Miguel

I have a new 393 strocker sportsman block made by DSS. I installed everything on the block and when I tried starting the engine, all hell breaks loose. I get popping, backfiring and fire catching on top of my carburator. And when it does start, when you rev it, the rpms back off by themselves 50-200 in idle. And the more load when in drive the more it loses, I can't pass 1500. All the parts installed are brand new, and the timing, firing order and carb have been inspected countless times by mechanics. Also, I had the heads removed and redone with new things because I thought it might of been something their. I even changed the whole ignition and fuel system over again, just to make sure their wasent something defective from the factory. The only thing I'm guessing it could be is the push rod length because I followed whatever a comp cams tech told me but no one really knew what length they should be. I've spent so much money and I'm still clueless. Please I need some help

dyno

sounds alot like the carb is blowing fuel all over is the carb new?check the float bowl levels check the firing order too! my .o2

Turbojack

You either have the wrong firing order or you timing is way off. Best way to set timing is to pull the # 1 spark plug. Disconnect coil wire. Put your finger in spark plug hole. Turn motor over until it blows your finger off the hole. Look at timing marks & you should be real close to TDC. Turn motor over to get it to the "0" mark. Remove dist. cap & see where rotor is pointed. This should be to the #1 cylinder. If not, start there with your plug wires & go around clockwise with the firing order.

Now that you have that close to being correct. Put coil wire back on & start motor. You may have to move distributer around alittle to get motor to start. Once started put timing light on & set timing.

If this does not fix problem then maybe the valves are adjusted too tight or cam timing is wrong.

Airpacker

do a compression test,if the push rods are too long,no or very low compression. Make sure you did not over tighten the intake valve adjusters as well.

Iggy

I'm with Turbojack.
Check the firing order and timing.

RumRunner

If an engine backfires through the carburetor 99% of the time it is too lean. This can be caused by a faulty carburetor, or ignition timing. As others have stated first check your firing order, check your ignition timing, and check that your cam is installed properly. Also go through your carb to make sure it is not gummed up, or blocked with anything.

mrv8outboard

also check your mechanical advance in the distributor, i would do this with an advance type timming light. just in case the advance is backwards? food for thought.

LapseofReason

Yes check the timing the way turbo said or if you have a good timing light you can turn the motor by hand and it will still flash, so you will see the flash at the same time your finger gets blown out of the hole.Remember you will have to have the key on. If that is right do a comp. test if it's a new motor and has been running as bad as you say it might have washed down the cylinder's so you may have to put a little oil in them. Anything over 130# will be good enough to get it running to set timing and break it in. Make sure your oil isn't full of gas.

Cord

iTrader: (2)

What is your cam timing set to? Could it be over advanced? Did you dial it in?

Miguel

I have done the timing many times exactly the same way described because I was told the same thing from mechanics, that the distributor could be backwards 180 deg, but thats not the case here. As for gas in the oil I have changed them twice, and saw nothing. Its not the timing because I have also installed a msd knob that you rotate advance and retard the timing with, rom 0-15, and still no luck. As for the carb, it's a holley 750 from dean nickerson, who I sent it back too and was dyno checked and sent back, with no problem. Compression is the same at 180 all eight cylinders, only one was 190. Thanks for the help guys, but I'm still stuck. The only thing I regret was not giving the whole motor to be dyno'd and then installed in my boat. maybe I could of blamed someone other than myself.