bogging 318

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VolksDuster

VolksDuster

Back Yard Guy
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Hi There,:D Im new to the fourm under this name and it has been a long time since I have been on here. But I have a Twister again and will for good now, I think.

This is a 1973 Plymouth Duster/Twister with a 318 and Automatic trans, I have an issue where the car will start and idle fine but under load (in any gear) the car boggs and dies as soon as I hit the pedal. At this point I thought it would be either dirty carb or bad vacume advance, so I cleaned the carb and replaced the vacume advance. No Change in symptome

At this point I decided to replace the carb and distributer as well as Coil, cap, wires, fuel filter and breather, Also I decided to replace the chain and gears because the was a little slack.

And this is where I am now... All parts replaced and adjusted, and the car is still to be doing the same thing, I`ve tried advancing timming, retarding the timming, adjusting the accelerator pump, adjusting the idle mixture. Also checked for vacume leaks (none) and nothing seems to change the bog.

So I`m hoping some can tell me something so I can drive the car for a while before the snow gets here.

Thank you very much
 
Sounds like you've hit all the basics. If timing & idle mixture (make sure to adjust under load) are optimum & you're sure there are no Vac leaks, you may need to go up a fuel shooter size.

what is the initial & total timing?
How much vac are you pulling?
what carb & what size shooter?
 
Your saying your timing is fine but what is it? Sounds like you might need about 16-18 initial 34-35 total and have it all in around 2200. Timing can do alot.
 
tekslk said:
Your saying your timing is fine but what is it? Sounds like you might need about 16-18 initial 34-35 total and have it all in around 2200. Timing can do alot.
Click to expand...

Yes...^^^^^^^^

Is this a completely stock car? Or are there mods, carb, intake, exhaust, etc.
 
Thanks for the fast feedback,

The car currently has headers and a dual exhaust as well as an open intake (ie. base plate and top plate with 14'' filter, no snorkle). Other then that all current parts are new or remanufactured Stock parts, like the 2bbl carter carb.

As for the timming it wa always at 0 running 750 rpm until all these updates, currently it is at (since the marks on the timming cover only range + or - 10 deg) 12 deg advanced with the vacume advance unhooked at 800 rpm idle. And with the advanced hooked back up there is a steady fast climb when its reved up.

And as for the vacume pressure when the car is at 800 rpm there is a very steady 2 psi (using a cheap Eques vacume/fuel pressure guage), and as the rpm is increased the vacume increases quick and steady.

And as for vacume leaks, nothing can be herd with a scope and nothing is showing up at any of the vacume ports (like a bouncing needle on the guage), and I also used starting fluid around the maniflod and carb.

So this is where I am:banghead:
 
Vacuum readings are more likely to be in the 16-20 inches mercury range taken at the manifold. Where are you Getting 2psi pressure from?

sounds like plugged exhaust.
 
If you have been reading the vacuum above the throttle blades,that's ported vacuum. Anything at the base of the Carb or on manifold,THAT's ported vacuum. Find a port,look for that 16 to 20 inches vacuum. Have you been adjusting the idle circuits(mixture screws),at all? This can have huge effect,on idle to 2500 rpm response.
 
The 2psi is from the cheap dial vacume guage, it measures blowing pressure and vacume pressure in (Pounds per Inch) and (Kilopascalas). And I had this attach to the vacume advance port when setting the timming which is when is showed 2psi at 800rpm.

As for the mercury vacume test, I'm not sure what that is?, I have never used that type, but I did see that test in the manual.

And for the timming, I set it in Neutral with no vacume advance attached and I was able to get it to about 12 degress at 800 rpm.

Also I was unaware that these setting and adjustments should be made under load, The repar manual does not state anything other then to set in nutural. Prior to this I had a manual trans.

Thanks for the Info
 
If you move the throttle open a little how much vacuum does it pull then? The port you are using is mostly blocked off with the throttle closed. 15 in hg = about 50 kPa. No load needed to set base timing "by the book" I don't use base timing but rather total mechanical advance. No vacuum hooked up set timing to 28-30 degrees at 3000 rpm. (most distributors stop advancing at or below 3k rpm) A good timing light with dial back capability is nice for this. Having not owned on yet (why I can not tell you as much as I tinker with this) I set my timing mark at 10 degrees btdc and make a mark at 0 degrees. Then move this mark to 10 btdc and make another mark a 0. now you have 20 degrees marked and 10 or more on the engine engine tab. Gets you close to 30 and you can fine tune from there. Add vacuum advance after total is set and you are satisfied there is no ping at WOT throughout the RPM range. Some vacuum advance cans with a hex shape near the vacuum port can be adjusted also. As for the bog, does it come back to life after letting off the gas or just die out? Will it eventually gather itself back up and take off? Does pumping the pedal while accelerating help or make it worse? Also check you Alternator output. Literally just had this happen with a failed battery and alternator yesterday.
 
Well I will check again tomorow after work what the vacume reads in kPa, and I didn't think it would need to be under load to set the timming.

But I don't really understand how to mark for 20 dergees? The car has a stock ballencer which is keyed to the crank shaft with a timming mark and the timming cover is stock and prevents me from seeing past 12- 14 degrees because of the shape and overhang. But I just realized you mean make marks on the ballencer above and below the stock mark, and now I understand
:cheers:.
And as for the bog if im in nutural, as I said there seems to be no issue but underload as soon as i hit the peddel (for normal or fast acceleration) it bogs instantly and dies. But sometimes if I lightly feather it, short and quick a couple of times it brings up the rpm enough to catch (but that has been about 1 in 5 tries). I never thought to check the altenator output because the car seems to charge after alot of cranking and maintain the battery which is only a couple of months old.

Thanks Again.
I will post back tomorow after I make another test also I will try and take a couple of picks as well or a videoif i can.
 
To mark you balancer the easy way is to buy a timing tape.
Or mark it with a scribe, pi x diameter.

Most re-manufactured carbs are junk...I hope you kept the old one.
Check to see actually how much is fuel shot you have when the motor is off looking down the air cleaner.
 
Have you checked to see if there is a fuel stream when opening the throttle by looking down the carb bore? Accelerator pump adjustment (or choke is not open) is most likely if you can eventually get it to giddyup and go all the way to it's top end. extreme advance on the timing would more likely be a buck and backfire situation.
 
Sorry for the slow response,

After getting the car warmed up again I plugged a new vacume guage back in at the advanced port and found it read around 6hg at 750 rpm with 12 degrees advance. So I shut it down and found that through all the adjusting to get it to idle, the curb idle screw was almost all the way in and there was about 2 1/2 turns out on the air/fuel screws which was creating creating vacume at the top port. So I started it back up and first strated backing out on the air/fuel screws 1/4 turn at a time until the rpm began to increase, then at 4 3/4 turns out i reached max rpm and was able to back out on the curb idle screw and brought it back down to 750rpm. At this point the curb idle screw was still about half way in and showing a very small pull on the vacume guage. So I began to back off on the Curb idle screw and rotate the distributer to keep idle speed at 750rpm and now the curb idle srew is only about 2 turns in and the vacume guage shows 0.

At this point I double checked to be sure the accelerator pump was smooth and even, and it was (2 clean strong streams). So I put the car in gear and it still bogged out?, So befor I flashed it back up I again took a light down into the carb to check the spray of the pump as well as watch venturies when it started back up. Now at this point I gave the throtle a couple of pumps and the accelerator seemed to be fine I flashed it back up, seemed ok, reved up fine, then a little stumble when I tried to rev with the peddle, so I looked with the light and the car running and just kept giving it small kicks.

And I see the Accelerator pump wasn't alway pumping right away on short small kicks, so I adjusted the travel of the pump rod to a point where I was always getting a squirt but it had shortened the travel of the plunger therefore a shorter squirt. But this seemed to correct the bog.
So I put the breather back on, and went for a test.
Now in drive there was a quick slight hesitation when i hit the gas, but it did start to accelerate, and I brought it up to 25mph slowly and then came to a stop.
And on the second try, hit the peddle harder and had a little more hesitation but a quick feather and I was on my way, this time with the peddle down. The did not have good acceleration and there was a noticealbe ping throught the range.

So I put it back in the garage to cool down and make this post, And I am thinking that I will have to back off on the timming slightly and increase the curb idle as much as I can without creating vacume at that top port while maintaining aroung 750rpm.

And this is where I am now, I hope Im still on track but I am wondering what the new thoughts are?

Thank you again for all the help
 
I also tried to get 0 vacuum at idle and found that without modification it is not likely. any vacuum up until the vacuum advance starts to pull in additional timing will not effect idle. Most guys here will advise you to get the max vacuum at the manifold (ie. pcv port) for idle timing. then adjust your total mechanical advance to achieve maximum total mechanical advance under WOT for best acceleration. your bog seems to be more a result of the acceleration pump than timing at this point. It should start to pump as soon as the throttle is pushed and all the way till Full throttle. It appears that the Acceleration pump has a problem pumping near the beginning of its travel. Check ball may not be installed or the piston seal is leaking. Check here first. Ethanol gas is notorious for causing problems in these carbs.
 
Hi, Sorry for the slow reply, I've been working a little more then expected...

So I am now at an 800 rpm idle with very little vacume at the advance port (not enough to read on the guage), and sitting at 14 degress initial timming.
And when the throtle is brought up to 2000 rpm there is about 18 hg in the vacume advance port and 32 degrees of timming. As for the accelerater pump I lubed the shaft with carb cleaner and reset it to a longer stroke and it looks like its acting correctly.

And now I have two small videos that show guages and settings but I can't seem to load them up? And I have a few pics as well but it seems I will have to take new pics at a lower quality and smaller size to upload.

Also, should the Accelerator pump shoot a stream the whole length of the throtle movement? or just the first bit?

Thank you
 
Well now I have been trying numerous things and I am sure of this, the car is still bogging at the start of acceleration, and never trust new or remand parts.
And I know my timming adjustments have been correct in their changes vs affect as well as air/fuel and voltage output are good. so it has to a quirky accelorator pump causing these problems.
Although the accerator pump seems to be spraying even streams throughout the throtle range. At slow and moderate acceleration the accelorator pump seems to be speratic in how it works (sometimes a dribble, sometime times late start, sometimes thin streams. So at this point I am in the process of preping the old carb to reinstall, knowing the accelorator pump was good. This will hopfully correct the problem and it will just be a matter of new seals and gaskets for the old carb (if it works).

My new question to an ongoing process is this, Since a moderate to fast acceloration on accelorator pump shoots 2 thick, fast and strong streams. What should the accelorator pump streams look like with very light, slow, constant accleration? Should they be thin, fast and strong? or thick, slow and week?

And I am sure of this...
A 318 with stock everything except headders and air breather does exactly what you would think it would do changing various adjustments, ie. timming, air/fuel. And it comes down to this...

Assuming all new parts are working correctly...

Start with timming (with vacume unhooked) to get it running, get it warm, then adjust cub idle screw to give you 750rpm and move to air/fuel screws (with a starting point of 2.5 turns out) adjust to a richer setting (1/4 turn at a time) to the highest rpm increase.
Then back off on the curb idle back to 750 and recheck the timming to have a starting point (2 - 12 degrees advanced @ 750rpm with no vacume advance or mechanical advance), and this should have a driveable car with basic stock performance

At this point is where the fine tuning for performance starts such as timing advance, which effects idle rpm and acceleration. Or Air/fuel idle mixture wich effects economy, heat, and idle rpm. And then there is vacume advance which changes the rate which timming is advanced at the beggining of the rpm curve.
And for me in nutural at least, it seems the 10 degrees advanced @ 750rpm prior to vacume advace hook up. Seems to work the best overall, allowing good throtle response, clean burn, easy starts, and even warm up.


Thank you for all the feedback and help,
I hope with the last bit of input of this thread will be able to ensure anyone will be able to have the stock small block running and put them on the track to fine tune for their own preference.

Thanks again I hope to here back
 

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Couple of other suggestions...pull the distributor cap and give the rotor a twist...it should move against the mech advance springs when you turn it one way, and return by itself. This will ensure that your mech advance system is not seized.

You also need to find a "Manifold Vacuum Port"...one that supplies full manifold vacuum, even at idle. This is where you hook your vacuum gauge and get the vacuum reading (16-20 in. vac). The "ported" port is only for distributor vacuum advance.

You can mark your damper by measuring the distance between "0" degrees and "10" degress, then mark that distance again for "20" degrees, again for "30" degrees, and so on using white paint or "White-Out". As for initial timing setting, set it as advanced as it will go without getting "starter kickback". That will be your "Initial Timing" setting.

Your accel pump should give a good, solid, continuous stream from crack of the throttle to almost all the way to full throttle.
 
Hi, thanks for the info and reply.
As for the mechanical Advance, as stated this is a new distributer, and there is good tension and recoil on the spring, as it was checked at install.

And yes there is about 22hg @800rpm at the brake booster port on the manifold, which will change a little bit based on the amount of curb throtle.

The Ballencer was remarked with 40 degree in totals and 5 degree incraments a few weeks ago and it is now at 12 degress initial, and once i'm sure the car is driveable, then I will tune the timming further.

And as for the accelerator pump, as mentioned I am aware of soild even streams with moderate to quik throtle movement, but my question is in light peddle pressure, do the just not shot as far or are they thinner streams?

Well this is where I am now, just finnished putting the old carb on and going to test it out tomorow, simply because the car is too loud for the neighbour, if it is the accelorator pump, or a carb setting causing this issue, this should correct it since the carb was only changed because of leaks.

Let me know what you think and if you have any other specific questions to narrow this down. And I will repost tomorow after the testing.

Thanks Again
 
:glasses7:So it seems to have been sorted out.....

The new carb was missing an ultra light spring and baffle located inside the top of the vent bowl cap, which seems to regulate plunger pressure. These were not in the book and I was unaware that they were used. So I removed the old vent cap assembly with the plunger from the old carb and placed it in the new one and it seems to be working fine,
That is 2 long even streams with quick full throttle movement (1.5 sec)
and,2 short even streams with slow throttle movement (4.5 sec)
I am able to hold the brake and apply any amount of throttle at any rate without the bog and I'm breaking the wheels free.

So here is how it lays out,
To have your car running with stock parts,

1 - Be sure the ballast resister is not cracked and the coil is good
2 - Replace wires, plugs, and cap if needed
3 - Be sure there is little to no slack in the timing chain
4 - Use new distributer, but inspect for correct settings
5 - Use rebuild kit on old carb or replace and set to required bench settings

This should allow the car to start and continue with adjustments

6 - Check timing to be sure it is in a useable range to start,
Cold engine 10-15 degrees timing at 1200rpm with closed choke on fast idle cam
7 - Allow the car to warm up and maintain the idle using the curb idle screw on the fast idle cam
8 - at this point remove the idle advance vacuum from the carb and attach a vacuum gauge, also attach an rpm gauge if needed as well as a timing light.
9 - Set the rpm to 750rpm using the curb idle screw with no fast idle cam and the choke now open and engine warm
10 - Set the initial timing about 12 degrees advanced on average, this will cause the idle to increase
11 - back off on the curb idle screw to bring it back to 750 rpm and confirm timing, this may take 2 or 3 attempts to get 12 degrees at 750 rpm
12 - now you can begin to adjust the air to fuel ratio to a point of max fuel with no smoke, this should smell a little rich and have minor moisture coming out of the exhaust pipes this will be about 3-7 turns out on average depending on gas quality and port size
13 - at this point you can determine weather you have enough vacuum at idle for the brake booster, about 22hg. if it is low increase the curb idle screw and reset the timing to maintain the 750rpm until you reach enough vacuum
14 - Now if the car seems to be running clean (no smoke) and not smell to lean, then listen for any unwanted noise and watch for any odd vibration, and if all seems ok it is time for a test drive to listed for valve pings.
15 - If there is no pinging during acceleration or at high rpm then all is good and you may be able to add more timing and you are good to go.


So with these 15 steps and the initial information throughout this thread,
I hope this will help anyone else in the future:D
Thank you for all your help to those replied:happy1:
 
Nice work & patience,Volks. Nice car,BTW.... That list (last post),dead on.
 
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