Help!! Backfiring after re-doing top end
 

Ok guys here goes,

I had stock E7's milled .035 and ported exhaust (removed therm.

bumps) port matched stock intake as well as adding 1.7 RR's.

I also blocked off EGR in intake and removed all smog equip.

blocked off passages on back of heads.I also added fuel press

reg. & guage.

I have the timing set at 10*,fuel press. at 39lbs & it is backfiring

a little at idle & at part throttle, not so much at WOT?? I can't

figure this out, its not loud(right in the header) no detonation

detected. It's a 88 GT speed density, stock cam.Why would

unburned fuel make it out of the exhaust valve?? too much fuel

press??I also added syn. oil & now it smokes a lot (shortblock

has a lot of miles but i couldn't afford re-build) I almost think the

syn oil is leaking past the o-ring style exhaust valve stem seals

can you get umbrella seals for the exhaust valves? will intake

seals work?

Thanks Guys!!

Did you make sure you set the rocker arms correctly? If your heads are miled .035, the point in which you reach zero lash is going to be different than on an untouched engine. Pull your valve covers off and loosen your rockers. Put the engine at O degrees TDC. Make sure the dist. is pointing to the number one plug. Slowly tighten the rocker arm, while spinning the pushrod al the while between your fingers. Whenever you feel the slightest resistence on the pushrod, stop, youve reached zero lash. Now tighten the rocker to 20 ft. lbs. If it takes you more than one full turn to reach 20 lbs, you need shims. Thick shims represent one full turn, and thin shins represent 1/2 turn. Ive gone through this before when i did my head swap, and all my rockers need .090 of shims! The motor was backfiring like crazy, but I forgot to check the rockers. Here is the exact procedure:

Get engine to tdc, make sure dist. is pointing to #1. Tighten the following rockers to zero lash, then to 20 ft. lbs. (make sure you note how many turns it takes)
cylinder #1 intake and exhaust
#3 exhaust
#4 intake
#7exhaust
#8 intake

Now rotate the engine 360 degrees, so it is at tdc again, repeat the procedure for:
#3 intake
#2 exhaust
#7 intake
#6 exhaust

Now rotate it 90 degrees and do:
#2 intake
#4 exhaust
#5 intake and exhaust
#6 intake
#8 exhaust

I am willing to bet money you are gonna need shims, the only place i found them was through jegs. Try that and keep us informed what you find out.

Notch...That's a good technique. I've been thinking about checking my lash (hear some extra ticking from the valve cover area).

Is this something that should be checked every xx thousand miles or is it a "set it and forget it" type deal?

Thanks,

Rich D.
'89 LX 5.0
removed silencer, rebuilt T-5 w/improved 2nd, 3rd ratios

I'll check them again , I did shim some of them as per cranes

instructions ,basicly as you described. Of course the are

nonadjustable as i'm sure you knew.

Thanks......Anything else? I believe I got them right? we'll see

You never said either way if you replaced the valave springs.....if you didnt I assure you the valves are bouncing with all that newfound flow....if you did then it's probably a valve lash problem...good luck

Yes new springs and valve job.
I think the rockers are set right, unless i'm doing it wrong??
Whould a compression check tell me anything?(exhaust valve not closing all the way on comp. stroke or opening erley??)

Are you sure that you have all the plug wires in the correct spots? I like to check the simple things first, but if you shaved that much and did not use adjustables....Good chance thats it.

Ok the rockers were right.I had put syn oil in for 1'st time when i re-did the heads & stuff, well the oil control ring on #2 is evidently gummed up cause the oil was flowing past so bad the plug was'nt firing very often hence the back firing.However compression is good on all (between 170# & 180#)
I ran some engine flush in it ,went to 10-40 conventional oil and
mostly solved prob. now it only backfires once (loud) either on the 1-2 or 2-3 shift when driving hard 5000-5500 shift point.
What should I try short of a re-build?
I always run cheap bosh supers .99 cent each & change them often, but I put a autolite rapid fire in #2 same as with bosh super,would a "hotter" plug help?
Sorry so long, thanks
Wes

re-torque the header bolts and redo the header flange bolts.. a backfire when you shift usually means you're sucking air.. you might have put the exhaust pipe on a little crooked..

Would'nt you hear an exhaust leak if that were the case?
Like I said it backfired at idle w/syn oil in it. A anti-foul adapter
helped with the cheap plugs,and with reg 10w-40 and the better plug in #2 is where i have my current backfire(usually on2-3 shift).
However today after driving it hard for a while it started hesatating bad and backfiring bad like the plug was really wet and not firing often(sputter&pull&sputter&pull,backfiring all the while).I was almost home and have'nt pulled the plug yet but I know it was "oil fouling".

TO QUOTE NED FLANDER'S BEATNIC DAD:"I've tried nuthin' and I'm all out of ideas."