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engine backfiring

General engine tech -- Drag Racing to Circle Track

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chevy art
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engine backfiring

Post by chevy art » Wed Oct 02, 2019 2:08 pm

would a bad ignition box(or going bad) cause an engine to belch flames out carb, sometimes start and run for only about 2 seconds, and sometimes just keep cranking and doing nothing(no combustion at all), this is my 3rd mallory hy-fire V box in car as the 1st 2 just started doing misfires etc and the 2nd just popped and quit when i turned it on. planning on putting in my mallory hy-fire7 box in(think its # 667c). any other ideas about why my car has these problems(ignition??). distributor did not move and the jessel belt is in place. thanks Art in NY

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Re: engine backfiring

Post by ClassAct » Wed Oct 02, 2019 2:26 pm

chevy art wrote:
Wed Oct 02, 2019 2:08 pm
would a bad ignition box(or going bad) cause an engine to belch flames out carb, sometimes start and run for only about 2 seconds, and sometimes just keep cranking and doing nothing(no combustion at all), this is my 3rd mallory hy-fire V box in car as the 1st 2 just started doing misfires etc and the 2nd just popped and quit when i turned it on. planning on putting in my mallory hy-fire7 box in(think its # 667c). any other ideas about why my car has these problems(ignition??). distributor did not move and the jessel belt is in place. thanks Art in NY


Did you contact Dave Telling? He's always responded quickly to any email I've sent him. I'd email him and ask him. Most of that Mallory stuff was stone reliable. I can't imagine 3 boxes all being bad and all doing the same thing.

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Re: engine backfiring

Post by FC-Pilot » Wed Oct 02, 2019 2:33 pm

With three boxes all being suspect I would check my wiring, then give all the basics a serous once over. I would also run the valves and make sure I don’t have a valve to tight and holding a valve open.

Paul
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Re: engine backfiring

Post by rebelrouser » Wed Oct 02, 2019 2:48 pm

Its all the basics, fire, fuel, compression, all at the right time. First thing I always do is a leak test to see if the engine will hold air. I like to use an ignition oscilloscope, I purchased a used snap-on modis very reasonably, you can tell a bunch if you can read a scope pattern. Cheapest way is to buy a spark checker, and just keep opening up the gap to see how many KV's the coil can jump a spark. I want to see at least 20KV at the plug. At the right time takes a little more effort, but a couple years ago I had an engine that popped and banged, customer had the cam card and swore it was 4/7 swap, but it was not, swapped the plug wires and it ran fine. Then the easiest to check is fuel, I like to check the specific gravity if it has been sitting, seen old gas do some weird things.

https://shop.advanceautoparts.com/p/aut ... lsrc=aw.ds

bill jones
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Re: engine backfiring

Post by bill jones » Wed Oct 02, 2019 3:06 pm

---might want to look at this link
---the errant sparks are pretty common.

http://www.ryanbrownracing.com/Bill_Jones_Page_11.html

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Re: engine backfiring

Post by ProPower engines » Wed Oct 02, 2019 5:42 pm

If the wiring to and from the box are in question as well as the rest of the system it can screw a box. resistance in the wrong ways can cause circuits to just burn up leaving you stranded.
If this is the 3rd box thats quit I would question all of the wiring for the system. A high voltage draw can cook a box in no time rendering it useless.
The pick up in the dist could also be bad as well as the coil. These will also cause no start issues as well.

I see it all the time where guys just replace the box and have issues cause they do not check the entire systems
connections to be 100% SURE ITS ALL GOOD.
Real Race Cars Don't Have Doors

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Re: engine backfiring

Post by bill jones » Wed Oct 02, 2019 5:49 pm

---for my stuff I build these threaded plugs to seal off the holes and short enough to allow the rotor over them.
plastic covers installed into cap adapter.jpg
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chevy art
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Re: engine backfiring

Post by chevy art » Wed Oct 02, 2019 9:58 pm

thanks guys for all the info. first of all the car had just ran a 10.64, 10.59 and 10.65. the last pass was perfect and engine ran like a charm. when i let off the gas the car popped a bit as it was de-acellerating. at end of track it would not idle and i had to really give it plenty of gas to get back to my pit area. tried to start it a little while later and it would belch and shoot a fire out of carb and sometimes just start and die. my cars engine loosens up every bolt on the engine after a few runs and after my last run i found something really crazy, the 4 carb hold down bolts were completely loose and i mean loose. tightened them up but still had same problem. at home a week later i took carb off, put in new front power valve and new gaskets on carb and under the spacer and under the carb. still have the same problem as of now.could be some wires to ignition box got loose and i will check out the distributor real good and i will check the wires to coil and will check the module in distributor. the 3 mallory boxes always had trouble with rev limiter and just staying in good shapre. took 25 years to use up the 3 mallory boxes. alot of guys had trouble with them back in the 1980s and 90s and just wouldnt use them. i always had good luck with them when they were working. car would come through the traps at 8,ooo rpms and never missed a beat.. i got 3 of them because alot of guys just would not use them at all. guess im done with them too. putting in thr hy-fire 7 and hope that solve the problem. i will definitely keep this post going and let you all know what the problem is. thanks again Art in NY

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Re: engine backfiring

Post by Geoff2 » Thu Oct 03, 2019 5:40 am

Check the dist. If it has a mag p/up, check that none of the reluctor tips make contact with the pole pieces [ must have an air gap ]. Worn shaft/bushings could allow contact.

Check the cap & rotor for carbon tracks/arcing.

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Re: engine backfiring

Post by novafornow » Thu Oct 03, 2019 12:49 pm

Had trouble early this year. It was the rotor that i replaced over the winter as "maintenance".

6.50camaro
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Re: engine backfiring

Post by 6.50camaro » Thu Oct 03, 2019 1:57 pm

Your description almost sounds like when I've tried to start a motor with the timing not advanced enough after having the distributor out and not marking where it was . Dan

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Re: engine backfiring

Post by bobmc » Thu Oct 03, 2019 2:42 pm

won't run after a pass sounds like it's out of fuel, do you have a fuel pressure gauge you can see during a run?

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Re: engine backfiring

Post by Kevin Johnson » Thu Oct 03, 2019 4:43 pm

ProPower engines wrote:
Wed Oct 02, 2019 5:42 pm
If the wiring to and from the box are in question as well as the rest of the system it can screw a box. resistance in the wrong ways can cause circuits to just burn up leaving you stranded.
If this is the 3rd box thats quit I would question all of the wiring for the system. A high voltage draw can cook a box in no time rendering it useless.
The pick up in the dist could also be bad as well as the coil. These will also cause no start issues as well.

I see it all the time where guys just replace the box and have issues cause they do not check the entire systems
connections to be 100% SURE ITS ALL GOOD.
The Molex connectors on my CNC stepper motors are only engineered to be removed/reconnected a maximum of 30 times. I talked to a tech and he said there are specs like this for all the connectors in an engine compartment. The amount of vibration you are describing and the age/history of the components likely means the connectors will all need to be replaced.

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