Engine Pops When Cold

blykins · #1 (**permalink**) 10-02-2003, 04:32 PM

Hey Guys...

Lately since the weather has changed and it's gotten significantly colder, my engine has been popping like a firecracker until it warms up. It's a 425W stroker, Demon 750, MSD 6AL (with full battery charge), and open headers. I can't seem to figure it out...but it's just done it in the past week since it's been colder outside. It doesn't have a choke...and it's not really hard to start...but when it does it pops really loud until it gets some heat in it. It kinda sounds like you're setting off a rack of firecrackers...just not that rapid in succession. I thought it could be the MSD box not being able to work properly due to a low battery charge...so I charged it overnight...and it did the same thing. Could it be that this is a normal thing, and it just sounds funky with open headers?...do I have water in the gas?....any ideas guys? Like I said, it just does it for the first 20-30 seconds or so...but if you rev it a little to build some heat in it, it stops and never does it again until the next day when the engine is completely cold. This has got me puzzled...it's probably nothing, but I like to worry about insignificant things. :-)

Thanks.

blykins · #2 (**permalink**) 10-02-2003, 06:38 PM

Anyone?

decooney · #3 (**permalink**) 10-02-2003, 07:56 PM

Did you change the jets in the Demon carb? If so, what were they before and what are they now; primary and secondary.

What # discharge nozzles are on the carb?

What are your idle mixture screws set at now? You can turn/count the turns in and start from scratch again too...

Are you sure you don't have some sort of a vacuum leak somewhere?

Did you run the car with this same engine and carb during a previous year of colder months, and did it do this then?

...just a guess, but I'm wondering if the popping you are hearing is a lean condition til the motor warms up just a tad...

Check your fuel pressure too. What is it?

KobraKarl · #4 (**permalink**) 10-02-2003, 08:57 PM

are you popping through the carb? or the pipes?...I'm guessing you meen the pipes.

header leakes will cause pipe popping , if you have a couple of small leaks when cold they may dissapear when either your heads or header connections get hot and swellup ,closing the leak

Just guessing KK

blykins · #5 (**permalink**) 10-03-2003, 03:44 AM

Duane, yes I have changed the jets...both primary and secondary. They were 68 and 72 from the factory I believe...now they are 88 and 98. We kept changing them in the dyno room, because the engine wasn't running rich enough in the mid range.

Not sure about discharge nozzles...pretty sure I don't have a vacuum leak as all ports are plugged except for the PCV.

I built the engine in March, so no....it's not really seen any cold weather at all.

I don't know what the fuel pressure is...it's a 7psi Holley electric fuel pump though. I guess I should buy a gauge...

I figured if anything, it would be really rich in the cold months...since the air is so dense, it would cause more fuel to be taken into the engine...but that was just a theory of mine. :-)

Karl....I'm popping through the pipes. They're very short headers from Shell Valley...no collectors on them. I had thought I had a header gasket leak the whole time...but have never changed them. You may be onto something.

If you guys can think of anything else, I would be very grateful. Like I said, I don't think it's anything bad...but I just wanna be on the safe side with a $9k engine.

Cracker · #6 (**permalink**) 10-03-2003, 07:02 AM

My car does the same thing most of the time. In my case it simply is a case of slightly fouled plugs that just needed to be cleaned (burned) off oil. May not be the case with yours but I can rev mine after warm at about 4K rpm for a 1/4 mile and it's fine from there on. Best wishes!

GOCATS · #7 (**permalink**) 10-03-2003, 07:08 AM

My mixture is a little on the rich side.. but that is how Bennett built the motor. I have also noticed that I get a little bit of popping out of the pipes. I wonder if your plugs could be a little fouled up? The only other thing I can think to check is the plug wires and connection. I had a bad plug wire on #1 cylinder caused it to run real rough. Never would have thought brand new plug wires from Ford Racing would be bad with less than 500 miles on the car last year. It is always the things you least expect. But that's why we love these things..

J.A.

Bill Wells · #8 (**permalink**) 10-03-2003, 07:12 AM

mine popped big time and low rpm's when cold and it was the idle mixture being too rich, reset the idle screws and voila, no more popping in cold or warm/hot weather...sometimes it is easy things, other times ya chase one problem only to find out there are more than one !! good luck. looks like you already have a shopping list of what to look for/check out. bill.

Kputz · #9 (**permalink**) 10-03-2003, 07:22 AM

Sounds more like condensation in the distributor to me. This is a common problem when cars are stored for long periods or when covered or when cold weather comes.