Help with back fire popping.

[Jason]

Okay, I have a 1973 scott II with a 345. Let me start by letting you know what I have done to have this problem. I first rebuilt my holly cab. Then add a msd blaster coil form hi only and new cap & rotor. After I installed, I also recheck my firing order and checked that it is timed starting tds on #8. I'm now getting a back fire, like a popping back fire. I have a holly distributor. I did loosen the distributor and move by hand to see if I could get it to run better. Fyi I have not taken a timing light to it yet. I will tonight. Any help would be awesome.

Thanks
jason

 

[Robert Kenney]

Jason,
it will run but pop's back through the carb? If so recheck that you had the correct spark plug wire order at the cap.

If it pops and won't start make sure you had the correct tdc on #8 when you wired the dizzy. You will have two tdc/power stroke, one at tdc between the compression and power stroke and one between the exhaust and intake stroke.

 

[Jason]

Hey Robert,
thanks for getting back to me. I should have said in my first posting that the motor starts right up and idles. I did check the spark plug wire order a few times. The back fire is more coming out of the exhaust when you crack the throttle.

Jason

 

[Robert Kenney]

How did it run before the carb redo? Is the idle smooth with no limp or miss.

The new coil will place a higher demand on your ignition system.

Sounds a lot like ignition so we've got to make sure all of that is correct. Electronic or points? If points verify dwell (don't have the spec off hand).


Verify the squirters are working immediatly off of the idle stop.

 

[Jason]

Sorry it has taken me so long to respond.
Robert,
it was running good before I redid the carb. It idles smooth and fires right up. I put the old coil back on and it runs better. I have a stumble when you step on the gas. Do you think if I change out my points and put in pertronix ignitor kit with my new hotter coil that would help? Oh and yes my squirters are working immediatly off idle.

Thanks again for any help.
Jason

 

[Robert Kenney]

No problemo! Not everybody is an IH/car addict like us.

If it ran good before, why did you rebuild the carburetor? Really sounds like two issues first do the ignition then if the flat spot still exists we can get back to the carb stuff.

Well the result of changing in the old coil says the points are either in need of a good adjustment or replacement and adjustment. The blaster coil will be a nice upgrade if the rest of the system is up to snuff. I stress the correct dwell setting to ensure you get good coil saturation. Also see that the distributer bearings are not wasted and loose. Excessive lateral or vertical clearance will do you in.

Points will work fine ..........but in todays world for a driver why not go electronic and "86" the points. The pertronics latest model module can fire your blaster or a msd series 6 cd box and blaster coil and give you a better ignition platform that IH ever dreamed of. The pertronix and blaster alone is fine for basic driving though. Possible causes are a weak run resistance balast or wire also.

After the ignition is up to par see how it runs.

You need to hit one system at a time so we can correlate fixes with results.

 

[Jason]

Hey Robert,
I finely had a sec to get back to my problem. I installed pertronix, blaster coil, and new wires. It started right up and ran so smooth! But I still have my stumble when I step on the gas. A guess we are back to my crab rebuild. I have a 2210 holly in my scott. Any hints into what I should look at? Maybe I need to start a new post.

Thanks
jason

 

[Robert Kenney]

Great progress!! Still hesitating, where is the timing? To far retarded will cause a lean condition at low speed. I would turn in a few more degrees of advance and see if it gets better when at full temp.

Many things can cause the condition, poor pcv valve, inop vacuum advance canister, slop in accel pump linkage, low fuel level in bowl or egr valve opening to early. There are others but this is a start.

 

[Michael Mayben]

Definitely do the power timing drill explained in the sticky thread at the top of this sub-forum.

You must start all over with timing when installing a p-tron.

We need to know which "slot" the link rod is in on the accel pump actuator lever. And the link rod must be adjusted (bent) so that there is an immediate pump shot with the slightest movement of the throttle lever. Imperative.

 

[Jason]

Thanks for the tip's! I will do the power timing tonight to see if that helps.
Now I'm in the bottom slot and when I put the crab back together I did have to bend the arm that goes to the a tab on the top of the carb that open and closes. Sorry I don't know what that part is called. Is that where is should be?

Jason

 

[Robert Kenney]

I marked up one of your carb photos with the linkage move to give you a bigger pump shot. The same applies to teh linkage slop after the move, there should be none.