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landlord2110

backfire with new Nova II

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landlord2110
Just installed new Nova II electronic ignition & worked great except I get a backfire once in a while. It backfires when starting or reving up & down rapidly. Is this a matter of carb adj?

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BLT
If that is on your CI Briggs 10HP, I had the same problem. I ended up wiring trigger unit thru the points and the problem went away. The points are camshaft operated and run at half engine speed. Mine is a Mega Fire and has been running that way since 1990.

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BLT
quote:
Originally posted by rsnik
Bob, I could not get a Mega Fire to work properly on my 2010. What is a "trigger unit through the points"?
The trigger is the 'Mega-Fire' unit and I wired in to replace the condenser. I made a sketch a long time ago, as I was going to a couple of other condensers and install the Mega-Fire, but the existing condensers are still working and if it isn't broke don't fix it. Some where I have a sketch but can't find it.

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BLT
quote:
Originally posted by BLT
quote:
Originally posted by rsnik
Bob, I could not get a Mega Fire to work properly on my 2010. What is a "trigger unit through the points"?
The trigger is the 'Mega-Fire' unit and I wired in to replace the condenser. I made a sketch a long time ago, as I was going to a couple of other condensers and install the Mega-Fire, but the existing condensers are still working and if it isn't broke don't fix it. Some where I have a sketch but can't find it.
I found the sketch in my Briggs stuff. PM me if you are interested.

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rsnik
My bad Bob. I thought you were saying you have a unique and different method of wiring up a Mega Fire. I have either a Mega Fire or Nova II on all my tractors with points except the 2010. I ended up with a repolarized flywheel and a post 1982 Magnatron 2 coil on that engine. If anybody wants to know, wiring a Mega Fire 2 is easy as pie. Hold the chip up in the air with the front facing you and the spade connectors in the air. Attach a pig tail to the left spade and that pig tail must be grounded, typically by just by running the screw you mount the chip with (must be grounded) through the pan head terminal on the pig tail. Oh heck, here's a pic:


Cut your points wire at some ideal spot and connect both ends of the cut points wire and your kill wire to the other pig tail. You are all set. Actually, come to think of it, my 101 LL runs on points. I installed this Mega Fire and got no spark. I am getting old and probably overlooked something simple. The points and condenser were in excellent condition (proves the rule of "if it ain't broke don't fix it) so I just reinstalled the points and condenser and it runs like a red tape.

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dentwizz
The reason is that the energy required to run a Megafire is a little higher than the Magnetron or Old style coil/points. The spec if I recall is 250 rpm come-in speed for Briggs OEM and 400 for Megafire/Atom modules. Someone touched on the gap issue. Yes the gap is critical to both energy and timing. Make sure you start with a fresh CJ-8 plug(I tried J-19) and set it to .020. You may need to extend the gap a minor amount to achieve retarded timing or reduce to advance it.

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BLT
I kept the points and and installed the Mega Fire in place of the condenser as per the attached sketch. That eliminated the backfiring on start. I mounted the Mega Fire outside on the point box to ground it.
[img]/club2/attach/BLT/MegaFireBriggsc.jpg[/img]

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powerking_one
Bob, With your diagram of how you wired in the Nova-II module, 1) I would think the ignition performance would be terrible; 2) Having the module in series like shown makes the ignition system still a breaker points based system in that the full primary coil current is still going through them. Thus the module is doing nothing for you. I'm somewhat surprised this setup even works. IMHO, you might as well just remove the Nova-II module. These types of modules are basically voltage threshold trigger devices and at that threshold, they behave as a high current short circuit (mimicking the breaker points function). Tom (PK)

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dentwizz
Agreed. The concept of the module is to replace the points and condenser entirely. If this arrangement is functional, you essentially just need a new condenser instead of the module.

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msiebern
I tried Bob's fix and it is working nicely on my 2012. It would be almost impossible to start sometimes due to serious firing on the wrong cycle. Without the points it tries to fire every revolution. I may try playing with the spark gap, but all I can say is that it was a PIA to start before routing it through the points.

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