New motor backfiring through carb

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doogievlg

doogievlg

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Got the new motor ready to fire up tonight. Got fuel primed to the pump. Got fuel pressure at the carburetor. Carburetor ran great on the dyno and the engine ran great on the dyno. Went to start it tonight and it would crank and crank and crank then the starter would slow down and then a backfire out of the carburetor. I worked on the car for about 5 hours tonight getting ready to fire it. This happened to me three times and finally I through in the towel at 10 and went home. Any clue what could be causing this?
 
what has changed since it ran on the dyno?....did the distributor come out...did it get moved.....are the plug wires on correctly....
 
70aarcuda said:
what has changed since it ran on the dyno?....did the distributor come out...did it get moved.....are the plug wires on correctly....
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I pulled the distributor to prime the pump. I made to marks on the block when I pulled it and made sure the line up when I dropped it back in. Numbered on the wires when I took them off the spark plugs and put them all back on the same ones. I’m leaning toward timing right now but it was so late that I didn’t have time to really dig into it. The shop isn’t at home.
 
Are you sure you set it back on the firing stroke?.....if it popping back thru the carb is usually a good sign that it is 180 out.
 
70aarcuda said:
Are you sure you set it back on the firing stroke?.....if it popping back thru the carb is usually a good sign that it is 180 out.
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If it was 180 degrees out then wouldn’t one of the lines not be lining up. I drew one line at 12 o’clock and another at 3. If it was 180 out wouldn’t the one at 3 be at 9 o’clock?
 
I know what you're saying but it depends where you drew lines. You can hold base still and spin distributor.
doogievlg said:
If it was 180 degrees out then wouldn’t one of the lines not be lining up. I drew one line at 12 o’clock and another at 3. If it was 180 out wouldn’t the one at 3 be at 9 o’clock?
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70aarcuda said:
Are you sure you set it back on the firing stroke?.....if it popping back thru the carb is usually a good sign that it is 180 out.
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Best way to check this is to pull the spark plug on cylinder #1 and make sure it’s on a compression stroke then point the rotor toward that cylinder right?
 
this is what i do went i am searching for tdc on the firing stroke...i take the driver side valve cover off....turn the engine over by hand....watch the intake valve close....keep moving the engine until the balancer is line up at TDC....pull the cap and see what the rotor is pointed...

many other ways to do it....this is mine.
 
I assume you pulled the oil pump drive shaft to do the priming. Did you rotate the eng during the priming?

I would start by pulling the dist. And reset everything to TDC #1 per the FSM. Recheck everything else, firing order, rotation direction etc
 
doogievlg said:
If it was 180 degrees out then wouldn’t one of the lines not be lining up. I drew one line at 12 o’clock and another at 3. If it was 180 out wouldn’t the one at 3 be at 9 o’clock?
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You can draw lines anywhere you want on the housing, but if that shaft rotated while you had it out your timing is now wrong. Plus, if the intermediate shaft wasn't put back in exactly the same, then the distributor shaft HAD to turn to get the distributor back in and for your marks to line up.
 
Yes, start with TDC, rotor pointing to #1 plug, firing order clockwise, 18436572. If you ran it on the dyno why did you think it needed pre lubed?
 
OP you need to learn to get on the firing stroke. There are only two ways to do so. If either valve cover is off, rotate the engine to TDC and examine the no1 or the no6 valves. Whichever pair is closed, that cylinder is ready to fire

The more popular method is pull out the no1 plug, crank the engine with your finger in the hole. As soon as you feel compression, look at the timing marks, and bring them up to where you want the timing, NOT TDC. Bring the marks up to 15BTC or wherever you want the timing.

Then look at the rotor. If it is not point at "just coming to" no1, adjust the dist/ plug wires as necessary. You can set timing on the starter. There is no reason you cannot static time these and start it right up.
 
69DodgeMan said:
You can draw lines anywhere you want on the housing, but if that shaft rotated while you had it out your timing is now wrong. Plus, if the intermediate shaft wasn't put back in exactly the same, then the distributor shaft HAD to turn to get the distributor back in and for your marks to line up.
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I put the intermediate shaft in to get the distributor to sit in the same exact spot it was when I pulled it out. I’m going to start from scratch next time I’m over there though.
 
Good advice all around , had a buddy pull his dist.once marked it put it back in the same spot, but he marked the cap NOT the rotor , it didn’t run either after that , no help just a funny story .....
 
Try this:
F O R G E T where you set it, what you did or did NOT do.
Follow the advice here as if you don't remember anything that you did before. Your memory is probably wrong or screwing with you.
 
Try this: Remove #1 spark plug. Put a threaded compression gauge or Sharpie marker or a friend's thumb in the spark plug hole. This is the compression stroke. Keep rotating the harmonic balancer bolt clockwise until the balancer line is on '0' [TDC]. Remove the distributor. Look down the distributor hole. The slot in the gear shaft should point to the left front intake manifold bolt. If not, pull up on the gear and turn it till it does. Note that the gear teeth will rotate the slot as it is fully seated. Also, a long straight screwdriver or tool may be necessary to turn [reposition slightly] the hex in the oil pump, as the gear and the hex must align for the oil pump shaft to seat fully. Drop in the distributor with the rotor tip pointing to the front of the car, and the vacuum advance unit nipple pointing to #8 spark plug [or 12 and 3 o'clock from the driver's seat]. Snug down the dist. clamp so you can turn the dist. by hand. Recheck plug wire location. Fire it up. Set timing. Road test!
 
If the balancer and timing cover are accurate ,'or at least have been marked to be accurate when timing...with a pen' you should be able to just line that mark up to 0*... and you're either going to be right on or 180 out ...so if it cranks and still coughs out the carburetor and even back fires once then it's 180 out, flip it and fire it up.
 
Lets review the scenario, engine runs, remove from test stand,dyno or whatever.
Install engine in car, bolt on torque convertor or flywheel. I suspect engine was turned during some part of this, likely with distributor out. And likely distributor was out.
If crankshaft was turned over once or any number of times,on odd numbers then distributor could very well be out 180.
 
Tooljunkie said:
Lets review the scenario, engine runs, remove from test stand,dyno or whatever.
Install engine in car, bolt on torque convertor or flywheel. I suspect engine was turned during some part of this, likely with distributor out. And likely distributor was out.
If crankshaft was turned over once or any number of times,on odd numbers then distributor could very well be out 180.
Click to expand...

I believe somehow it is 180 out. Not sure how but I screwed up somewhere. I also actually never did remove the distributor during installation. I took the cap off when dropping the motor in but it was marked as well.
 
I think its 180 out like everyone else thinks. Use the advice of sticking your finger in the #1 hole & go from there. Easiest way to find out.
 
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