Keita

Hope someone can help me, I have just bought myself a 302 and put it into my xf ute, it has an even compresion in all cylinders of 170 psi, I have put in new sparkplugs and leads, it has an electronic dizzy which has been rebuilt and a new coil. But it still seems to be running on about 5 cylinder and constently backfiring. Any ideas would be a great help.

RPO-083

The obvious choice would be timing...

But, failing that; is it a factory dizzy? If so, take off the cap and the rotor button. There will be a circlip holding the star-wheel (rotor) onto the shaft. Remove the circlip and check to see how many slots are in the rotor. If it has two slots, remove the rotor and refit with the other slot now aligned with the shaft (be careful not to lose the locating pin). Not too many have two slots, but it can be a problem, especially on a rebuilt dizzy.....

Keita

I have looked at the dizzy but it only has one locating slot,any other ideas???

brenx

Timing, lean condition, vacuum leak I'd guess. If it's stupidly rich? it'll foul the plugs again.

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XB Fairmont (street car) 11.07@123.02mph.

RPO-083

OK, here's another long shot. Has it got a single vacuum advance unit, or a dual? If it is a single, then no probs. If it has had a dual fitted, then you may have problems.

Actually starting up an engine after a rebuild/carb change/dizzy change shouldn't be a problem. If everything is set to "basics" then it should fire and run "OK". If it is backfiring then you have a problem. But, other than what has been posted so far........

I would go along with the vacuum leak up to a certain point, it should make it impossible to set the idle, but not backfire. If the static timing is around 6 before, and the idle mixtures are about 1 and a half out, then it shouldn't backfire. (please, no critism on the "spec's", it should run...... then again, it should run anywhere from 20 before to zero, and the mixtures are "flexible" on a startup as well)

Oh yeah, I try and think of "extreme" problems, like the slots on the dizzy rotor (that's always a good one when it happens....)

xdclevo

I had this star-wheel spin awhile ago, and caused bad backfiring and running.
The rotor/star-wheel just wasn't phased together, causing weak spark,
then it would spin a bit more putting the timing right out.
Check that starwheel, rotor button and lead on cap are in line.

TruBlu351

Welcome to FF Keita.

Are your accelerator pump arm(s) connected on the fuel bowls?

Sometimes people forget forget and let them dangle when refitting a fuel bowl. It will splutter and backfire when you try to accelerate.

Try pulling one ignition lead off at a time and seeing if its related to one cylinder/plug/lead. ie: rev it a little and see if it stays the same or gets worse.

__________________
XE Falcon
393 Tremec TKO 9"

russxr67

sounds like you may have the firing order screwed up.check the basics first.

Keita

I have just pulled the carby and intake manifold off and have noticed that the intake valve on the no.8 cylinder dosnt open up as much as all the rest, follower it down and it seems that the cam lump isnt as high as the others could this be part of the problem? Can i take the cam out easily to have a closer look?

russxr67

The easiest way to check lobe lift is with a dial indicator with a magnetic base . Chances are if it looks physically different by eye ,then you have probably lost a lobe on the camshaft. Pull the lifter out of that particular lobe and check the underside.If it is severely gouged then it is rooted.
Pull the water pump,timing cover ,harmonic balncer( you will need a special tool for this),timing gears out. Acces to the cam is via the camshaft retaining plate.PS ,you need to remove radiator as well if its in the car and the grill etc.Cam slides out easily once rockers and lifters have been removed.