Question about backfire

[raven]

Well, I just got the motor back from the machine shop and it's in. After doing all the necessary stuff for initial fire-up, I find that this engine wants to fire through the carb so much that I can't get it started. I ran it up to TDC and re-installed the distributor and re-wired the plugs. Still nothing but backfire through the carb. What am I missing?
I've started it using the same procedure many times before, but now it's possessed.
It's a '57 235 with an electronic distributor.
Any ideas?
r

[HotRodJosh]

Is the cam in correctly? That would be my guess.

[C9]

[ QUOTE ]
I ran it up to TDC and re-installed the distributor and re-wired the plugs.

[/ QUOTE ]

Was it at TDC at the end of the compression stroke or at the end of the exhaust stroke?
It should be set at the end of the compression stroke - both valves on #1 cylinder will be closed.

If you used the harmonic dampener zero mark to indicate TDC you could be 180 out at the distributor.

Do you have the distributors plug wires installed in the correct rotation?

[raven]

I can't answer the question about the cam. The machine shop installed it. As far as TDC, it's not 180 degree off TDC, it's right and the distributor turns clockwise (from the top) and the plugs are wired in the correct order. I thought about that initially and re-set the distributor and plug wires just in case, but no good.
r

[DrJ]

Turn the engine over till #1 intake and exhaust are rocking oe up one down when you turn the engine over and back and check to see if it's at TDC there, (180º out, but still right). If not the cam is out of time.
Put a distributor with points in it, then start it up.
(235"s don't know shit from electronic ignition and it's bitching back at you for doing it!) http://www.jalopyjournal.com/ubbthreads/images/graemlins/wink.gif

[Deyomatic]

You may want to just take the dizzy out and move the rotor one or two teeth in either direction until it goes away.
OldCarPilot had a problem with his motor doing that for awhile, only yours sounds worse, so I might be wrong. We looked for vacuum leaks and problems with the tranny and all kinds of shit for a full week but found nothing.
After I left, he just took out the dizzy, moved the rotor one way, and put it back in and it ran 100x better.

[SKR8PN]

I am not familier with that engine. Does it have adjustable rocker arms? If so,they may be set to tight and are holding the intake valves open.

[raven]

Rocker not adjustable.
I thought of that.
That's why I set them a little loose just for initial start up, to be properly adjusted after cam break in.
r

[DrJ]

Do you have solid or hydraulic lifters? Car 235s came with hydraulic and they shouldn't be set "loose."
I usually rock the crank back and forth by hand, with all the plugs out it shouldn't be too hard, and at TDC, 180º out you should see an even valve overlap.
The exhaust should be about the same amount from closing as the intake is just starting to open.
That's all I meant.
It's just for confirmation that all is ok inside.
Then turn it over and observe that each other valve is opening and closing when it should and as high as it should.
Bad (flat) cams have accidentally happened, and a flat cam will make it backfire, even a brand new flat cam, if a lobe didn't get machined.
Bring it up to #1 TDC on compression and pull the dissy cap and confirm that the rotor is indeed pointing to #1 plug wire, I put some "unipoints" in a chevy V8 distributor that wasn't made for them and it idled ok but where the points opened relative to the cap was 1/2 way between plug wires and at higher RPM the advance made it fire the next plug in line and backfired like a mutha on the freeway.
I put the regular style separate plugs and condenser in it and it worked ok.
If you have an add-on electronic ignition something like this could be happening.
That's why I'm suggested trying a stock, known to work in another car, points distributor.
and tripple check your firing order....
Hope this helps.
My Dad usta tell me that backfiring is 99% ignition, and the other 1% is mechanical or carburetion.

[visor]

If all the above suggestions fail,
it could be the module in the dizzy.
If you have an old points dizzy, switch them out and
see if that does the trick.
We put a brand new out of the box electronic in
a V-8 last year and the motor had the same symptoms.......
drove us nuts, until we changed distributors.
Had a bad module from the factory.
Good luck.
--------------------------------------------------------
"OPOSSUM BENDERS"
Central Missouri Chapter

[porknbeaner]

Ravin,
Sorry I didn't make it for the greasy evening at The Ravin's Digs.
DrJ's Dad was right (as dads always are). Sounds like a timing problem.
If I'm not mistaken the distributer is a proven part. But if you have access to another it might not hurt to give it a whirl.
This mill has had cam problems from the git. I wouldn't hope that that is the problem. But if I couldn't sort it out with the distributer pretty soon, I might consider takin' a look at the cam timing and maybe even the cam itself.
I'm sending you a PM
The PknBner http://www.jalopyjournal.com/ubbthreads/images/graemlins/grin.gif

[raven]

DrJ,
It's a solid lifter motor.
I've got an old points dizzy, that I'll try.
Let you know Thursday as I'll be out tomorrow...
thanks again for all the suggestions.
r

[OldCarPilot]

Advance the dizzy more than you think it should be advanced and see what happens. Mine was firing through the carb like crazy (its not a 235). When I advanced the dizzy it was better but still not right. I advanced it as far as the intake would allow and nothing. As Deyomatic said I pulled the dizzy, moved it over a tooth so that I could spin more advance into it and all my problems went away.