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Thomas C Potter
02-18-2004, 02:40 PM
Any knowledgeable carb/ignition folks out there who can help with my situation?? My '68 Galaxie XL 390 4 speed bucks when I shift into next higher gear, if I do not have rpm's higher than what I would normally shift at. Also bucks if I take off at low rpm in 1st gear. I'm talking just normal driving, not hard acceleration.

Carb is a Holley 4010 (similar to autolite 4100), plugs look slighlty lean (not bad), gas mileage lousy though!! (9-10 mpg suburban driving) Stock ignition/distributor, stock exhaust. Retard timing does little, advance makes it worse. Runs very good other than bucking into 2nd or 3rd, 4th is fine.

TP

DOHC 4.6
02-18-2004, 03:13 PM
Tom,

I would check several things:

1. Make sure the accelerator pump is operating properly. If your carb is basically the same as an Autolite 4100, it should have two or three adjustment holes in the accelerator pump linkage. They correspond basically to cold weather, normal weather, and hot weather. They set the actuation of the accelerator pump to prevent bogging in the various temperature ranges.

2. Make sure that your choke is opening all the way. If it is not, it can cause a bog as well as poor gas mileage.

3. Make sure the power valve is working properly. The diaphragms on these tend to leak.

Good luck.

TripleTransAm
02-18-2004, 06:12 PM
I'm not at all familiar with the old Holleys but if the secondaries are vacuum controlled or at least staggered versus the primaries, is there a possibility the secondaries are opening too soon (causing a lean bog)?

If it hadn't been for your symptoms in 1st gear at low RPM I would have suggested also looking at the fuel filter for possible clogging... but I thought that only happened at low RPM during cruising conditions.

GordonB
02-18-2004, 09:20 PM
TP,
Two things come to mind:
1. One has already been mentioned -- the Accelerator Pump cup/washer adjustment. If this does not correct or mask the problem, then pls try the next one.
2. Try replacing the accelerator pump cup/washer. It may not look worn, but it might be the cause of most of your problem. I had a Chrysler with a 400, 2bbl, AT and it bogged/hesitated evrytime my wife pushed down on the pedal. I'm not sure that this is your problem, but it might bear investigating. After you push in the clutch and start to let it back out you are pushing down on the gas pedal in a corresp. fashion every time you shift.

GordonB

vegasmarauder
02-18-2004, 09:31 PM
Miss under load usually points (hey, nice pun) to ignition. The stock set-up needs to go. The way points are made now they don't last more than 5,000 miles. I swapped the points out of all my old Fords for the Pertronix set up. Converts it to electronci ignition with only one extra wire. Uses the stock distributor too. The newer Pertronix has better low end dwell and high RPM stability. It is more than adequate for most modified street or stock applications. I had a marginally failing ignition coil once that did the same thing. Kept checking out good on the ohm meter, but missing under load. Changed the coil and fixed the problem. So if you go with the Pertronix set up, get their coil too and paint the top yellow and not many people can tell it's not stock. You will get much better slow speed and cold drivability.

Heavy351
02-19-2004, 07:28 AM
Lean condition is real likely here. If, for example, in 3rd gear you can smoothly accelerate very gradually on flat ground (no acceerator pump enrichment required) but when you stab it, the motor nearly dies (sometimes even backfires) then your accelerator pump needs attention.

You can shine a flashlight down the throat of the carb and goose the throttle with your hand and look for the little stream of gas.....

BillyGman
02-19-2004, 08:19 AM
I agree w/heavy on this one. I'd say look for the accelerator pump first. I've worked on Holly carbs a lot, but only on the double pumper 4150, and 4160 models which are different than the 4010's are. I didn't think that the 4010's had a power valve, but I'm not positive on that. If they do, then a ruptured power vavle can be the culprit as suggested, or it can simply be the wrong one that youhave on there.

if the accelrator pump is working correctly, you'll see a momentary squirt of gas come out of the nozzles immediately upon pulling the throttle lever to full wide open position while looking down the carb throat w/the air cleaner off.

TripleTransAm
02-19-2004, 10:13 AM
Yeah, didn't Holley's have an incredible tendency to blow power valves on a backfire?

BillyGman
02-19-2004, 10:46 AM
Yeah, didn't Holley's have an incredible tendency to blow power valves on a backfire?

they used to, but now they come equipped w/a ball type check valve installed in a stategic area of the carb to prevent that from happening. So it would depend on how old the Holley carb in question actually is.

Ross
02-19-2004, 01:11 PM
Gee, all of this kind of makes me miss the good old days! Just think, carbuerators! Points!

jgc61sr2002
02-19-2004, 04:17 PM
I would also tend to go with ignition. Also had a bad coil that gave the same symptoms.

BillyGman
02-19-2004, 09:45 PM
Gee, all of this kind of makes me miss the good old days! Just think, carbuerators! Points!

....in my 73 Vette, there isn't very much meachanicaly stock on the car. I installed an aftermarket hi output MSD electronic ignition box along w/a new distribitor so the points are long gone. However I use a double pumper mechanical secondary Holley carb on it. I like them because they're very simple. You can rebuild them very easily, and they allow the engine to breath pretty good since they're non-restrictive.

merc406
02-20-2004, 05:53 PM
Check all of the above^^ and float level.
Fuel pressure
Fuel pick-up tube sock