425 olds motor

first start on a newly rebuilt 1965 425 super rocket olds motor. and it was poping out of the carb. everything is new and .030 over. any ideas? shut it down right away.

 

First thing I'd check is the timing; second would be the firing order.

 

^^^^^ yep ^^^^

 

And if that doesn't fix it check the valve adjustment.

 

I'd check the firing order, then the timing.

 

olds dist. turns opposite of a chevy..

 

no adjustment....

 

Crap I need to learn more about non Chevy powerplants.

 

After thinking about it, doing it in this order makes more sense.

 

If it is a steady rapid fire pop back through the carb then it is intake valve related, too tight, bent pushrod, cam lobe down. If erratic backfire through carb then look at timing, crossed plugwires,lean mixture and that type of thing.

 

No their isn't but if the heads and or block were surfaced to much and the push rods not checked they could be to long keeping the valve open, or one of the trunnions are wore out doing the same thing.

 

My guess is timing is off. Either the distributor is 180 out of phase or advanced or retarded too far. Next guess is wiring sequence is incorrect. Just go back to square one and start over. Bring the number one piston up until it blows your finger off the spark plug hole, then put the timing mark on zero. Now look at the rotor and it should be pointing at number one.

Next, check the wire rotation on the cap to make sure they are going around in the right direction. This should get you close enough for the motor to fire up, and a little twisting both ways on the distributor should make it run smooth and quit the popping.

Don

 

Oldsmobiles have non adjustable rockers. If you go over 500 lift on the cam and you dont shim them or go to an adjustable set you will have that same problem. The valves stay open and the exhaust feeds back thru the intake. Check to make sure you dont have the dist 180 out. If it starts and runs but keeps back firing thru the carb back off all the rocker bolts a 1/4 turn and if the problem stops you need to shim the rockers.

 

Had the same problem with my 324. It was the distributor being 180 off. After getting that sorted out it ran fine.

 

Not true, as long as the number one wire is where the rotor is it will run. That is done for ease of placement and marking.

 

Sure, you can put number one anywhere you want it as long as you put the rest of the wires in the correct direction and order, but why make it difficult for a man who is already having problems ? I just gave him the most straight forward/ most simple way of arranging the wires and finding number one.

What I was steering him toward was to see if when he did find number one cylinder on TDC if the rotor was pointing at number 6 instead of number 1.




Don

 

Since the heads are not hard seats I have to ask what you did to them. If the engine was ran a lot on unleaded, the seats could have receded and if the person who did your heads didn't check the installed height, you will have the (already mentioned) valve lash issues. I have had to shim the pedestals on stock ones before.
That 425 is a great engine, one of Olds best IMO, but all of those engines need different rockers and oil restrictors to keep the oil on the crank (if you plan on revving it past about 4600 with any regularity)

 

Firing order is an absolute, timing is a variable. Makes perfect sense.

Bob

 

Will it even start at 180* out? I guess I never got that far ,when it spits back through the carb I kill it and the 1st thing I do is check the distributor and rough timing.

Bob

 

I've never seen a V8 that would actually run at 180 out.

 

That was the one thing I couldn't tell from his description of "popping back", was it running and just making an occasional pop, or were flames and explosions coming out of the top of the carb so bad it wouldn't run at all.

Don.

 

That's what I thought, I never pushed the issue... it was always an "oops shit" moment when it happened to me (once maybe...) and it was a quick fix.

Bob

 

Until I learned the trick of putting your thumb over number one spark plug hole to find when the piston was at TDC I would almost always get a new engine 180 out of phase the first time I tried to fire it up. It was a standing joke in the family that I was going to screw it up again. Usually the light show coming out of the top of the carb would be my first indicator.

I hope the OP comes back on to tell us what he found.

Don

 

lean

 

hey guys, its my brothers motor. and he told me it started, but was poping out the carb,, just noise no flames so he shut it down. he's saying he has it a tooth off on the dist. cam is a 496 lift, hyd. edelbrock alum. heads, ,030 over. waiting to here more from him. will post when he resets dist. JAN

 

Sounds like a bent valve or very wore valve guides.

 

That year Olds had a 6* different lifter angle from later ones. Not enough to cause all this, but something else to worry about.

 

my brother told me today, the dist. was off a tooth. it started right up and no pop.

 

That's all it takes. I had one off a tooth on a SBC when I was a kid... and it ran surprisingly well, it was advanced too far and impossible to start when it was good and hot.

Bob