225 bogs taking off from stop while hot

[JL0708]

For a while I’ve been having issues with the engine in my 73 slant 6 Duster. Starting up the car and driving around while it’s still cold, the car drives great. Once the temp gauge reads the first mark on the gauge (130-140ish) the engine starts to bog really bad taking off from a stop. It has caused it to stall a few times but not consistently. Runs great while cruising and at idle, both in and out of gear, even two footing the brake and gas while stationary to see if it bogs under the resistance of the brakes, reacts fine, only while accelerating from a stop does it bog.

So far I’ve rebuilt and adjusted the carb and float, checked for intake leaks, and checked the timing and ignition advance (set to TDC according to the fender sticker, OSAC is not currently connected but has been for diag, has no effect on issue). The engines is factory 225 but has a 72 Holley 1920 from a dodge truck and has been adjusted to both 72 truck specs and 73 duster specs, still no effect (is currently adjusted to truck specs according to list number 6260.) Has anyone else had this issue and found a fix? I’ve thought about EGR but still has no effect whether it’s disconnected or connected, I have not pulled off the valve and checked if it’s stuck open or not and was going to be my next check after making this post.
Thanks

 

[abdywgn]

vacuam advance on distributor?

 

[AJ/FormS]

Ok so my thinking is that the Transfers have dried up, and they are sluggish to wake up. This leads to a Tip-in sag, which leads to a hesitation, which terminates in a bog.
My recommendation, is to fix the Tip-in sag first.

Ok then;
I hate to flog a dead horse, but I wouldn't touch your engine without having fresh compression numbers, and knowing for sure exactly what the valve lash is set to. see note-4
Make sure the VA is NOT on full-time vacuum.
If it is, then put it on the sparkport, make the necessary idle-speed and mixture screw changes, and then try again.
But if it was and is already on the sparkport; then ;

1) make sure the PCV is hooked up correctly and is operational, see note-1;
2) then increase the IN-GEAR idle-speed 200rpm and try it again.
If it works, you found your problem, which was, dead Transfer slots.. See note-2
3) if it doesn't work, see note-3
4) Make sure your TC is functioning correctly.
5) that's all I got, and I could be wrong


Note-1
The PCV must enter the carb BELOW the throttle plates, and in between them, to mix with the fuels coming from the low-speed systems which are A) the transfer slots, and B) the mixture screws.
You may have to retard your ignition timing back closer to ~TDC, to get a wide enough throttle-opening to keep the transfers awake. Until you get this sorted, do not try to idle the engine too slow, which will just shut the transfers down.

Note-2
decrease your in-gear idle-speed, 50 or so rpm atta time until the problem returns.
When it returns, go back up 50rpm. after this, do NOT change the Curb-Idle-Screw adjustment. Now,
if the idle-speed is too fast, retard the timing until it gets back to normal, but; Do not try to idle the engine too slowly.

Note-3
Check your manifold vacuum, and make sure that ALL the air that the engine is getting, is coming thru and past the Throttle blades and or the PCV.
Make sure the Accelerator pump begins fuel delivery, the instant that throttles begin to open, and that the fuel comes out in a continuous strong stream.
Check your WET fuel level. If there is room in the specs, increase it ~1/16th inch.
Make sure, that your manifold heat-control valve is functional.
Then try again.

Note-4
I can't tell you how many times I have been bitten by too-tight lash settings or one low pressure cylinder that was sending pressure back up into the intake.
IMO, the factory settings of 010/.020(IIRC) are too tight. Reset them to .013/.023, and make sure that this is a true setting, with your feelers NOT straddling a groove in the arms, worn there by time. I have had excellent results with 13 and 23.
If you have a cylinder with low pressure, do a Leakdown test, and find out why. If it's a leaky intake, you gotta fix it. Forget trying to tune your engine with a leaky intake valve.

 

[TrailBeast]

Try tying the choke 1/2 closed and see if it’s better or worse.

Better means you have an off idle lean condition.
Worse could mean either it’s already too rich, or more likely not a fuel issue at all.

Misadjusted points can do this as well.

There are more that can cause this, but eliminating one thing at a time could only help.

 

[Rug_Trucker]

When driving around on errands is it hard to start hot? Have to put it to the floor and hold it like it is flooded?

Does the gas boil out of the carb with a wafting mist when it sits hot?

The fuel line is the original, and in the original configuration? Not good with E10. Insulate and reroute it.

Make sure the flapper for the manifold heat under the plenum is opening, and the bi-metallic coil spring is still present.

A vacuum gauge is a great tuning tool.

 

[Oldmanmopar]

Had one come here from a dealer years back . They could not fix it. It was timing chain slack. Take the distributor cap off and watch the rotor while turning the crank back and forth. How far does the crank move before the rotor moves.

 

[KosmicKuda]

Lots of good advice alteady given.

You said static timing is at TDC.
Try advancing to 8° BTC for a start.. It may not fix the hot condition much but it will make a difference.

 

[slantsixdan]

8° BTDC is a bit much; use 5° BTDC.

Do the Fuel line mod.

Carburetor operation and repair manuals and links to training movies and carb repair/modification threads are posted here for free download, and find tune-up parts and technique suggestions in this post.

 

[JL0708]

So to answer as many replies as I can in one post, I’ll try to keep it as detailed as I can.

I checked the throttle plate both after I rebuilt the carb to ensure nothing was loose and needed replacement, and after adjusting the idle screw to ensure it didnt have too much tip in sag.

The vacuum lines for everything are set up as per factory spec (according to the factory service manual).

Compression is good in all 6 cylinders (I don’t have the exact numbers off the top of my head, but again within spec according to the manual).

Timing is set to TDC per the fender sticker but I did notice the adjustment bracket was bottomed out completely and I couldn’t make any further clockwise adjustments.

Tying the choke off has no effect on it, which is why I originally thought I had a constantly opened EGR since I removed and plugged off the EGR vacuum lines and it still does it. I even covered the top of the carb with my hands and it still ran fine, again thinking vacuum leak but found nothing with a can of carb cleaner. i was thinking using a smoke machine to smoke the intake when I get a chance.

I could stop and start the car running errands as many times as I have places to go and it starts without issue. I could rev it as hard and as much in park and it runs like a champ. It’s only when I accelerate from a stop.

I will have more info next time I have the car out and I try some more suggestions

 

[RustyRatRod]

Have you actually looked down the carburetor throat and seen the accelerator pump squirting fuel?

 

[Bewy]

I think it is lean. When cold, choke is on [ or partially on] & that richens the mixture. Hence ok when cold. If throttle shaft has a lot of wear, it is going to act like an air leak & lean the mixture. I would try raising the float level 0.100". Might seem a lot, but unless you make a significant change, you might not notice a difference.

 

[BillGrissom]

Dealt with that in my first car for almost 20 years, a 1969 Dart slant 225. No mechanic could figure it out. I was sure it was due to being lean at idle. I finally tried a 4th Holley 1920 and it purred like a kitten. I had tried changing almost everything under the carburetor, yes even a new long-block, so figured it must be that dang carburetor. As related here, it has a sealed metering block for the idle circuit that gets clogged and most rebuilders don't touch it. Some guys here said they know how to clear those passages, blowing compressed air thru some of the holes in the base. BTW, other manufacturers used the Holley 1920, so might find the same issue discussed in Ford and GM owner forums.

If you give up on the 1920, a Holley 1945 should fit, though I don't know the pros and cons of those. A harder option, though nice, is to find a rare "Super Six" manifold to use the common Carter BBD 2-barrel carburetor. Another is a 4 bbl intake (Offenhauser, Clifford, or Aussie Hurricane) with the smallest 4 bbl carburetor you can find (~370 cfm). At the highest end would be an MPFI intake. A company in TN began making them for the slant. But that requires other things like high pressure (60 psig) fuel delivery. At least one guy here rolled his own MPFI.

 

[RustyRatRod]

Another hit and run.

 

[BillGrissom]

Another hit and run.

I term a "fly-by poster". Common among newbies on web forums.

 

[JL0708]

Sorry for not responding, not a “fly by poster”, just haven’t had time to try out everyone’s suggestions. Anywho, it’s fixed. Bad carb. Smoked the intake, the throttle linkage, and just about every vacuum port was smoking from the body. Threw on a knock off 1945 and now it runs like a dream

 

[slantsixdan]

Threw on a knock off 1945

A which, now? Got a link?

 

[JL0708]

A which, now? Got a link?

Unfortunately no, it came with the car. It’s an Elkton, the pic attached has all the part and list numbers if that helps on your search. I couldn’t find any info on it but it sets up and adjusts to the factory Holley adjustments

 

[slantsixdan]

That appears to be a Holley 1945. I'm tryna figure out the "knock off" aspect. That term means an imitation/copycat/counterfeit/lookalike part, and while there are Chinese things that look like Carter BBDs, there aren't any 1945-shaped gumball-machine trinkets, that I know of.

 

[JL0708]

That appears to be a Holley 1945. I'm tryna figure out the "knock off" aspect.

That I didn’t know. I thought it was a knock off/replacement since I didn’t see “Holley” anywhere on it, I figured Elkton was an aftermarket-type brand

 

[Mattax]

EGR is generally supposed to be working with the engine warm and from light to moderate throttle.
Since its only warmed up, and is not the choke, might be worth investigating the temperature control switches. Sometimes the distributor's vacuum advance is also on the switch. If you have the emissions diagram for your car it should show there.

 

[slantsixdan]

That I didn’t know. I thought it was a knock off/replacement since I didn’t see “Holley” anywhere on it, I figured Elkton was an aftermarket-type brand

Not seein' "Elkton" in your photo, but I do see a Chrysler part number (4179 021) and a Holley list number (8831), which is an early-production '80 (thru 1 Feb 1980) carb for 225/automatic passenger cars with 49-state emissions, no A/C, and automatic trans.

 

[JL0708]

EGR is generally supposed to be working with the engine warm and from light to moderate throttle.
Since its only warmed up, and is not the choke, might be worth investigating the temperature control switches. Sometimes the distributor's vacuum advance is also on the switch. If you have the emissions diagram for your car it should show there.

I currently have the EGR disconnected, and don’t have an emissions diagram. My car didn’t have/come with the head mounted vacuum amplifier and I can’t find a diagram for the slants without them. I do know it has the firewall mounted temp control switch for the EGR, but can’t find vacuum line small enough locally to reconnect it

 

[JL0708]

Not seein' "Elkton" in your photo, but I do see a Chrysler part number (4179 021) and a Holley list number (8831), which is an early-production '80 (thru 1 Feb 1980) carb for 225/automatic passenger cars with 49-state emissions, no A/C, and automatic trans.

It says “Elkton” on the base of the carb next to the PCV valve hookup. I unfortunately don’t have a picture of that. I did see the Chrysler part number and Holley list number, that’s where I got the adjustment references from. Do you know of any drawbacks using a Non-AC carb on an AC car?

 

[Mattax]

I currently have the EGR disconnected, and don’t have an emissions diagram. My car didn’t have/come with the head mounted vacuum amplifier and I can’t find a diagram for the slants without them.

There's one in the shop manual.
AFAIK '73 just had the sticker with the timing info etc, not the full diagram.
Of course a Calif car might have something different.
I would think the EGR valve is normally closed and only opened whith enough air going through the venturi and the temperatures warm enough.

I did some of the footwork for someone else not long ago.
Optimize the spark curve for a SlantSix.

Also don't forget the Master Tech Conference for tips and further explanations.

 

[slantsixdan]

It says “Elkton” on the base of the carb next to the PCV valve hookup.

Donno. Could be a Holley plant…could be a rebuilder's mark.

Do you know of any drawbacks using a Non-AC carb on an AC car?

The non-A/C carb won't have a throttle kicker solenoid to bump the idle up when the A/C compressor kicks on.