Popping, Backfiring, Catching on Fire, Need Helppp
 

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

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

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.

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.

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

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.

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.

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.

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

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.

Do you have leaking exhaust. I had some pinholes in my headers and thought I had a timing issue.

Sounds like a timing problem. Did you degree the cam in? Usually if it's a timing problem and it backfires through the carb, it is retarded.

sounds like a timing chain off or some valves sticking.

I had the same type of problem, reviewed timing and firing order literaly 100's of times, found I had mixed #7 and #8 wires....Dumb thing was I checked firing order over and over.

I had paid 300 only for the company to degree the comp cams hydraulic roller cam in at D.S.S. The block came complete i just bolted the external things on like heads and intake.

Get a vacum gauge and check for a intake or carb leak. If that dont work double check your valve adjustment, it could be too tight, then get rid of the advance/retard knob, set up the dist with the black spacer and the springs that allow all timing in at 3500. I forget which ones they are. Start motor run it up to 3500 and set full timing at 34*. If you dont have wires crossed that has to work. I assume you have a msd distrib and box. What was the cam degreed in at?

I had the exact same symptoms when I changes my intake manifold. I had removed the old intake one day and covered the top of the motor. The next day, I put the new manifold on. I had pulled the Dist. cap off with the wires attached and set it off to the side. Apparently, condensation formed inside the cap and it was all wet. I looked for the problem for many hours before I turned the cap over and looked inside.

Assuming that your timing is correct, it sounds to me like your valves are too tight. How did you set the valve lash? What type of cam is it? Hydraulic roller , or ????

you can't deg a cam with the head's off, if they said they deg. the cam and then you put the heads on you got robbed.

I don't see why a cam can't be degreed with the heads off. You still have TDC to reference off of. The cam can be advanced or retarded just fine. You can also read when a lifter will start to move. I just can't think of anything that would be missing which would affect the cam timing.

Yes you can degree a cam with the heads off, in fact it's the only way I have ever done it.

Miguel-
You probably have a simple problem and are overlooking it.
You have compression, fuel, and spark- so you have got to verify cam, ignition timing and valve operation. It is not hard to do. You will need a dial indicator and a degree wheel.

Another concern with backfires is to make sure that you don't have a bad exhaust lobe. spin the motor and watch the exhaust rockers real good....

First check to make sure the timing mark on the balancer is correct- my brother has a late 350 balancer that has TDC straight up at TDC, and the older style pointer that is about 30 degrees towards #1. Ran like crap until we went through the verification procedure.

If you know the cam number, find out the intake lobe centerline degree point. This will be about 10 degrees AFTER top dead center and is the point at which the intake is fully open. This method eliminates any concern over a mis-marked timing mark- it directly ensures the cam is where it is supposed to be.

Next, make SURE the ignition timing is right. I rotate the engine until the exhaust is closing and intake is opening on #6 cylinder, at Top dead center. At this point, #1 cylinder will be at TDC on the firing stroke. Then check plug wires for firing order, 1-8-4-3-6-5-7-2, clockwise at the distributor top.


Next, I would check the valve lash.

Solid- use feeler gauges.

Hydraulic- Start at #1, TDC by looking at the distributor rotor. loosen valve adjusters on #1 in & ex valves. tighten adjusters until the slack just disappears, and go 1/4 turn more. Rotate the engine to #8 cylinder and repeat lash procedure. Continue through the firing order.

Some people rotate the pushrod betwwen the thumb and index finger to feel when the slack disappears- I also know of a guy that uses a thin feeler gage and then goes 1/2 turn more.

gotta go
Bulldog

check the distributor cap for cracks or moisture

I just don't see how you can get a exact reading of when the valve is opening with the heads off, you can get close with a reading off the lifter but if your going to bother to deg. the cam don't you want it exact. I have built a lot of motors and read a lot of books on it and have never seen it done with out the heads on. With rockers at different ratio's it sure seems to me it would be a lot easier with the heads on. But I see what you are talking about.

what were your cam timing numbers when you dialed it in?? and do not forget to run the numers on more than one hole....i do 4, that way i know for sure. I also use a very large degree wheel. dig those numbers up for us! your timing should have been set to a ballpark at the very least when the wheel was still on.
bulldog had some really good points!...
LoR is correct

i just skimmmed over the posts...sorry if i repeated something.

Degreeing a cam is based on the crank location. Thus all you need is the crank, the #1 rod & piston, camshaft & #1 lifters installed

bulldog is 1000% correct!! "Miguel-
You probably have a simple problem and are overlooking it.
You have compression, fuel, and spark- so you have got to verify cam, ignition timing and valve operation. It is not hard to do. You will need a dial indicator and a degree wheel. "

remember this procedure IS NOT FOR DIAGNOSTICS! it is a 100% must for building an engine...if you put this engine together and installed with out doing this one BASIC thing...you are not only asking for problems but will have no data to support ANY future diagnostics.

turbojack is also correct...it is done both ways and there are benefits for both...i prefer to do mine after the heads...i can then see valve terrain geometry and play with racker ratio and PR length.

This so simple I felt really stupid when I screw it up one time. Make sure you have the correct side of the engine for your #1 cylinder. On International gas engines it is backwards from Ford and GM. I could get the engine to idle reasonable well but it had no power. Even had some very good mechanics look at it that didn't check something so simple. I ended up replacing a perfectly good engine. (duh)

I had a similar problem and it turned out to be the microprocessor in the distributor arcing across to a wire which had been replaced recently. Check the little wire running out the lower external aspect if the cap.

I agree with Turbojack, Rum Runner and Bulldog. When the timing marks on the harmonic balancer of a Chevy V8 are at TDC, your distributor rotor will be pointed at #1 or #6.You're at #1 if you pass the "finger test" or both rocker arms for #1 are not under tension (both valves closed). I'm very suspicious of how the cam was installed. Some timing chain setups allow you to advance/retard the cam by moving the gear on the crankshaft to a different position. The cam sprocket also has a mark that has to be at 6 o'clock when #1 is at TDC. Popping thru the carb tells me your timing is retarded or your timing isn't advancing. I've lost exhaust lobes on the cam that also causes backfiring thru the carb. Good luck!

Since you said MSD back there, it sounds to me like an ignition problem. Did you use solid wire plug wires? Can you disconnect ALL of your MSD equipment and run on the dist & coil? A failing coil will do EXACTLY what you are describing, have you made sure the polarity is correct or substituted the coil? Hell, if all else fails, drop a GM HEI large cap distributor in it for test purposes. 1 wire to 12 volts and wala... test unit. Below is how to trouble shoot MSD ignition, but not specific to your problem


The following test will determine if your MSD is producing a spark.

White Wire Trigger:
If you are using the White wire (points or electronic amplifier) of the MSD to trigger the ignition, follow these steps.

1. Make sure the ignition switch is in the Off position.
2. Remove the coil wire from the distributor cap and position the terminal so it is approximately 1/2" from a good ground.
3. Disconnect the MSD White wire from the distributor points or the ignition amplifier.
4. Turn the ignition to the On position. DO NOT CRANK THE ENGINE.
5. Tap the White wire to ground several times. Each time the wire is pulled away from ground a spark should jump from the coil wire to ground. If spark is present, the ignition is working properly.

If there is no spark:

A. Inspect all of the wiring.
B. Substitute another coil and test again. If there is now spark, the coil is at fault.
C. If there is still no spark, check to make sure there is 12 volts on the small Red wire from the MSD when the key is in the On position. If 12 volts are not present, find another 12 volt source and repeat the test.
D. After inspecting the test procedures and inspecting all of the wiring, there is still no spark, the Ignition is at fault.

Magnetic Pickup Trigger:
If you are using the 2-Pin Magnetic Pickup of the MSD to trigger the ignition, follow these steps.

1. Make sure the ignition switch is in the Off position.
2. Remove the coil wire from the distributor cap and position the terminal so it is approximately 1/2" from a good ground.
3. Disconnect the MSD Magnetic Pickup connector from the distributor.
4. Turn the ignition to the On position. DO NOT CRANK THE ENGINE.
5. With a small jumper wire, short the Green and Violet magnetic pickup wires together then pull the jumper off. Each time the short is removed a spark should jump If spark is present, the ignition is working properly.


good luck my friend...