I'm lost...hesitation issue...bad acc pump symptoms??

I'm lost...hesitation issue...bad acc pump symptoms?? - 04/06/12 03:38 AM

Not too long ago, I swapped a 360 cam into my 318. I always had a SLIGHT hesitation/flatspot right off idle, but its more noticeable now that the truck is running "right"

-I set the initial timing at 12 before
-Stripped the carb and cleared/cleaned every orifice and passageway I could. Put back together with new gaskets
-new accel coil
-new firecore plug wires
-new "brain box"/stock replacement
-newer distributor
-new dist cap
-new rotor cap
-newer plugs (maybe 10k miles)
-dont know fuel pressure, but verified flow
-new fuel filter
-just flushed gas tank
-replaced vacuum line to distributor vacuum advance
-have the a/f screws set to 2 out (carter 2 bbl)
-Running 91 octane
-3 speed A745

Firing order IS correct. Once she revs past that spot, she will

but it is that initial step on the gas that I always wince, because she wants to stall. What am I missing? I was thinking accelerator pump, but can't justify the $20 to "guess" and HOPE that was the problem...

Sometimes she starts first hit of the key in the AM, and sometimes I have to crank like hell, while pumping like hell to get her to start.

Could the fuel pump be "just good enough" to pump gas, but leak down/back to the tank over night, or even have low pressure at low RPM..maybe a bad valve in the fuel pump??

Someone PLEASE help point me in ANY direction

Posted By: DARTH V8Я

Re: I'm lost...hesitation issue...bad acc pump symptoms?? - 04/06/12 04:18 AM

What make carb?

Posted By: magnum440d100

Re: I'm lost...hesitation issue...bad acc pump symptoms?? - 04/06/12 04:51 AM

Quote:

What make carb?

The stock one from 1972

Posted By: Secret Chimp

Re: I'm lost...hesitation issue...bad acc pump symptoms?? - 04/06/12 04:55 AM

Take the air cleaner off after running it (so you know the bowl is 100% full) and look down the barrels while you push the throttle lever back. Whether or not the accel pump is working should be pretty obvious. Pay close attention to what it's doing at the beginning of its travel.

If it is working, have you actually tuned your idle mixture based on RPM or vacuum? Two turns out could be completely off for your engine if you haven't checked anything beyond the number of turns you made initially.

Posted By: DARTH V8Я

Re: I'm lost...hesitation issue...bad acc pump symptoms?? - 04/06/12 04:56 AM

Wow! Read it 3 times and still I managed to miss it lol

Posted By: GMP440

Re: I'm lost...hesitation issue...bad acc pump symptoms?? - 04/06/12 05:03 AM

Are you running spark ported vacuum or manifold vacuum?. If you're, as a result you will get hesitation or a flat spot. running manifold vacuum to the distributer vacuum advance , you will lose some of your vacuum advance when you stab on the pedal.
You may want to check fuel pressure at the carb.
I would also check the the curb idle mixture with the car in gear. It could be lean in this area. You may not have enough carburetion for the cam you're using.
Another thing to check with the carb off is the butterfly in relation to the off idle slot. If it's below the slot you will get some flat spot on acceleration.

Posted By: magnum440d100

Re: I'm lost...hesitation issue...bad acc pump symptoms?? - 04/06/12 05:17 AM

Quote:

Take the air cleaner off after running it (so you know the bowl is 100% full) and look down the barrels while you push the throttle lever back. Whether or not the accel pump is working should be pretty obvious. Pay close attention to what it's doing at the beginning of its travel.

If it is working, have you actually tuned your idle mixture based on RPM or vacuum? Two turns out could be completely off for your engine if you haven't checked anything beyond the number of turns you made initially.

OK...with the air cleaner off, and engine warm (after running) when I push the throttle slowly, it dribbles out for the first split second, then squirts almost enough to hit the other side...

all adjustments are based on RPM. I havent had the pleasure of doing it by vacuum YET. I'm not sure what kind of gauge I need anyway...just a regular vacuum gauge??

Posted By: magnum440d100

Re: I'm lost...hesitation issue...bad acc pump symptoms?? - 04/06/12 05:22 AM

Quote:

Are you running spark ported vacuum or manifold vacuum?. If you're, as a result you will get hesitation or a flat spot. running manifold vacuum to the distributer vacuum advance , you will lose some of your vacuum advance when you stab on the pedal.
You may want to check fuel pressure at the carb.
I would also check the the curb idle mixture with the car in gear. It could be lean in this area. You may not have enough carburetion for the cam you're using.
Another thing to check with the carb off is the butterfly in relation to the off idle slot. If it's below the slot you will get some flat spot on acceleration.

That was going to be another question of mine...Where do I hook the vacuum line from the distributor to? Right now it goes from the vacuum advance, to the back of the carb. Is that the right spot? the only other spot for a vacuum line, is where the line to the air cleaner goes.

I havent switched yet to see if it makes a difference

where its hooked up now, it has vacuum at idle

Posted By: GMP440

Re: I'm lost...hesitation issue...bad acc pump symptoms?? - 04/06/12 06:27 AM

You mentioned that you checked accelerator pump operation and noticed the pump shot dribbles first and then gives you a good pump shot stream. Should just be a solid pump shot stream. Also, go ahead and switch the vacuum line to the other port. Should be the spark ported vacuum port. To verify this just put your finger on the port to see if you have vacuum at idle. If no vacuum at idle , that's the one. Also with a vacuum guage, check to see what the vacuum readings are when you rev up the engine. This will also check that you are getting a vacuum rise at precisely the same time as you blip the throttle lever. If you are that's good; if it's delayed then just increase the idle speed to allow the throttle blades to be just at the base of the idle slot so at the time the slots are uncovered you will get vacuum to the vacuum advance instantaneously. If you find the idle speed too high you can back it down by lowering the timing. 12 degrees advanced maybe too much; you can back it down to about 1 or 2 degrees BTDC or just have it straight up at 0 degrees top center. Another way of lowering the idle speed too is to enrichen the idle mixture.

Posted By: Secret Chimp

Re: I'm lost...hesitation issue...bad acc pump symptoms?? - 04/06/12 06:35 AM

Depending on your carb, sometimes you can fix the "initial dribble" problem by adjusting the pump rod so the pump starts off further down in the bore. It may even be out of spec with respect to that adjustment, or your float level may be too low. But it should be easy enough to measure where your pump is sitting at right now (in case you need to change it back) and bend the rod so it sits another few millimeters further down at rest.

Posted By: magnum440d100

Re: I'm lost...hesitation issue...bad acc pump symptoms?? - 04/06/12 06:47 AM

Quote:

You mentioned that you checked accelerator pump operation and noticed the pump shot dribbles first and then gives you a good pump shot stream. Should just be a solid pump shot stream.

ok..going to get the new accelerator pump in the morning, and swap for peace of mind..

Quote:

Also, go ahead and switch the vacuum line to the other port. Should be the spark ported vacuum port. To verify this just put your finger on the port to see if you have vacuum at idle. If no vacuum at idle , that's the one.

where it is hooked now, there is a lot of vacuum. Enough so, that when I put my finger over the tip of the hose, the hose stick to my finger

Quote:

Also with a vacuum guage, check to see what the vacuum readings are when you rev up the engine. This will also check that you are getting a vacuum rise at precisely the same time as you blip the throttle lever. If you are that's good; if it's delayed then just increase the idle speed to allow the throttle blades to be just at the base of the idle slot so at the time the slots are uncovered you will get vacuum to the vacuum advance instantaneously. If you find the idle speed too high you can back it down by lowering the timing. 12 degrees advanced maybe too much; you can back it down to about 1 or 2 degrees BTDC or just have it straight up at 0 degrees top center. Another way of lowering the idle speed too is to enrichen the idle mixture.

at TDC, she backfires when I attempt to give her gas. At 12 BTDC, the screws out 2 turns, and the idle adjustment screw adjusted, I have a VERY healthy idle ~750 - 800 RPM.

Cruising down the highway it is OK, same with idle..at idle it is ok, but taking off it is a pain, unless I high rev it (~2000 RPM) then let the clutch out SLOWLY

I'm going to do what you reccomended in the morning, and I hope I'm done before work lol

Thanks for the leads

Posted By: magnum440d100

Re: I'm lost...hesitation issue...bad acc pump symptoms?? - 04/06/12 06:53 AM

Quote:

Depending on your carb, sometimes you can fix the "initial dribble" problem by adjusting the pump rod so the pump starts off further down in the bore. It may even be out of spec with respect to that adjustment, or your float level may be too low. But it should be easy enough to measure where your pump is sitting at right now (in case you need to change it back) and bend the rod so it sits another few millimeters further down at rest.

yeah, there were two slots the rod could have gone in. it HAD been in the inner slot(closest to carb) but since I changed it to the outer slot, I havent noticed any change. I could try to bend the rod to make it shorter. The float was set to whatever the instructions said to set it to. IIRC, level with the bowl, or am I thinking the ford carb again

All I remember is setting it to what the piece of paper in the kit said

Posted By: calrobb2000

Re: I'm lost...hesitation issue...bad acc pump symptoms?? - 04/06/12 07:08 AM

hi
do yourself a favor and get a 4 bbl intake an carb.

best thing i ever did to my 318 van ws install a performer intake with a 600 holley electric choke !
it also had the 360 cam !

8-12 deg timing should be fine with stock dist .

Posted By: magnum440d100

Re: I'm lost...hesitation issue...bad acc pump symptoms?? - 04/06/12 07:21 AM

Quote:

hi
do yourself a favor and get a 4 bbl intake an carb.

best thing i ever did to my 318 van ws install a performer intake with a 600 holley electric choke !
it also had the 360 cam !
8-12 deg timing should be fine with stock dist .

Don't laugh. I have a complete top end from a 360 including a 4bbl intake I've been resisting the urge to swap onto this 318. I just don't know what condition the valves are in. I am SERIOUSLY tempted since I have that brand new Qjet itchin to be used

Posted By: calrobb2000

Re: I'm lost...hesitation issue...bad acc pump symptoms?? - 04/06/12 07:40 AM

hi
what heads do you have now ?

you dont want to lower your compression .

a pair of 302 heads with mild port bowel work would be good !

too large a valve and port and combustion chamber will make a truck a slug ,that cam does not want to big a ports on a smaller engine !

Posted By: magnum440d100

Re: I'm lost...hesitation issue...bad acc pump symptoms?? - 04/06/12 07:55 AM

Not sure what heads I have now, but I would be using the 596's off the 360 with steel shim head gaskets, since I already have them. That shouldn't drop my compression too much I don't think

Posted By: JohnRR

Re: I'm lost...hesitation issue...bad acc pump symptoms?? - 04/06/12 03:30 PM

Quote:

where it is hooked now, there is a lot of vacuum. Enough so, that when I put my finger over the tip of the hose, the hose stick to my finger

Do you have a timing light ? If so hook it up and look at your idle timing with the vac line disconnected , then connect it up , if the timing move you either have the wrong port or your throttle is open to far uncovering the transfer slots .

Posted By: RapidRobert

Re: I'm lost...hesitation issue...bad acc pump symptoms?? - 04/06/12 04:08 PM

I'd invest the twenty & R&R the accel pump

Posted By: Secret Chimp

Re: I'm lost...hesitation issue...bad acc pump symptoms?? - 04/06/12 06:58 PM

Quote:

Quote:

hi
do yourself a favor and get a 4 bbl intake an carb.

best thing i ever did to my 318 van ws install a performer intake with a 600 holley electric choke !
it also had the 360 cam !
8-12 deg timing should be fine with stock dist .

Don't laugh. I have a complete top end from a 360 including a 4bbl intake I've been resisting the urge to swap onto this 318. I just don't know what condition the valves are in. I am SERIOUSLY tempted since I have that brand new Qjet itchin to be used

Pft valves schmalves, I put a 4 barrel on my 105,000 mile 1967 motor (valve stem end heights were all even) and it just rips shiznit now. Throw that BBD or whatever out the window and have fun :P

Posted By: magnum440d100

Re: I'm lost...hesitation issue...bad acc pump symptoms?? - 04/06/12 11:28 PM

ok, an update..missed work, but thats fine since the machine shop called and said my 360 was ready for pick up...

had to wait for the accelerator pump to come in, but once it came in, I rushed down there and got it. I put it in, and now there is a steadier shot of gas. I think it could be better, but its better than it WAS.

Switched hoses on vacuum ports on the carb. no noticeable difference.

REtimed to 10 before TDC...still no HUGE difference.

Shifts are WAY smoother, and surge is gone, but that flat spot upon take off is still there. Its a LITTLE more tolerable though..

I'm going to tweak the accelerator pump rod a bit to see if I can make it better...

OR I can just swap to the 4bbl intake, run the almost brand new Qjet, and call it done

ASSuming the Qjet can be adjusted to run better than this 2 bbl

Posted By: Locomotion

Re: I'm lost...hesitation issue...bad acc pump symptoms?? - 04/07/12 02:02 PM

Since the 360 cam is likely bigger than the 318 cam, then the vacuum signal would be a little weaker. That could explain why the existing "flat spot" got worse. Unless someone suggested it and I missed it, is there any way to get an accellerator pump squirter with bigger nozzles, or finding another one to drill out with wire drills? Change in small increments, like .003" - .005".

Changing the pump arm position changes the total volume of fuel delivered throughout the travel. (longer or shorter squirt) The pump squirter nozzles determine the "rate" of delivery. i.e.: bigger squirters will squirt more, but for a shorter time.

Carb may even need to be jetted a size or two bigger, which could help the "flat spot". But that shouldn't be used to actually cure the "flat spot" because then you'll be too rich the rest of the time.

Posted By: CUDA8U

Re: I'm lost...hesitation issue...bad acc pump symptoms?? - 04/07/12 02:24 PM

I have a slight dead spot off the line too and i was told to measure clearance of accelerator pump arm and adjustment screw then up size the squirters by 3 each time.It was explained that the carb is getting too much air at (idle) with low vac and stumbles until the engine gets enough fuel to rev up and increase vac. Also he said the main jets don't have anything to do with low rpm when you are launching the car.

The vac reading seams high?

Posted By: 79powerwagon

Re: I'm lost...hesitation issue...bad acc pump symptoms?? - 04/07/12 02:42 PM

Quote:

Throw that BBD or whatever out the window and have fun :P

The wisest statement of them all in this whole thread!

To me, this sounds like a tuning/mechanical issue, not immediately a carb issue (as is the case in 98% of these kinds of posts). Throwing parts and money at the symptoms does not correct the problem. Proper understanding and diagnosis does.

Posted By: Secret Chimp

Re: I'm lost...hesitation issue...bad acc pump symptoms?? - 04/07/12 06:02 PM

Quote:

Quote:

Throw that BBD or whatever out the window and have fun :P

The wisest statement of them all in this whole thread!

To me, this sounds like a tuning/mechanical issue, not immediately a carb issue (as is the case in 98% of these kinds of posts). Throwing parts and money at the symptoms does not correct the problem. Proper understanding and diagnosis does.

Awhile after I first came here I had to learn that any question was going to get a lot of weird irrelevant mechanical questions half the time.

"My car is really hard to start in the morning"

"What converter are you running?"

Posted By: kilroy

Re: I'm lost...hesitation issue...bad acc pump symptoms?? - 04/08/12 03:19 AM

This is a free fix if it works so try it first.

If it is low speed just off idle hesitation/lean spot, that is created when you hold the throttle at a slight postition with out actuating the accelerator pump (like when you are pulling out of the driveway easily).

If this is the problem, try richening the idle mixture screws half a turn each. If it gets better, do an additional eighth of turn each until it goes away.

The explanation of this is the main wells are not active yet because of lack of engine speed, and the accelerator pump isnt moving so it cannot supply fuel, the only thing left to fix would be the idle mixture screws or idle system.

Ive fixed a lot of hesitations this way, just try it and see if it works, you wont be out anything and it only takes minutes to see if it worked.

Posted By: CUDA8U

Re: I'm lost...hesitation issue...bad acc pump symptoms?? - 04/11/12 11:00 PM

Quote:

This is a free fix if it works so try it first.

If it is low speed just off idle hesitation/lean spot, that is created when you hold the throttle at a slight postition with out actuating the accelerator pump (like when you are pulling out of the driveway easily).

If this is the problem, try richening the idle mixture screws half a turn each. If it gets better, do an additional eighth of turn each until it goes away.

The explanation of this is the main wells are not active yet because of lack of engine speed, and the accelerator pump isnt moving so it cannot supply fuel, the only thing left to fix would be the idle mixture screws or idle system.

Ive fixed a lot of hesitations this way, just try it and see if it works, you wont be out anything and it only takes minutes to see if it worked.

the squirters were too small on my car,with the 2800 stall,4:11 gears it needed a huge dump of fuel,first i went to 32's from 29's,as soon as i rechecked my accel pump and installed the 35's the problem was gone.

Posted By: magnum440d100

Re: I'm lost...hesitation issue...bad acc pump symptoms?? - 04/11/12 11:48 PM

Quote:

Quote:

Throw that BBD or whatever out the window and have fun :P

The wisest statement of them all in this whole thread!

To me, this sounds like a tuning/mechanical issue, not immediately a carb issue (as is the case in 98% of these kinds of posts). Throwing parts and money at the symptoms does not correct the problem. Proper understanding and diagnosis does.

I'm actually waiting for another set of intake gaskets/thermostat gasket so I can put the 4bbl intake on. I'm done messing with this 2bbl. I borrowed a friends 2bbl (same EXACT carb) and she runs like a sewing machine. I am borrowing it for the time being until the gaskets come in

Posted By: kilroy

Re: I'm lost...hesitation issue...bad acc pump symptoms?? - 04/12/12 12:55 AM

keeper roll'n