Moparts Tech Archive
Fuel System
Holley Q ?'s
How can you tell when your Power Valve is blown?da demon
Moparts Member
Posts: 313
From: Genoa, Illinois, USA
Registered: May 2001
posted 05-21-2002 11:33 AM
Picked up the Demon last night after my brother-in-law finished the brake conversion (came out real well). Now, it just does'nt 'sound right' when starting. Not running a choke and it's been real cold here, so I expected it to fight me starting, but I got my first backfire out of it. Figured my bro. had the same problem when test driving it, but he's not used to it like I am and maybe he got a BIG backfire and popped the P.V. (it's a big Holley). Seems OK at all RPM's, power and launches. Was still a little hard starting even after it got warm (never did that before). Would a damaged P.V. be really obvious? (Also for the first time, noted the smoke from the backfire seep under the dash by the glove box - the evening sun was just right I guess, what's up with that?) DD
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Scotty
Moparts Member
Posts: 1396
From: Lumberton, TX
Registered: Nov 1999
posted 05-21-2002 11:47 AM
I would think that you would have a whole bunch of black smoke out the tailpipe if it were blown. Hard starts are possible, too. It will drain the fuel bowl when it's not running and possibly flood it. Pull it out and check it if you're not sure.
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69 1/2 Sixpack Bee
Moparts Member
Posts: 964
From: Ontario, California USofA
Registered: Nov 1999
posted 05-21-2002 02:05 PM
With the engine idling look down the throat of the carb. If you see fuel being exerted out of the booster venturis (the ring shaped "thingys") then it is blown.
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WingCars
Moparts Member
Posts: 1342
From: Cherry Hill New Jersey USA
Registered: Aug 2001
posted 05-21-2002 02:19 PM
All the above and wont want to idle as its getting excessive fuel .And burning eyes and black fouled plugs to.The backfire is known to blow out the power valve on holleys
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da demon
Moparts Member
Posts: 313
From: Genoa, Illinois, USA
Registered: May 2001
posted 05-21-2002 03:23 PM
Thanks, guys. I knew the P.V. was subject to damage via the backfire, that's why I thought of this first. Suppose maybe electrical too. If the ballest resistor or a harness got knocked around during the brake refit. I'll check it out tonight. DD
(Forgot to mention that it seemed to catch when releasing the key from cranking, AKA a bad dual ballest resistor)
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shwing.er
Moparts Member
Posts: 942
From: south bend, indiana
Registered: Jan 2002
posted 05-21-2002 04:20 PM
a PV protection kit is available and installs fairly easy.....
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Ramman
New Member
Posts: 88
From: Findlay ,Ohio
Registered: Apr 2001
posted 05-21-2002 05:03 PM
All of the above plus the idle mixture srews will have little or no effect on idle quality, since it's already way rich at idle with a blown valve.
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mopardad
Moparts Member
Posts: 371
From: Manheim Pa.
Registered: Sep 2001
posted 05-21-2002 05:10 PM
Lift the carb & see if there is fuel dripping out of the holes that feed vacuum to the PV.
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dbdartman
Moparts
Posts: 3981
From: Trenton, NJ
Registered: Nov 1999
posted 05-21-2002 05:15 PM
Single ballast & it doesn't fire until you release the key to the run position? Bad ignition switch. Been there, done that, got the T-shirt!
DB
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da demon
Moparts Member
Posts: 313
From: Genoa, Illinois, USA
Registered: May 2001
posted 05-22-2002 11:13 AM
Success!! Took all of 5 seconds to see a wire had pulled off a ballast resistor terminal (obviously the start side).
Gave me a chance to look closely at the cobbled/cut/screwed up wiring harness under the hood. I must have forgotten, but it's a real piece of work. Oh goodie, another project
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Holley Carb won't idle down, Why?
demon34071
New Member
Posts: 20
From: Warwick, RI USA
Registered: Oct 2002
posted 01-12-2003 05:42 PM
A friend of mine just did some modifications to his Holley 3310 750 cfm. This is what was done. He milled the choke horn off. Added a power valve protection kit. Upped his jets from68s to 72s and put a new power valve 6.5 with a 1 inch fenolic spacer. The motor seems to run very smoothly but we can't get it to idle below 1200 rpm. It idled at about 900 rpm before. The idle screw is backed out all the way, the linkage is not hooked up yet. Any ideas? Thanks Bill.
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Don1
Moparts Member
Posts: 5253
From: Valley City, ND. USA
Registered: Oct 2001
posted 01-12-2003 05:46 PM
Have you tried to adjust the idle mixture screws on the front metering block. If this won't change it there is very posibly a vacume leak.
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70340DART
Moparts Member
Posts: 717
From: SAN FRANCISCO CA USA
Registered: Jun 2000
posted 01-12-2003 05:46 PM
Check for a vacume leak or interference with the spacer. also recheck timing.
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70SPRTSAT
New Member
Posts: 42
From: Newark,Ca. USA
Registered: Dec 2002
posted 01-12-2003 05:49 PM
it sounds like the secondary plates are being held open. you should be able to look in with flashlight and see.
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Glen
Moparts Member
Posts: 1433
From: Pacific Northwest
Registered: Dec 1999
posted 01-12-2003 05:51 PM
Did he use a different base gasket? I wonder if the problem could be a vacuum leak there.
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demon34071
New Member
Posts: 20
From: Warwick, RI USA
Registered: Oct 2002
posted 01-12-2003 06:30 PM
We checked for vac leaks it does not seem to have any. I checked the secondarys to see if they might be hanging up they are not.all the base gaskets are new. Also tried moving the timing. If you pull the throttle forward with your hand it will come down. But it is too much pressure for the return springs to supply. It would wear the throttle plate bushings also. Is tis one of those times you drill holes in the throttle plates? Bill.
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70SPRTSAT
New Member
Posts: 42
From: Newark,Ca. USA
Registered: Dec 2002
posted 01-12-2003 06:48 PM
if you can pull on the linkage and the idle comes down it sounds like the primary plates are being held open.look inside. you may even have to remove the carb to get a good look. check for bound/misadjusted linkage. if it's a vacuum leak you should be able to "hit it" with carb clean and the idle quality should change.
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dlgrossman
New Member
Posts: 80
From: N.E. OHIO
Registered: Dec 2002
posted 01-12-2003 09:44 PM
If its idles too fast with throttle linkage hooked up, maybe linkage is too short now that carb is higher. Also bigger jets mean richer idle mixture-- may be out of range of adjustment.
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Chico
Moparts Member
Posts: 486
From: NH ,USA
Registered: Nov 2000
posted 01-12-2003 09:55 PM
The spacer raised the carb and affected the throttle cable. Not enough slack!
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wayne_township
Moparts Member
Posts: 3659
From: Rural Eastern, IA USA Baby! Or is it the NW burbs of chicago today?
Registered: Dec 1999
posted 01-12-2003 09:58 PM
if you still have some of the choke linkage on there after milling the horn off, you may have the linkage set to choke, which will keep the carb on high idle
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MY340
Moparts Member
Posts: 2307
From: missouri
Registered: Mar 2001
posted 01-13-2003 12:39 PM
I have no length problems with the stock throttle cable on my 340 with RPM manifold and 1" tall spacer. I use a Carter AFB and not a Holley though.
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Don1
Moparts Member
Posts: 5253
From: Valley City, ND. USA
Registered: Oct 2001
posted 01-13-2003 02:44 PM
Thw throttle cabe with a Holley will more than likely be too short and when you pull it back by hand you stretch the cable more than the spring is able to do. Get yourself a /6 cable (it is longer) and see what happens. Also check the agle of the cable so that it isn't binding.
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Bryan Plotkowski
Moparts Member
Posts: 184
From: St. Clair Shores,Michigan
Registered: Dec 1999
posted 01-13-2003 03:58 PM
My son's 650 Holley on his 383 RoadRunner did the same thing after he messed with it. The guy who built the carb. ,told me to loosen the throttle plate screws ,let it slap shut a couple times to set them, and then tighten the screws....guess what? It worked!
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CUDAGTX
New Member
Posts: 99
From: PITTSBURGH
Registered: Jul 2002
posted 01-13-2003 06:19 PM
check your power valve again. one backfire and they are toast. also i recall the metering plate gaskets only line up one way but can be installed either way. spray it down with carb cleaner while running to check for vacuume leaks.
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Abody
Moparts Member
Posts: 256
From: R.I.
Registered: Dec 1999
posted 01-13-2003 07:08 PM
Hey Bill! you should have bought my 950! It would have woke that Demon up for sure. Overkill yes! But hey, you got to keep up with the big boys now!
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demon34071
New Member
Posts: 20
From: Warwick, RI USA
Registered: Oct 2002
posted 01-13-2003 07:34 PM
Thanks For the replys I'll have to try that one with the throttle plates, that could be it. The cable and linkage do need to be modified, but im having this problem without them being hooked up. We are going to spend more time on it tomorrow We will recheck for vacume leaks, although the motor seems to run very smoothly. Its always possible. Thanks again Bill.
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