backfiring trouble

carboy · 02-08-2002, 11:48 PM

what would make both valve cover caps get blown off when my engine is trying to start and it backfires. this is a newly rebuilt engine and i seem to have the timing correct now. it scared the hell out of me when it happened and a little bit of smoke came out of the hole in the top of the valvecovers where the grommet is where my caps go.. the engine is finally running good now. someone told me i should replace the power valve on my holley since it isn't idling correctly.
anyone got any experience with this.

PKRWUD · 02-09-2002, 02:28 AM

If you had a backfire through the intake, you need to replace your power valve. They are very delicate. The only way I can think of to have a backfire blow your caps off would be a burnt piston (which you don't seem to have), or an intake backfire that was so violent it blew back through the PCV hose, with no (or a bad) PCV valve in place.

Take care,
-Chris

carboy · 02-09-2002, 09:41 PM

thanks for the info. that makes sense about the fumes backing into my valvecovers through the pcv hose, could that be why i would need to put a pcv valve into my valvecover?

PKRWUD · 02-09-2002, 10:48 PM

Yes. The PCV valve serves two purposes. It regulates the flow of crankcase gasses back into the intake for burning in such a way that you don't run lean, and it acts as a one way check valve in case of an intake backfire, preventing it from reaching the crankcase. If you have a hose going from your valve cover to a manifold vacuum source, usually on the carburetor throttle plate, it MUST have a pcv valve installed in line.

Take care,
-Chris

carboy · 02-10-2002, 12:36 AM

thanks Chris
that all makes sense. my dad was a crack mechanic and he worked for rolls royce for 20+ yrs. he was allways able to help me out and train me on a lot of engine knowledge. now that He's passed on i just have to rely on asking questions everywhere from everyone on the internet and around town. i have only been in Corpus Christi for 2 yrs now and am just starting to connect with some knowledgable car guys.
i just happened on this web site about 2 yrs ago and you and the other guys on this site have really helped me out.
thanks again!
David H.
p.s. i'll be at the parts store tomorow and get that pcv valve.

PKRWUD · 02-10-2002, 01:47 AM

Dave-
I'm sorry to hear about your Dad. That's gotta be rough. There are some pretty smart people on this site, who will be happy to help you. You can email me if you need to ( pkrwuds@pacbell.net ).

Don't forget your Holley parts too! You'll need a power valve (probably a 65), and a bowl gasket and a metering plate gasket.

One more thing, no matter where you ask for info, who ever it is that gives it should be able to explain it so that you can understand why the solution is what they are suggesting. If they can't, then verify the info with someone who can, before acting on it.

Take care,
-Chris

02-08-2002, 11:48 PM	#1
carboy Registered Member Join Date: Jan 2000 Location: Corpus Christi, Texas Posts: 66	backfiring trouble what would make both valve cover caps get blown off when my engine is trying to start and it backfires. this is a newly rebuilt engine and i seem to have the timing correct now. it scared the hell out of me when it happened and a little bit of smoke came out of the hole in the top of the valvecovers where the grommet is where my caps go.. the engine is finally running good now. someone told me i should replace the power valve on my holley since it isn't idling correctly. anyone got any experience with this. __________________ 66 coupe, 306 balanced bluprinted, performer intake,725 Road Demon, Crane Cam, Tri-Y Headers, factory Shelby glass packs 2 1/4 with exit in front of rear wheels, 3:50 rear, 8 inch rear, mustang plus suspension, 41/2 mideye leafs, 620 springs on front, kyb gas shocks. tony branda shelby hood, r-model valance, rear side scoops(functional),stainless steel slotted front brake system,,13.39 1/4 mile with no slicks and no posi.

02-09-2002, 02:28 AM	#2
PKRWUD Junior Member Join Date: Mar 1999 Location: Ventura, California Posts: 8,981	If you had a backfire through the intake, you need to replace your power valve. They are very delicate. The only way I can think of to have a backfire blow your caps off would be a burnt piston (which you don't seem to have), or an intake backfire that was so violent it blew back through the PCV hose, with no (or a bad) PCV valve in place. Take care, -Chris __________________ Webmaster: Rice Haters Club Jim Porter Racing Peckerwoods Pit Stop Support Your Local RED & WHITE!

02-09-2002, 09:41 PM	#3
carboy Registered Member Join Date: Jan 2000 Location: Corpus Christi, Texas Posts: 66	pcv valve? thanks for the info. that makes sense about the fumes backing into my valvecovers through the pcv hose, could that be why i would need to put a pcv valve into my valvecover? __________________ 66 coupe, 306 balanced bluprinted, performer intake,725 Road Demon, Crane Cam, Tri-Y Headers, factory Shelby glass packs 2 1/4 with exit in front of rear wheels, 3:50 rear, 8 inch rear, mustang plus suspension, 41/2 mideye leafs, 620 springs on front, kyb gas shocks. tony branda shelby hood, r-model valance, rear side scoops(functional),stainless steel slotted front brake system,,13.39 1/4 mile with no slicks and no posi.

02-09-2002, 10:48 PM	#4
PKRWUD Junior Member Join Date: Mar 1999 Location: Ventura, California Posts: 8,981	Yes. The PCV valve serves two purposes. It regulates the flow of crankcase gasses back into the intake for burning in such a way that you don't run lean, and it acts as a one way check valve in case of an intake backfire, preventing it from reaching the crankcase. If you have a hose going from your valve cover to a manifold vacuum source, usually on the carburetor throttle plate, it MUST have a pcv valve installed in line. Take care, -Chris __________________ Webmaster: Rice Haters Club Jim Porter Racing Peckerwoods Pit Stop Support Your Local RED & WHITE!

02-10-2002, 12:36 AM	#5
carboy Registered Member Join Date: Jan 2000 Location: Corpus Christi, Texas Posts: 66	buying a pcv thanks Chris that all makes sense. my dad was a crack mechanic and he worked for rolls royce for 20+ yrs. he was allways able to help me out and train me on a lot of engine knowledge. now that He's passed on i just have to rely on asking questions everywhere from everyone on the internet and around town. i have only been in Corpus Christi for 2 yrs now and am just starting to connect with some knowledgable car guys. i just happened on this web site about 2 yrs ago and you and the other guys on this site have really helped me out. thanks again! David H. p.s. i'll be at the parts store tomorow and get that pcv valve. __________________ 66 coupe, 306 balanced bluprinted, performer intake,725 Road Demon, Crane Cam, Tri-Y Headers, factory Shelby glass packs 2 1/4 with exit in front of rear wheels, 3:50 rear, 8 inch rear, mustang plus suspension, 41/2 mideye leafs, 620 springs on front, kyb gas shocks. tony branda shelby hood, r-model valance, rear side scoops(functional),stainless steel slotted front brake system,,13.39 1/4 mile with no slicks and no posi.

02-10-2002, 01:47 AM	#6
PKRWUD Junior Member Join Date: Mar 1999 Location: Ventura, California Posts: 8,981	Dave- I'm sorry to hear about your Dad. That's gotta be rough. There are some pretty smart people on this site, who will be happy to help you. You can email me if you need to ( pkrwuds@pacbell.net ). Don't forget your Holley parts too! You'll need a power valve (probably a 65), and a bowl gasket and a metering plate gasket. One more thing, no matter where you ask for info, who ever it is that gives it should be able to explain it so that you can understand why the solution is what they are suggesting. If they can't, then verify the info with someone who can, before acting on it. Take care, -Chris __________________ Webmaster: Rice Haters Club Jim Porter Racing Peckerwoods Pit Stop Support Your Local RED & WHITE!

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