Hesitation when first putting foot on gas.

74monacoHT

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What are some things unique to this vehicle (if any) that would cause a hesitation when first applying the gas, while in gear. If I ease on it very gently, it could easily stall and has. If I hit it harder, it still hesitates very briefly but powers through it fine. I played with timing a bit, it's at 17 advance at idle now, was 22 advance at idle before. I know those are high relative to spec, but I didn't see any change when I dialed back to 17. It wasnt doing this a few months ago, but I'm not aware of anything that's changed. So what are the top few things I should be looking at? I want to dial it in just right for that smooth dignified takeoff. It has no issue in park. Picture for attention. 74 monaco stock carb, 400ci.
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Oh I should also mention you can hear the hesitation while already rolling too, but it's most obvious of course when pulling away. Thanks in advance for all replies!
 
"Maybe the accelerator pump on your carb?"

^^This^^. Classic symptom.

Move it to the middle or closest hole to the centre of the pump piston to get more of a fuel squirt.
 
Yes, and Retarded timing or a loose timing chain. Smog motor anyway so it’s never great . The 2.7 or 2 something rear end gears hurt it also.
 
Does this happen when starting from cold, after driving 10+ miles, hot, or "all the time"? Putting it in gear as soon as it has started or letting it run a bit before starting off?

This IS an emissions-era motor, when many things were getting tried to get the engines to be in compliance with emissions standards. They were generally running as lean as they could, so modern-era (or even GM-style) cold start driveability can be an elusive goal.

BUT, there MIGHT be a few things you can do to make things better. Involving some tweaking of the automatic choke thermostat setting, some tweaking of the vac pull-off adjustment, idle speed while in fast idle mode, AND even some of the fine-wire electrode spark plugs. ALL using approx. factory base timing specs!!!

As for the base timing specs mentioned, are these mechanical-only numbers and is the vac advance hose hooked up to the distributor for ported vacuum?

When you advance the base timing on an engine with a carb designed for less timing, you generally get a faster base idle speed, which to maintain the normal base idle speed, you close down the idle blades more, which puts the throttle blade position below the transition ports on the carb base. Which CAN cause a hesitation off-idle as it takes more time for the main system to start flowing, which the accel pump can't cover that lean situation. NO matter which rear axle ratio is in the car OR how loose or tight the torque converter might be.

DO ensure the choke thermostat in the manifold is set to specs. IF it is the OEM item, then you might try going one notch lean, as with age, the springs tighten-up, so a slightly leaner setting is needed. The choke plate should just close easily at 70 degrees F ambient (engine, choke thermostat, air around the engine, everything . . . with the engine cold). Then with the engine stopped, compress the choke pull-off plunger and see how far it opens the choke plate. Use the "V-area" in the link to adjust, open for a bit richer and close for a bit leaner. On the fast idle cam/screw, back off the fast idle speed screw until the lowest step on the cam will clear (not touch) the screw, but will raise the idle sped on the 2nd from lowest step. Aim for the lowest step to increase the base idle speed by about 50rpm, if that much.

Set the base timing to factory OEM specs. Distributor vac advance hose unhooked and plugged.

Then make sure the hot base idle speed and mixture are adjusted to "lean best idle" orientations at the OEM-spec hot base idle speed. Probably in the neighborhood of 700rpm on that model?

Now, where do the fine-wire electrode spark plugs come it? NGK claims they will fire a leaner mixture easier. They also exposes more of the ignition spark to the fuel/air mixture, for a better "pow" combustion. A few YouTube videos on that in lawn mower engines. So they can help things along a bit, but not completely necessary, from my experiences BEFORE they came out.

The Holley 2245 2bbl does not have the Chrysler factory-fix "Bridge Kit" on it, so make sure the choke blade is not touching the air horn as it closes. Or has put a small shiny spot on it from repeated contact. PM me about this. Is the EGR valve OEM, too?

Are the carb and distributor OEM to the engine or have they been changed? Are the carb hold-down nuts snug on their studs?

I realize that at this time in the vehicle's life, seeking to get it to make as few emissions as it might have when right off the assembly line might be an onerous task, so just getting it to work its best is the main issue at hand. BUT also getting it to do it as the leanest orientation is generally best, from my experiences. Any little bit of richness should be just to get it past a particular time-frame in its various operational modes rather than "constant". But not so lean that it has "spit-backs" and such. By using some of the tweaks mentioned, I got our '72 Newport 400 2bbl to work better from a cold start, back when it was "a used car", with a similar Holley 2210 2bbl. And then later with a '70 383 spec Holley 2210 on our '66 Newport 383 2bbl.

Thoughts and experiences,
CBODY67
 
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If you tighten the breather lid too tight on those carbs it can warp the top of the carb. The issue you are describing are all too common with those carbs. I suggest a 4bbl intake and carb upgrade. But I could be wrong. Take all advice you get with a grain of salt. And a couple aspirin.
 
On the Holley 2210/2245 and Stromberg WWC carbs, when the air horn warps due to air cleaner top over-torque, it also kills the vac signal to the power valve to keep it closed. Therefore, "10mpg no matter what" happens. Plus, as that is also the rear upper seal on the float bowl, when the choke valve is mostly closed, it can also suck gas out of the float bowl into the venturi area, which causes some very rich running. I've been to all of those places!

At least with the Holley 2210/2245, Chrylser did issue a TSB and a "Bridge Kit" to install on the Holleys to lessen/prevent the warpage. ONE benefit of the Carter BBDs is that their air cleaner stud is part of a heavy wire holder that snaps into the edge of the air cleaner circle on the air horn, which puts any over-torque forces on the edge of the air horn rather than in the center. FWIW.

Happy Holidays!
CBODY67
 
So - looking at you picture, I see it's not a Carter AFB - and hence my advice may be wrong. To increase the fuel squirt, you want the arm that pushes the pump diaphragm to get the longest push... so the shorter/lower slot (which in your carb's case is opposite to where I thought it would be) will give you that result... I think.
 
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When you advance the base timing on an engine with a carb designed for less timing, you generally get a faster base idle speed, which to maintain the normal base idle speed, you close down the idle blades more, which puts the throttle blade position below the transition ports on the carb base. Which CAN cause a hesitation off-idle as it takes more time for the main system to start flowing, which the accel pump can't cover that lean situation.
This makes perfect sense! The hesitation happens when fully warmed up even after driving it a while. Also I don't think I've tried to drive away before it's had several minutes to get up to temperature. I'll look into and respond to your other points as well after getting behind the wheel. Thanks!
 
This issue has been covered over and over on this site and @CBODY67 has very likely identified the real cause for this on all these Holley carburetors after some time.

I would send the carburetor to be rebuilt by RD Autoline in Canada and when you send it in, alert the technical manager at the company your are sending it in so they can press the air horn flat again and plane things as necessary (most of there workers get this right but sometimes the newbies there might miss that operation, hence the suggestion to talk to their technical guy before you send it in). They are well aware of this issue.

And in the future, make sure you do not tighten down the air cleaner any more than just needed to hold it in place, because overtightening the wing nut will cause it to happen all over again after more multiple warm up and cool down cycles.

Most good carburetor designs have the rod that the wing nut attaches to mounted to the carburetor baseplate that is much more rigid than attaching the rod to the air horn as in this Holley 2 bbl, where they just warp and leak and causing just the issue you are describing. After some more time you won't even be able to idle the engine if it gets bad enough.

When the carburetor air horn is flat and sealing well though, this carburetor usually runs very well.
 
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Ok so an update... Turned back the timing (@ idle, vac disconnected) to 10 and raised idle. That didn't help, and of course it had a lot less power. Increased timing to 25 and lowered idle back down... It seems quite a bit better, almost no hesitation, and really strong. That's not what I expected at least given the theory above regarding transition ports. I will try a cold start to be sure this isn't creating a new problem. Everything else, idle, cruise, acceleration, has been excellent otherwise. I know how to do a rebuild if necessary (i have the parts kit already) but this may have taken care of it. Running excellently now.
 
Has the harmonic balancer showed evidence of the outer ring moving on the inner hub? Usually, it will also move outward when it does that.

For decades, the base timing on 383 2bbls was 12.5 degrees BTDC. NO issues with idle or hesitation of any kind, from my experiences. Even bumped it to 15 degrees with no problems, although we were already using premium octane level fuel in it. Which makes me wonder why your engine allegedly needs so much advance to work right.


For 1972, the 400 2bbl base timing was 5 degrees BTDC + or - 2.5 degrees BTDC, so we ran it at 7.5 degrees BTDC base timing. No issues with hesitation, either.

Might need to take the distributor apart to see if the advance weights return to their starting point from being advanced (slung-out against the spring tension). Or you can twist the rotor, with the engine stopped, to see if it turns and then snaps back to "no advance".

The other issue might be that, with that much initial timing, ANY acceleration should be making it clatter big-time. Even with the 8.2 rated compression ratio. Yet that has not been mentioned.

So, at what hot base idle speed is that timing being set at? Most factory ignition curves started at the 1000rrpm area. With the factory timing curve, at the spec base timing, total advance at 4200rpm should be in the 34 degrees BTDC area. Adding another 10 degrees or so to it would put it past the optimum timing area.

Back in the middle 1970s, I was at the local Chrysler dealer when a TX DPS car came in for "poor running". It idled rough and "not right" (400-TQ HO motor). The old-line Chrysler service manager went over, loosened the hold-down bolt for the distributor, and twisted the distributor one-spark-plug-wire advanced. Suddenly, the engine ran better, but still was a bit harder to start. His diagnosis was that the timing chain had jumped, so it needed a new timing chain set in it. Which it got. IF it had jumper and effectively retarded the cam timing, then advancing the distributor would compensate for that, yet the timing would still be retarded to the piston position. NOT SURE if that might be an issue on your engine, though, but wanted to mention it.

Happy Holidays!
CBODY67
 
The timing doesn't seem to change when I reconnect the vaccum. I don't know if that gives any clues. Can I measure anything from the outside with a caliper to see if the horn is warped? Idle is about 800. Certainly possible the balancer has turned, I have no history on the car. I'll check the other things if weather permits tomorrow.
 
The timing doesn't seem to change when I reconnect the vaccum. I don't know if that gives any clues.
If the vacuum is connected to a ported source it won't change until you open the throttle. If you put full vacuum on the advance and it still doesn't advance the timing then your vacuum advance cannister is bad.
 
There should be no change at idle with the vac advance line on or off, so that’s normal.

That is no surprise that the car runs better with more initial timing.

all these threads that talk of the balancer slipping, how many actual move? Very few.

when the timing chain jumps it retards the cam which drives the distributor so it is retarded also. You can advance the timing easy enough, but the valve timing is still retarded.
 
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