Slant Six Forum
https://slantsix.org/forum/

Same old low speed bog
https://slantsix.org/forum/viewtopic.php?t=29680		 Page 1 of 2
Author:  Royceflo [ Mon Jun 23, 2008 2:20 pm ]
Post subject:  Same old low speed bog
I have removed the EGR system, the OSAC and installed a new coil, tune up (champion plugs i believe 405s gapped to .035), oil flush, valve lash (.022 and .012). Rebuilt the carb with a GP sorenson kit. I've replaced the vacuum pot on the distributor. Also, I've adjusted the acc. pump trying its different settings.

Yet still, when I stomp the gas the car wants to stall. When its in park I can stomp the gas and it has no issues. It has back fired once through the carb however. The idle is set at 800, and the initial timing is 10 BTDC. What is weird, is that at the carb where the vacuum advance plugs in, it pulls vacuum at idle. I haven't tested it yet for a reading, but when my finger plugs the hole, i definitely feel suction. At idle, when i unplug the carb and adjust, the timing jumps. I don't have a dial-back and don't know the exact degree it goes to. I feel, this is the most suspect of my problems.

Something, that i considered is that the engine only warms up to about 145. I just replaced the thermostat, and I know that it was probably miss-packaged. I had asked for a 195. I don't feel that that should have such an effect, but that will be replaced. ( the temp sender was replaced too so i know it's the thermostat)

I have no idea what to check for now. I've been told to drill out the plugged Idle air bleeder port? in the 1920 holley. I've never had to do that before, and I'm not positive where to begin on that.

I'm about to go fiddle a little bit with the choke and try adjusting it a little.

Any ideas though please let me know.
Author:  Wizard [ Mon Jun 23, 2008 2:38 pm ]
Post subject: 
The throttle is too OPEN exposing the progression holes. THis bedeviled mine too.

Advance has vacuum at idle is biggest clue.

So, sounds like ignition is way off forcing you to screw with the throttle idle rpm?

Cheers, Wizard
Author:  68barracuda [ Mon Jun 23, 2008 2:41 pm ]
Post subject: 
Hi
What is the condition of your distributor?

Are you sure it is the right vacuum port - as the vac advance should only see vac in the mid ranges

Is your accelerator pump functioning - and if so - is it setup correctly after the rebuild.

Have you made double sure you have no vac leaks?

Just a couple of questions to follow up - maybe it helps
Author:  SlantSixDan [ Mon Jun 23, 2008 2:46 pm ]
Post subject: 
Yup, you should not be getting vacuum at the distributor advance port at idle. This what you're finding is the interplay amongst base (initial) ignition timing, distributor advance curves, and throttle position. Advancing the base timing will speed up the idle, so you can back off the idle speed adjusting screw, which should cover the spark advance port and stop supplying vacuum to the distributor at idle.

What year and model vehicle is this?
Author:  LUCKY13 [ Mon Jun 23, 2008 2:53 pm ]
Post subject: 
Knowing th etemp for sure would be a good idea, many times the sending unit they sale just dont function right, or are just not calibrated right. A infra red gun is one good way to comfirm your water temp
if you have one, or can get a freind to use his and check it.


With that said, it really should not be causing the bog, unless you are on the very ragged edge of being to lean ( very possible to be to lean ).


The timing vacuum line should be hooked up to a port that has vacuum after you open the throttle, not a port that has vacuum at idle. This can cause the bog sometimes.


What main jet do you have in the carb. Depending on where you live it may just need a bigger main jet, #58 is on average the norm for working good in these carbs when things like a slightly better flowing exhaust has been added. EVen when no mads have been done the fule we have today runs a lot lener than our old fuel and needing to richin up the carb may be needed just because of the fuel (10% ethenol added in many places).


You need to check though and make sure that the accell pump squirts as soon as you touch the throttle.


Jess
Author:  Doc [ Mon Jun 23, 2008 2:56 pm ]
Post subject: 
As already discussed, it sounds like you have the vacuum advance hooked to manifold vacuum or the throttle plates are too far open, giving you a ported vacuum signal at idle.
Either way, when you hit the throttle under load, advance comes out, instead of "pulling-in" like it should, that causes the bog.

You will have to make sure you are working with the ported (venturi) vacuum signal and then make sure it is timed correctly to throttle opening. There should be no signal at 800 RPMs and it should "tip-in" when you crack-open the throttle blades.
DD
Author:  Royceflo [ Mon Jun 23, 2008 2:57 pm ]
Post subject: 
Its a 73 dart swinger. I'll have to wait for my buddy to come over with his tach and readjust the idle with the new timing. I guess i should have thought of that, but i guess thats why Im on this site in the 1st place.

When i stomp the gas and keep my foot down, ill get a nasty back fire right now or it stalls. But, ill adjust the idle before i do anything else. My idle was set at around 800 before i re-timed. Could i just put my finger over the nipple and back off on the idle screw until i stop feeling vacuum?

Barracuda, I the accel pump was adjusted and tried at all 3 settings. i've found the best setting to be the middle hole for me. The vacuum port im plugged into is passanger side, bottom most left of carb. I've tested vacuum leak on all hose, even the charcoal canister with no problems.

Anyone feel that maybe the engine not running at 195 could have something to do with fuel atomization? I personally don't think it would cause stalling. Although, i am switching out for 195 a little better mileage. Not to mention, its OEM so why not.
Author:  LUCKY13 [ Mon Jun 23, 2008 3:16 pm ]
Post subject: 
The temp thing can cause it to stall, but you would about have to be on the edge of being lean for it to be doing so.


The backfire is telling you a possibility of two things (as long as no machanical problems are there) either its to lean, or the timing is so retarted its firing way to late. The harmonic balancer outer ring slipping out o fplace is a nother possibility for this. If the ring slipped, then it is not telling you the true timing and you may have to advance it up farther.


Jess
Author:  Royceflo [ Mon Jun 23, 2008 10:05 pm ]
Post subject: 
I didn't have the tach to check where my rpm was or is now. But i dialed down the idle control screw until I couldn't feel any more vacuum. Then, i put the timing light on the motor and made sure that the initial timing stayed the same when the carb port was plugged and when the vacuum advanced was hooked up (at idle). That way i know it has zero vacuum.

It DOES run a lot better. But i think I have a little bit more to go.

There has been a relatively dramatic change in its performance from a dead stop. But, if I stomp the gas and hold it, the car still stumbles and wants to stall. On occasion it still will stall or at least sputter hard. I think I may gap my plugs a little more from .035 because I do have a better MSD blaster coil. I think I can probably mange .044, but we'll see. Also, I think maybe my running temp may have more to do with it than I think.

So far everything else thats been suggested has checked okay.

It doesn't seem to have the problem nearly as much as when it is in park. Although when I actuate the throttle by hand on the carb in park it occasionally will stumble too.
Author:  DusterIdiot [ Tue Jun 24, 2008 5:38 am ]
Post subject:  Acc.Pump link...
Quote:
Although when I actuate the throttle by hand on the carb in park it occasionally will stumble too.
First I would check for vacc. leaks at the manifold...


You will need to get a picture of your carb, and find the accelerator pump linkage rod(it's a Holley 1920, right?)... it sounds like the timing of the pump squirt is a bit off...
If the rod is in the middle hole you will need to move it to the outer hole.


-D.Idiot
Author:  SlantSixDan [ Tue Jun 24, 2008 8:08 am ]
Post subject: 
You may want to review the tune-up parts and technique suggestions in this thread, paying particular attention to the distributor rotor, spark plug, and spark plug washer info.

When I go through carbs like yours, I usually stretch and/or shim the accelerator pump spring (without overdoing it) to provide a more positive accelerator pump shot. The springs tend to take a set over the years. Changing the accelerator pump cam link to the outer hole as DI suggests may be a workable temporary or permanent solution, depending on how your accelerator pump is performing presently.

You've checked to make sure your vacuum advance pod and hose hold vacuum OK, right?

For more info on Holley 1920 tuning and dial-in to eliminate hesitation, see this thread and the threads linked therefrom.

Also make sure that since you've disabled the EGR, the venturi vacuum port (the small one up near the top of the carb on the passenger side) is securely plugged off. A leak here will spoil the carb's calibration.

The idle air bleed drill-out modification may or may not apply to your carburetor, depending on whether your carb's air bleed is plugged or open, but your '73 1920 will have the air bleed adjustment screw, and you may make some headway by paying it some attention. See thread here (pics start on page 5).
Author:  Doc [ Tue Jun 24, 2008 9:11 am ]
Post subject: 
Do you have a vacuum gauge?
It sounds like it's time to drive around with a vacuum gauge to see if the stumbe happens at the same pressure drop-point.
You may need to shim the "economizer valve" (power valve) so it tips-in a little sooner.
DD
Author:  Royceflo [ Tue Jun 24, 2008 10:02 am ]
Post subject: 
I have used Champion Plugs 405s with the metal washers attached. I probably need the fix that. I also used a bosch wire set, with a blue-streak cap. Also an MSD blaster coil, as I had one just laying around.

I had used a GO sorenson kit, since i can't get walker around here. I replaced the acc pump spring, a local carb shop around here "carbs r us" had the spring, and a new float. I had already experimented with different acc pump cam link placement. But, Ill take the advice and go to the outter hole again with the new timing.

The vacuum port on the carb is capped with a rubber vacuum plug and its damn tight on there.

Ill fiddle with the Air bleed adjustment.

Thanks a bunch. I have 3 more ideas to try. AND JUST WHEN I THOUGHT I HAD TRIED EVERYTHING!
Author:  Royceflo [ Tue Jun 24, 2008 11:41 am ]
Post subject:  Re-jetting
Does anyone have an opinion on re-jetting the carb. Consider it's a completely bone stock Slant 6 with a holley 1920 carb. Only thing thats maybe not stock is the lack of EGR and Osac. Any opinions as to what jet size to consider, I was thinking maybe a #62.

Ted said he had ran a #57 then a #62. I believe his compression is higher. I'm tuning more for MPG, would #62 be too high?

Let me know what ya think...thanks again
Author:  Doc [ Tue Jun 24, 2008 1:11 pm ]
Post subject: 
Go 2 steps higher then the jet that is in there now.
If I were to guess on a size... it has a #58 so try a #60... this is a guess.
Page 1 of 2 All times are UTC-07:00
Powered by phpBB® Forum Software © phpBB Limited
https://www.phpbb.com/