390 CFM carb starving on uphill?

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   I've got a 67 Rogue with 258, aluminum intake, Holley 390 carb. On uphills with steady throttle, the car sputters slightly like it's not getting enough fuel. If I give it more throttle it will accelerate with no problems. Any input? Do I need to adjust the float level or the mixture jets?

Thanks!  

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jdarosa Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Nut Joined: Oct/31/2014 Location: Portland, OR Status: Offline Points: 264	Post Options Post Reply Quote jdarosa Report Post Thanks(0) Quote Reply Topic: 390 CFM carb starving on uphill? Posted: Aug/06/2018 at 6:25pm
	I've got a 67 Rogue with 258, aluminum intake, Holley 390 carb. On uphills with steady throttle, the car sputters slightly like it's not getting enough fuel. If I give it more throttle it will accelerate with no problems. Any input? Do I need to adjust the float level or the mixture jets? Thanks!
	1968 American 440 – 232/AT 4dr

matty 401 Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Addicted Joined: Jul/06/2007 Location: Iowa Status: Offline Points: 1727	Post Options Post Reply Quote matty 401 Report Post Thanks(0) Quote Reply Posted: Aug/06/2018 at 7:01pm
	so at 1/2 throttle or a little more ? if over 1/2 throttle check the power valve
	72 matador 401 the beast 79 concord 2 door 72 matador 304 grasshopper 68 Rogue 406 93 Cherokee 4.0 5 speed

tomj Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Addicted Joined: Jan/27/2010 Location: earth Status: Offline Points: 7553	Post Options Post Reply Quote tomj Report Post Thanks(0) Quote Reply Posted: Aug/07/2018 at 12:38am
	no carb should change behavior on a hill even a steep one. sounds like crazy-wrong float level. is this a change? or has it always done it? did you install the carb? do you know it's history? when was it last apart for rebuild? etc...
	1960 Rambler Super two-door wagon, OHV auto 1961 Roadster American, 195.6 OHV, T5 http://www.ramblerLore.com

jdarosa Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Nut Joined: Oct/31/2014 Location: Portland, OR Status: Offline Points: 264	Post Options Post Reply Quote jdarosa Report Post Thanks(0) Quote Reply Posted: Aug/07/2018 at 8:53am
	It's a new carb, less than 1500 miles on it and the engine. This particular issue is new, and it's been since I started driving the car again this summer. It sat for most of the year and didn't have the issue before. The carb also will cut out for a second if I increase throttle quickly, like trying to pass someone or take off quickly from a stop. Carbs are on the edge of my expertise level, and the mechanic that installed the carb and tuned it for me put in a spacer to help lessen this issue because he said it was due to fuel/air mixture. The two are related I'm sure, just this uphill issue is new. Thanks
	1968 American 440 – 232/AT 4dr

tomj Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Addicted Joined: Jan/27/2010 Location: earth Status: Offline Points: 7553	Post Options Post Reply Quote tomj Report Post Thanks(0) Quote Reply Posted: Aug/08/2018 at 12:34am
	ahh ok. yeah, carbs are very "analog" by today's standards. not so much complex as subtle. aka tricky. persist and they will make sense (mostly :-) first, carb and spark issues can be almost interchangeable in symptom! especially throttle-open-flat-spot-low-speed -- a classic symptom of not enough accell pump squirt, AND spark timing retard due to throttle-open (retarding timing via the vacuum advance unit). vac advance is mostly for improved light-load (eg. highway) cruise MPG. for disambiguating problems like yours, i recommend pulling the hose off the distributor and plugging it. just to untangle causes. you'll do no harm (except to MPG). then make sure spark timing is (1) at least approximately correct at idle (5 to 15 BTDC) and (2)that timing increases as you rev up the engine (should approach 30 degrees or whatever by 2000 or so). to make sure mechanical advance is OK. if so, even half those numbers, move on to the carb. but if spark is A.F.U. fix that. back to carb, if you accel smoothly and slowly, do you get a bog/flatspot/stall/etc? at least on flat and level? if that's OK, approaching a hill, smoothly opening throttle to compensate for the load, at some steepness, alone, it begins to lose power, stall etc? IF SO then who knows (lol). hmmm on a 390, like most carbs, the main jets are towards the rear of the car, SPECIFICALLY SO THEY DONT STARVE accellerating. pretty much all carbs in the last 80 years are like this, for this very reason. so i suspect the problem is spark or squirter... especially if carbs are new to you, spend some time "characterizing" the symptoms. it's also cheaper, easier, and requires no tools. figure out exactly when and what screws up. find a long smooth very slight incline, or at least long and flat. accell extremely lightly; does that work? accell more rapidly. is there a point where that gets worse? go past it; what happens at hard acceleration? (if a flashomatic, do this in "2" from idle so the engine is loaded, if a manual, in one gear too high.) a flat spot or bog "feels like" the gas pedal has gone soft; it feels like there's a range in the middle of travel where less does something, more does something, but in the middle, nothing. "bog" usually sounds funny too. drive with the air cleaner element removed -- you can hear it more clearly. if during a bog you can "blip" the throttle (rapidly press past halfway then release back to the original position, super-quick), to ensure a good squirt from the pump, and that makes it feel better for a second, THAT is accellerator pump! OR! spark retard! hence the need to disambiguate before you start. Edited by tomj - Aug/08/2018 at 12:41am
	1960 Rambler Super two-door wagon, OHV auto 1961 Roadster American, 195.6 OHV, T5 http://www.ramblerLore.com

farna Members Profile Send Private Message Find Members Posts Add to Buddy List Supporter of TheAMCForum Moderator Lost Dealership Project Joined: Jul/08/2007 Location: South Carolina Status: Offline Points: 19686	Post Options Post Reply Quote farna Report Post Thanks(0) Quote Reply Posted: Aug/08/2018 at 6:18am
	And since it's a Holley, check that power valve!!
	Frank Swygert

Thikstik Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Addicted Joined: Mar/20/2008 Location: Alabama Status: Offline Points: 1327	Post Options Post Reply Quote Thikstik Report Post Thanks(0) Quote Reply Posted: Aug/08/2018 at 8:46am
	Tomj. Yes i agree , the Vac advance is a cruising mechanism only...ive had so many disagreements on that! Farna-Yes, P valves harden in only a few years which makes them stage richer. Damn ethanol. BTW, Hows that AW-4, I bet running perfect! That said, i realize he's probably lean on the hills. Have you blown into the fuel filter? If it restricts your lung pressure, it will do the same for gas. Does the car act more cold natured?
	75 gremlin x, jeep 4.0 headed 258, 264H Cliff cam, intake,header. 390 holley. I want a 282 VAM motor! AC/PS/PDB. 72 AMX , 304 2bbl, 3speed, now disks...probably will sell, want an automatic /AC.

Greyhounds_AMX Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Addicted Joined: Nov/14/2009 Location: Kansas City Status: Offline Points: 1268	Post Options Post Reply Quote Greyhounds_AMX Report Post Thanks(0) Quote Reply Posted: Aug/09/2018 at 11:13am
	On a hill you should be running on the main jets and power valve for additional enrichment. Your engine may be making enough vacuum to hold the PV closed even in that scenario. I would put a vacuum gauge on it and see how low the vacuum drops during the hill climb, then order a PV a little lower than that value.
	1968 AMX 390 w/T5

jdarosa Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Nut Joined: Oct/31/2014 Location: Portland, OR Status: Offline Points: 264	Post Options Post Reply Quote jdarosa Report Post Thanks(0) Quote Reply Posted: Aug/12/2018 at 9:08pm
	Thanks for the input. I'm switching out the squirters, going up in size, checking the vacuum this week, and checking the fuel filter... The power valve looks to be good too, so hopefully this does it.
	1968 American 440 – 232/AT 4dr

Thikstik Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Addicted Joined: Mar/20/2008 Location: Alabama Status: Offline Points: 1327	Post Options Post Reply Quote Thikstik Report Post Thanks(0) Quote Reply Posted: Aug/13/2018 at 7:54pm
	If it drove fine before it sat what happened? Your about to add to confusion by switching stuff. The squirters are only for quick throttle demand movements. Your first bit of info says it cruises badly until more pedal. That means primary system is lean, maybe rich, but id bet lean. Have you blown compressed air and carb spray into air bleeds? This is very routine for Holleys. Ill add, My 390 was bad outta the box with an overly lean cruise mixture. A new front metering plate fixed it...auto parts arent what they used to be. Edited by Thikstik - Aug/13/2018 at 8:02pm
	75 gremlin x, jeep 4.0 headed 258, 264H Cliff cam, intake,header. 390 holley. I want a 282 VAM motor! AC/PS/PDB. 72 AMX , 304 2bbl, 3speed, now disks...probably will sell, want an automatic /AC.