need wisdom?

waypastcrazy · 07-07-2007, 07:49 PM

ok i am helping a buddy work out some bugs. got a dss 331 victor jr heads and intake comp 280 290 i beleive not quiet sure has 560 580 lift msd 6al new and new msd dizzy 750 promform dp comectic mls .100 head gaskets 1.7 rollers ok here it is engine cold is running fine after you turn it up or get warm setting at idle it will have a loud backfire in exhaust. i am thinking plug not dissipating heat good. something in dizzy or plug wire. or engine to frame ground bad.not so sure about these plugs they are the ones that have a flat plug to head seal not tapered they look small to. they are autolite 3924.I have never run the victor jr heads so I am not familiar with which plug and gap to use.any help would be greatly appreciated. thx ps i also have fixed all header leaks. what bugs me is just idlingit will do it. have also swapped carb off my gt which runs great

coupe · 07-07-2007, 10:42 PM

Maybe one of the holes not getting an equal fuel/air distribution? Is there a carb spacer being used? The plugs are the right number, They are a good heat range too, I don't think that's the problem, unless they're gapped like .060. They should be anywhere from .035-.045.

Check also to see that there's not a fuel line running near an exhaust. That might be causing fuel vapor lock at warm temps. And check pressure. Fuel pressure gauge will help you out.

Craig K. · 07-07-2007, 10:53 PM

Quote:

Originally Posted by coupe

Maybe one of the holes not getting an equal fuel/air distribution? Is there a carb spacer being used? The plugs are the right number, They are a good heat range too, I don't think that's the problem, unless they're gapped like .060. They should be anywhere from .035-.045.

Matt,

With the MSD he should be running a higher gap, or atleast I always did in the '85, I ran around 40-45 once and the engine ran like crap, open the gap to around 60 and it would rev real nice.

Have you pulled the plug wires off and checked them with an ohm meter, and made sure all the ends are crimped well? What is the timing set at, is it high enough?

coupe · 07-07-2007, 11:07 PM

timing is a good idea. what type of advance on it? I know MSD and other high-energy spark systems allow more gap, but never really thought it a requirement. Some engines take different to things. Checking it out would not hurt.

97cobrasvt · 07-07-2007, 11:47 PM

Quote:

Originally Posted by coupe

timing is a good idea. what type of advance on it? I know MSD and other high-energy spark systems allow more gap, but never really thought it a requirement. Some engines take different to things. Checking it out would not hurt.

I run my gap at 35 with a full msd set up.

Blown 5.0 · 07-08-2007, 05:59 AM

Rotor phase, MSD says that their dis. are rotor phased from the factory,Not always true.

waypastcrazy · 07-08-2007, 08:14 AM

no carb spacer. gap has been at .50 then now at .45 fuel line is away frome exhaust and already have pressure gauge.plug wire ohmed good and have played with timing already it is at 40 right now.it is amechanical advace. tried all the combonations of springs yesterday.rotor phase ok got my attention how do i check rotor phase?

waypastcrazy · 07-08-2007, 08:39 AM

the rotor is not the adjustable one do i need to get one to phase the rotor thx

Italian LX · 07-08-2007, 11:53 AM

Quote:

Originally Posted by waypastcrazy

. . .not so sure about these plugs they are the ones that have a flat plug to head seal not tapered they look small to. they are autolite 3924.

The 392x series of plugs comes with a gasket (metal tapered washer) that is required for proper sealing. It sounds like whomever put those plugs in may have just thrown them away. I suggest buyinh a new set and using the gaskets. The flat edge of those plugs will not seal properly without them.

waypastcrazy · 07-08-2007, 12:15 PM

have already changed plugs and they do have the metal gaskets thx

07-07-2007, 07:49 PM	#1
waypastcrazy ADDICTED TO SMALL BLOCKS Join Date: Jan 2007 Location: lookout mt Posts: 1,757	need wisdom? ok i am helping a buddy work out some bugs. got a dss 331 victor jr heads and intake comp 280 290 i beleive not quiet sure has 560 580 lift msd 6al new and new msd dizzy 750 promform dp comectic mls .100 head gaskets 1.7 rollers ok here it is engine cold is running fine after you turn it up or get warm setting at idle it will have a loud backfire in exhaust. i am thinking plug not dissipating heat good. something in dizzy or plug wire. or engine to frame ground bad.not so sure about these plugs they are the ones that have a flat plug to head seal not tapered they look small to. they are autolite 3924.I have never run the victor jr heads so I am not familiar with which plug and gap to use.any help would be greatly appreciated. thx ps i also have fixed all header leaks. what bugs me is just idlingit will do it. have also swapped carb off my gt which runs great Last edited by waypastcrazy; 07-07-2007 at 07:54 PM.

07-07-2007, 10:42 PM	#2
coupe Super Moderator Join Date: Dec 2004 Posts: 6,313	Maybe one of the holes not getting an equal fuel/air distribution? Is there a carb spacer being used? The plugs are the right number, They are a good heat range too, I don't think that's the problem, unless they're gapped like .060. They should be anywhere from .035-.045. Check also to see that there's not a fuel line running near an exhaust. That might be causing fuel vapor lock at warm temps. And check pressure. Fuel pressure gauge will help you out. __________________ " If you can't explain it simply, you don't understand it well enough. " - Albert Einstein

07-07-2007, 11:07 PM	#4
coupe Super Moderator Join Date: Dec 2004 Posts: 6,313	timing is a good idea. what type of advance on it? I know MSD and other high-energy spark systems allow more gap, but never really thought it a requirement. Some engines take different to things. Checking it out would not hurt. __________________ " If you can't explain it simply, you don't understand it well enough. " - Albert Einstein

07-08-2007, 05:59 AM	#6
Blown 5.0 Senior Member Join Date: Jan 2006 Location: Looking for more ways to add BOOST Posts: 167	Rotor phase, MSD says that their dis. are rotor phased from the factory,Not always true. __________________ Hauling A** on Pump Gas !!!!!

07-08-2007, 08:39 AM	#8
waypastcrazy ADDICTED TO SMALL BLOCKS Join Date: Jan 2007 Location: lookout mt Posts: 1,757	ps the rotor is not the adjustable one do i need to get one to phase the rotor thx

07-08-2007, 08:14 AM	#7
waypastcrazy ADDICTED TO SMALL BLOCKS Join Date: Jan 2007 Location: lookout mt Posts: 1,757	no carb spacer. gap has been at .50 then now at .45 fuel line is away frome exhaust and already have pressure gauge.plug wire ohmed good and have played with timing already it is at 40 right now.it is amechanical advace. tried all the combonations of springs yesterday.rotor phase ok got my attention how do i check rotor phase?

07-08-2007, 12:15 PM	#10
waypastcrazy ADDICTED TO SMALL BLOCKS Join Date: Jan 2007 Location: lookout mt Posts: 1,757	plugs have already changed plugs and they do have the metal gaskets thx