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Fuel Pressure Regulator...??? Help |
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Mopar_guy 
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Joined: Jun/07/2009 Location: Ohio Status: Offline Points: 4837 |
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 Posted: Sep/12/2021 at 4:13pm |
If you have that low of vacuum at idle, it sounds like you need a 6.5 - 8.5 power valve. The key to selecting the right power valve is to watch a vacuum gauge while driving. When the power gets flat from pulling a grade, that vacuum reading is where the valve should be opening up. Not cruising down the road or idling.
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amcenthusiast
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Joined: Jul/02/2012 Location: SW Atlanta GA Status: Offline Points: 1778 |
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Posted: Sep/12/2021 at 10:59pm |
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5 psi recommended.
(you got 4 inlet needles on dual carb cross ram = not a flow prob) IMO your carbs are too big for street strip use. Should be CID x 2... for 390, good running cfm rating should be around 800 = two 400 carbs... like two old school 390 Holleys... Think of the cross ram as a low rise tunnel ram. As I understand it, AMC had Edlebrock make those with much anticipation of larger CID race engines... in the future, at that time, way back when... ...apparently Trans Am rules forced cross ram design for hood height or something like that... =no tunnel rams allowed on TA cars back then? ...naw... 1200 cfm/two 600 cfm carbs is too much -will be a tall challenge to tune without reworking transition slots on old school Holley design carbs. (gonna bog mid throttle -reason why is basically all those 2 jet carbs (idle & main jet) carbs are calibrated 'fat' for single carb intakes...) Note Holley made 3 jet Dominator carbs for this reason...-to create more tunable carb for semi IR Mold school tunnel ram etc.. Frankly, I believe your car will run much better street/strip. if u ditch the cross ram & go with Torker intake & 800/850 cfm carb Just keep the cross ram for nostalgia... Hard to make it run sweet in street/strip application due to huge plenum volume...that intake is made to run 4 to 8K rpm IMO... = not a sweet choice for a street machine that needs to run good under 5K rpm Edited by amcenthusiast - Sep/12/2021 at 11:08pm |
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443 XRV8 Gremlin YouTube video: https://www.youtube.com/watch?reload=9&v=2DmFOKRuzUc
XRV8 Race Parts website: http://amcramblermarlin.1colony.com/ |
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PHAT69AMX
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Joined: Jul/07/2007 Location: West Virginia Status: Offline Points: 5926 |
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Posted: Sep/13/2021 at 1:31am |
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BrotheBamc - is there a crossram intake involved here, if so I missed something...
Were the primary throttle blades to transfer slots bench set?
How many turns opened from fully closed on the primary idle speed screw?
Has any adjustments been made to the Secondary Idle Speed Set Screw? How many turns from fully seated are the Mixtures Screws? What is the timing curve, initial at idle, & how many degrees mechanical, all in by when? Ever heard of putting 0.010" wire in the IFR's as Holley DP's are set-up with rich idle circuits? Edited by PHAT69AMX - Sep/13/2021 at 1:35am |
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BrotherBamc
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Joined: Jan/22/2009 Location: Lewiston Status: Offline Points: 2248 |
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Posted: Sep/13/2021 at 7:36am |
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There is no cross ram intake.
Just a Torker. Had too much to do yesterday afternoon and I wasn't able to get to do anything to it.
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PHAT69AMX
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Joined: Jul/07/2007 Location: West Virginia Status: Offline Points: 5926 |
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Posted: Sep/13/2021 at 11:23am |
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BrotherBamc - how many turns out from fully seated are the Idle Mixture Screws?
But to generalize, sounds like the thing you are describing is right there at the crucial spot where the carb is transitioning from the Idle Circuit & Transfer Slots ( which are fed by the same circuit ) to the Main Circuit which is what is discharged out of the boosters and a product of main jets & main air bleeds and Power Valve. I myself do not think your main circuit or any of it's components is coming into play. It is the Idle & Transition circuit, or possibly a fuel bowl / fuel level / fuel pressure issue. 2-Corner or 4-Corner Idle ? How many turns out on the Idle Mixture Screws gives a hint of how your motor likes the Idle circuit set-up. Idle circuit feeds both the curb idle & the Transfer Slot. BUT the Idle Mixture Screws have NO EFFECT on the Transfer Slot discharge, only the curb idle discharge. the primary butterflies MUST be kept closed down so that only a sliver or square of Transfer Slot is exposed below the throttle blades at idle. Otherwise loss of idle mixture control by way of the idle mixture screws is lost. Bench set the primary idle speed screw for proper Transfer slot exposure then never touch the primary idle speed screw ever again ! LOL Make any & all further Idle Speed adjustments ONLY by way of the pita SECONDARY IDLE SPEED SET SCREW. Secondary Idle Speed Screw is adjusted on-the-car, running, up to temp, on-the-fly by making a apir of custom Allen Wrench .120" wide flat blade screwdrivers from a couple 1/8" or 5/32" Allen wrenches using a grinder (see picture). Two are needed due to limited access and available swing. Once you get that secondary idle screw in the "sweet spot" there is 1,000 rpms in about 100 degrees of screw rotation. No harm in maybe trying this approach to see if there are any improvements, none of this is irreversible. More I can go on about if ya think it might help. Peace  Edited by PHAT69AMX - Sep/13/2021 at 11:46am |
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BrotherBamc
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Joined: Jan/22/2009 Location: Lewiston Status: Offline Points: 2248 |
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Posted: Sep/13/2021 at 7:48pm |
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Phat...
It's a 4 corner and I really don't think that there is anything wrong with the idle circuit. I use a vacuum gauge to set the mixture screws. I try to get as much vacuum as I possibly can and with the 280H cam, there's not a lot of vacuum to be had. At the best I get about 11 or 12 at idle. I think that it's getting too much vacuum from the vacuum can on the dizzy. Still haven't had time to mess with it, but I will keep everyone posted on what I find.
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PHAT69AMX
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Joined: Jul/07/2007 Location: West Virginia Status: Offline Points: 5926 |
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Posted: Sep/14/2021 at 1:34pm |
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Agree, could possibly be the Vacuum Advance Canister. What is the Number stamped on the flange of the vacuum Advance Canister? What distributor is it, if posted I failed to catch it.
But believe it or not, at 2,000 engine rpms steady state cruise the engine is most likely running on ONLY the Idle Circuit, albeit the emulsion is being discharged out of the Transfer Slots, and the Main Circuit is not even on-line yet and is not discharging fuel air emulsion yet. The Idle / Transfer Slot emulsion is the product of the Idle Air Bleed and the IFR, Idle Feed Restriction, or the Idle Fuel Jet. The Main Jets, Main Air Bleed, and Power Valve circuit have nothing to do with the Idle Circuit emulsion and only effect the emulsion discharged from the main boosters. the Transfer Slots get the same emulsion that the curb idle discharge port gets, except the Transfer Slot is upstream of the Idle Mixture Screws, so the Idle Mixture Screws have NO EFFECT of what is discharged out of the Transfer Slots, only the IAB's & IFR's do, which are fixed orifices. And in a strictly technical sense, the Idle Mixture Screws do not actually change the Idle Mixture emulsion which is the product of the fixed orifice IAB's & IFR's. The Idle Mixtures Screws actually only change the VOLUME of predetermined Idle Emulsion supplied to and discharged by the idle discharge port which is a round hole located in the base plate bore below the throttle blades. This is why it is CRITICAL to have correct primary throttle blade park position at idle and to make idle speed adjustments only via the Pita Secondary Idle Speed Set Screw. If the primary Transfer Slots are over exposed below the primary throttle blades at idle the Idle Mixture Screw have less or no effect on idle mixture as the Transfer Slot discharge which comes from the idle circuit is delivered to the slots UPSTREAM of the idle mixture screws so is not affected by idle mixture screw adjustments. If you might be so inclined, and have a smart phone, there is something I think would be very very interesting to see... In park with engine running and no air cleaner, make a smart phone video, with good lighting, hold your phone directly squarely somewhat closely over the top of the carburetor, then slowly gradually with your other hand open up the throttle somehow making some kind of reference of the engine rpms... such a video would create a visual reference as to just when at what engine rpm the Main Circuit Main Boosters come on line and actually begin to deliver emulsion to the engine.
Edited by PHAT69AMX - Sep/14/2021 at 1:39pm |
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BrotherBamc
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Joined: Jan/22/2009 Location: Lewiston Status: Offline Points: 2248 |
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Posted: Sep/14/2021 at 6:17pm |
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Phat.. So if it was in the metering block that would mean a new one..??
Saying this hypothetically.. I won't be able to do anything again tonight. My work truck broke down 200 miles away from home and the mechanic can't seem to figure it out..
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javtopgun
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Joined: Aug/03/2021 Location: NV. Status: Offline Points: 342 |
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Posted: Sep/14/2021 at 8:34pm |
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I have the same comp cam in my 343 build and i have the exact same issue ... the same . i also only pull 12 / 13 lbs vacuum and at start ups chunky idle for about a min and all smooths out and chunky low throttle up till 2000 r's even tho idle smoothed out then all good over 2000 r's . i run a stock distributor , points that will not stay set unless you get it just at 29. 4 dwell ( elec dwell meter ) and it will stay set for 5 /6 days instead of hours . Vac advance is a new one . BUT . i have found my distributor shaft has a slight wobble and changing it out this sunday . And i suspect my valve geometry is off . going thru that exercise this week end also if i find the time . Could this maybe be inherant to the cam ?/ 280 280 lift 270 duration comp cam . Its not really a radical cam ! as i run the stock afb carter carb but i do have a edelbrock power valve in it as i could not find a carter leather one at the time . i now have a weber rebuild kit for it that has the leather one and correct for the carb . i did run rich , may still but the mixture screws are 1 and 7/8 out from full close ! ODD .. !!
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1968 Javelin SSt 343ci semi restomod .
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javtopgun
AMC Nut
Joined: Aug/03/2021 Location: NV. Status: Offline Points: 342 |
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Posted: Sep/14/2021 at 8:39pm |
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Oh , im running a 5-9 psi elec fuel pump gauged at carb also . . Two things things in common , 5-9 pressure fuel pump and 280 comp cam ??? but i know i have a wobble dis. shaft tho !
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1968 Javelin SSt 343ci semi restomod .
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BrotherBamc wrote:
