cleveland heads on them though.

Its 335 series ;)

[1Quik85GT]

Check the carb, gasket between the metering plate and bowls. There could be a hole that is bein blocked on the metering plate by a gasket. I have ran into that before.

385 series included 352,390,406,410,427,428 these are BBF's

351M,351 clevelands are considered SBF's

[streetstang88]

see... i lernt sumthin'.... 385 series are FE motors

about the carb i guess that would cause a lean pop??
....if that is holding gas back

[streetstang88]

yeah i ment to type 335 .....

wait i am callin :bs: on my self

[streatleathul]

Back firing through the carb all the time even at an idle , you should ck the cam. One of your exh. valves are not opening, the presure is coming back through the intake.
You said the carb is new right?
Does the back fire get worse with a load. say going up hill?
Rick

[1Quik85GT]

Also could have jumped timing...

[streetstang88]

nope it does fine under load...

yeah ..new holley 2 barrel (power valve is probably shot now )
a timeing chain ,and harmonic balancer ...... we will see if it has jumped time
i appreciate everyones ideas, it is probably a mixture of these problems
and the only way to cure this for shure is start the parts swapping ...:darwin: ha ,ha and some machine work along the way